IPAC2016 - Table of Session: MOPOR (Poster Session)

Paper	Title	Page
MOPOR002	Impedance Simulations and Measurements for ThomX Storage Ring	586
	A.R. Gamelin, C. Bruni, V. Chaumat, D. Le Guidec, P. Lepercq, R. Marie LAL, Orsay, France
	Funding: Work is supported by ANR-10-EQPX-51, by grants from Région Ile-de-France, IN2P3 and Pheniics Doctoral School ThomX is a compact Compton Backscattering Source (CBS) which is being built at LAL, Orsay, France. ThomX ring has a short circumference of 18 m and a design energy of 50 MeV. Due to the low energy of the beam and in order to avoid beam degradation it is important to evaluate the ring components impedance. A CST Particle Studio impedance simulation of the different components of the ring (BPM, bellows, optical chamber, etc.) is under way. It will be followed by a bench measurement of the longitudinal and transverse impedance using the coaxial wire method. This paper will detail the preliminary results of the ThomX storage ring impedance simulations and the measurement principle we will use.
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MOPOR003	Simulation Studies and Measurements of Beam Instabilities Caused by the Kicker Impedance at High Intensities in the 3-GeV RCS of J-PARC	589
	P.K. Saha, H. Harada, N. Hayashi, H. Hotchi, M. Kinshopresenter, M. Nomura, Y. Shobuda, F. Tamura, N. Tani, Y. Watanabe, M. Yamamoto JAEA/J-PARC, Tokai-mura, Japan
	The transverse impedance of the extraction kickers is a significant beam instability source in the 3-GeV Rapid Cycling Synchrotron of J-PARC. ORBIT code was developed for space charge and beam instability simulations by successfully introducing realistic time dependent machine parameters. The beam instability at high intensities, especially at the designed 1 MW beam power was found be very critical. As there was no practical measure yet to reduce the kicker impedance, a detail simulation studies were done in order to determine realistic machine parameters to suppress the beam instability. The simulation results were found to be very consistent with measurements to successfully accomplish 1 MW beam power. The simulation and beam study results in detail are presented in this paper.
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MOPOR004	Recent Progress of 1-MW Beam Tuning in the J-PARC 3-GeV RCS	592
	H. Hotchi, H. Harada, S. Kato, M. Kinshopresenter, K. Okabe, P.K. Saha, Y. Shobuda, F. Tamura, N. Tani, Y. Watanabe, K. Yamamoto, M. Yoshimoto JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
	The J-PARC 3-GeV RCS started 1 MW beam test from October 2014, and successfully achieved a 1 MW beam acceleration in January 2015. Since then, a large fraction of our effort has been focused on reducing and managing beam losses. This paper presents the recent progress of 1 MW beam tuning, especially focusing on our approaches to beam loss issues, such as space-charge induced beam loss and foil scattering beam loss during charge-exchange injection, etc.
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MOPOR005	Longitudinal Wakefields in the Undulator Section of SXFEL User Facility	595
SUPSS052	use link to see paper's listing under its alternate paper code
	M. Song, H.X. Deng, C. Feng, D. Huang, B. Liu, D. Wang SINAP, Shanghai, People's Republic of China
	Shanghai soft x-ray free electron laser (SXFEL) user facility based on multi-stage seeded-FEL and self-amplified spontaneous emission (SASE) is recently proposed, which is aiming at generating 4-2nm fully-coherent, high-brightness FEL pulse. In this paper, the wakefields arise from the resistive wall and surface roughness in the vacuum chamber is obtained by theoretical models. And the computations of geometric wakefields are carried out using ABCI. According to the tracked beam profile, the overall wakefields in the undulator section of SXFEL user facility are presented. K. Bane, G. Stupakov, SLAC-PUB-15951, May 2014. ** ABCI website: http://abci.kek.jp/abci.htm
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MOPOR007	Local Impedance Measurements at ALBA from Turn-by-Turn Acquisition	598
	M. Carlà, G. Benedetti, T.F.G. Günzel, U. Irisopresenter, Z. Martí ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain
	A transverse impedance source manifests itself, among other ways, by producing a small defocusing kick which depends on the beam bunch charge. By repeating optics measurements for different bunch charges, it is possible to disentangle the contribution produced by each impedance source from the dominating focusing effects given by the machine optics. But hunting for such faint defocusing effects poses strong requirements on the precision and sensibility of the measurements, and slow machine drifts or different thermal conditions shall be avoided. In this report, we present a novel method to assess in a fast and precise manner machine optics for different bunch charges using BPM turn-by-turn data and hybrid filling patterns. Finally, measurements for different ALBA machine components like scrapers and In-vacuum undulators are compared with simulation results.
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MOPOR008	Beam Induced RF Heating in LHC in 2015	602
	B. Salvant, O. Aberle, M. Albert, R. Alemany-Fernandez, G. Arduini, J. Baechler, M.J. Barnes, P. Baudrenghien, O.E. Berrig, N. Biancaccipresenter, G. Bregliozzi, J.V. Campelo, F. Carra, F. Caspers, P. Chiggiato, A. Danisi, H.A. Day, M. Deile, D. Druzhkin, J.F. Esteban Müller, S. Jakobsen, J. Kuczerowski, A. Lechner, R. Losito, A. Masi, N. Minafra, E. Métral, A.A. Nosych, A. Perillo Marcone, D. Perini, S. Redaelli, F. Roncarolo, G. Rumolo, E.N. Shaposhnikova, J.A. Uythoven, C. Vollinger, A.J. Välimaa, N. Wang, M. Wendt, J. Wenninger, C. Zannini CERN, Geneva, Switzerland M. Bozzo INFN Genova, Genova, Italy J.F. Esteban Müller EPFL, Lausanne, Switzerland N. Wang IHEP, Beijing, People's Republic of China
	Following the recurrent beam induced RF issues that perturbed LHC operation during LHC Run 1, a series of actions were put in place to minimize the risk that similar issues would occur in LHC Run 2: longitudinal impedance reduction campaign and/or improvement of cooling for equipment that were problematic or at the limit during Run 1, stringent constraints enforced on new equipment that would be installed in the machine, tests to control the bunch length and longitudinal distribution, additional monitoring of temperature, new monitoring tools and warning chains. This contribution reports the outcome of these actions, both successes as well as shortcomings, and details the lessons learnt for the future runs.
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MOPOR009	The HL-LHC Impedance Model and Aspects of Beam Stability	606
	N. Biancacci, K.S.B. Li, E. Métral, B. Salvant CERN, Geneva, Switzerland
	Funding: Research supported by the High Luminosity LHC project The LHC upgrade to the HLLHC foresees new challenging operational scenarios from the beam dynamics point of view. In order to ensure good machine operation and performance, the machine impedance, among other possible sources of instabilities like beam-beam and electron cloud, needs to be carefully quantified profiting also from the current LHC operation. In this work we present the HLLHC impedance model mainly focusing on the contribution of low-impedance collimators and crab cavities: the first reduces the broad-band impedance baseline thanks to the higher jaw material conductivity, the second increases the machine luminosity at the price of increasing the coupled bunch stabilizing octupole current threshold. Other elements like the injection protection absorber (TDI) will be also discussed.
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MOPOR010	Impedance Measurements and Simulations on the TCTP and TDI LHC Collimators	610
	N. Biancacci, F. Caspers, A. Grudiev, J. Kuczerowski, I. Lamas Garcia, A. Lechner, E. Métral, A. Passarelli, A. Perillo Marcone, B. Salvant, J.A. Uythoven CERN, Geneva, Switzerland O. Frasciello, M. Zobov INFN/LNF, Frascati (Roma), Italy A. Mostacci Rome University La Sapienza, Roma, Italy N. Mounet EPFL, Lausanne, Switzerland
	The LHC collimation system is a critical element for the safe operation of the LHC machine and is subject to continuous performance monitoring, hardware upgrade and optimization. In this work we will address the impact on impedance of the upgrades performed on the TDI injection protection collimator, where the absorber material has been changed to mitigate the device heating observed in machine operation, and on selected secondary (TCS) and tertiary (TCT) collimators, where beam position monitors (BPM) have been embedded for faster jaw alignment. Concerning the TDI, we will present the RF measurements performed before and after the upgrade, comparing the result to heating and tune shift beam measurements. For the TCTs, we will study how the higher order modes (HOM) introduced by the BPM addition have been cured by means of ferrite placement in the device. The impedance mitigation campaign has been supported by RF measurements whose results are in good agreement with GdfidL and CST simulations. The presence of undamped low frequency modes is proved not to be detrimental to the safe LHC operation.
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MOPOR011	Impedance Localization Measurements using AC Dipoles in the LHC	614
	N. Biancacci, L.R. Carver, G. Papotti, T. Persson, B. Salvant, R. Tomás CERN, Geneva, Switzerland
	The knowledge of the LHC impedance is of primary importance to predict the machine performance and allow for the HL-LHC upgrade. The developed impedance model can be benchmarked with beam measurements in order to assess its validity and limit. This is routinely done, for example, moving the LHC collimator jaws and measuring the induced tune shift. In order to localize possible unknown impedance sources, the variation of phase advance with intensity between beam position monitors can be measured. In this work we will present the impedance localization measurements performed at injection in the LHC using AC dipoles as exciter as well as the underlying theory.
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MOPOR012	Study of the Beam-Cavity Interaction in the PS 10 MHz RF System	618
	G. Favia, H. Damerau, M. Morvillo, C. Rossi CERN, Geneva, Switzerland M. Migliorati University of Rome "La Sapienza", Rome, Italy
	The eleven main accelerating cavities of the Proton Synchrotron (PS) at CERN consist of two ferrite-loaded coaxial λ/4 resonators each. Both resonators oscillate in phase, as their gaps are electrically connected by short bars. They are in addition magnetically coupled via the bias loop used for cavity tuning. The cavities are equipped with a wide-band feedback system, limiting the beam loading, and a further reduction of the beam induced voltage is achieved by relays which short-circuit each half-resonator gap when the cavity is not in use. Asymmetries of the beam induced voltage observed in the two half-cavities indicate that the coupling between the two resonators is not as tight as expected. The total cavity impedance coupling to the beam may be affected differently by the contributions of both resonators. A dedicated measurement campaign with high-intensity proton beam and numerical simulation have been performed to investigate the beam-cavity interaction. This paper reports the result of the study and the work aiming at the development of a model of the system, including the wide-band feedback, which reproduces this interaction.
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MOPOR013	The PS 10 MHz High Level RF System Upgrade	622
	G. Favia, H. Damerau, V.D. Desquiens, S. Energico, M. Morvillo, D. Perrelet, C. Rossi CERN, Geneva, Switzerland
	In view of the upgrade of the injectors for the High Luminosity LHC, significantly higher bunch intensity is required for LHC-type beams. In this context an upgrade of the main accelerating RF system of the Proton Synchrotron (PS) is necessary, aiming at reducing the cavity impedance which is the source of longitudinal coupled-bunch oscillations. These instabilities pose as a major limitation for the increase of the beam intensity as planned after LS2. The 10 MHz RF system consists in 11 ferrite loaded cavities, driven by tube-based power amplifiers for reasons of radiation hardness. The cavity-amplifier system is equipped with a wide-band feedback that reduces the beam induced voltage. A further reduction of the beam loading is foreseen by upgrading the feedback system, which can be reasonably achieved by increasing the loop gain of the existing amplification chain. This paper describes the progress of the design of the upgraded feedback system and shows the results of the tests on the new amplifier prototype, installed in the PS during the 2015-16 technical stop. It also reports the first results of its performance with beam, observed in the beginning of the 2016 run.
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MOPOR014	Measurements of the CERN PS Longitudinal Resistive Coupling Impedance	626
	M. Migliorati, N. Biancacci, H. Damerau, G. Sterbini CERN, Geneva, Switzerland M. Migliorati University of Rome "La Sapienza", Rome, Italy M. Migliorati, L. Venturapresenter INFN-Roma1, Rome, Italy S. Persichelli University of Rome La Sapienza, Rome, Italy
	The longitudinal coupling impedance of the CERN PS has been studied in the past years in order to better understand collective effects which could produce beam intensity limitations for the LHC Injectors Upgrade project. By measuring the incoherent quadrupole synchrotron frequency vs beam intensity, the inductive impedance was evaluated and compared with the impedance model obtained by taking into account the contribution of the most important machine devices. In this paper, we present the results of the measurements performed during a dedicated campaign, of the real part of the longitudinal coupling impedance by means of the synchronous phase shift vs beam intensity. The phase shift has been measured by using two different techniques: in one case, we injected in the machine two bunches, one used as a reference with constant intensity, and the second one changing its intensity; in the second case, more conventional, we measured the bunch position with respect to the RF signal of the 40 MHz cavities. The obtained dependence of the synchrotron phase with intensity is then related to the loss factor and the resistive coupling impedance, which is compared to the real part of the PS impedance model.
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MOPOR016	Impedance Study with Single Bunch Beam at Taiwan Photon Source	630
	C.-C. Kuo, P.J. Chou, K.T. Hsu, K.H. Hu, C.C. Liang, C.Y. Liao, Z.K. Liu, H.-J. Tsaipresenter, F.H. Tseng NSRRC, Hsinchu, Taiwan
	The impedance at Taiwan Photon Source was investigated. The effects of bunch current such as a tune change, a synchronous phase shift and a bunch lengthening under operation conditions at various stages were measured; the machine impedances were deduced. This report presents the results with insertion devices in various configurations.
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MOPOR017	First Year Performance of the TPS Booster Ring	634
	H.-J. Tsai, P.J. Chou, K.T. Hsu, K.H. Hu, C.-C. Kuo, C.Y. Liao, Y.-C. Liu, G.-H. Luo, F.H. Tseng NSRRC, Hsinchu, Taiwan
	The Taiwan Photon Source (TPS) is a 3-GeV low- emittance light source of circumference 518.4 m. The booster ring is in the same tunnel with the storage ring; its circumference at 496.8 m makes it the largest booster ring in operation in existing light sources. Since the successful commissioning at the end of 2014, the TPS booster ring has been optimized in performance for routine operation. In this paper, we present the system upgrade and the improvement of the ramping procedure to increase the capture and ramping efficiency of the beam charge, the characterization of the optics, etc.
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MOPOR018	Single Bunch Instability Studies at Diamond Light Source	637
	E. Koukovini-Platia, M. Apollonio, R. Bartolinipresenter, R.T. Fielder, I.P.S. Martin DLS, Oxfordshire, United Kingdom R. Bartolinipresenter JAI, Oxford, United Kingdom
	Single bunch instability thresholds, the associated coherent tune shifts and the bunch lengthening have been studied at Diamond light source for nominal optics. Measurements were taken under different settings of chromaticity, radio-frequency (RF) voltage and aperture of the insertion devices (IDs). The macro-particle code sbtrack was used to evaluate the instability thresholds and bunch lengthening where different impedance contributions are taken into account such as the resistive wall impedance, a broad-band resonator model and inductive impedance for the longitudinal plane. A comparison of simulation using the developed model impedance with measurements is shown for all cases.
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MOPOR019	Beta Function Measurement and Resonances Induced by Space Charge Force and Lattice Magnets	641
	K. Ohmi, K.G. Sonnad KEK, Ibaraki, Japan
	J-PARC MR has been operated at tune (ν_x,ν_y)=(22.40,20.75). A new operating point around (21.4,21.4) has been proposed by simulation studies on space charge effect since 2013. Machine experiments at the operating point has been performed since 2014 and many encouraging results are being obtained. We discuss why new operating point is better than present one from view point of space charge effects.
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MOPOR021	Space Charge Studies with High Intensity Single Bunch Beams in the CERN SPS	644
	H. Bartosik, F. Schmidt CERN, Geneva, Switzerland A. Oeftiger EPFL, Lausanne, Switzerland M. Titze HZB, Berlin, Germany
	In order to reach the target beam parameters of the LHC injectors upgrade (LIU) project the beam degradation due to losses and emittance growth on the long injection plateau of the SPS needs to be minimized. A detailed study of the dependence of losses, transverse emittance blow-up and transverse beam tail creation as function of the working point is presented here for a high brightness single bunch beam with a vertical space charge tune spread of about 0.2 on the 26 GeV injection plateau. The beam behaviour close to important betatron resonances is characterised and a region in the tune diagram with minimal beam degradation is identified. Implications about the performance for LIU beams are discussed.
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MOPOR022	Beam Dynamics Observations of the 2015 High Intensity Scrubbing Runs at the Cern Sps	648
	H. Bartosik, G. Iadarola, K.S.B. Li, L. Mether, A. Romano, G. Rumolo, M. Schenk CERN, Geneva, Switzerland
	Beam quality degradation caused by e-cloud effects has been identified as one of the main performance limitations for high intensity LHC beams with 25 ns bunch spacing in the SPS. In view of the beam parameters targeted with the LHC injectors upgrade (LIU) project, about two weeks of SPS machine time in 2015 were devoted to dedicated scrubbing runs with high intensity LHC 25 ns and dedicated 'doublet' beams in order to study the achievable reduction of e-cloud effects and quantify the consequent beam performance improvements. This paper describes the main observations concerning the coherent instabilities and beam dynamics limitations encountered as well as a detailed characterisation of the performance reach with the highest beam intensity presently available from the pre-injectors.
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MOPOR023	Flat Bunches with a Hollow Distribution for Space Charge Mitigation	652
	A. Oeftiger, H. Bartosikpresenter, A. Findlay, S. Hancock, G. Rumolo CERN, Geneva, Switzerland A. Oeftiger EPFL, Lausanne, Switzerland
	Funding: CERN, Doctoral Studentship EPFL, Doctorate Longitudinally hollow bunches provide one means to mitigate the impact of transverse space charge. The hollow distributions are created via dipolar parametric excitation during acceleration in CERN's Proton Synchrotron Booster. We present simulation work and beam measurements. Particular emphasis is given to the alleviation of space charge effects on the long injection plateau of the downstream Proton Synchrotron machine, which is the main goal of this study.
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MOPOR024	Evolution of High Intensity Beams in the CERN PS Booster after H⁻ Injection and Phase Space Painting	656
	M. Cieslak-Kowalska, J.L. Abelleira, E. Benedetto, C. Braccopresenter CERN, Geneva, Switzerland
	With the LHC Injector Upgrade (LIU) project, the injection energy of PS Booster (PSB) ' first circular accelerator in the LHC injector chain ' will be raised from 50 MeV to 160 MeV and the present multiturn injection will be upgraded to H⁻ injection with transverse and longitudinal painting. In the scope of this project, it is planned to double the beam intensities, profiting from the fact that the βγ2 factor will be two times larger (0.35 at 50 MeV and 0.71 at 160 MeV), so the resulting tune spread driven by a direct space charge should remain similar. This paper describes the feasibility to double the intensity of high intensity and large emittance beams, looking into the evolution under space charge and taking into account losses constrains in the ring and in the extraction lines.
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MOPOR025	3D Emittances Tailoring Techniques and Optimization with Space Charge for the Future CERN PS Booster Operations with Linac4	660
	V. Forte, J.L. Abelleira, E. Benedetto, C. Braccopresenter, M. Cieslak-Kowalska, G.P. Di Giovanni CERN, Geneva, Switzerland
	In the frame of the LIU (LHC Injectors Upgrade) project, the CERN PS Booster is going to be renovated to host a new H⁻ charge-exchange injection from the Linac4. One important feature of the new injection scheme is the possibility to tailor a wide range of 3D emittances for CERN's different users in an intensity span in the order of 5·10⁹ to 1.6·10¹³ protons per PSB ring. This paper gives an overview of 3D multi-turn injection techniques, focusing on the future LHC beams, which aim at reaching high brightness, and on highest intensity beams (ISOLDE), where losses are the main concern. Complete RF capture simulations and transverse injection maps, including space charge effects, are presented and also intended to be used during the commissioning with Linac4.
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MOPOR026	Measurement of the Energy Distribution Function of Electrons Generated by Radio-frequency Induced Multipacting in a Beam Pipe	664
	M. Van Gompel, F. Caspers, P. Costa Pinto, R. Leber, A. Romano, R. Salemmepresenter, M. Taborelli CERN, Geneva, Switzerland
	The development of Electron Multipacting (EM) in high intensity particle accelerators depends, amongst others, on the Secondary Electron Yield (SEY) of surfaces facing the beam. In-situ studies of electron clouds in particle accelerators must cope with operation schedule and other technical constrains. To overcome these difficulties, CERN implemented a Multipactor test bench, where EM is generated by Radio-Frequency (RF), using the beam pipes as a coaxial resonators. This tool was already successfully used to assess the effectiveness of low SEY carbon coatings on dipoles of the SPS at CERN and to study the conditioning dynamics of beam pipes. In this paper we present the development of an in-house built Retarding Field Energy Analyser (RFEA) to measure the Electrons Energy Distribution Function (EEDF) in the Multipactor test bench. The design of the electrodes was based on simulations in order to optimize sensitivity and energy resolution. The setup was tested with an electron gun at different energies before insertion in the Multipactor test bench. The evolution of the EEDF is measured at different RF powers. Feasibility to perform measurements in the machine is discussed.
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MOPOR032	Using of the MENT Method for Reconstruction of 2D Particle Distributions in IFMIF Accelerators	668
	P.A.P. Nghiem, N. Chauvin, L. Ducrot, M. Valette CEA/DSM/IRFU, France
	Beam particles are characterized by their coordinates in real spaces or phase spaces that are at least two-dimensional. It is often necessary to reconstruct such a 2D-distribution from the knowledge of only its projections on some axes, either for making use of tomography measurement results or for setting up an input beam for transport simulations. In this article, the use of the MENT (Maximum Entropy) reconstruction method is reported for the IFMIF accelerators where high intensity beam distributions are far from Gaussian ones.
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MOPOR033	Simulations of Dark Current from the BERLinPro Booster Module	671
	M. McAteer, M. Abo-Bakr, B.C. Kuske, A. Neumann HZB, Berlin, Germany
	Funding: Work supported by the German Bundesministerium f\"ur Bildung und Forschung, Land Berlin and grants of Helmholtz Association Dark current emitted from the surface of high-field RF cavities can contribute to radiation levels and cryo budget and can cause damage to sensitive accelerator components such as the photocathode. The superconducting niobium cavities in the booster module of BERLinPro will have surface fields strong enough to produce significant dark current from field emission, so simulations were made using Astra to track the propagation of emitted electrons from the surfaces of the cavities to examine the effects of dark current in the BERLinPro injector. Results of these simulations, including optimization of the layout to reduce propagation of electrons to the cathode and an estimation of power from dark current deposited throughout the injector, are presented.
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MOPOR034	Numerical Space-Charge Compensation Studies and Comparison of Different Models	674
	D. Noll, M. Droba, O. Meusel, U. Ratzinger, K. Schulte, C. Wiesner IAP, Frankfurt am Main, Germany
	The design of many Low-Energy Beam Transport sections relies on the presence of space-charge compensation by particles of opposing charge. To improve understanding of the processes involved in the built-up and steady-state, simulations using the Particle-in-Cell code bender were made. We will present the influence of various system parameters on the results. Furthermore, the electron velocity distribution was found to be approximately thermal. The spatial distribution can then be found by solving the Poisson-Boltzmann equation. Such a model for the electron distribution was implemented in a 2D PIC code and applied to typical beam transport situations. We will present results in comparison to the 3D simulations.
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MOPOR035	Space Charge Neutralization Studies with H⁻ Beam in Low Energy Beam Transport Test Stand	677
	S. Artikova Private Address, Tsukuba, Japan K. Ikegami J-PARC, KEK & JAEA, Ibaraki-ken, Japan T. Shibata, A. Takagi KEK, Tokai, Ibaraki, Japan
	J-PARC is intensity-upgraded up to pulse current of 50 mA of H⁻ beam. Two-solenoid based LEBT test stand is being built to support the operation of J-PARC linac. It imitates the actual LEBT of linac, yet contains the diagnostics chamber composed of horizontal and vertical beam emittance-meters and Faraday-cup for the current measurement. Vacuum composition of LEBT is predominantly H2 gas. The pressure inside the LEBT can be varied by the differential pumps allowing us to study the beam phase space evolution under space charge effects. The measurements of the beam phase space emittance were made as a function of the residual gas pressure. This paper presents the results and discussion on beam space charge neutralization and its effect on the beam phase space emittance.
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MOPOR037	Beam Halo Measurements using Vibrating Wire at the KOMAC	680
SUPSS057	use link to see paper's listing under its alternate paper code
	D. Choe, M. Chung, S.Y. Kim UNIST, Ulsan, Republic of Korea S.G. Arutunian, A.V. Margaryan ANSL, Yerevan, Armenia E.G. Lazareva YSU, Yerevan, Armenia
	In high-intensity particle accelerators, due to the fact that preventing beam loss plays a crucial role in con-ducting any experiments, it is important to measure and control the beam halo. Fortunately, it is feasible nowadays to measure the beam halo region thanks to the development of several sensitive beam scanning methods, including the vibrating wire technique. Since the vibrating wire is exceptionally sensitive to the heat deposition by the beam particles, it can be used to scanning the beam profile. This study will be concentrated on the precise beam profile measurement using the vibrating wire at the Korea Multi-Purpose Accelerator Complex (KOMAC) facility. First, we describe the best condition to construct beam profile measurement experiment. Finally, we present the results of the beam halo measurements performed with 20 MeV proton beam at the KOMAC facility
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MOPOR038	Implications of Resonantly Driven Higher Order Modes on the ESS Beam	683
	A. Farricker, R.M. Jones, N.Y. Joshipresenter UMAN, Manchester, United Kingdom S. Molloy ESS, Lund, Sweden
	The European Spallation Source (ESS) in Lund, Sweden, will be a facility for fundamental physics studies of atomic structure using a spallation source of unparalleled brightness. To achieve this end, a 2.86 ms long pulsed proton beam will be accelerated up to a final energy of 2 GeV using three suites of superconducting cavities. If a Higher Order Mode (HOM) lies on a harmonic of the bunch frequency the HOM will be resonantly driven. This will dilute the beam quality significantly. Errors in fabricating these cavities are inevitable, and this sets a tolerance on how close the HOM can be within a harmonic of the bunch frequency. The baseline design for ESS requires HOMs to be at least 5 MHz from a machine line. Here we provide details of several finite element electromagnetic simulations on the HOMS anticipated in these ESS cavities. We analyse their impact on the beam emittance using a drift-kick-drift model with the potential for relaxed tolerances.
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MOPOR039	Measurement of Beam Phase at FLASH using HOMs in Accelerating Cavities	686
	L. Shi, R.M. Jones UMAN, Manchester, United Kingdom N. Baboi, L. Shi DESY, Hamburg, Germany N.Y. Joshipresenter University of Manchester, Manchester, United Kingdom
	The beam phase relative to the accelerating field is of vital importance for the quality of photon beams produced in modern Free Electron Lasers based on superconducting (SC) cavities. Normally, the phase is determined by detecting the transient field induced by the beam. In this way the phase of each cavity is checked and adjusted typically every few months. In this paper, we present another means of beam phase determination, based on higher order modes (HOMs) excited in the 2nd monopole band by the beam inside the SC cavities. A circuit model of this HOM band is also presented. Various effects on the resolution have been studied. Circuit model simulations indicate the resolution is strongly dependent on the signal to noise ratio. Preliminary experimental results, based on a broadband setup, reveal an approximately 0.1o RMS resolution. These are in good agreement with simulation results. The work will pave the way for a dedicated system of beam phase monitoring, which is under development for the European XFEL. This will be the first implementation of a dedicated beam phase monitor, based on beam-excited HOMs in accelerating cavities.
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MOPOR042	Beam Dynamics Modeling of Drift-tube Linacs with CST Particle Studio	689
	S.S. Kurennoy LANL, Los Alamos, New Mexico, USA
	The CST Studio provides convenient tools for self-consistent 3D modeling of accelerators, even large ones. Here we demonstrate this approach for the LANSCE drift-tube linac (DTL) taken as an example. The RF fields in 3D models of full DTL tanks are calculated and tuned with MicroWave Studio (MWS). Beam dynamics in the DTL is modeled with Particle Studio for bunches and bunch trains with realistic initial beam distributions using the MWS-calculated RF fields and quadrupole magnetic fields. The output beam parameters and locations of particle losses are calculated and compared for different beam distributions. Our main emphasis is on the formation of low-energy tails (longitudinal halo) and their interaction with regular bunches. Such effects are usually not taken into account in standard multi-particle phase-space codes.
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MOPOR043	High-gradient Structures for Proton Energy Boosters	692
	S.S. Kurennoy, L. Rybarcyk LANL, Los Alamos, New Mexico, USA
	Increasing energy of proton beam at LANSCE from 800 MeV to 3 GeV can improve radiography resolution ~10 times. The best current practice to achieve this energy boost is to employ superconducting (SC) RF cavities with gradients about 15 MV/m after the existing linac, which results in a long and expensive booster. We propose accomplishing the same with a room-sized booster based on high-gradient (100s MV/m) room-temperature RF accelerating structures operating at low duty factors. Such high-gradient (HG) structures at very high RF frequencies have been demonstrated for electrons. However, they have never been used for protons because typical RF wavelengths are smaller than the proton bunch length. This is not a problem for proton radiography (pRad): a train of very short proton bunches with the same total length (10s ps) and charge as the original proton bunch will work as well, i.e., will create one radiography frame. Such a compact HG pRad booster can also be about an order of magnitude cheaper than the SC one. We explore feasibility of HG structures for protons and their application for a compact pRad booster at LANSCE.
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MOPOR046	Studies on Depolarization by Synchrotron Radiation using Elegant Particle Tracking	695
	J.F. Schmidt, W. Hillertpresenter ELSA, Bonn, Germany
	Funding: BMBF Spin dynamics in circular electron accelerators are significantly influenced by the emission of synchrotron light. In storage rings, Sokolov-Ternov polarization build-up and radiative depolarization have crucial impact on equilibrium polarization. On shorter timescales, as in damping rings or synchrotrons with fast energy ramp, the temporal development of polarization depends on spin decoherence caused by stochastic momentum changes. Thus, especially longitudinal beam dynamics affect depolarization. This contribution presents the implementation of particle tracking with synchrotron radiation from Elegant in an in-house developed spin tracking code. Exemplary results on depolarization including synchrotron radiation are shown.
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MOPOR047	Numerical and Experimental Substantiation of the Ion Density Beam Transfer Function Measurements	698
	D. Sauerland, W. Hillert ELSA, Bonn, Germany
	Funding: Funded by the BMBF, Germany under grant 05K13PDA In the ELSA stretcher ring electrons are accelerated to a beam energy of 3.2 GeV utilizing a fast energy ramp of 6 GeV/s. Ions being generated by collision with the residual gas molecules accumulate inside the beam potential, causing incoherent tune shifts and coherent beam instabilities. Since the ion induced incoherent tune shift rises linearly with the beam neutralisation, it offers a suitable approach for evaluating the efficiency of several ion clearing measures. It was indirectly measured using a new experimental approach: By measuring the beam transfer function using a broadband transversal kicker, one was able to perceive a shift and broadening of the tune peak. Both effects could be adequately parameterized providing a quantity proportional to the incoherent tune shift and thus the average neutralisation. The impact of incoherent effects to the coherent electron beam response during the measurement has not been subject to intensive theoretical attention yet. This leaves the obtained quantity unscaled. Here new numerical simulations and experimental investigations will be presented in order to further substantiate the results of this new method.
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Paper

Title

Page

Impedance Simulations and Measurements for ThomX Storage Ring

586

A.R. Gamelin, C. Bruni, V. Chaumat, D. Le Guidec, P. Lepercq, R. Marie
LAL, Orsay, France

Funding: Work is supported by ANR-10-EQPX-51, by grants from Région Ile-de-France, IN2P3 and Pheniics Doctoral School
ThomX is a compact Compton Backscattering Source (CBS) which is being built at LAL, Orsay, France. ThomX ring has a short circumference of 18 m and a design energy of 50 MeV. Due to the low energy of the beam and in order to avoid beam degradation it is important to evaluate the ring components impedance. A CST Particle Studio impedance simulation of the different components of the ring (BPM, bellows, optical chamber, etc.) is under way. It will be followed by a bench measurement of the longitudinal and transverse impedance using the coaxial wire method. This paper will detail the preliminary results of the ThomX storage ring impedance simulations and the measurement principle we will use.

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MOPOR003

Simulation Studies and Measurements of Beam Instabilities Caused by the Kicker Impedance at High Intensities in the 3-GeV RCS of J-PARC

589

P.K. Saha, H. Harada, N. Hayashi, H. Hotchi, M. Kinshopresenter, M. Nomura, Y. Shobuda, F. Tamura, N. Tani, Y. Watanabe, M. Yamamoto
JAEA/J-PARC, Tokai-mura, Japan

The transverse impedance of the extraction kickers is a significant beam instability source in the 3-GeV Rapid Cycling Synchrotron of J-PARC. ORBIT code was developed for space charge and beam instability simulations by successfully introducing realistic time dependent machine parameters. The beam instability at high intensities, especially at the designed 1 MW beam power was found be very critical. As there was no practical measure yet to reduce the kicker impedance, a detail simulation studies were done in order to determine realistic machine parameters to suppress the beam instability. The simulation results were found to be very consistent with measurements to successfully accomplish 1 MW beam power. The simulation and beam study results in detail are presented in this paper.

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MOPOR004

Recent Progress of 1-MW Beam Tuning in the J-PARC 3-GeV RCS

592

H. Hotchi, H. Harada, S. Kato, M. Kinshopresenter, K. Okabe, P.K. Saha, Y. Shobuda, F. Tamura, N. Tani, Y. Watanabe, K. Yamamoto, M. Yoshimoto
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan

The J-PARC 3-GeV RCS started 1 MW beam test from October 2014, and successfully achieved a 1 MW beam acceleration in January 2015. Since then, a large fraction of our effort has been focused on reducing and managing beam losses. This paper presents the recent progress of 1 MW beam tuning, especially focusing on our approaches to beam loss issues, such as space-charge induced beam loss and foil scattering beam loss during charge-exchange injection, etc.

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MOPOR005

Longitudinal Wakefields in the Undulator Section of SXFEL User Facility

595

SUPSS052

use link to see paper's listing under its alternate paper code

M. Song, H.X. Deng, C. Feng, D. Huang, B. Liu, D. Wang
SINAP, Shanghai, People's Republic of China

Shanghai soft x-ray free electron laser (SXFEL) user facility based on multi-stage seeded-FEL and self-amplified spontaneous emission (SASE) is recently proposed, which is aiming at generating 4-2nm fully-coherent, high-brightness FEL pulse. In this paper, the wakefields arise from the resistive wall and surface roughness in the vacuum chamber is obtained by theoretical models*. And the computations of geometric wakefields are carried out using ABCI**. According to the tracked beam profile, the overall wakefields in the undulator section of SXFEL user facility are presented.
* K. Bane, G. Stupakov, SLAC-PUB-15951, May 2014.
** ABCI website: http://abci.kek.jp/abci.htm

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MOPOR007

Local Impedance Measurements at ALBA from Turn-by-Turn Acquisition

598

M. Carlà, G. Benedetti, T.F.G. Günzel, U. Irisopresenter, Z. Martí
ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain

A transverse impedance source manifests itself, among other ways, by producing a small defocusing kick which depends on the beam bunch charge. By repeating optics measurements for different bunch charges, it is possible to disentangle the contribution produced by each impedance source from the dominating focusing effects given by the machine optics. But hunting for such faint defocusing effects poses strong requirements on the precision and sensibility of the measurements, and slow machine drifts or different thermal conditions shall be avoided. In this report, we present a novel method to assess in a fast and precise manner machine optics for different bunch charges using BPM turn-by-turn data and hybrid filling patterns. Finally, measurements for different ALBA machine components like scrapers and In-vacuum undulators are compared with simulation results.

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MOPOR008

Beam Induced RF Heating in LHC in 2015

602

B. Salvant, O. Aberle, M. Albert, R. Alemany-Fernandez, G. Arduini, J. Baechler, M.J. Barnes, P. Baudrenghien, O.E. Berrig, N. Biancaccipresenter, G. Bregliozzi, J.V. Campelo, F. Carra, F. Caspers, P. Chiggiato, A. Danisi, H.A. Day, M. Deile, D. Druzhkin, J.F. Esteban Müller, S. Jakobsen, J. Kuczerowski, A. Lechner, R. Losito, A. Masi, N. Minafra, E. Métral, A.A. Nosych, A. Perillo Marcone, D. Perini, S. Redaelli, F. Roncarolo, G. Rumolo, E.N. Shaposhnikova, J.A. Uythoven, C. Vollinger, A.J. Välimaa, N. Wang, M. Wendt, J. Wenninger, C. Zannini
CERN, Geneva, Switzerland
M. Bozzo
INFN Genova, Genova, Italy
J.F. Esteban Müller
EPFL, Lausanne, Switzerland
N. Wang
IHEP, Beijing, People's Republic of China

Following the recurrent beam induced RF issues that perturbed LHC operation during LHC Run 1, a series of actions were put in place to minimize the risk that similar issues would occur in LHC Run 2: longitudinal impedance reduction campaign and/or improvement of cooling for equipment that were problematic or at the limit during Run 1, stringent constraints enforced on new equipment that would be installed in the machine, tests to control the bunch length and longitudinal distribution, additional monitoring of temperature, new monitoring tools and warning chains. This contribution reports the outcome of these actions, both successes as well as shortcomings, and details the lessons learnt for the future runs.

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MOPOR009

The HL-LHC Impedance Model and Aspects of Beam Stability

606

N. Biancacci, K.S.B. Li, E. Métral, B. Salvant
CERN, Geneva, Switzerland

Funding: Research supported by the High Luminosity LHC project
The LHC upgrade to the HLLHC foresees new challenging operational scenarios from the beam dynamics point of view. In order to ensure good machine operation and performance, the machine impedance, among other possible sources of instabilities like beam-beam and electron cloud, needs to be carefully quantified profiting also from the current LHC operation. In this work we present the HLLHC impedance model mainly focusing on the contribution of low-impedance collimators and crab cavities: the first reduces the broad-band impedance baseline thanks to the higher jaw material conductivity, the second increases the machine luminosity at the price of increasing the coupled bunch stabilizing octupole current threshold. Other elements like the injection protection absorber (TDI) will be also discussed.

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MOPOR010

Impedance Measurements and Simulations on the TCTP and TDI LHC Collimators

610

N. Biancacci, F. Caspers, A. Grudiev, J. Kuczerowski, I. Lamas Garcia, A. Lechner, E. Métral, A. Passarelli, A. Perillo Marcone, B. Salvant, J.A. Uythoven
CERN, Geneva, Switzerland
O. Frasciello, M. Zobov
INFN/LNF, Frascati (Roma), Italy
A. Mostacci
Rome University La Sapienza, Roma, Italy
N. Mounet
EPFL, Lausanne, Switzerland

The LHC collimation system is a critical element for the safe operation of the LHC machine and is subject to continuous performance monitoring, hardware upgrade and optimization. In this work we will address the impact on impedance of the upgrades performed on the TDI injection protection collimator, where the absorber material has been changed to mitigate the device heating observed in machine operation, and on selected secondary (TCS) and tertiary (TCT) collimators, where beam position monitors (BPM) have been embedded for faster jaw alignment. Concerning the TDI, we will present the RF measurements performed before and after the upgrade, comparing the result to heating and tune shift beam measurements. For the TCTs, we will study how the higher order modes (HOM) introduced by the BPM addition have been cured by means of ferrite placement in the device. The impedance mitigation campaign has been supported by RF measurements whose results are in good agreement with GdfidL and CST simulations. The presence of undamped low frequency modes is proved not to be detrimental to the safe LHC operation.

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MOPOR011

Impedance Localization Measurements using AC Dipoles in the LHC

614

N. Biancacci, L.R. Carver, G. Papotti, T. Persson, B. Salvant, R. Tomás
CERN, Geneva, Switzerland

The knowledge of the LHC impedance is of primary importance to predict the machine performance and allow for the HL-LHC upgrade. The developed impedance model can be benchmarked with beam measurements in order to assess its validity and limit. This is routinely done, for example, moving the LHC collimator jaws and measuring the induced tune shift. In order to localize possible unknown impedance sources, the variation of phase advance with intensity between beam position monitors can be measured. In this work we will present the impedance localization measurements performed at injection in the LHC using AC dipoles as exciter as well as the underlying theory.

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MOPOR012

Study of the Beam-Cavity Interaction in the PS 10 MHz RF System

618

G. Favia, H. Damerau, M. Morvillo, C. Rossi
CERN, Geneva, Switzerland
M. Migliorati
University of Rome "La Sapienza", Rome, Italy

The eleven main accelerating cavities of the Proton Synchrotron (PS) at CERN consist of two ferrite-loaded coaxial λ/4 resonators each. Both resonators oscillate in phase, as their gaps are electrically connected by short bars. They are in addition magnetically coupled via the bias loop used for cavity tuning. The cavities are equipped with a wide-band feedback system, limiting the beam loading, and a further reduction of the beam induced voltage is achieved by relays which short-circuit each half-resonator gap when the cavity is not in use. Asymmetries of the beam induced voltage observed in the two half-cavities indicate that the coupling between the two resonators is not as tight as expected. The total cavity impedance coupling to the beam may be affected differently by the contributions of both resonators. A dedicated measurement campaign with high-intensity proton beam and numerical simulation have been performed to investigate the beam-cavity interaction. This paper reports the result of the study and the work aiming at the development of a model of the system, including the wide-band feedback, which reproduces this interaction.

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MOPOR013

The PS 10 MHz High Level RF System Upgrade

622

G. Favia, H. Damerau, V.D. Desquiens, S. Energico, M. Morvillo, D. Perrelet, C. Rossi
CERN, Geneva, Switzerland

In view of the upgrade of the injectors for the High Luminosity LHC, significantly higher bunch intensity is required for LHC-type beams. In this context an upgrade of the main accelerating RF system of the Proton Synchrotron (PS) is necessary, aiming at reducing the cavity impedance which is the source of longitudinal coupled-bunch oscillations. These instabilities pose as a major limitation for the increase of the beam intensity as planned after LS2. The 10 MHz RF system consists in 11 ferrite loaded cavities, driven by tube-based power amplifiers for reasons of radiation hardness. The cavity-amplifier system is equipped with a wide-band feedback that reduces the beam induced voltage. A further reduction of the beam loading is foreseen by upgrading the feedback system, which can be reasonably achieved by increasing the loop gain of the existing amplification chain. This paper describes the progress of the design of the upgraded feedback system and shows the results of the tests on the new amplifier prototype, installed in the PS during the 2015-16 technical stop. It also reports the first results of its performance with beam, observed in the beginning of the 2016 run.

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MOPOR014

Measurements of the CERN PS Longitudinal Resistive Coupling Impedance

626

M. Migliorati, N. Biancacci, H. Damerau, G. Sterbini
CERN, Geneva, Switzerland
M. Migliorati
University of Rome "La Sapienza", Rome, Italy
M. Migliorati, L. Venturapresenter
INFN-Roma1, Rome, Italy
S. Persichelli
University of Rome La Sapienza, Rome, Italy

The longitudinal coupling impedance of the CERN PS has been studied in the past years in order to better understand collective effects which could produce beam intensity limitations for the LHC Injectors Upgrade project. By measuring the incoherent quadrupole synchrotron frequency vs beam intensity, the inductive impedance was evaluated and compared with the impedance model obtained by taking into account the contribution of the most important machine devices. In this paper, we present the results of the measurements performed during a dedicated campaign, of the real part of the longitudinal coupling impedance by means of the synchronous phase shift vs beam intensity. The phase shift has been measured by using two different techniques: in one case, we injected in the machine two bunches, one used as a reference with constant intensity, and the second one changing its intensity; in the second case, more conventional, we measured the bunch position with respect to the RF signal of the 40 MHz cavities. The obtained dependence of the synchrotron phase with intensity is then related to the loss factor and the resistive coupling impedance, which is compared to the real part of the PS impedance model.

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MOPOR016

Impedance Study with Single Bunch Beam at Taiwan Photon Source

630

C.-C. Kuo, P.J. Chou, K.T. Hsu, K.H. Hu, C.C. Liang, C.Y. Liao, Z.K. Liu, H.-J. Tsaipresenter, F.H. Tseng
NSRRC, Hsinchu, Taiwan

The impedance at Taiwan Photon Source was investigated. The effects of bunch current such as a tune change, a synchronous phase shift and a bunch lengthening under operation conditions at various stages were measured; the machine impedances were deduced. This report presents the results with insertion devices in various configurations.

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MOPOR017

First Year Performance of the TPS Booster Ring

634

H.-J. Tsai, P.J. Chou, K.T. Hsu, K.H. Hu, C.-C. Kuo, C.Y. Liao, Y.-C. Liu, G.-H. Luo, F.H. Tseng
NSRRC, Hsinchu, Taiwan

The Taiwan Photon Source (TPS) is a 3-GeV low- emittance light source of circumference 518.4 m. The booster ring is in the same tunnel with the storage ring; its circumference at 496.8 m makes it the largest booster ring in operation in existing light sources. Since the successful commissioning at the end of 2014, the TPS booster ring has been optimized in performance for routine operation. In this paper, we present the system upgrade and the improvement of the ramping procedure to increase the capture and ramping efficiency of the beam charge, the characterization of the optics, etc.

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MOPOR018

Single Bunch Instability Studies at Diamond Light Source

637

E. Koukovini-Platia, M. Apollonio, R. Bartolinipresenter, R.T. Fielder, I.P.S. Martin
DLS, Oxfordshire, United Kingdom
R. Bartolinipresenter
JAI, Oxford, United Kingdom

Single bunch instability thresholds, the associated coherent tune shifts and the bunch lengthening have been studied at Diamond light source for nominal optics. Measurements were taken under different settings of chromaticity, radio-frequency (RF) voltage and aperture of the insertion devices (IDs). The macro-particle code sbtrack was used to evaluate the instability thresholds and bunch lengthening where different impedance contributions are taken into account such as the resistive wall impedance, a broad-band resonator model and inductive impedance for the longitudinal plane. A comparison of simulation using the developed model impedance with measurements is shown for all cases.

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MOPOR019

Beta Function Measurement and Resonances Induced by Space Charge Force and Lattice Magnets

641

K. Ohmi, K.G. Sonnad
KEK, Ibaraki, Japan

J-PARC MR has been operated at tune (ν_x,ν_y)=(22.40,20.75). A new operating point around (21.4,21.4) has been proposed by simulation studies on space charge effect since 2013. Machine experiments at the operating point has been performed since 2014 and many encouraging results are being obtained. We discuss why new operating point is better than present one from view point of space charge effects.

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MOPOR021

Space Charge Studies with High Intensity Single Bunch Beams in the CERN SPS

644

H. Bartosik, F. Schmidt
CERN, Geneva, Switzerland
A. Oeftiger
EPFL, Lausanne, Switzerland
M. Titze
HZB, Berlin, Germany

In order to reach the target beam parameters of the LHC injectors upgrade (LIU) project the beam degradation due to losses and emittance growth on the long injection plateau of the SPS needs to be minimized. A detailed study of the dependence of losses, transverse emittance blow-up and transverse beam tail creation as function of the working point is presented here for a high brightness single bunch beam with a vertical space charge tune spread of about 0.2 on the 26 GeV injection plateau. The beam behaviour close to important betatron resonances is characterised and a region in the tune diagram with minimal beam degradation is identified. Implications about the performance for LIU beams are discussed.

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MOPOR022

Beam Dynamics Observations of the 2015 High Intensity Scrubbing Runs at the Cern Sps

648

H. Bartosik, G. Iadarola, K.S.B. Li, L. Mether, A. Romano, G. Rumolo, M. Schenk
CERN, Geneva, Switzerland

Beam quality degradation caused by e-cloud effects has been identified as one of the main performance limitations for high intensity LHC beams with 25 ns bunch spacing in the SPS. In view of the beam parameters targeted with the LHC injectors upgrade (LIU) project, about two weeks of SPS machine time in 2015 were devoted to dedicated scrubbing runs with high intensity LHC 25 ns and dedicated 'doublet' beams in order to study the achievable reduction of e-cloud effects and quantify the consequent beam performance improvements. This paper describes the main observations concerning the coherent instabilities and beam dynamics limitations encountered as well as a detailed characterisation of the performance reach with the highest beam intensity presently available from the pre-injectors.

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MOPOR023

Flat Bunches with a Hollow Distribution for Space Charge Mitigation

652

A. Oeftiger, H. Bartosikpresenter, A. Findlay, S. Hancock, G. Rumolo
CERN, Geneva, Switzerland
A. Oeftiger
EPFL, Lausanne, Switzerland

Funding: CERN, Doctoral Studentship EPFL, Doctorate
Longitudinally hollow bunches provide one means to mitigate the impact of transverse space charge. The hollow distributions are created via dipolar parametric excitation during acceleration in CERN's Proton Synchrotron Booster. We present simulation work and beam measurements. Particular emphasis is given to the alleviation of space charge effects on the long injection plateau of the downstream Proton Synchrotron machine, which is the main goal of this study.

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MOPOR024

Evolution of High Intensity Beams in the CERN PS Booster after H⁻ Injection and Phase Space Painting

656

M. Cieslak-Kowalska, J.L. Abelleira, E. Benedetto, C. Braccopresenter
CERN, Geneva, Switzerland

With the LHC Injector Upgrade (LIU) project, the injection energy of PS Booster (PSB) ' first circular accelerator in the LHC injector chain ' will be raised from 50 MeV to 160 MeV and the present multiturn injection will be upgraded to H⁻ injection with transverse and longitudinal painting. In the scope of this project, it is planned to double the beam intensities, profiting from the fact that the βγ2 factor will be two times larger (0.35 at 50 MeV and 0.71 at 160 MeV), so the resulting tune spread driven by a direct space charge should remain similar. This paper describes the feasibility to double the intensity of high intensity and large emittance beams, looking into the evolution under space charge and taking into account losses constrains in the ring and in the extraction lines.

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MOPOR025

3D Emittances Tailoring Techniques and Optimization with Space Charge for the Future CERN PS Booster Operations with Linac4

660

V. Forte, J.L. Abelleira, E. Benedetto, C. Braccopresenter, M. Cieslak-Kowalska, G.P. Di Giovanni
CERN, Geneva, Switzerland

In the frame of the LIU (LHC Injectors Upgrade) project, the CERN PS Booster is going to be renovated to host a new H⁻ charge-exchange injection from the Linac4. One important feature of the new injection scheme is the possibility to tailor a wide range of 3D emittances for CERN's different users in an intensity span in the order of 5·10⁹ to 1.6·10¹³ protons per PSB ring. This paper gives an overview of 3D multi-turn injection techniques, focusing on the future LHC beams, which aim at reaching high brightness, and on highest intensity beams (ISOLDE), where losses are the main concern. Complete RF capture simulations and transverse injection maps, including space charge effects, are presented and also intended to be used during the commissioning with Linac4.

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MOPOR026

Measurement of the Energy Distribution Function of Electrons Generated by Radio-frequency Induced Multipacting in a Beam Pipe

664

M. Van Gompel, F. Caspers, P. Costa Pinto, R. Leber, A. Romano, R. Salemmepresenter, M. Taborelli
CERN, Geneva, Switzerland

The development of Electron Multipacting (EM) in high intensity particle accelerators depends, amongst others, on the Secondary Electron Yield (SEY) of surfaces facing the beam. In-situ studies of electron clouds in particle accelerators must cope with operation schedule and other technical constrains. To overcome these difficulties, CERN implemented a Multipactor test bench, where EM is generated by Radio-Frequency (RF), using the beam pipes as a coaxial resonators. This tool was already successfully used to assess the effectiveness of low SEY carbon coatings on dipoles of the SPS at CERN and to study the conditioning dynamics of beam pipes. In this paper we present the development of an in-house built Retarding Field Energy Analyser (RFEA) to measure the Electrons Energy Distribution Function (EEDF) in the Multipactor test bench. The design of the electrodes was based on simulations in order to optimize sensitivity and energy resolution. The setup was tested with an electron gun at different energies before insertion in the Multipactor test bench. The evolution of the EEDF is measured at different RF powers. Feasibility to perform measurements in the machine is discussed.

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MOPOR032

Using of the MENT Method for Reconstruction of 2D Particle Distributions in IFMIF Accelerators

668

P.A.P. Nghiem, N. Chauvin, L. Ducrot, M. Valette
CEA/DSM/IRFU, France

Beam particles are characterized by their coordinates in real spaces or phase spaces that are at least two-dimensional. It is often necessary to reconstruct such a 2D-distribution from the knowledge of only its projections on some axes, either for making use of tomography measurement results or for setting up an input beam for transport simulations. In this article, the use of the MENT (Maximum Entropy) reconstruction method is reported for the IFMIF accelerators where high intensity beam distributions are far from Gaussian ones.

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MOPOR033

Simulations of Dark Current from the BERLinPro Booster Module

671

M. McAteer, M. Abo-Bakr, B.C. Kuske, A. Neumann
HZB, Berlin, Germany

Funding: Work supported by the German Bundesministerium f\"ur Bildung und Forschung, Land Berlin and grants of Helmholtz Association
Dark current emitted from the surface of high-field RF cavities can contribute to radiation levels and cryo budget and can cause damage to sensitive accelerator components such as the photocathode. The superconducting niobium cavities in the booster module of BERLinPro will have surface fields strong enough to produce significant dark current from field emission, so simulations were made using Astra to track the propagation of emitted electrons from the surfaces of the cavities to examine the effects of dark current in the BERLinPro injector. Results of these simulations, including optimization of the layout to reduce propagation of electrons to the cathode and an estimation of power from dark current deposited throughout the injector, are presented.

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MOPOR034

Numerical Space-Charge Compensation Studies and Comparison of Different Models

674

D. Noll, M. Droba, O. Meusel, U. Ratzinger, K. Schulte, C. Wiesner
IAP, Frankfurt am Main, Germany

The design of many Low-Energy Beam Transport sections relies on the presence of space-charge compensation by particles of opposing charge. To improve understanding of the processes involved in the built-up and steady-state, simulations using the Particle-in-Cell code bender were made. We will present the influence of various system parameters on the results. Furthermore, the electron velocity distribution was found to be approximately thermal. The spatial distribution can then be found by solving the Poisson-Boltzmann equation. Such a model for the electron distribution was implemented in a 2D PIC code and applied to typical beam transport situations. We will present results in comparison to the 3D simulations.

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MOPOR035

Space Charge Neutralization Studies with H⁻ Beam in Low Energy Beam Transport Test Stand

677

S. Artikova
Private Address, Tsukuba, Japan
K. Ikegami
J-PARC, KEK & JAEA, Ibaraki-ken, Japan
T. Shibata, A. Takagi
KEK, Tokai, Ibaraki, Japan

J-PARC is intensity-upgraded up to pulse current of 50 mA of H⁻ beam. Two-solenoid based LEBT test stand is being built to support the operation of J-PARC linac. It imitates the actual LEBT of linac, yet contains the diagnostics chamber composed of horizontal and vertical beam emittance-meters and Faraday-cup for the current measurement. Vacuum composition of LEBT is predominantly H2 gas. The pressure inside the LEBT can be varied by the differential pumps allowing us to study the beam phase space evolution under space charge effects. The measurements of the beam phase space emittance were made as a function of the residual gas pressure. This paper presents the results and discussion on beam space charge neutralization and its effect on the beam phase space emittance.

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MOPOR037

Beam Halo Measurements using Vibrating Wire at the KOMAC

680

SUPSS057

use link to see paper's listing under its alternate paper code

D. Choe, M. Chung, S.Y. Kim
UNIST, Ulsan, Republic of Korea
S.G. Arutunian, A.V. Margaryan
ANSL, Yerevan, Armenia
E.G. Lazareva
YSU, Yerevan, Armenia

In high-intensity particle accelerators, due to the fact that preventing beam loss plays a crucial role in con-ducting any experiments, it is important to measure and control the beam halo. Fortunately, it is feasible nowadays to measure the beam halo region thanks to the development of several sensitive beam scanning methods, including the vibrating wire technique. Since the vibrating wire is exceptionally sensitive to the heat deposition by the beam particles, it can be used to scanning the beam profile. This study will be concentrated on the precise beam profile measurement using the vibrating wire at the Korea Multi-Purpose Accelerator Complex (KOMAC) facility. First, we describe the best condition to construct beam profile measurement experiment. Finally, we present the results of the beam halo measurements performed with 20 MeV proton beam at the KOMAC facility

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MOPOR038

Implications of Resonantly Driven Higher Order Modes on the ESS Beam

683

A. Farricker, R.M. Jones, N.Y. Joshipresenter
UMAN, Manchester, United Kingdom
S. Molloy
ESS, Lund, Sweden

The European Spallation Source (ESS) in Lund, Sweden, will be a facility for fundamental physics studies of atomic structure using a spallation source of unparalleled brightness. To achieve this end, a 2.86 ms long pulsed proton beam will be accelerated up to a final energy of 2 GeV using three suites of superconducting cavities. If a Higher Order Mode (HOM) lies on a harmonic of the bunch frequency the HOM will be resonantly driven. This will dilute the beam quality significantly. Errors in fabricating these cavities are inevitable, and this sets a tolerance on how close the HOM can be within a harmonic of the bunch frequency. The baseline design for ESS requires HOMs to be at least 5 MHz from a machine line. Here we provide details of several finite element electromagnetic simulations on the HOMS anticipated in these ESS cavities. We analyse their impact on the beam emittance using a drift-kick-drift model with the potential for relaxed tolerances.

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MOPOR039

Measurement of Beam Phase at FLASH using HOMs in Accelerating Cavities

686

L. Shi, R.M. Jones
UMAN, Manchester, United Kingdom
N. Baboi, L. Shi
DESY, Hamburg, Germany
N.Y. Joshipresenter
University of Manchester, Manchester, United Kingdom

The beam phase relative to the accelerating field is of vital importance for the quality of photon beams produced in modern Free Electron Lasers based on superconducting (SC) cavities. Normally, the phase is determined by detecting the transient field induced by the beam. In this way the phase of each cavity is checked and adjusted typically every few months. In this paper, we present another means of beam phase determination, based on higher order modes (HOMs) excited in the 2nd monopole band by the beam inside the SC cavities. A circuit model of this HOM band is also presented. Various effects on the resolution have been studied. Circuit model simulations indicate the resolution is strongly dependent on the signal to noise ratio. Preliminary experimental results, based on a broadband setup, reveal an approximately 0.1o RMS resolution. These are in good agreement with simulation results. The work will pave the way for a dedicated system of beam phase monitoring, which is under development for the European XFEL. This will be the first implementation of a dedicated beam phase monitor, based on beam-excited HOMs in accelerating cavities.

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MOPOR042

Beam Dynamics Modeling of Drift-tube Linacs with CST Particle Studio

689

S.S. Kurennoy
LANL, Los Alamos, New Mexico, USA

The CST Studio provides convenient tools for self-consistent 3D modeling of accelerators, even large ones. Here we demonstrate this approach for the LANSCE drift-tube linac (DTL) taken as an example. The RF fields in 3D models of full DTL tanks are calculated and tuned with MicroWave Studio (MWS). Beam dynamics in the DTL is modeled with Particle Studio for bunches and bunch trains with realistic initial beam distributions using the MWS-calculated RF fields and quadrupole magnetic fields. The output beam parameters and locations of particle losses are calculated and compared for different beam distributions. Our main emphasis is on the formation of low-energy tails (longitudinal halo) and their interaction with regular bunches. Such effects are usually not taken into account in standard multi-particle phase-space codes.

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MOPOR043

High-gradient Structures for Proton Energy Boosters

692

S.S. Kurennoy, L. Rybarcyk
LANL, Los Alamos, New Mexico, USA

Increasing energy of proton beam at LANSCE from 800 MeV to 3 GeV can improve radiography resolution ~10 times. The best current practice to achieve this energy boost is to employ superconducting (SC) RF cavities with gradients about 15 MV/m after the existing linac, which results in a long and expensive booster. We propose accomplishing the same with a room-sized booster based on high-gradient (100s MV/m) room-temperature RF accelerating structures operating at low duty factors. Such high-gradient (HG) structures at very high RF frequencies have been demonstrated for electrons. However, they have never been used for protons because typical RF wavelengths are smaller than the proton bunch length. This is not a problem for proton radiography (pRad): a train of very short proton bunches with the same total length (10s ps) and charge as the original proton bunch will work as well, i.e., will create one radiography frame. Such a compact HG pRad booster can also be about an order of magnitude cheaper than the SC one. We explore feasibility of HG structures for protons and their application for a compact pRad booster at LANSCE.

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MOPOR046

Studies on Depolarization by Synchrotron Radiation using Elegant Particle Tracking

695

J.F. Schmidt, W. Hillertpresenter
ELSA, Bonn, Germany

Funding: BMBF
Spin dynamics in circular electron accelerators are significantly influenced by the emission of synchrotron light. In storage rings, Sokolov-Ternov polarization build-up and radiative depolarization have crucial impact on equilibrium polarization. On shorter timescales, as in damping rings or synchrotrons with fast energy ramp, the temporal development of polarization depends on spin decoherence caused by stochastic momentum changes. Thus, especially longitudinal beam dynamics affect depolarization. This contribution presents the implementation of particle tracking with synchrotron radiation from Elegant in an in-house developed spin tracking code. Exemplary results on depolarization including synchrotron radiation are shown.

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MOPOR047

Numerical and Experimental Substantiation of the Ion Density Beam Transfer Function Measurements

698

D. Sauerland, W. Hillert
ELSA, Bonn, Germany

Funding: Funded by the BMBF, Germany under grant 05K13PDA
In the ELSA stretcher ring electrons are accelerated to a beam energy of 3.2 GeV utilizing a fast energy ramp of 6 GeV/s. Ions being generated by collision with the residual gas molecules accumulate inside the beam potential, causing incoherent tune shifts and coherent beam instabilities. Since the ion induced incoherent tune shift rises linearly with the beam neutralisation, it offers a suitable approach for evaluating the efficiency of several ion clearing measures. It was indirectly measured using a new experimental approach: By measuring the beam transfer function using a broadband transversal kicker, one was able to perceive a shift and broadening of the tune peak. Both effects could be adequately parameterized providing a quantity proportional to the incoherent tune shift and thus the average neutralisation. The impact of incoherent effects to the coherent electron beam response during the measurement has not been subject to intensive theoretical attention yet. This leaves the obtained quantity unscaled. Here new numerical simulations and experimental investigations will be presented in order to further substantiate the results of this new method.

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