IPAC2011 - List of Keywords (bunching)

Paper	Title	Other Keywords	Page
MOOCB02	Commissioning and Performance of the Beam Monitor System for XFEL/SPring-8 “SACLA”	cavity, electron, undulator, FEL	47
	Y. Otake, C. Kondo, H. Maesaka RIKEN Spring-8 Harima, Hyogo, Japan H. Ego, S. Matsubara, T. Matsumoto, T. Sakurai, H. Tomizawa, K. Yanagida JASRI/SPring-8, Hyogo-ken, Japan S.I. Inoue SES, Hyogo-pref., Japan
	The construction of a beam monitor system for XFEL/SPring 8 “SACLA” was completed. The system was developed to realize a spatial resolution of less than 3 um to align a beam orbit for an undulator section with about 100 m long and a temporal resolution to measure bunch lengths from 1 ns to 30 fs to maintain a constant peak beam current conducting stable SASE lasing. The system principally comprises cavity type beam position monitors (BPM), current monitors (CT), screen monitors (SCM) and bunch length measurement instruments, such as an rf deflector and CSR detectors. Commissioning of SACLA started from March 2011, and the monitors performed sufficient roles to tune beams for the lasing. The achieved over-all performances of the system including DAQ are: the BPM have spatial resolution of 300 nm, the bunch length monitors observe bunch lengths from 1ns in an injector with velocity bunching to less than 30 fs after three-stage bunch compressors. The less than a 3 um spatial resolution of the SCM was also confirmed in practical beam operation. By these fulfilled performances, the stable lasing of SACLA will be achieved. This report describes commissioning, performance of the system.
	Slides MOOCB02 [7.516 MB]

MOPC023	Design of a C-band 6 MeV Standing-wave Linear Accelerating Structure	coupling, electron, impedance, simulation	119
	J.H. Shao, H. Chen, Q.Z. Xing TUB, Beijing, People's Republic of China
	We design a C-band standing-wave biperiodic on-axis coupled linear accelerating structure for industrial and medical applications. It’s less than 300mm long; consists of 3 bunching cells and 9 normal cells. It can accelerate electrons to 6MeV and the pulsed beam current is 100mA. The RF power source is a 2.5MW magnetron. We implement 2D cells geometry optimization by SUPERFISH, beam dynamics study by PARMELA and full scale 3D calculations by MAFIA codes.

MOPC060	Bunching-frequency Multiplication for a THz Pulse-train Photoinjector	electron, linac, laser, acceleration	220
	Y.-C. Huang, F.H. Chao, C.H. Chen, K.Y. Huang NTHU, Hsinchu, Taiwan
	Funding: This work is supported by National Science Council under Contract NSC 99-2112-M-007 -013 -MY3. A THz-pulse-train photoinjector* employs a THz-pulse-train laser as its driver laser to generate a beam with a bunching frequency in the THz range. However a laser frequency is on the order of a few hundred THz. It is not possible to generate a beam from the pulse-train photoinjector with a bunching frequency exceeding the laser’s carrier frequency. In view of the strong demand for a compact x-ray free-electron laser (FEL), it is highly desirable to multiply the bunching frequency of the beam from a pulse-train injector to the x-ray frequencies. We propose to chirp the energy of the THz electron pulse train in an accelerator and compress the whole beam in a magnet to increase the electron bunching frequency. Our study shows a compression ratio or a bunching-frequency multiplication factor of a few tens is achievable from a properly designed magnetic chicane compressor. The bunching factor, however, is unfortunately degraded due to the energy chirp, emittance growth, and wake-field generation. In the conference, we will show that a bunching factor of a few ppm in the bunch-frequency multiplied beam is sufficient to build up the FEL power from a 10-time length reduced undulator. * Y. C. Huang, “Laser-beat-wave bunched beam for compact superradiance sources,” International Journal of Modern Physics B, Vol. 21 Issue 3/4, p277-286 (2007).

MOPC150	High Charge PHIN Photo Injector at CERN with Fast Phase Switching within the Bunch Train for Beam Combination	laser, cathode, vacuum, gun	430
	M. Divall Csatari, A. Andersson, B. Bolzon, E. Bravin, E. Chevallay, A.E. Dabrowski, S. Döbert, V. Fedosseev, C. Heßler, T. Lefèvre, S. Livesley, R. Losito, O. Mete, M. Olvegård, M. Petrarca, A. Rabiller CERN, Geneva, Switzerland A. Drozdy BUTE, Budapest, Hungary D. Egger EPFL, Lausanne, Switzerland
	The high charge PHIN photo-injector was developed within the frame of the European CARE program to provide an alternative to the drive beam thermionic gun in CTF3 (CLIC Test Facility) at CERN. In PHIN 1908 bunches are delivered with bunch spacing of 1.5 GHz and 2.33 nC charge per bunch. Furthermore the drive beam generated by CTF3 requires several fast 180 deg phase-shifts with respect to the 1.5 GHz bunch repetition frequency in order to allow the beam combination scheme developed at CTF3. A total of 8 sub-trains, each 140 ns long and shifted in phase with respect to each other, have to be produced with very high phase and amplitude stability. A novel fiber modulator based phase-switching technique developed on the laser system provides this phase-shift between two consecutive pulses much faster and cleaner than the base line scheme, where a thermionic electron gun and sub-harmonic bunching are used. The paper describes the fiber-based switching system and the measurements verifying the scheme. Stability measurements are presented for the phase-coded system. The paper also discusses the latest 8nC charge production and cathode life-time studies on Cs2Te.

MOPS004	Mitigation of Beam Instability due to Space Charge Effects at 3 GeV RCS in J-PARC	impedance, space-charge, kicker, injection	595
	Y. Shobuda, M. Yamamoto JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan Y.H. Chin KEK, Ibaraki, Japan F. Tamura KEK/JAEA, Ibaraki-Ken, Japan
	In order to accomplish high intensity proton beams, it is important to identify the impedance source in accelerators. At 3 GeV rapid cycling synchrotron (RCS) in Japan Proton Research Complex (J-PARC), the kicker impedance is the most dominant among such impedance sources. Beam instability can be observed by correcting chromaticity during the acceleration. Growth rate due to the beam instability can be reduced by making peak current larger (bunching factor smaller). In other words, it is experimentally found that space charge effects mitigate the beam instability.

MOPS008	Simulation of Longitudinal Emittance Control in J-PARC RCS for 400 MeV Injection	extraction, emittance, injection, simulation	607
	M. Yamamoto, M. Nomura, A. Schnase, T. Shimada, F. Tamura JAEA/J-PARC, Tokai-mura, Japan E. Ezura, K. Hara, K. Hasegawa, C. Ohmori, A. Takagi, K. Takata, M. Toda, M. Yoshii KEK, Ibaraki, Japan
	The injection energy upgrade of the J-PARC RCS from 181 MeV to 400 MeV is scheduled, this is necessary to achieve the design beam intensity. The high intensity beam is delivered to the MR, and the space charge effect at the MR injection should be alleviated by optimizing the longitudinal beam emittance at RCS extraction. This is realized by matching the shape of the beam emittance between the RCS and the MR. We describe the results of particle tracking simulation with the longitudinal emittance control during the whole acceleration period of the RCS.

MOPS019	High Intensity Longitudinal Dynamics Studies for Higher Energy Injection into the ISIS Synchrotron	injection, simulation, space-charge, linac	640
	R.E. Williamson, D.J. Adams, C.M. Warsop STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
	ISIS is the world’s most productive pulsed neutron and muon source, at the Rutherford Appleton Laboratory in the UK. Operation is centred on a loss-limited 50 Hz proton synchrotron which accelerates 3·10¹³ protons per pulse from 70 MeV to 800 MeV, delivering a mean beam power of 0.2 MW. Present studies on ISIS upgrades are focussed on a new linac for higher energy injection into the existing ring, potentially increasing beam current through reduction in space charge and optimized injection. Studies assume injection of a chopped beam at 180 MeV and offer the possibility of beam powers in the 0.5 MW regime. A critical aspect of such an upgrade is the longitudinal dynamics, associated RF parameters, space charge levels and stringent requirements on beam loss. This paper outlines studies optimizing longitudinal parameters including key design requirements such as bunching factor and satisfying the Keil-Schnell-Boussard stability criterion throughout acceleration. Work developing and benchmarking the in-house longitudinal dynamics code used for these studies is also summarized.

MOPS035	Energy Spreads by Transient Beam Loading Effect in Pulsed RF Linac	gun, electron, linac, beam-loading	679
	S.H. Kim, M.-H. Cho, G. Ha, H.R. Yang POSTECH, Pohang, Kyungbuk, Republic of Korea W. Namkung, S.J. Park PAL, Pohang, Kyungbuk, Republic of Korea J.-S. Oh NFRI, Daejon, Republic of Korea
	Funding: Work partly supported by KAPRA and POSTECH Physics BK21 Program RF linacs for high power beams are operated in the fully beam-loaded condition for the power efficiency. In this condition, temporal energy spreads are induced by the transient beam loading effect. Irradiation sources require the beam energy of less than 10 MeV to prevent undesirable neutron production. In order to maximize the beam power and maintain the beam energy in a safe value, we need to suppress the temporal energy spreads. In an L-band traveling-wave linac for irradiation sources, the high energy electrons are suppressed by the beam current modulation with the RF power modulation. As a result, the average beam energy and the corresponding beam power are improved by nearly 60% compared to the case without any modulations.

TUPC038	A Low Energy Thermionic RF Gun Linac for Ultrashort Electron Beam	linac, gun, electron, klystron	1081
	J.-Y. Hwang, J.H. Chen, W.K. Lau, A.P. Lee, T.H. Wu NSRRC, Hsinchu, Taiwan N.Y. Huang NTHU, Hsinchu, Taiwan
	A low energy test linac is being constructed at NSRRC for technological development of high brightness electron injector. It is a 29 MeV S-band linac that equipped with a high gradient thermionic cathode rf gun for generation of ultrashort relativistic electron beam by velocity bunching in the rf linac section located at downstream. High quality GHz-repetition-rate electron pulses of about 30 pC in bunch charge, pulse duration as short as 100 fsec can be produced from this test facility. It can be used as the driver for future light source experiments such as ultrafast head-on inverse Compton scattering (ICS) X-ray source and intense coherent THz free electron lasers.

TUPC094	Development of High-speed Differential Current-transformer Monitor	electron, gun, monitoring, status	1227
	S. Matsubara, H. Ego, K. Yanagida JASRI/SPring-8, Hyogo-ken, Japan A. Higashiya, S.I. Inoue, Y. Otake RIKEN/SPring-8, Hyogo, Japan H. Maesaka RIKEN Spring-8 Harima, Hyogo, Japan
	The XFEL, which was named SACLA, was constructed in the SPring-8 site. In the SACLA, the bunch length of an electron beam is compressed from 1 ns to 30 fs, and the beam charge is decreased to obtain a genuine electron beam from 1nC to 0.3 nC for lasing. A new current-transformer (CT) monitor, which should measure the charge of the electron beam and make bunch length observation in velocity bunching process, was developed with two advantageous properties. One is differential output signal which suppresses common-mode noise from the thyratron of a klystron modulator by a factor of ten. Another property is high-speed signal output which provides a possibility to measure the bunch length and the time-of-flight (TOF) at the injector part of the SACLA. The output signal has 200 ps rise-time and a pulse width of 400 ps (FWHM) for an impulse beam. We successfully observed the bunch length between 1 ns and 400 ps around a 238 MHz buncher cavity. Moreover, we measured the TOF between two CTs with a few picoseconds resolution for a low-energy beam around 1 MeV. Thus, the new CT performance was confirmed to be sufficient for the SACLA.

TUPS080	Low Energy Bunching with a Double Gap RF Buncher	ion, ion-source, proton, injection	1725
	H. von Jagwitz, U. Hagen, O. Heid, S. Setzer Siemens AG, Erlangen, Germany
	A compact double gap bunching system for low energy proton beams is presented. The system is designed for the bunching of a low current proton beam (less than 50μA) with an energy of 10 keV. The buncher operates at 150 MHz and bunches without significantly changing the beam energy. The beam is generated by an Electron Beam Ion Source and has to be bunched for the subsequent acceleration in a 150 MHz linear accelerator. The buncher contains two short gaps and an RF electrode inbetween. Thus the full length of the buncher in the beamline is in the range of 2 cm. The location of the bunch focus depends on the buncher power. The bunched beam was analysed at a distance of 550 mm with a fast faraday cup. The bunching effectivity was determined as 50%, which means that 50% of the protons of the beam were located in bunches with a width of 60°, which is a reasonable value of acceptance for a conventional accelerator cavity. Some theory and detailed results will be presented.

WEPC018	Self-focusing Effects in Compact C-band Standing-wave Accelerating Structure for X-ray Imaging Applications	focusing, electron, accelerating-gradient, linac	2046
	H.R. Yang, M.-H. Cho, S.H. Kim, W. Namkung, S.J. Park POSTECH, Pohang, Kyungbuk, Republic of Korea J.-S. Oh NFRI, Daejon, Republic of Korea
	In electron RF linacs for industrial X-ray imaging applications, compact structures are preferred for mobility. The electron beam spot size of 1 – 2 mm is required for the spatial resolution of images at the X-ray conversion target. Applying self-focusing effects to the accelerating structure, external magnets can be removed and then the accelerator system becomes more compact. We design a C-band electron linac, which is capable of producing 6-MeV, 80-mA pulsed electron beams with an RF power of 1.5 MW. It uses a bi-periodic and on-axis-coupled accelerating structure with a built-in bunching section. It uses the π/2-mode standing-waves. The first bunching cell has an asymmetric geometry which maximizes the RF phase focusing. On the other hand, the normal cells are designed for the electrostatic focusing to be maximized. In this paper, we present design details of the accelerating cells and the beam dynamics simulation by the PARMELA code.

WEPS005	Investigation of Intrabeam Scattering in the Heavy Ion Storage Ring TSR	ion, electron, scattering, storage-ring	2490
	S.T. Artikova, M. Grieser, J. Ullrich MPI-K, Heidelberg, Germany
	Intrabeam scattering (IBS) is a multiple scattering effect between stored beam particles. It leads to diffusion in all three spatial dimensions and thus, causes an expansion of the whole beam. IBS plays an important role in the equilibrium diameter of a low-velocity, electron-cooled ion beam. IBS effects for coasting and bunched 12C⁶⁺ ion beams at an energy of 73.3 MeV were studied using the TSR heavy ion cooler storage ring. Experimental results of the IBS rates are presented.

WEPZ006	Forming Attosecond Electron Pulses in Space-charge Dominated Regime	electron, radiation, laser, acceleration	2775
	V.A. Papadichev LPI, Moscow, Russia
	Production of high-current attosecond electron pulses requires studying of the final bunching stage, which inevitably is space-charge dominated [, , *]. Two models are studied, both allow solving a one-dimensional equation of motion. The first is for a spherical bunch, which corresponds to a short emitted pulse from a one-spike cathode of diameter approximately equal to its length. The second model is suited for pulses emitted from a multi-spike or multi-blade cathode. The bunch in the latter case is a thin plate and its evolution can be studied by also solving one-dimensional equation of motion. It was shown that bunches of 10-attosecond (as) duration with peak current of dozens of amperes can be obtained when using a carbon dioxide laser and less than 0.1-as duration with currents up to 1 MA when employing a neodymium laser. Beam focusing in transverse directions is also studied using a model. Possible applications of such electron bunches are reviewed, including obtaining attosecond pulses of tunable coherent radiation in UV and X-ray regions. V.A.Papadichev, Proceedings of EPAC08, p.2815. V.A.Papadichev, Proceedings of IPAC'10, Kyoto, Japan, p. 4372. * V.A.Papadichev, Proc. RUPAC-2010, TUPSAO10, p. 56.

THPC068	CSR and THz Emission Measurements at the Diamond Light Source	radiation, electron, dipole, vacuum	3050
	R. Bartolini, G. Cinque, G. Rehm, C.A. Thomas Diamond, Oxfordshire, United Kingdom I.P.S. Martin JAI, Oxford, United Kingdom
	After the successful implementation of the low alpha optics at Diamond we have started a characterisation of coherent THz emission with the aim of classifying the rich phenomenology of stable and bursting emission and to devise the best operational mode for potential THz users. In conjunction with the Diamond IR beamline B22, THz spectral data were acquired simultaneously with Schottky diode signals in the mm-wave region of the spectrum. We also report the results of comparison with numerical simulations made with the aim of reproducing the measured THz emission spectra and gaining further understanding on the mechanisms of the instability.

THPC079	Echo-enabled Harmonic Generation at DELTA	undulator, laser, electron, storage-ring	3074
	R. Molo, M. Bakr, H. Huck, M. Höner, S. Khan, A. Nowaczyk, A. Schick, P. Ungelenk, M. Zeinalzadeh DELTA, Dortmund, Germany
	Funding: Supported by DFG, BMBF, and the Federal State NRW We present conceptual studies of the realization of the echo-enabled harmonic generation (EEHG) technique proposed by G. Stupakov* as an upgrade of the present coherent harmonic generation (CHG) project at the DELTA storage ring*. EEHG allows to reach shorter wavelengths compared to the CHG scheme. In addition to the optical klystron used for CHG, a third undulator is needed for a second energy modulation of the electron bunch, followed by an additional strong dispersive section. Installing these insertion devices requires a new long straight section in the storage ring and a new lattice configuration. G. Stupakov Phys. Rev. Lett. 10², 074801 (2009) ** A. Schick et al., this conference

THPC087	Saturation Effect on VUV Coherent Harmonic Generation at UVSOR-II	laser, electron, simulation, FEL	3098
	T. Tanikawa, M. Adachi, M. Katoh, J. Yamazaki, H. Zen UVSOR, Okazaki, Japan M. Hosaka, Y. Taira, N. Yamamoto Nagoya University, Nagoya, Japan
	Light source technologies based on laser seeding are under development at the UVSOR-II electron storage ring. In the past experiments, we have succeeded in generating coherent harmonics (CHs) in deep ultraviolet (UV) and vacuum UV (VUV) region and also in generating CH with variable polarizations in deep UV. In previous conference, we reported an introduction of new-constructed spectrometer for VUV and results of spectra measurement, undulator gap dependence, and injection laser power dependence on VUV CHs. This time we have successfully observed saturation on CHs intensities　and have found some interesting phenomena in different harmonic orders. In this conference, we will discuss the results of some systematic measurements and those analytical and particle tracking simulations*. M. Labat et al., Phys. Rev. Lett. 10¹ (2008) 164803. T. Tanikawa et al., Proc. IPAC'10, TUPE029, p. 2206 (2010). *T. Tanikawa et al., Appl. Phys. Express 3 (2010) 122702.

THPC096	Soft X-ray Free-electron Laser with a 10-time Reduced Size	electron, undulator, FEL, laser	3113
	Y.-C. Huang, F.H. Chao, C.H. Chen, K.Y. Huang NTHU, Hsinchu, Taiwan P.J. Chou NSRRC, Hsinchu, Taiwan
	Funding: This work is supported by National Science Council under Contract NSC 99-2112-M-007 -013 -MY3. We present a 30-m long soft x-ray FEL consisting of a 5-MeV photoinjector, a 150 MeV linac, a magnetic chicane compressor, and a 3-m long undulator. We employ both the 3rd and the 4th harmoincs of a Nd laser at 355 and 266 nm, respectively, to illuminate the cathode of the photoinjector. Owing to the beating of the two lasers, the emitted electron beam is modulated at 282 THz. The electrons are further accelerated to 150 MeV and, after acceleration, compressed by 33 times in a magnetic chicane. The temporal compression of the electron macropulse increases the electron bunching frequency to 9.3 PHz, corresponding to a soft x-ray wavelength of 32.2 nm. We adopt a solenoid-derived staggered array undulator* with a 3-m length, 5 mm undulator period, and 1.2 mm gap. With a solenoid field of 10 kG, we estimate an undulator parameter of 0.4 and a corresponding radiation wavelength of 32.2 nm for a 150 MeV driving beam. With 3.3-kA peak current, 0.03% energy spread, 2 mm-mrad emittance, and 80-micron beam radius at the undulator entrance, the GENESIS code predicts 0.2 GW radiation power from the 3-m long undulator for an initial bunching factor of merely 10 ppm. * Y.C. Huang, H.C. Wang, R.H. Pantell, and J. Feinstein, "A staggered-array wiggler for far infrared, free-electron laser operation," IEEE J. Quantum Electronics 30 (1994) 1289.

THPO035	Computer Investigation of Efficiency Enhancement in Coaxial Gyrotron Backward Wave Oscillators	electron, simulation, plasma, injection	3418
	V.M. Khoruzhiy NSC/KIPT, Kharkov, Ukraine
	The gyrotron backward wave oscillator (gyro-BWO) is a high frequency (HF) powerful oscillator for cm and mm wavelengths,,*.Gyro-oscillators are possible devices for accelerators techniques. For efficiency enhancement in gyro-devices we suggest profiling of guiding magnetic field Hg(z) at longitudinal direction z by special law, namely Hg(z)=Hg0(1+alfa(z/L)f(z/L))*0.5 where Hg0 is amplitude of homogenous guiding magnetic field, alfa is non-homogeneity amplitude, L is waveguide length and function f(z/L))is similarly to the shape (envelope) of longitudinal distribution of HF electrical field E(z) in gyro-device along longitudinal coordinate z. For investigated gyro-BWO f(z/L)=(cos(piz/2L))*m, f(0)=1, f(L)=0, L=60cm, m=6 and pi=3.14. We obtained enhancing of gyro-BWO’s efficiency from 11% (homogenous distribution of guiding magnetic field) up to 32% (non-homogenous one) due to profiling of magnetic field under conditions above. A.V.Gaponov et al., Izv. VUZov(USSR), Radiofizika 10(9), 10, 1967. V.Khoruzhiy et al., Phys. J.of Ukraine 49(2), 126, 2004. * V.Khoruzhiy et al., Phys. J.of Ukraine 50(11), 1230, 2005.

THPS001	Experimental Studies of Beam Loss during Low Energy Operation with Electron Cooled Heavy Ions in the ESR	ion, emittance, space-charge, resonance	3424
	P.A. Görgen, O. Boine-Frankenheim TEMF, TU Darmstadt, Darmstadt, Germany S. Appel, C. Dimopoulou, S.A. Litvinov, M. Steck GSI, Darmstadt, Germany
	At the ESR at GSI electron cooled heavy ion beams are decelerated to 4 MeV/u and extracted for the HITRAP experiment. We will report about cooling equilibrium measurements at 4 and 30 MeV/u for Ar¹⁸⁺ coasting beams. We compare the equilibrium beam parameters with results from beam dynamics simulations using the BETACOOL code and an analytic model of reduced complexity. The time slot in which HITRAP accepts beam is 2μs long. For optimum efficiency the beam has to be bunched to this length before extraction. The obtained bunch profiles are compared to longitudinal beam dynamics simulations. Our measurements show that at both energies bunching leads to severe beam loss. The estimated transverse space charge tune shifts during the rf bunching indicate that resonance crossing might be responsible for the observed the beam loss. The influence of the tune shift will be further evaluated through resonance measurements.

Paper

Title

Other Keywords

Page

MOOCB02

Commissioning and Performance of the Beam Monitor System for XFEL/SPring-8 “SACLA”

cavity, electron, undulator, FEL

47

Y. Otake, C. Kondo, H. Maesaka
RIKEN Spring-8 Harima, Hyogo, Japan
H. Ego, S. Matsubara, T. Matsumoto, T. Sakurai, H. Tomizawa, K. Yanagida
JASRI/SPring-8, Hyogo-ken, Japan
S.I. Inoue
SES, Hyogo-pref., Japan

The construction of a beam monitor system for XFEL/SPring 8 “SACLA” was completed. The system was developed to realize a spatial resolution of less than 3 um to align a beam orbit for an undulator section with about 100 m long and a temporal resolution to measure bunch lengths from 1 ns to 30 fs to maintain a constant peak beam current conducting stable SASE lasing. The system principally comprises cavity type beam position monitors (BPM), current monitors (CT), screen monitors (SCM) and bunch length measurement instruments, such as an rf deflector and CSR detectors. Commissioning of SACLA started from March 2011, and the monitors performed sufficient roles to tune beams for the lasing. The achieved over-all performances of the system including DAQ are: the BPM have spatial resolution of 300 nm, the bunch length monitors observe bunch lengths from 1ns in an injector with velocity bunching to less than 30 fs after three-stage bunch compressors. The less than a 3 um spatial resolution of the SCM was also confirmed in practical beam operation. By these fulfilled performances, the stable lasing of SACLA will be achieved. This report describes commissioning, performance of the system.

Slides MOOCB02 [7.516 MB]

MOPC023

Design of a C-band 6 MeV Standing-wave Linear Accelerating Structure

coupling, electron, impedance, simulation

119

J.H. Shao, H. Chen, Q.Z. Xing
TUB, Beijing, People's Republic of China

We design a C-band standing-wave biperiodic on-axis coupled linear accelerating structure for industrial and medical applications. It’s less than 300mm long; consists of 3 bunching cells and 9 normal cells. It can accelerate electrons to 6MeV and the pulsed beam current is 100mA. The RF power source is a 2.5MW magnetron. We implement 2D cells geometry optimization by SUPERFISH, beam dynamics study by PARMELA and full scale 3D calculations by MAFIA codes.

MOPC060

Bunching-frequency Multiplication for a THz Pulse-train Photoinjector

electron, linac, laser, acceleration

220

Y.-C. Huang, F.H. Chao, C.H. Chen, K.Y. Huang
NTHU, Hsinchu, Taiwan

Funding: This work is supported by National Science Council under Contract NSC 99-2112-M-007 -013 -MY3.
A THz-pulse-train photoinjector* employs a THz-pulse-train laser as its driver laser to generate a beam with a bunching frequency in the THz range. However a laser frequency is on the order of a few hundred THz. It is not possible to generate a beam from the pulse-train photoinjector with a bunching frequency exceeding the laser’s carrier frequency. In view of the strong demand for a compact x-ray free-electron laser (FEL), it is highly desirable to multiply the bunching frequency of the beam from a pulse-train injector to the x-ray frequencies. We propose to chirp the energy of the THz electron pulse train in an accelerator and compress the whole beam in a magnet to increase the electron bunching frequency. Our study shows a compression ratio or a bunching-frequency multiplication factor of a few tens is achievable from a properly designed magnetic chicane compressor. The bunching factor, however, is unfortunately degraded due to the energy chirp, emittance growth, and wake-field generation. In the conference, we will show that a bunching factor of a few ppm in the bunch-frequency multiplied beam is sufficient to build up the FEL power from a 10-time length reduced undulator.
* Y. C. Huang, “Laser-beat-wave bunched beam for compact superradiance sources,” International Journal of Modern Physics B, Vol. 21 Issue 3/4, p277-286 (2007).

MOPC150

High Charge PHIN Photo Injector at CERN with Fast Phase Switching within the Bunch Train for Beam Combination

laser, cathode, vacuum, gun

430

M. Divall Csatari, A. Andersson, B. Bolzon, E. Bravin, E. Chevallay, A.E. Dabrowski, S. Döbert, V. Fedosseev, C. Heßler, T. Lefèvre, S. Livesley, R. Losito, O. Mete, M. Olvegård, M. Petrarca, A. Rabiller
CERN, Geneva, Switzerland
A. Drozdy
BUTE, Budapest, Hungary
D. Egger
EPFL, Lausanne, Switzerland

The high charge PHIN photo-injector was developed within the frame of the European CARE program to provide an alternative to the drive beam thermionic gun in CTF3 (CLIC Test Facility) at CERN. In PHIN 1908 bunches are delivered with bunch spacing of 1.5 GHz and 2.33 nC charge per bunch. Furthermore the drive beam generated by CTF3 requires several fast 180 deg phase-shifts with respect to the 1.5 GHz bunch repetition frequency in order to allow the beam combination scheme developed at CTF3. A total of 8 sub-trains, each 140 ns long and shifted in phase with respect to each other, have to be produced with very high phase and amplitude stability. A novel fiber modulator based phase-switching technique developed on the laser system provides this phase-shift between two consecutive pulses much faster and cleaner than the base line scheme, where a thermionic electron gun and sub-harmonic bunching are used. The paper describes the fiber-based switching system and the measurements verifying the scheme. Stability measurements are presented for the phase-coded system. The paper also discusses the latest 8nC charge production and cathode life-time studies on Cs2Te.

MOPS004

Mitigation of Beam Instability due to Space Charge Effects at 3 GeV RCS in J-PARC

impedance, space-charge, kicker, injection

595

Y. Shobuda, M. Yamamoto
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
Y.H. Chin
KEK, Ibaraki, Japan
F. Tamura
KEK/JAEA, Ibaraki-Ken, Japan

In order to accomplish high intensity proton beams, it is important to identify the impedance source in accelerators. At 3 GeV rapid cycling synchrotron (RCS) in Japan Proton Research Complex (J-PARC), the kicker impedance is the most dominant among such impedance sources. Beam instability can be observed by correcting chromaticity during the acceleration. Growth rate due to the beam instability can be reduced by making peak current larger (bunching factor smaller). In other words, it is experimentally found that space charge effects mitigate the beam instability.

MOPS008

Simulation of Longitudinal Emittance Control in J-PARC RCS for 400 MeV Injection

extraction, emittance, injection, simulation

607

M. Yamamoto, M. Nomura, A. Schnase, T. Shimada, F. Tamura
JAEA/J-PARC, Tokai-mura, Japan
E. Ezura, K. Hara, K. Hasegawa, C. Ohmori, A. Takagi, K. Takata, M. Toda, M. Yoshii
KEK, Ibaraki, Japan

The injection energy upgrade of the J-PARC RCS from 181 MeV to 400 MeV is scheduled, this is necessary to achieve the design beam intensity. The high intensity beam is delivered to the MR, and the space charge effect at the MR injection should be alleviated by optimizing the longitudinal beam emittance at RCS extraction. This is realized by matching the shape of the beam emittance between the RCS and the MR. We describe the results of particle tracking simulation with the longitudinal emittance control during the whole acceleration period of the RCS.

MOPS019

High Intensity Longitudinal Dynamics Studies for Higher Energy Injection into the ISIS Synchrotron

injection, simulation, space-charge, linac

640

R.E. Williamson, D.J. Adams, C.M. Warsop
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom

ISIS is the world’s most productive pulsed neutron and muon source, at the Rutherford Appleton Laboratory in the UK. Operation is centred on a loss-limited 50 Hz proton synchrotron which accelerates 3·10¹³ protons per pulse from 70 MeV to 800 MeV, delivering a mean beam power of 0.2 MW. Present studies on ISIS upgrades are focussed on a new linac for higher energy injection into the existing ring, potentially increasing beam current through reduction in space charge and optimized injection. Studies assume injection of a chopped beam at 180 MeV and offer the possibility of beam powers in the 0.5 MW regime. A critical aspect of such an upgrade is the longitudinal dynamics, associated RF parameters, space charge levels and stringent requirements on beam loss. This paper outlines studies optimizing longitudinal parameters including key design requirements such as bunching factor and satisfying the Keil-Schnell-Boussard stability criterion throughout acceleration. Work developing and benchmarking the in-house longitudinal dynamics code used for these studies is also summarized.

MOPS035

Energy Spreads by Transient Beam Loading Effect in Pulsed RF Linac

gun, electron, linac, beam-loading

679

S.H. Kim, M.-H. Cho, G. Ha, H.R. Yang
POSTECH, Pohang, Kyungbuk, Republic of Korea
W. Namkung, S.J. Park
PAL, Pohang, Kyungbuk, Republic of Korea
J.-S. Oh
NFRI, Daejon, Republic of Korea

Funding: Work partly supported by KAPRA and POSTECH Physics BK21 Program
RF linacs for high power beams are operated in the fully beam-loaded condition for the power efficiency. In this condition, temporal energy spreads are induced by the transient beam loading effect. Irradiation sources require the beam energy of less than 10 MeV to prevent undesirable neutron production. In order to maximize the beam power and maintain the beam energy in a safe value, we need to suppress the temporal energy spreads. In an L-band traveling-wave linac for irradiation sources, the high energy electrons are suppressed by the beam current modulation with the RF power modulation. As a result, the average beam energy and the corresponding beam power are improved by nearly 60% compared to the case without any modulations.

TUPC038

A Low Energy Thermionic RF Gun Linac for Ultrashort Electron Beam

linac, gun, electron, klystron

1081

J.-Y. Hwang, J.H. Chen, W.K. Lau, A.P. Lee, T.H. Wu
NSRRC, Hsinchu, Taiwan
N.Y. Huang
NTHU, Hsinchu, Taiwan

A low energy test linac is being constructed at NSRRC for technological development of high brightness electron injector. It is a 29 MeV S-band linac that equipped with a high gradient thermionic cathode rf gun for generation of ultrashort relativistic electron beam by velocity bunching in the rf linac section located at downstream. High quality GHz-repetition-rate electron pulses of about 30 pC in bunch charge, pulse duration as short as 100 fsec can be produced from this test facility. It can be used as the driver for future light source experiments such as ultrafast head-on inverse Compton scattering (ICS) X-ray source and intense coherent THz free electron lasers.

TUPC094

Development of High-speed Differential Current-transformer Monitor

electron, gun, monitoring, status

1227

S. Matsubara, H. Ego, K. Yanagida
JASRI/SPring-8, Hyogo-ken, Japan
A. Higashiya, S.I. Inoue, Y. Otake
RIKEN/SPring-8, Hyogo, Japan
H. Maesaka
RIKEN Spring-8 Harima, Hyogo, Japan

The XFEL, which was named SACLA, was constructed in the SPring-8 site. In the SACLA, the bunch length of an electron beam is compressed from 1 ns to 30 fs, and the beam charge is decreased to obtain a genuine electron beam from 1nC to 0.3 nC for lasing. A new current-transformer (CT) monitor, which should measure the charge of the electron beam and make bunch length observation in velocity bunching process, was developed with two advantageous properties. One is differential output signal which suppresses common-mode noise from the thyratron of a klystron modulator by a factor of ten. Another property is high-speed signal output which provides a possibility to measure the bunch length and the time-of-flight (TOF) at the injector part of the SACLA. The output signal has 200 ps rise-time and a pulse width of 400 ps (FWHM) for an impulse beam. We successfully observed the bunch length between 1 ns and 400 ps around a 238 MHz buncher cavity. Moreover, we measured the TOF between two CTs with a few picoseconds resolution for a low-energy beam around 1 MeV. Thus, the new CT performance was confirmed to be sufficient for the SACLA.

TUPS080

Low Energy Bunching with a Double Gap RF Buncher

ion, ion-source, proton, injection

1725

H. von Jagwitz, U. Hagen, O. Heid, S. Setzer
Siemens AG, Erlangen, Germany

A compact double gap bunching system for low energy proton beams is presented. The system is designed for the bunching of a low current proton beam (less than 50μA) with an energy of 10 keV. The buncher operates at 150 MHz and bunches without significantly changing the beam energy. The beam is generated by an Electron Beam Ion Source and has to be bunched for the subsequent acceleration in a 150 MHz linear accelerator. The buncher contains two short gaps and an RF electrode inbetween. Thus the full length of the buncher in the beamline is in the range of 2 cm. The location of the bunch focus depends on the buncher power. The bunched beam was analysed at a distance of 550 mm with a fast faraday cup. The bunching effectivity was determined as 50%, which means that 50% of the protons of the beam were located in bunches with a width of 60°, which is a reasonable value of acceptance for a conventional accelerator cavity. Some theory and detailed results will be presented.

WEPC018

Self-focusing Effects in Compact C-band Standing-wave Accelerating Structure for X-ray Imaging Applications

focusing, electron, accelerating-gradient, linac

2046

H.R. Yang, M.-H. Cho, S.H. Kim, W. Namkung, S.J. Park
POSTECH, Pohang, Kyungbuk, Republic of Korea
J.-S. Oh
NFRI, Daejon, Republic of Korea

In electron RF linacs for industrial X-ray imaging applications, compact structures are preferred for mobility. The electron beam spot size of 1 – 2 mm is required for the spatial resolution of images at the X-ray conversion target. Applying self-focusing effects to the accelerating structure, external magnets can be removed and then the accelerator system becomes more compact. We design a C-band electron linac, which is capable of producing 6-MeV, 80-mA pulsed electron beams with an RF power of 1.5 MW. It uses a bi-periodic and on-axis-coupled accelerating structure with a built-in bunching section. It uses the π/2-mode standing-waves. The first bunching cell has an asymmetric geometry which maximizes the RF phase focusing. On the other hand, the normal cells are designed for the electrostatic focusing to be maximized. In this paper, we present design details of the accelerating cells and the beam dynamics simulation by the PARMELA code.

WEPS005

Investigation of Intrabeam Scattering in the Heavy Ion Storage Ring TSR

ion, electron, scattering, storage-ring

2490

S.T. Artikova, M. Grieser, J. Ullrich
MPI-K, Heidelberg, Germany

Intrabeam scattering (IBS) is a multiple scattering effect between stored beam particles. It leads to diffusion in all three spatial dimensions and thus, causes an expansion of the whole beam. IBS plays an important role in the equilibrium diameter of a low-velocity, electron-cooled ion beam. IBS effects for coasting and bunched 12C⁶⁺ ion beams at an energy of 73.3 MeV were studied using the TSR heavy ion cooler storage ring. Experimental results of the IBS rates are presented.

WEPZ006

Forming Attosecond Electron Pulses in Space-charge Dominated Regime

electron, radiation, laser, acceleration

2775

V.A. Papadichev
LPI, Moscow, Russia

Production of high-current attosecond electron pulses requires studying of the final bunching stage, which inevitably is space-charge dominated [*, **, ***]. Two models are studied, both allow solving a one-dimensional equation of motion. The first is for a spherical bunch, which corresponds to a short emitted pulse from a one-spike cathode of diameter approximately equal to its length. The second model is suited for pulses emitted from a multi-spike or multi-blade cathode. The bunch in the latter case is a thin plate and its evolution can be studied by also solving one-dimensional equation of motion. It was shown that bunches of 10-attosecond (as) duration with peak current of dozens of amperes can be obtained when using a carbon dioxide laser and less than 0.1-as duration with currents up to 1 MA when employing a neodymium laser. Beam focusing in transverse directions is also studied using a model. Possible applications of such electron bunches are reviewed, including obtaining attosecond pulses of tunable coherent radiation in UV and X-ray regions.
* V.A.Papadichev, Proceedings of EPAC08, p.2815.
** V.A.Papadichev, Proceedings of IPAC'10, Kyoto, Japan, p. 4372.
*** V.A.Papadichev, Proc. RUPAC-2010, TUPSAO10, p. 56.

THPC068

CSR and THz Emission Measurements at the Diamond Light Source

radiation, electron, dipole, vacuum

3050

R. Bartolini, G. Cinque, G. Rehm, C.A. Thomas
Diamond, Oxfordshire, United Kingdom
I.P.S. Martin
JAI, Oxford, United Kingdom

After the successful implementation of the low alpha optics at Diamond we have started a characterisation of coherent THz emission with the aim of classifying the rich phenomenology of stable and bursting emission and to devise the best operational mode for potential THz users. In conjunction with the Diamond IR beamline B22, THz spectral data were acquired simultaneously with Schottky diode signals in the mm-wave region of the spectrum. We also report the results of comparison with numerical simulations made with the aim of reproducing the measured THz emission spectra and gaining further understanding on the mechanisms of the instability.

THPC079

Echo-enabled Harmonic Generation at DELTA

undulator, laser, electron, storage-ring

3074

R. Molo, M. Bakr, H. Huck, M. Höner, S. Khan, A. Nowaczyk, A. Schick, P. Ungelenk, M. Zeinalzadeh
DELTA, Dortmund, Germany

Funding: Supported by DFG, BMBF, and the Federal State NRW
We present conceptual studies of the realization of the echo-enabled harmonic generation (EEHG) technique proposed by G. Stupakov* as an upgrade of the present coherent harmonic generation (CHG) project at the DELTA storage ring**. EEHG allows to reach shorter wavelengths compared to the CHG scheme. In addition to the optical klystron used for CHG, a third undulator is needed for a second energy modulation of the electron bunch, followed by an additional strong dispersive section. Installing these insertion devices requires a new long straight section in the storage ring and a new lattice configuration.
* G. Stupakov Phys. Rev. Lett. 10², 074801 (2009)
** A. Schick et al., this conference

THPC087

Saturation Effect on VUV Coherent Harmonic Generation at UVSOR-II

laser, electron, simulation, FEL

3098

T. Tanikawa, M. Adachi, M. Katoh, J. Yamazaki, H. Zen
UVSOR, Okazaki, Japan
M. Hosaka, Y. Taira, N. Yamamoto
Nagoya University, Nagoya, Japan

Light source technologies based on laser seeding are under development at the UVSOR-II electron storage ring. In the past experiments, we have succeeded in generating coherent harmonics (CHs) in deep ultraviolet (UV) and vacuum UV (VUV) region and also in generating CH with variable polarizations in deep UV*. In previous conference, we reported an introduction of new-constructed spectrometer for VUV and results of spectra measurement, undulator gap dependence, and injection laser power dependence on VUV CHs**. This time we have successfully observed saturation on CHs intensities　and have found some interesting phenomena in different harmonic orders. In this conference, we will discuss the results of some systematic measurements and those analytical and particle tracking simulations***.
*M. Labat et al., Phys. Rev. Lett. 10¹ (2008) 164803.
**T. Tanikawa et al., Proc. IPAC'10, TUPE029, p. 2206 (2010).
***T. Tanikawa et al., Appl. Phys. Express 3 (2010) 122702.

THPC096

Soft X-ray Free-electron Laser with a 10-time Reduced Size

electron, undulator, FEL, laser

3113

Y.-C. Huang, F.H. Chao, C.H. Chen, K.Y. Huang
NTHU, Hsinchu, Taiwan
P.J. Chou
NSRRC, Hsinchu, Taiwan

Funding: This work is supported by National Science Council under Contract NSC 99-2112-M-007 -013 -MY3.
We present a 30-m long soft x-ray FEL consisting of a 5-MeV photoinjector, a 150 MeV linac, a magnetic chicane compressor, and a 3-m long undulator. We employ both the 3rd and the 4th harmoincs of a Nd laser at 355 and 266 nm, respectively, to illuminate the cathode of the photoinjector. Owing to the beating of the two lasers, the emitted electron beam is modulated at 282 THz. The electrons are further accelerated to 150 MeV and, after acceleration, compressed by 33 times in a magnetic chicane. The temporal compression of the electron macropulse increases the electron bunching frequency to 9.3 PHz, corresponding to a soft x-ray wavelength of 32.2 nm. We adopt a solenoid-derived staggered array undulator* with a 3-m length, 5 mm undulator period, and 1.2 mm gap. With a solenoid field of 10 kG, we estimate an undulator parameter of 0.4 and a corresponding radiation wavelength of 32.2 nm for a 150 MeV driving beam. With 3.3-kA peak current, 0.03% energy spread, 2 mm-mrad emittance, and 80-micron beam radius at the undulator entrance, the GENESIS code predicts 0.2 GW radiation power from the 3-m long undulator for an initial bunching factor of merely 10 ppm.
* Y.C. Huang, H.C. Wang, R.H. Pantell, and J. Feinstein, "A staggered-array wiggler for far infrared, free-electron laser operation," IEEE J. Quantum Electronics 30 (1994) 1289.

THPO035

Computer Investigation of Efficiency Enhancement in Coaxial Gyrotron Backward Wave Oscillators

electron, simulation, plasma, injection

3418

V.M. Khoruzhiy
NSC/KIPT, Kharkov, Ukraine

The gyrotron backward wave oscillator (gyro-BWO) is a high frequency (HF) powerful oscillator for cm and mm wavelengths*,**,***.Gyro-oscillators are possible devices for accelerators techniques. For efficiency enhancement in gyro-devices we suggest profiling of guiding magnetic field Hg(z) at longitudinal direction z by special law, namely Hg(z)=Hg0*(1+alfa*(z/L)*f(z/L))**0.5 where Hg0 is amplitude of homogenous guiding magnetic field, alfa is non-homogeneity amplitude, L is waveguide length and function f(z/L))is similarly to the shape (envelope) of longitudinal distribution of HF electrical field E(z) in gyro-device along longitudinal coordinate z. For investigated gyro-BWO f(z/L)=(cos(pi*z/2L))**m, f(0)=1, f(L)=0, L=60cm, m=6 and pi=3.14. We obtained enhancing of gyro-BWO’s efficiency from 11% (homogenous distribution of guiding magnetic field) up to 32% (non-homogenous one) due to profiling of magnetic field under conditions above.
* A.V.Gaponov et al., Izv. VUZov(USSR), Radiofizika 10(9), 10, 1967.
** V.Khoruzhiy et al., Phys. J.of Ukraine 49(2), 126, 2004.
*** V.Khoruzhiy et al., Phys. J.of Ukraine 50(11), 1230, 2005.

THPS001

Experimental Studies of Beam Loss during Low Energy Operation with Electron Cooled Heavy Ions in the ESR

ion, emittance, space-charge, resonance

3424

P.A. Görgen, O. Boine-Frankenheim
TEMF, TU Darmstadt, Darmstadt, Germany
S. Appel, C. Dimopoulou, S.A. Litvinov, M. Steck
GSI, Darmstadt, Germany

At the ESR at GSI electron cooled heavy ion beams are decelerated to 4 MeV/u and extracted for the HITRAP experiment. We will report about cooling equilibrium measurements at 4 and 30 MeV/u for Ar¹⁸⁺ coasting beams. We compare the equilibrium beam parameters with results from beam dynamics simulations using the BETACOOL code and an analytic model of reduced complexity. The time slot in which HITRAP accepts beam is 2μs long. For optimum efficiency the beam has to be bunched to this length before extraction. The obtained bunch profiles are compared to longitudinal beam dynamics simulations. Our measurements show that at both energies bunching leads to severe beam loss. The estimated transverse space charge tune shifts during the rf bunching indicate that resonance crossing might be responsible for the observed the beam loss. The influence of the tune shift will be further evaluated through resonance measurements.