Keyword: cathode
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MOPWA002 Nonequilibrium Phase Transitions in Crossed-Field Devices electron, space-charge, simulation, injection 74
 
  • S. Marini, R. Pakter, F.B. Rizzato
    IF-UFRGS, Porto Alegre, Brazil
  
  Funding: This work was partially supported by CNPq and FAPERGS, Brazil, and by the US-AFOSR under the grant FA9550-09-1-0283.
This work presents a fully kinetic description to model the electron flow in the electronic crossed-field configuration observed in a smooth-bore magnetron. Through this model, it has been observed that, according to the electromagnetic field, the injection temperature and the charge density, the electron flow can be classified in two different stationary modes: magnetic insulation mode where most of the electrons returning to the cathode after a transient time and Child-Langmuir mode where most of the electrons reach the anode after a transient time. Focusing on magnetic insulated mode, it has been found that charge density and injection temperature define whether electrons are accelerated (accelerating regime) or decelerated (space-charge limited regime) on the cathode. Besides, when the injection temperature is relatively low (high), a small charge increase causes (does not cause) an abrupt transition between accelerating and space-charge limited regime. Basing on the results, it was possible to identify a critical temperature that separates abrupt and continuous behavior. The results have been verified by using self-consistent computer simulations*.
*S. Marini, F. B. Rizzato, and R. Pakter, Phys. Plasmas 21, 083111 (2014). 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPWA002  
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MOPWA029 Investigations of the Space-Charge-Limited Emission in the L-Band E-Xfel Photoinjector at Desy-Pitz simulation, space-charge, gun, electron 162
 
  • Y. Chen, H. De Gersem, E. Gjonaj, A.V. Tsakanian, T. Weiland
    TEMF, TU Darmstadt, Darmstadt, Germany
  • C. Hernandez-Garcia
    JLab, Newport News, Virginia, USA
  • M. Krasilnikov, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  
  Funding: work supported by DESY Hamburg and Zeuthen Sites
This paper discusses the numerical modelling of electron bunch emission for an L-band normal conducting RF photogun. The main objective is clarifying the discrepancies between measurements and simulations performed for the European X-ray Free Electron Laser (E-XFEL) injector at DESY-PITZ. An iterative beam dynamics simulation procedure is proposed for the calculation of the total extracted bunch charge under the assumption that the emission source operates at the space-charge limit of the gun. This algorithm has been implemented in the three-dimensional full electromagnetic PIC Solver of the CST Particle Studio (CST-PS)*. Simulation results are in good agreements with measurements for a series of operation parameters. Further comparisons with a conventional Poisson-solver-based (PSB) tracking algorithm demonstrates the great significance of transient electromagnetic field effects for the beam dynamics in high brightness electron sources.
* Computer Simulation Technology AG, http://www.cst.com/
 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPWA029  
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MOPJE081 Longitudinal Stability in Multi-Harmonic Accelerating Cavities cavity, acceleration, accelerating-gradient, controls 506
 
  • R.M. Jones, L.R. Carver
    UMAN, Manchester, United Kingdom
  • J.L. Hirshfield
    Yale University, Physics Department, New Haven, CT, USA
  • Y. Jiang
    Yale University, Beam Physics Laboratory, New Haven, Connecticut, USA
  
  Accelerating cavities that excite multiple modes at integer harmonics of the fundamental frequency can potentially be used to limit the effects of rf breakdown and pulsed surface heating at high accelerating gradients. Understanding the longitudinal stability and the acceptance of such a cavity is important to their development and use. The general Hamiltonian for longitudinal stability in multi harmonic cavities is derived and the particle dynamics are explored.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPJE081  
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MOPMA033 Modeling Electron Emission and Surface Effects from Diamond Cathodes electron, simulation, vacuum, scattering 620
 
  • D.A. Dimitrov, J.R. Cary, D.N. Smithe, C.D. Zhou
    Tech-X, Boulder, Colorado, USA
  • I. Ben-Zvi, T. Rao, J. Smedley, E. Wang
    BNL, Upton, Long Island, New York, USA
  
  Funding: We are grateful to the U.S. DoE Office of Basic Energy Sciences for supporting this work under grants DE-SC0006246 and DE-SC0007577.
We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional (3D) simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surface potentials, effective mass and band bending field effects. We applied these models, in combination with previously implemented capabilities for modeling charge generation and transport in diamond, to investigate the emission dependence on applied electric field in the range from approximately 2 to 17 MV/m along the [100] direction. The simulation results were compared to experimental data when using different emission models, band bending effects, and surface-dependent electron affinity. Simulations using surface patches with different levels of hydrogenation lead to the closest agreement with the experimental data. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPMA033  
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TUPWA009 50 MeV Electron Linac with a RF Gun and a Thermoionic Cathode gun, linac, cavity, focusing 1413
 
  • A.S. Setty, A.S. Chauchat, D. Fasse, D. Jousse, P. Sirot
    Thales Communications & Security (TCS), Gennevilliers Cedex, France
  
  The low energy part of our pre injectors is made up of a 90 kV DC themoionic trioode gun, followed by a 500 MHz sub harmonic prebuncher and a 3 GHz prebuncher. We propose a new design for a 50 MeV linac with a RF gun *. this study will compare the beam dynamics simulations for the new design and for our previous pre injectors.
* A. Setty et al. "Study of a RF gun with a Thermoionic Cathode", Proceeding IPAC 2014, Germany, Dresden, June 2014. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPWA009  
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TUPWA023 A Step Closer to the CW High Brilliant Beam with the ELBE SRF-Gun-II gun, SRF, cavity, electron 1456
 
  • R. Xiang, A. Arnold, P.N. Lu, P. Michel, P. Murcek, J. Teichert, H. Vennekate
    HZDR, Dresden, Germany
  
  In order to achieve the CW electron beam with a high average current up to 1 mA and a very low emittance of 1 μm, an improved superconducting photo-injector (ELBE SRF-Gun-II) has been installed and commissioned at HZDR since 2014. This new gun replaces the first 3.5-cell SRF gun (SRF-Gun-I) at the SC Linac ELBE. The RF performance of the niobium cavity has been evaluated, the beam parameters for low charge bunches have been measured, and the first beam has been guided into the ELBE beam line. The results agree with the simulation very well. The photocathode transfer system has been installed for the first high current beam test planned in 2015. However, the unexpected strong degradation on the cavity and also on the photocathode was found soon after the first photocathode exchange. In this contribution the results of the SRF-Gun-II commissioning and the latest experiment will be presented in detail.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPWA023  
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TUPWA031 Compression of Train of Bunches with Ramped Intensity Profile at SPARC_LAB linac, laser, plasma, electron 1476
 
  • B. Marchetti
    DESY, Hamburg, Germany
  • A. Bacci
    Istituto Nazionale di Fisica Nucleare, Milano, Italy
  • E. Chiadroni, M. Ferrario, R. Pompili
    INFN/LNF, Frascati (Roma), Italy
  • A. Cianchi
    Università di Roma II Tor Vergata, Roma, Italy
  
  The production and acceleration of train of bunches with variable spacing in the ps/sub-ps range having ramped intensity profile are interesting to drive a plasma wave in the so-called resonant Plasma Wake-Fields Acceleration (r-PWFA)*. At SPARC_LAB trains having a constant intensity profile have been produced for the first time by using a shaped photo-cathode laser combined with the use of the velocity bunching compression technique**,***,****. If the sub-bunches have ramped intensity, i.e. they have different charge density, the space charge force affects differently the development of the longitudinal phase space of each one of them during the compression. In this paper we present preliminary simulations for the compression of a ramped train of bunches. The differences between the beam dynamics for a train of bunches having constant intensity profile and the ramped train are underlined. We discuss also the possibility of properly tuning the shaping of the photocathode laser to balance the space charge effect.
* SLAC-PUB-3528
** M. Ferrario et al., Phys. Rev. Lett. 104, 054801 (2010).
*** M. Ferrario et al. NIM A 637, S43-S46 (2011).
**** E. Chiadroni et al., Rev. Sci. Instrum. 84, 022703
 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPWA031  
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TUPWA044 Test electron source for increased brightness emission by near band gap photoemission electron, emittance, vacuum, simulation 1512
 
  • S. Friederich, K. Aulenbacher
    IKP, Mainz, Germany
  
  Funding: Bundesministerium für Bildung und Forschung/Federal Ministry of Education and Research; Joint project HOPE
A new photoemissive electron source is being built in order to make use of the reduction of ensemble temperature in near band gap photoemission. It will operate at up to 200 kV bias voltage with NEA GaAs photocathodes. High bunch charges will be investigated in pulsed mode with respect to the conservation of emittances at low energy excitations. High field gradients at the cathode surface will also allow further investigation of the field emission process of these photocathodes. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPWA044  
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TUPWA047 First Results Attained With the Quasi 3-D Ellipsoidal Photo Cathode Laser Pulse System at the High Brightness Photo Injector PITZ laser, electron, emittance, simulation 1522
 
  • T. Rublack, J.D. Good, M. Khojoyan, M. Krasilnikov, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  • A.V. Andrianov, E. Gacheva, E. Khazanov, S. Mironov, A. Poteomkin, V. Zelenogorsky
    IAP/RAS, Nizhny Novgorod, Russia
  • I. Hartl, S. Schreiber
    DESY, Hamburg, Germany
  • E. Syresin
    JINR, Dubna, Moscow Region, Russia
  
  Funding: Funded by the German Federal Ministry of Education and Research (BMBF) project 05K10CHE in the framework of the German-Russian collaboration "Development and Use of Accelerator-Based Photon Sources".
3-D ellipsoidal photo cathode laser pulses are considered as the next step in optimization of photo injectors required for a successful operation of linac based free electron lasers. Beam dynamics simulations using such laser pulses compared to conventional cylindrical pulses have shown a significant improvement in electron beam emittance. In collaboration with the Institute of Applied Physics (Nizhny Novgorod, Russia) and the Joint Institute of Nuclear Research (Dubna, Russia) such a 3-D ellipsoidal laser pulse system has been developed and afterwards installed at the Photo Injector Test facility at DESY, Zeuthen site (PITZ). The pulse shaping is realized using the spatial light modulator technique. This allows very fine amplitude modulation within a laser pulse. The characterization of the shape of the laser pulses can be done by cross-correlation measurements. Using this method the ability to generate and measure quasi ellipsoidal laser pulses has been demonstrated. In this contribution the overall set-up, working principle and first results received with the new photo cathode laser system at PITZ will be reported. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPWA047  
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TUPWA056 New Gun Implementation and Performance of the DAΦNE LINAC gun, linac, electron, operation 1546
 
  • B. Buonomo, L.G. Foggetta, G. Piermarini
    INFN/LNF, Frascati (Roma), Italy
  
  A new electron gun system has been developed for DAΦNE LINAC, and put into operation since January 2014. Several elements of the system were upgraded, including a new grid pulser, an improved bias voltage system and a renewed cathode socket. The new LINAC gun has now a wider range of parameters, i.e. the emission pulse length spans from 1.4ns up to 40ns, while the better control of the grid and bias voltage allows a maximum peak current of 5A with a pulse repetition rate of 50 Hz. This paper describes the details of the pulser, the power supply, the socket, all the service components of the upgraded gun and its integration in the main LINAC control system. A report on the performance of the LINAC with the new gun will follow.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPWA056  
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TUPWA062 GaAs Photocathode Activation with CsTe Thin Film photon, electron, vacuum, experiment 1567
 
  • M. Kuriki, Y. Seimiya, K. Uchida
    HU/AdSM, Higashi-Hiroshima, Japan
  • S. Kashiwagi
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  
  Funding: This work is partly supported by MEXT/JSPS KAKENHI (Grant-in-Aid for scientific research) 24654054.
GaAs is an unique and advanced photocathode which can generate highly polarized and extremely low emittance electron beam. The photo-emission is possible up to 900nm wavelength. These advantages are due to NEA (Negative Electron Affinity) surface where the conduction band minimum is higher than the vacuum energy state. The NEA surface is artificially made with Cs-O/F evaporation on the cleaned GaAs surface, but the NEA surface is fragile, so that the emission is easily lost by poor vacuum environment and high emission density. NEA activation with any vital material is desirable. We found that the GaAs can be activated by CsTe thin film which is known as a vital photo-cathode material. The photo-electron emission spectrum extends up to 900 nm wavelength which corresponds to the band-gap energy of GaAs. The result strongly suggests that the surface becomes effectively NEA state by the CsTe thin film. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPWA062  
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TUPJE003 Quasi-Traveling Wave RF Gun and Beam Commissioning for SuperKEKB gun, laser, emittance, cavity 1610
 
  • T. Natsui
    The University of Tokyo, Nuclear Professional School, Ibaraki-ken, Japan
  • Y. Ogawa, M. Yoshida, X. Zhou
    KEK, Ibaraki, Japan
  
  We are developing a new RF gun for SuperKEKB. High charge low emittance electron and positron beams are required for SuperKEKB. We will generate 7.0 GeV electron beam at 5 nC 20 mm-mrad by J-linac. In this linac, a photo cathode S-band RF gun will be used as the electron beam source. For this reason, we are developing an advanced RF gun which has two side coupled standing wave field. We call it quasi-traveling wave side couple RF gun. This gun has a strong focusing field at the cathode and the acceleration field distribution also has a focusing effect. This RF gun has been installed in the KEK J-linac. Beam commissioning with the RF gun is in progress.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPJE003  
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TUPJE009 Study on Frequency Multiplier of a Pulsed Laser Repetition using an Optical Cavity laser, cavity, gun, electron 1629
 
  • T. Kobayashi
    Waseda University, Tokyo, Japan
  
  We have been studying a compact electron accelerator based on an S-band Cs-Te photo-cathode rf gun at Waseda University. The system is using S-band rf of 2856MHz. When a repetition of the electron bunch is integral multiple of rf, it enables a lot of electron bunch acceleration for the rf gun. The repetition of the electron bunch generated by a photo-cathode rf gun depends on the oscillating frequency of the pulsed mode-locked laser. We have been developing a mode-locked Yb-doped fiber laser based on Non-Linear Polarization Rotation (NLPR). However, its repetition is limited by the fiber length to produce NLPR. Therefore, we have started to develop the external optical cavity which is multiplier of a pulsed laser repetition. It would enable the rf gun to generate high-dose electron beam in a very short time. In this conference, we will report design of the external optical cavity to multiply the pulsed laser repetition, the experimental results of the frequency multiplying of a mode-locked Yb-doped fiber laser, and the future prospects.
Work supported by Photon and Quantum Basic Research Coordinated Development Program from the Ministry of Education, Culture, Sports, Science and Technology, Japan. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPJE009  
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TUPJE017 The Generation of Highly Intense THz Radiation based on Smith-Purcell Radiation radiation, electron, factory, gun 1654
 
  • Y.F. Xu, Z.G. He, Q.K. Jia, W.W. Li
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  
  A photocathode RF gun can generate trains of THz subpicosecond electron bunches by illuminating the cathode with trains of laser pulses. Let this electron bunches passes close to the surface of a lamellar grating, THz radiation will be emitted, which is the so-called Smith-Purcell Radiation (SPR). If the lamellar grating has a narrow groove, this radiation will be narrow-band. By choosing suitable parameter, the SPR frequency can be resonant with the electron bunches frequency, and then generate high intense, narrow band THz radiation.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPJE017  
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TUPJE039 Recent Results on the Performance of Cs3Sb Photocathodes in the PHIN RF-Gun gun, laser, vacuum, operation 1699
 
  • C. Heßler, E. Chevallay, S. Döbert, V. Fedosseev, I. Martini, M. Martyanov
    CERN, Geneva, Switzerland
  
  For the CLIC drive beam a photoinjector option is under study at CERN as an alternative to the thermionic electron gun in the CLIC baseline design. The CLIC drive beam requires a high bunch charge of 8.4 nC and 0.14 ms long trains with 2 ns bunch spacing, which is challenging for a photoinjector. In particular the required long and high intensity laser pulses cause a degradation of the beam quality during the frequency conversion process, which generates the ultra-violet laser beam needed for standard Cs2Te photocathodes. To overcome this issue Cs3Sb cathodes sensitive to green light have been studied at the high-charge PHIN photoinjector since a few years. In this paper recent measurements of fundamental properties of Cs3Sb photocathodes such as quantum efficiency, cathode lifetime and dark current from summer 2014 will be presented, and compared with previous measurements and with the performance of Cs2Te photocathodes.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPJE039  
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TUPJE040 Surface Characterization at CERN of Photocathodes for Photoinjector Applications laser, gun, electron, operation 1703
 
  • I. Martini, E. Chevallay, V. Fedosseev, C. Heßler, H. Neupert, V. Nistor, M. Taborelli
    CERN, Geneva, Switzerland
  
  R&D on photocathodes takes place at CERN within the CLIC (Compact Linear Collider) project. Photocathodes are produced as thin films on Oxygen Free copper substrate using a co-deposition technique, and characterized in a dedicated laboratory with a DC photo-electron gun. A new UHV carrier vessel compatible with CERN’s XPS (X-ray Photoelectron Spectroscopy) analysis equipment has been commissioned and is used to transport photocathodes from the production laboratory to perform a systematic study of different compounds used as photoemissive materials. In this paper photocathodes used in a RF photoinjector will be characterized and the correlation of their surface properties with their performance will be investigated.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPJE040  
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TUPJE055 The Evolution of the Transverse Energy Distribution of Electrons from a GaAs Photocathode as a Function of its Degradation State electron, detector, brightness, vacuum 1748
 
  • L.B. Jones, B.L. Militsyn, T.C.Q. Noakes
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • H.E. Scheibler, A.S. Terekhov
    ISP, Novosibirsk, Russia
  
  The brightness of a photoelectron injector is fundamentally limited by the mean longitudinal and transverse energy distributions of the photoelectrons emitted from its photocathode, and is increased significantly if the mean values of these quantities are reduced. To address this, ASTeC constructed a Transverse Energy Spread Spectrometer (TESS)* – an experimental facility designed to measure these transverse and longitudinal energy distributions which can be used for III-V semiconductor, alkali antimonide/telluride and metal photocathode research. We present measurements showing evolution of the transverse energy distribution of electrons from GaAs photocathodes as a function of their degradation state. Photocathodes were activated to negative electron affinity in our photocathode preparation facility (PPF)** with quantum efficiency around 10.5%. They were then transferred to TESS under XHV conditions, and progressively degraded through controlled exposure to oxygen. Data has been collected under photocathode illumination at 635 nm, and demonstrates a constant relationship between energy distribution and the level of electron affinity.
* Proc. FEL ’13, TUPPS033, 290-293
** Proc. IPAC '10, TUPE095, 2347-2349, Proc. IPAC ’11, THPC129, 3185-3187 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPJE055  
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TUPJE056 VELA Machine Development and Beam Characterisation cavity, electron, gun, klystron 1752
 
  • D.J. Scott, D. Angal-Kalinin, A.D. Brynes, F. Jackson, J.K. Jones, A. Kalinin, S.L. Mathisen, J.W. McKenzie, B.L. Militsyn, B.D. Muratori, T.C.Q. Noakes, L.K. Rudge, E. Sneddon, M. Surman, R. Valizadeh, A.E. Wheelhouse, P.H. Williams
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • S.D. Barrett, C.P. Topping, A. Wolski
    The University of Liverpool, Liverpool, United Kingdom
  • A. Lyapin
    JAI, Egham, Surrey, United Kingdom
  • M.D. Roper
    STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
  • C.P. Topping, A. Wolski
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • E. Yamakawa
    Royal Holloway, University of London, Surrey, United Kingdom
  
  Recent developments on the VELA (Versatile Electron Linear Accelerator) RF photo-injector at Daresbury Laboratory are presented. These are three-fold; commissioning/installation, characterising and providing beam to users. Measurements for characterising the dark current (DC), 4-D transverse emittance, lattice functions and photoinjector stability are presented. User beam set ups to provide beam for electron diffraction and Cavity Beam Position Monitor development are summarised.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPJE056  
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TUPJE058 Preparation of Polycrystalline and Thin Film Metal Photocathodes for Normal Conducting RF Guns gun, electron, experiment, cavity 1759
 
  • S. Mistry, M.D. Cropper
    Loughborough University, Leicestershre, United Kingdom
  • A.N. Hannah, K.J. Middleman, B.L. Militsyn, T.C.Q. Noakes, R. Valizadeh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  
  A comparison of quantum efficiency (QE) and work function (wf) measurements of polycrystalline and thin film metal photocathodes for use in NCRF guns, similar to the S-band gun under development for CLARA project at Daresbury, are reported. Cu and Nb thin films were grown onto a Si substrate by magnetron sputtering and subsequently were prepared by annealing and Ar ion sputtering. To determine the surface chemistry, x-ray photoelectron spectroscopy was employed. QE measurements were enabled using a UV laser source giving 266 nm light. Wf measurements were carried out using a kelvin probe and ultraviolet photoelectron spectroscopy. Annealing the Cu thin film to 250°C yielded a QE of 1.2E-4; one order of magnitude higher than the QE for sputter cleaned and post annealed polycrystalline Cu. The optimum QE measurement for Nb thin film was 2.6·10-4, which was found to be comparable to the results obtained for cleaned bulk Nb. Analysis of XPS data of these metals suggest surface composition and surface chemistry are main contributing factors to the QE and WF.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPJE058  
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TUPMA004 Synthesis of Ultra-Thin Single Crystal MgO/Ag/MgO Multilayer for Controlled Photocathode Emissive Properties electron, emittance, laser, simulation 1846
 
  • D.G. Velázquez, R.L. Seibert, L.K. Spentzouris, J. Terry, Z.M. Yusof
    Illinois Institute of Technology, Chicago, Illinois, USA
  
  Photocathode emission properties are critical for electron beam applications such as photoinjectors for free electron lasers (FEL) and energy recovery Linacs (ERL). We investigate whether emission properties of photocathodes can be manipulated through the engineering of the surface electronic structure. The multilayers described here have been predicted to have emission properties in correlation with the film thickness. This paper describes how ultra-thin multilayered MgO/Ag/MgO films in the crystallographic orientations (001) and (111) multilayers were synthesized and characterized. Preliminary results of work function measurements are provided. Films were grown by pulsed laser deposition at 130 °C for the (001) orientation and 210 °C for the (111) orientation at a background pressure of ~ 5×10-9 Torr. Epitaxial growth was monitored in-situ using reflection high-energy electron diffraction, which showed single crystal island growth for each stage of the multilayer formation. Photoelectron spectroscopy was used to track the chemical state transition from Ag to MgO during the deposition of successive layers. The Kelvin probe technique was used to measure the change in contact potential difference, and thus work function, for various MgO layer thicknesses in comparison with bare single crystal Ag(001)and Ag(111) thin films. The work function was observed to reduce with increasing thickness of MgO from 0 to 4 monolayers as much as 0.89 eV and 0.72 eV for the (001) and (111) orientations, respectively. Photoelectron spectra near the Fermi level revealed electron density shifts toward zero binding energy for the multilayered surfaces with respect to the clean Ag surfaces.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPMA004  
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TUPMA010 Development of a Field-Emission Type S-band RF-Gun System for High Brightness Electron Source Applications gun, electron, emittance, vacuum 1856
 
  • Y.-M. Shin
    Northern Illinois University, DeKalb, Illinois, USA
  • N. Barov
    Far-Tech, Inc., San Diego, California, USA
  • A.T. Green
    Northern Illinois Univerity, Dekalb, Illinois, USA
  
  Electron beams emitted from a cold cathode are thermally stable and mono-energetic with a small phase-space volume*. We have been developing a field-emission type RF-gun system for high brightness electron source applications, including electron scattering/diffraction and tunable coherent X-ray/THz generation. The system consists of a single-gap gun-cavity and an S-band klystron/modulator capable of powering the gun with up to 5.5 MW peak (PRR = 1 Hz, duration = 2.5 μs). The designed gun built with the symmetrised side-couplers has surface field on the cathode ranging 50 – 100 MV/m with 1.3 – 1.7 MW klystron-power and 1.2 field ratio (HFSS). ASTRA simulations also indicate that the gun produces the beam with transverse emittances of less than 1 mm-mrad with 10 – 20 pC bunch charge at 500 keV beam energy. Under the gun operating condition, particle tracking/PIC simulations (CST) show that a single-tip CNT field-emitter** produces short pulsed bunches (~ 1/10 RF-cycle) with small emittance ( 0.01 mm-mrad) and high peak current density ( 10,000 kA/cm2). After the gun is fully installed and commissioned, a CNT-tip cathode will be tested with RF-field emission.
* N. De Jonge, J.-M. Bonard, Phil. Trans. R. Soc. Lond. A 362, 2239 (2004)
** G. S. Bocharov, and A. V. Eletskii, Nanomaterials 3, 393 (2013)
 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPMA010  
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TUPMA018 An Improved Analytic Model of Electron Back-Bombardment in Thermionic Cathode RF Guns simulation, gun, electron, cavity 1872
 
  • J.P. Edelen, S. Biedron, J.R. Harris, S.V. Milton
    CSU, Fort Collins, Colorado, USA
  • J.W. Lewellen
    LANL, Los Alamos, New Mexico, USA
  
  This paper describes work done at Colorado State University to improve upon the recent theory developed to predict the back-bombardment power in single-cell thermionic-cathode electron guns. The previous theory used a square-wave approximation of the time varying field to solve for the total kinetic energy deposited on the cathode due to the back-bombarded electrons. In addition the transit time factor was added as a correction to compensate for the non-sinusoidal field. By solving for the back-bombardment power using a sinusoidal field, the transit time factor can be removed and therefore a better overall model is produced. These alterations continue to accurately predict how back-bombardment varies as a function of the gun parameters and provides improvement when compared to the existing theory.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPMA018  
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TUPMA038 Observation of Significant Quantum Efficiency Enhancement from a Polarized Photocathode with Distributed Brag Reflector laser, polarization, electron, vacuum 1923
 
  • S. Zhang, M. Poelker, M.L. Stutzman
    JLab, Newport News, Virginia, USA
  • Y. Chen, A. Moy
    SVT Associates, Eden Prairie, Minnesota, USA
  
  Funding: This project was supported by the U.S. DOE Basic Energy Sciences under contract No. DE-AC05-060R23177.
Polarized photocathodes with higher Quantum efficiency (QE) would help to reduce the technological challenge associated with producing polarized beams at milliampere levels, because less laser light would be required, which simplifies photocathode cooling requirements. And for a given amount of available laser power, higher QE would extend the photogun operating lifetime. The distributed Bragg reflector (DBR) concept was proposed to enhance the QE of strained-superlattice photocathodes by increasing the absorption of the incident photons using a Fabry-Perot cavity formed between the front surface of the photocathode and the substrate that includes a DBR, without compromising electron polarization. Here we present recent results showing QE enhancement of a GaAs/GaAsP strained-superlattice photocathode made with a DBR structure. Typically, a GaAs/GaAsP strained-superlattice photocathode without DBR provides a QE of 1%, at a laser wavelength corresponding to peak polarization. In comparison, the GaAs/GaAsP strained-superlattice photocathodes with DBR exhibited an enhancement of over 2 when the incident laser wavelength was tuned to meet the resonant condition for the Fabry-Perot resonator. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPMA038  
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TUPMA047 Multipacting-free Quarter-wavelength Choke Joint Design for BNL SRF gun, SRF, cavity, electron 1935
 
  • W. Xu, S.A. Belomestnykh, I. Ben-Zvi, C.J. Liaw, G.T. McIntyre, K.S. Smith, R. Than, J.E. Tuozzolo, E. Wang, D. Weiss, A. Zaltsman
    BNL, Upton, Long Island, New York, USA
  • S.A. Belomestnykh, I. Ben-Zvi
    Stony Brook University, Stony Brook, USA
  
  The BNL SRF gun cavity was operated well at CW mode up to 2 MV. However, the performance suffered due to multipacting in the quarter-wavelength choke-joint. A new multipacting-free cathode stalk was designed and will be conditioned. This paper will describes RF and thermal design of new cathode stalk and conditioning results.
This work is supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPMA047  
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TUPMA048 Experimental and Simulational Result of Multipactors in 112 MHz QWR Injector gun, electron, cavity, simulation 1938
 
  • T. Xin
    Stony Brook University, Stony Brook, USA
  • S.A. Belomestnykh, I. Ben-Zvi, J.C. Brutus, V. Litvinenko, I. Pinayev, J. Skaritka, Q. Wu, B. P. Xiao
    BNL, Upton, Long Island, New York, USA
  
  Funding: This work was carried out at Brookhaven Science Associates, LLC under Contracts No. DE-AC02-98CH10886 and at Stony Brook University under grant DE-SC0005713 with the U.S. DOE.
The first RF commissioning of 112 MHz QWR superconducting electron gun was done in late 2014. The coaxial Fundamental Power Coupler (FPC) and Cathode Stalk (stalk) were install and tested for the first time. During this experiment, we observed several multipacting barriers at varied gun voltage levels. The simulation work was done within the same range. The comparison between the experimental observation and the simulation results are presented in this paper. The observations during the test are consisted with the simulation predictions. We were able to overcome most of the multipacting barriers and reach 1.7 MV gun voltage under pulsed mode after several round of conditioning processes. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPMA048  
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TUPMA049 First Beam Commissioning at BNL ERL SRF Gun SRF, gun, electron, cavity 1941
 
  • W. Xu, Z. Altinbas, S.A. Belomestnykh, I. Ben-Zvi, S. Deonarine, D.M. Gassner, H. Hahn, L.R. Hammons, T. Hayes, J.P. Jamilkowski, P. K. Kankiya, D. Kayran, N. Laloudakis, R.F. Lambiase, V. Litvinenko, L. Masi, G.T. McIntyre, K. Mernick, T.A. Miller, G. Narayan, D. Phillips, V. Ptitsyn, T. Rao, T. Seda, F. Severino, B. Sheehy, K.S. Smith, A.N. Steszyn, T.N. Tallerico, R. Than, J.E. Tuozzolo, E. Wang, D. Weiss, M. Wilinski, A. Zaltsman
    BNL, Upton, Long Island, New York, USA
  • S.A. Belomestnykh, I. Ben-Zvi, V. Litvinenko, V. Ptitsyn
    Stony Brook University, Stony Brook, USA
  
  Funding: This work is supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE.
The 704 MHz superconducting RF gun successfully generated the first photoemission beam on Nov. 17 2014. This paper will report the latest results of SRF beam commissioning, including the SRF cavity performance, cathode QE measurements, and beam parameter measurements. The beam commissioning setup is described in the paper as well. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPMA049  
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TUPHA003 Sputter Growth of Alkali Antimonide Photocathodes: An in Operando Materials Analysis target, emittance, gun, radiation 1965
 
  • J. Smedley, K. Attenkofer, M. Gaowei, J. Sinsheimer, J. Walsh
    BNL, Upton, Long Island, New York, USA
  • H. Bhandari
    Radiation Monitoring Devices, Watertown, USA
  • Z. Ding, E.M. Muller
    SBU, Stony Brook, New York, USA
  • H.J. Frisch
    Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA
  • H.A. Padmore, S.G. Schubert, J.J. Wong
    LBNL, Berkeley, California, USA
  
  Funding: Work supported by U.S. DoE, under KC0407-ALSJNT-I0013 and SBIR grant # DE-SC0009540. NSLS was supported by DOE DE-AC02-98CH10886, CHESS is supported by NSF & NIH/NIGMS via NSF DMR-1332208
Alkali antimonide photocathodes are a strong contender for the cathode of choice for next-generation photon sources such as LCLS II or the XFEL. These materials have already found extensive use in photodetectors and image intensifiers. However, only recently have modern synchrotron techniques enabled a systematic study of the formation chemistry of these materials. Such analysis has led to the understanding that these materials are inherently rough when grown through traditional sequential deposition; this roughness has a detrimental impact on the intrinsic emittance of the emitted beam. Sputter deposition may provide a path to achieving a far smoother photocathode, while maintaining adequate quantum efficiency. We report on the creation and vacuum transport of a K2CsSb sputter target, and its use to create an ultra-smooth (sub nm roughness) cathode with a 2% quantum efficiency at 532 nm. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPHA003  
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TUPWI008 RF Gun Based Ultrafast Electron Microscopy electron, gun, emittance, cavity 2259
 
  • J. Yang, K. Tanimura, Y. Yoshida
    ISIR, Osaka, Japan
  • J. Urakawa
    KEK, Ibaraki, Japan
  
  Ultrafast electron microscopy (UEM) would be a powerful tool for the direct visualization of structural dynamic processes in matter. The resolutions of the observation on femtosecond time scales over sub-nanometer (even atomic) spatial dimensions have long been a goal in science. To achieve such resolutions, we have designed and constructed a femtosecond time-resolved relativistic-energy electron microscopy using a photocathode radio-frequency (RF) electron gun (RF based UEM). The RF gun has successfully generated a high-brightness electron beam with bunch length of 100 fs and emittance of 0.2 mm-mrad, which are essential beam parameters for the achievement of nm-fs space-time resolution in the microscopy. Both the static measurements of both relativistic-energy electron diffraction and image have been succeeded. In this presentation, the activities on RF based UEM are introduced. The requirements and limitations of the beam parameters are reviewed. The concept and design of RF based UEM are reported. Finally, some demonstrations of the relativistic-energy UEM images are reported.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPWI008  
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TUPWI010 Development of a Pulse Radiolysis System by Ultra-fast Super Continuum Probe at Waseda University laser, polarization, gun, electron 2265
 
  • Y. Ito
    Waseda University, Tokyo, Japan
  • Y. Hosaka, K. Sakaue, M. Washio
    RISE, Tokyo, Japan
  
  We have been studying the pulse radiolysis using photo-cathode rf gun at Waseda Univ. Pulse radiolysis is one of the powerful methods to trace early chemical reactions by ionizing radiation. In pulse radiolysis, the probe light absorption, which produced by active species formed by electron beam of rf gun, is measured at each wavelength and made possible to trace reactions. Therefore, we have used the super continuum (SC) light for the probe light. The SC light has a broad spectrum and is generated by nonlinear optical effect caused by injecting picosecond laser to photonic crystal fiber. However, the resulting SC light was unstable because its peak intensity was not enough. We need to use a femtosecond pulsed laser which is expected to be stronger peak intensity than a picosecond laser. We have developed a mode-locked Yb-doped fiber laser based on Non-Linear Polarization Rotation as a femtosecond pulsed laser and the chirped pulse amplification system which will be able to amplify the femtosecond pulse. In this conference, we will report the performance of the SC light using this fiber laser system, recent results of pulse radiolysis experiments and the future plans.
Work supported by NEDO(New Energy and Industrial Technology Development Organization). 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPWI010  
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WEAD2 Experimental Results of Carbon NanoTube Cathodes inside RF Environment gun, electron, emittance, laser 2475
 
  • L. Faillace, S. Boucher, J.J. Hartzell, A.Y. Murokh
    RadiaBeam, Santa Monica, California, USA
  • D. Mihalcea, P. Piot, J.C.T. Thangaraj
    Fermilab, Batavia, Illinois, USA
  • H. Panuganti
    Northern Illinois University, DeKalb, Illinois, USA
  
  Funding: Work supported by US DOE SBIR grant # DE-SC0004459
Carbon Nano Tubes (CNT’s) as field-emitters have been investigated for more than two decades and can produce relatively low emittance electron beams for a given cathode size. Unlike thermionic cathodes, CNT cathodes are able to produce electrons at room temperature and relatively low electric field (a few MV/m). In collaboration with FermiLab, we have recently tested CNT cathodes both with DC and RF fields. We observed a beam current close to 1A with a ~1cm2 CNT cathode inside an L-band RF gun. Steady operation was obtained up to 650 mA and the measured current vs. surface field plot showed perfect agreement with the Fowler-Nordheim distribution. 		 
slides icon Slides WEAD2 [10.445 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEAD2  
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WEPWA016 CsKSb Photocathode R&D with High Quantum Efficiency and Long Lifetime laser, electron, vacuum, linac 2526
 
  • Y. Seimiya, R. Kaku, M. Kuriki, A. Yokota
    HU/AdSM, Higashi-Hiroshima, Japan
  • T. Konomi
    UVSOR, Okazaki, Japan
  • T. Miyajima, M. Yamamoto
    KEK, Ibaraki, Japan
  
  Advanced electron linear accelerator such as Energy Recovery Linac and Free Electron Laser needs high brightness electron source. Photocathode is suitable for the high brightness requirement because some of them has low emittance and high quantum efficiency. In the photocathode, CsKSb multi-alkali photocathode has excellent features: high quantum efficiency, long lifetime, and driven by visible light, for example green laser. Therefore, the multi-alkali photocathode is considered to be one of the best candidates for the high brightness electron source of the advanced electron accelerator. We report developments of our evaporation system and results of quantum efficiency and lifetime measurement in Hiroshima University. Multi-alkali surface analyzation has being measured by ultra-violet photoemission spectroscopy to study conditions between the multi-alkali performances and the surface condition in Institute Molecular Science. We also report the status of the progress abort the study.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWA016  
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WEPWA024 Development of a C-band RF Gun with a Coniferous-tree-type Carbon Nanostructure Field Emission Cathode cavity, gun, electron, radiation 2545
 
  • Y. Taira, H. Kato, R. Kuroda, H. Toyokawa
    AIST, Tsukuba, Ibaraki, Japan
  
  A C-band RF gun for compact radiation sources such as a high energy x-ray and a terahertz radiation is developed at AIST, which is designed to work at the frequency of 5.3 GHz*. A coniferous-tree-type carbon nanostructure (CCNS) is used for a field emission cathode in the C-band RF gun. A graphene sheet composed of carbon has a coniferous form, and the tip has a nanometer-size tubular structure that becomes thicker on the substrate side**. Owing to this configuration, the CCNS has a large field enhancement factor, and is considered to be more stable in high electric fields than Carbon nanotubes. We have fabricated the C-band RF gun of the single cell cavity. Emission current depending on the electric field strength on the CCNS cathode surface was measured. When the electric field strength was 30 MV/m, the total charge per a macro pulse was 30 nC. After applying a stronger electric field, a decline of the field enhancement factor was observed. We will present the experimental result of the field emission measurement of the CCNS and the simulation result of a beam trajectory using a C-band RF gun of a multi cell cavity.
* Y. Taira et al., Nucl. Instr. and Meth. Phys. Res. B 331 (2014) 27.
** R. Suzuki, Synthesiology 2 (3) (2009) 221. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWA024  
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WEPWA028 Numerical Simulation on Emittance Growth Caused by Roughness of a Metallic Photocathode simulation, emittance, electron, laser 2559
 
  • Z. Zhang, C.-X. Tang
    TUB, Beijing, People's Republic of China
  
  The roughness of a photocathode could lead to an additional uncorrelated divergence of the emitted electrons and therefore to an increased thermal emittance. The randomness of the real-life photocathode surface makes it unrealistic to perform typical beam dynamics simulation to study the roughness emittance growth. We developed a numerical simulation code based on the point spread function (PSF) and an estimated form of electric field distribution on an arbitrary gently undulating surface to deal with the problem. The simulation result surprisingly shows that the emittance growth factor is much smaller than expected (1.5 ~ 2).  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWA028  
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WEPWA032 CsK2Sb Growth Studies: Towards High Quantum Efficiency and Smooth Surfaces simulation, emittance, detector, experiment 2566
 
  • S.G. Schubert, M. Gaowei, J. Sinsheimer, J. Smedley
    BNL, Upton, Long Island, New York, USA
  • Z. Ding, E.M. Muller
    SBU, Stony Brook, New York, USA
  • J. Kühn
    HZB, Berlin, Germany
  • H.A. Padmore, J.J. Wong
    LBNL, Berkeley, California, USA
  • J. Xie
    ANL, Argonne, Illinois, USA
  
  Funding: This work was supported by the US DOE, under Contracts DE-AC02-05CH11231, DE-AC02-98CH10886, KC0407-ALSJNT-I0013, DE-FG02-12ER41837 and the German BMBF, Helmholtz-Association and Land Berlin.
The properties of CsK2Sb, make this material an ideal candidate as photocathode for electron injector use. Producing photocathodes with quantum efficiencies with 7% and greater at 532 nm poses no challenge, nevertheless the traditional growth mechanisms, which are based on a sequential deposition of Antimony, Potassium and Cesium at a temperature gradient yield a rough surface with a rms roughness in the range of 25 nm. Surface roughness’s in this region impacts the emittance. At an accelerating field of 3 MV/m an rms surface roughness of 25 nm is the dominant effect on emittance and will limit injector performance. Studies are performed to optimize roughness. Various growth procedures are exploited and the surface roughness compared. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWA032  
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WEPWA040 Generation and Radiation of PHz Ring-Like Electron-Pulse Train electron, radiation, acceleration, bunching 2587
 
  • F.H. Chao, C.H. Chen, Y.-C. Huang
    NTHU, Hsinchu, Taiwan
  • P.J. Chou
    NSRRC, Hsinchu, Taiwan
  
  In a superradiant FEL, the constructive interference of the radiation fields from a periodic electron-pulse train rapidly increases the radiation power at the harmonics of the pulse frequency with a narrow spectrum bandwidth. To generate radiation in the X-ray spectrum, the corresponding pulse frequency of the pre-bunched electron beam should be few tens or even few hundreds PHz. The repetition rate of electron pulses generated from an ordinary RF photoinjector is usually at 10-100 Hz. Even though a superconducting RF accelerator could further increase the repetition rate of electron pulses to few MHz, it is far below the pulse frequency required for a superradiant XFEL. In this paper, we study a technique to generate a PHz ring-like electron-pulse train from an RF photoinjector with a spatially modulated driver laser and a structured photocathode. Our simulation in PARMELA confirms the feasibility of generating such a structured electron-pulse train from the photoinjector. We present our study on the beam dynamics of the structured electron-pulse train during acceleration and the radiation behavior of it in the far field in comparison with that of an ordinary electron beam.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWA040  
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WEPWA046 Time Domain Simulations of Detuned Accelerating Cavities for Two Beam Applications cavity, simulation, impedance, accelerating-gradient 2605
 
  • R.M. Jones, L.R. Carver
    UMAN, Manchester, United Kingdom
  
  A multi-harmonic accelerating cavity that has its fundamental and harmonic mode frequency detuned away from the bunch repetition frequency could provide the basis for a beam driven wakefield accelerator with high transformer ratios. The excitation of multiple harmonic eigenmodes will allow high gradients to be achieved without encouraging the onset of rf breakdown or pulsed surface heating. This accelerating cavity will be introduced, and time domain simulations verifying the theory will be shown.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWA046  
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WEPWA052 RF Conditioning of the Photo-Cathode RF Gun at the Advanced Photon Source - NWA RF Measurements gun, detector, linac, vacuum 2621
 
  • T.L. Smith, N.P. DiMonte, A. Nassiri, Y.-E. Sun, A. Zholents
    ANL, Argonne, Illinois, USA
  
  Funding: Work supported by U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357
A new S-band photo-cathode (PC) gun was recently installed and RF conditioned at the Advanced Photon Source (APS) Injector Test-stand (ITS) at Argonne National Lab (ANL). The APS PC gun is a LCLS type gun fabricated at SLAC [1]. The PC gun was delivered to the APS in October 2013 and installed in the APS ITS in December 2013. At ANL, we developed a new method of fast detection and mitigation of the gun’s internal arcs during the RF conditioning process to protect the gun from arc damage and to RF condition more efficiently. Here, we report the results of RF measurements for the PC gun and an Auto-Restart method for high power RF conditioning. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWA052  
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WEPJE019 Simulations of Field-Emission Electron Beams from CNT Cathodes in RF Photoinjectors electron, simulation, gun, emittance 2711
 
  • D. Mihalcea, H. Panuganti, P. Piot
    Northern Illinois University, DeKalb, Illinois, USA
  • L. Faillace
    RadiaBeam, Santa Monica, California, USA
  • P. Piot, J.C.T. Thangaraj
    Fermilab, Batavia, Illinois, USA
  
  Average field emission currents of up to 700 mA were produced by Carbon Nano Tube (CNT) cathodes in a 1.3 GHz RF gun at Fermilab High Brightness Electron Source Lab. (HBESL). The CNT cathodes were manufactured at Xintek and tested under DC conditions at RadiaBeam. The electron beam intensity as well as the other beam properties are directly related to the time-dependent electric field at the cathode and the geometry of the RF gun. This report focuses on simulations of the electron beam generated through field-emission and the results are compared with experimental measurements. These simulations were performed with the time-dependent Particle In Cell (PIC) code WARP.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPJE019  
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WEPJE023 Cathode Performance during Two Beam Operation of the High Current High Polarization Electron Gun for eRHIC gun, electron, vacuum, operation 2720
 
  • O.H. Rahman
    Stony Brook University, Stony Brook, USA
  • M.A. Ackeret, J.R. Pietz
    Transfer Engineering and Manufacturing, Inc, Fremont, California, USA
  • I. Ben-Zvi, C. Degen, D.M. Gassner, R.F. Lambiase, A.I. Pikin, T. Rao, B. Sheehy, J. Skaritka, E. Wang
    BNL, Upton, Long Island, New York, USA
  • E. Dobrin, R.C. Miller, K.A. Thompson, C. Yeckel
    Stangenes Industries, Palo Alto, California, USA
  
  Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
Two electron beams from two activated bulk GaAs photocathodes were successfully combined during the recent beam test of the High Current High Polarization Electron gun for eRHIC. The beam test took place at Stangenes Industries in Palo Alto, CA, where the cathodes were placed in radially opposite locations inside the high voltage shroud. No significant cross talking between the cathodes were found for the pertinent vacuum and low average current operation, which is very promising towards combining multiple beams for higher average current. This paper describes the cathode preparation, transport and cathode performance in the gun for the combining test, including the QE and lifetimes of the photocathodes at various steps of the experiment. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPJE023  
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WEPJE033 The Progress of Funnelling Gun High Voltage Condition and Beam Test gun, electron, high-voltage, radiation 2735
 
  • E. Wang, I. Ben-Zvi, D.M. Gassner, R.F. Lambiase, W. Meng, A.I. Pikin, T. Rao, B. Sheehy, J. Skaritka
    BNL, Upton, Long Island, New York, USA
  • M.A. Ackeret, J.R. Pietz
    Transfer Engineering and Manufacturing, Inc, Fremont, California, USA
  • E. Dobrin, R.C. Miller, K.A. Thompson, C. Yeckel
    Stangenes Industries, Palo Alto, California, USA
  • O.H. Rahman
    Stony Brook University, Stony Brook, USA
  
  Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
A prototype of a high average current polarized electron funneling gun as an eRHIC injector has been built at BNL. The gun was assembled and tested at Stangenes Incorporated. Two beams were generated from GaAs photocathodes and combined by a switched combiner field. We observed the combined beams on a YAG crystal and measured the photocurrent by a Faraday cup. The gun has been shipped to Stony Brook University and is being tested there. In this paper we will describe the major components of the gun and recent beam test results. High voltage conditioning is discussed as well. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPJE033  
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WEPMA036 Double-Cell Notch Filter for SRF Gun Investigations gun, SRF, cavity, simulation 2838
 
  • E.N. Zaplatin
    FZJ, Jülich, Germany
  • A. Kanareykin
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • J. Knobloch, A. Neumann
    HZB, Berlin, Germany
  • V.P. Yakovlev
    Fermilab, Batavia, Illinois, USA
  
  Some projects of SRF guns apply the design where the cathode can be easily and quickly removed. One of the disadvantages of this design is the RF power leakage from the accelerating gun cavity cells to the cathode housing that results in the excessive cathode heating. To minimize the RF power leak different kinds of choke filters are used to protect the cathode structure. These choke filters represent resonant circuits with a zero input impedance and installed at the entrance of the cathode structure that shunt the cathode housing. Still, since the choke filter frequency shift under working conditions is bigger than its bandwidth a filter tuning during assembly only in the warm stage seems insufficient and requires also fine-tuning during operation. To eliminate the problems of the choke filter fine-tuning and hence ensure its stability during operation, a combination of the resonance choke elements can be implemented. In the paper we demonstrate advantages of the double-cell notch filter using BERLinPro SRF gun cavity as an example with its simple design modifications.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPMA036  
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WEPMN012 Cathode Stalk Optimization for a 325 MHz Superconducting QWR Electron Gun cavity, gun, electron, impedance 2940
 
  • P.L. Fan, Y.M. Li, L. Lin, K.X. Liu, S.W. Quan, F. Zhu
    PKU, Beijing, People's Republic of China
  
  Funding: Work supported by National Basic Research Project (No. 2011CB808302)
The structure of cathode stalk is very important for the performance of a superconducting QWR (Quarter Wave Resonator) gun. With improper design, RF power dissipation on the surface of cathode stalk and its surrounding tube can lead to a serious decrease of quality factor for superconducting QWR injector. We present here an optimized design of the cathode stalk for the 325 MHz superconducting QWR gun and special considerations are taken to minimize the power dissipation. The details of microwave simulation, beam dynamic simulation of the cavity with cathode stalks in different length, diameter and position are presented in this paper. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPMN012  
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WEPMN013 Development of DC-SRF Injector at Peking University SRF, cavity, laser, electron 2944
 
  • J.K. Hao, J.E. Chen, P.L. Fan, L.W. Feng, S. Huang, L. Lin, K.X. Liu, S.W. Quan, F. Wang, Zh.W. Wang, X.D. Wen, H.M. Xie, K. Zhao, F. Zhu
    PKU, Beijing, People's Republic of China
  
  DC-SRF electron injector, which combines a DC Pierce gun and a 3.5 cell 1.3 GHz superconductor cavity in a cryomodule, has been developed at Peking University. Based on the improvements of beam line, LLRF system and 2K cryogenic system, stable operation of the DC-SRF injector has been carried out recently. Electron beams with 3.4 MeV energy and the currents of ~1mA in a macro-pulse mode was obtained. As the first application of this DC-SRF injector, THz radiation produced with a 10 period undulator was also detected. The description of the experiment process and results will be presented in this paper.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPMN013  
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WEPMN015 Dark Current Imaging Experiment in an L-band RF Gun solenoid, gun, electron, experiment 2952
 
  • J.H. Shao, H.B. Chen, J. Shi, D. Wang
    TUB, Beijing, People's Republic of China
  • S.P. Antipov, S.V. Baryshev, C.-J. Jing, J.Q. Qiu
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • M.E. Conde, D.S. Doran, W. Gai, W. Liu, J.G. Power, C. Whiteford, E.E. Wisniewski
    ANL, Argonne, Illinois, USA
  • F.Y. Wang, L. Xiao
    SLAC, Menlo Park, California, USA
  
  The localized high electric field enhancement or low work function is the trigger for strong field emission, which however has yet been well experimentally studied. Using an L-band photocathode gun test stand at Argonne Wakefield Accelerator Facility (AWA), we’ve constructed an imaging beam line to observe field emission current from predefined emitters on cathode. Preliminary experiment results are present. Future plan is discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPMN015  
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WEPMN016 Observation of Dark Current Dependence on Stored Energy in an L-Band RF Gun gun, solenoid, experiment, simulation 2956
 
  • J.H. Shao, H.B. Chen, J. Shi, D. Wang
    TUB, Beijing, People's Republic of China
  • S.P. Antipov, S.V. Baryshev, C.-J. Jing, J.Q. Qiu
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • M.E. Conde, D.S. Doran, W. Gai, W. Liu, J.G. Power, C. Whiteford, E.E. Wisniewski
    ANL, Argonne, Illinois, USA
  • F.Y. Wang, L. Xiao
    SLAC, Menlo Park, California, USA
  
  A pin cathode has been installed into an L-band photocathode gun to study the influence of stored energy on field emission. The stored energy was varied by tuning the recess of the cathode in order to have the same E-field on the cathode tip. We have observed 5 times difference of dark current level at the same E-field, while by varying the stored energy by three fold. Dynamics study reveals the difference is not caused by transmission, but by emission process itself. We'll present experiment results and discuss possible mechanisms about the phenomena.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPMN016  
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WEPMN018 Measurement of Cell-Cell Coupling Coefficient in Photocathode RF Gun gun, coupling, simulation, laser 2963
 
  • P. Wang, H.B. Chen, Q. Gao, J. Shi, L. Zhang
    TUB, Beijing, People's Republic of China
  
  A photocathode RF gun is under cold rest in Tsinghua University. We measured the single cavity frequency and the cell-cell coupling coefficient by the detuning method with high accuracy. We use a simplified model to illustrate the whole process of the measurement. The data obtained in the cold test seem to accord with that from the model very well.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPMN018  
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WEPMN022 Optimization Design of Ti Cathode in Ceramic Pipe Film Coating Based on the Simulation Result of CST electron, vacuum, simulation, target 2973
 
  • J. Wang, L. Fan, Y.Z. Hong, X.T. Pei, Y. Wang, W. Wei, Y.H. Xu, B. Zhang
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  
  The injection chamber at Hefei Light Source II (HLS II) consists of four ceramic vacuum chambers whose inner surface were coated with TiN thin film. The cross section of ceramic pipes is special racetrack structure. In order to improve the uniformity of the film, the structure of the cathode Ti plate needed to be optimized. In this article, CST PARTICLE STUDIOTM software had been used to simulate the influence of different target structure on discharge electric field distribution and electrons trajectories. Furthermore, the reliability of the simulation were analysed compared with the experimental results. Also, we put forward the optimization design of Ti cathode structure which could satisfy the requirement of uniformity of the thin film.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPMN022  
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WEPMN028 Preliminary Mechanical Design of Ceramic Pipe Film Coating Equipment at Hefei Light Source II vacuum, injection, simulation, experiment 2988
 
  • J. Lu
    NPU, Xi'an Shaanxi, People's Republic of China
  • L. Fan, Y.Z. Hong, X.T. Pei, J. Wang, Y. Wang, W. Wei, Y.H. Xu, B. Zhang
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  
  Ceramic vacuum chambers are important components of the injection chamber at Hefei Light Source II (HLS II). The length of each Ceramic vacuum chamber is 350 mm and their inner surface is coated with TiN thin film whose properties are low secondary electron yield (SEY), good electrical conductivity, stability of performance, ability to block hydrogen permeation. Considering that the cross section of Ceramic pipe is racetrack structure, Ti plate was chose as the cathode to improve TiN thin film deposition rate. Meanwhile, the authors designed a motor drive magnetron sputtering film coating equipment to obtain uniform TiN film.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPMN028  
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WEPMN037 High Power Klystron Amplifiers for the PLS & PLS-II Storage Ring klystron, operation, storage-ring, high-voltage 3012
 
  • M.-H. Chun, Y.D. Joo, H.J. Park, I.S. Park, Y.U. Sohn, I.H. Yu
    PAL, Pohang, Kyungbuk, Republic of Korea
  
  Funding: Ministry of Science, ICT and Future Planning in Korea
The RF system of the Pohang Light Source-II (PLS-II) storage ring is operating at the 3.0 GeV/340 mA with three superconducting RF cavities. PLS-II RF system was upgraded to 3.0 GeV/400 mA (max.) beam storage from 2.5 GeV/ 200 mA of PLS. Each high power RF (HPRF) station is composed of a 300 kW klystron with power supplies, transmission components including a 350 kW circulator and load, and water cooling system. The klystrons are generally operated as a RF power source with high gain amplification for RF system of light sources. This paper describes the present operation status of 300 kW klystron amplifier and experiences of the former PLS 75 kW klystron amplifiers as well as RF system.
*Supported by the Ministry of Science, ICT and Future Planning in Korea 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPMN037  
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WEPHA019 Development and Production of Non-evaporable Getter Coatings for MAX IV photon, electron, vacuum, cavity 3145
 
  • P. Costa Pinto, B. Bártová, B. Holliger, S. Marques Dos Santos, V. Nistor, A. Sapountzis, M. Taborelli, I. Wevers
    CERN, Geneva, Switzerland
  • J. Ahlbäck, E. Al-Dmour, M.J. Grabski, C. Pasquino
    MAX-lab, Lund, Sweden
  
  MAX IV is presently under construction at Lund, Sweden, and the first beam for the production of synchrotron radiation is expected to circulate in 2016. The whole set of 3-GeV ring beam pipes is coated with Ti-Zr-V Non Evaporable Getter (NEG) thin film in order to fulfil the average pressure requirement of 1x10-9 mbar, despite the compact magnet layout and the large aspect ratio of the vacuum chambers. In this work, we present the optimisations of the coating process performed at CERN to coat different geometries and mechanical assembling used for the MAX IV vacuum chambers; the morphology of the thin films is analysed by Scanning Electron Microscopy; the composition and thickness is measured by Energy Dispersive X-ray analysis; the activation of the NEG thin film is monitored by X-ray Photoemission Spectroscopy; the vacuum performance of the coated beam pipes is evaluated by the measurement of hydrogen sticking coefficient. The results of the coating production characterisation for the 84 units coated at CERN are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA019  
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WEPHA020 Titanium Coating of Ceramics for Accelerator Applications vacuum, Windows, electron, target 3148
 
  • W. Vollenberg, P. Costa Pinto, B. Holliger, A. Sapountzis, M. Taborelli
    CERN, Geneva, Switzerland
  
  Titanium thin films can be deposited on ceramics, in particular alumina, without adherence problems. Even after air exposure their secondary electron yield is low compared to alumina and can be further reduced by conditioning or beam scrubbing. In addition, depending on the film thickness, titanium provides different surface resistances that fulfil requirements of ceramics in particle accelerators. Titanium thin films (MOhm square range) are used to suppress electron multipacting and evacuate charges from ceramic surfaces. Thicker films (5-25 Ω square range) are applied to lower the surface resistance so that the beam impedance is reduced. In this contribution, we present the results of a development aimed at coating 2-meter long alumina vacuum chambers with a uniform surface resistivity by a dedicated DC magnetron sputtering configuration.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA020  
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WEPTY010 Electropolishing for Low-Beta and Quasi-Waveguide SRF Cavities cavity, SRF, niobium, controls 3273
 
  • T. Reid, Z.A. Conway, S.M. Gerbick, M. Kedzie, M.P. Kelly, P.N. Ostroumov
    ANL, Argonne, Illinois, USA
  
  Argonne National Laboratory (ANL) has extended high quality electropolishing techniques based on those developed for the International Linear Collider to several more complex superconducting RF cavities. These include the co-axial TEM-mode quarter-wave and half-wave cavities as well as a 2.8 GHz quasi-waveguide structure intended for beam bunch rotation. This system is an improved version of the one developed for 1.3 GHz 9-cell cavities and includes easy provision for direct water cooling using the helium jacket. The performance of these SRF cavities both in terms of RF fields and losses equals or exceeds that of most 9-cell elliptical cavities built and tested today.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY010  
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WEPTY013 Cs2Te Photocathode Performance in the AWA High-charge High-gradient Drive Gun laser, gun, wakefield, space-charge 3283
 
  • E.E. Wisniewski, S.P. Antipov, M.E. Conde, D.S. Doran, W. Gai, C.-J. Jing, W. Liu, J.G. Power, C. Whiteford
    ANL, Argonne, Illinois, USA
  • S.P. Antipov, C.-J. Jing
    Euclid TechLabs, LLC, Solon, Ohio, USA
  
  Funding: U.S. Dept of Energy Office of Science under contract number DE-AC02-06CH11357
The unique high-charge L-band, 1.3 GHz, 1.5 cell gun for the new 75 MeV drive beam is in operation at the Argonne Wakefield Accelerator (AWA) facility (see M.E. Conde, this proceedings.) The high-field (> 80 MV/m) photoinjector has a large area, high QE Cesium telluride photocathode (diameter > 30 mm). The photocathode, a crucial component of the upgraded facility, is fabricated on-site. The photoinjector generates high-charge, short pulse, single bunches (Q > 100 nC) and long bunch-trains (Q > 600 nC) for wakefield experiments. The performance of the photocathode for the AWA drive gun is detailed. Quantum efficiency (QE) measurements indicate long, stable photocathode lifetime under demanding conditions. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY013  
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WEPTY027 Kicker Pulsers for Recycler Nova Upgrades kicker, impedance, high-voltage, controls 3324
 
  • C.C. Jensen
    Fermilab, Batavia, Illinois, USA
  
  Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
An upgrade of the Recycler injection kicker system required a faster rise time pulser. This system required a field rise and fall time of < 57 ns and a field flattop of 1.6 μs. This paper describes the variety of improvements made over the years that have resulted in this latest thyratron pulser. The effects of the trigger, the reservoir and the load impedance on delay and rise time will be discussed. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY027  
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WEPTY056 Novel High Power Sources for the Physics of Ionospheric Modification gun, simulation, electron, impedance 3398
 
  • B. Beaudoin, T.M. Antonsen, I. Haber, T.W. Koeth, A.H. Narayan, G.S. Nusinovich, K.J. Ruisard
    UMD, College Park, Maryland, USA
  • J. Rodgers
    Naval Research Laboratory (NRL), Washington, USA
  
  Funding: This work is supported by the Air Force Office of Scientific Research under grant FA95501410019.
The ionosphere plays a controlling role in the performance of critical civilian and DoD systems including the ELF-ULF communications. The objective of Ionospheric Modification is to control triggered processes to improve the performance of trans-ionospheric C3I systems and develop new applications that take advantage of the ionosphere as an active plasma medium. A key instrument is the Ionospheric Heater, a powerful HF transmitter that modifies the properties of the ionospheric plasma by modulating the electron temperature at preselected altitudes. A major reason for the development of a mobile source is that it would allow investigators to conduct the needed research at different latitudes without building permanent installations. As part of a MURI, UMD will develop a powerful RF source utilizing IOT technology in class-D amplifier mode. This technology was chosen because it has the potential to operate at very high efficiency. Some of the technical challenges presented in this paper will include a gun design that minimizes intercepted current, a compact tunable cavity, an efficient modulator system capable of modulating a high power beam and output couplers to feed the antennas. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY056  
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WEPWI016 Investigation of Differential Surface Removal due to Electropolishing at JLab cavity, simulation, radio-frequency, SRF 3525
 
  • F. Marhauser, J. Follkie, C.E. Reece
    JLab, Newport News, Virginia, USA
  
  Surface chemistry carried out for Superconducting Radio Frequency (SRF) cavities such as Buffered Chemical Polishing (BCP) and Electropolishing (EP) aims to uniformly remove the internal surface of a cavity along the entire structure and within each cell from equator to iris in order to obtain an equally etched surface. A uniform removal however is not readily achievable due to the complex fluid flow and varying temperatures of the acid mixture, which can lead to differential etching. This needs to be considered when envisaging a certain surface damage removal throughout the interior. The process-specific differential etching influences the target frequency set at the manufacturing stage as well as the field flatness and length of the as-built cavity. We report on analyses of JLab's present EP system using experimental data for six nine-cell cavities that have been processed recently in the frame of the LCLS-II high-Q development plan. In conjunction with numerical simulations, the differential etching and the impact on field flatness is assessed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI016  
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THPF059 RHIC Electron Lenses Upgrades electron, proton, ion, controls 3830
 
  • X. Gu, Z. Altinbas, S. Binello, D. Bruno, M.R. Costanzo, K.A. Drees, W. Fischer, D.M. Gassner, M. Harvey, J. Hock, K. Hock, Y. Luo, A. Marusic, K. Mernick, C. Mi, R.J. Michnoff, T.A. Miller, M.G. Minty, A.I. Pikin, G. Robert-Demolaize, T. Samms, V. Schoefer, T.C. Shrey, Y. Tan, R. Than, P. Thieberger
    BNL, Upton, Long Island, New York, USA
  • S.M. White
    ESRF, Grenoble, France
  
  Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
In the Relativistic Heavy Ion Collider (RHIC) 100 GeV polarized proton run in 2015[1], two electron lenses [2] were used for the first time to partially compensate for the head-on beam-beam effect. Here, we describe the design of the current electron lens, detailing the hardware modifications made after the 2014 commissioning run with heavy ions. A new electron gun with 15-mm diameter cathode is characterized. The electron beam transverse profile was measured using a YAG screen and fitted with a Gaussian distribution. During operation, the overlap of the electron and proton beams was achieved using the electron backscattering detector in conjunction with an automated orbit control program. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-THPF059  
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THPF104 Design of a Scaled High Duty Factor High Current Negative Penning Surface Plasma Source plasma, ion, electron, simulation 3956
 
  • D.C. Faircloth, S.R. Lawrie, T. Rutter, M. Whitehead, T. Wood
    STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
  • V.G. Dudnikov
    Muons, Inc, Illinois, USA
  
  The Front End Test Stand (FETS) at the Rutherford Appleton Laboratory (RAL) requires a 60 mA, 2 ms, 50 Hz H− beam. The present source can only deliver the current and pulse length requirements at 25 Hz. At 50 Hz there is too much droop in the beam current. To rectify this, a scaled source is being developed. This paper details the new source design and the experiments conducted that are guiding the design.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-THPF104  
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