EPAC 2006 - Classification:03 Linear Colliders, Lepton Accelerators and New Acceleration Techniques/T02 Lepton Sources

03 Linear Colliders, Lepton Accelerators and New Acceleration Techniques

T02 Lepton Sources

Paper	Title	Page
WEPLS043	Progress of the Rossendorf SRF Gun Project	2469
	D. Janssen, A. Arnold, H. Buettig, R. Hempel, U. Lehnert, P. Michel, K. Moeller, P. Murcek, Ch. Schneider, R. Schurig, F. Staufenbiel, J. Teichert, R. Xiang FZR, Dresden T. Kamps, D. Lipka, F. Marhauser BESSY GmbH, Berlin W.-D. Lehmann IfE, Dresden J. Stephan IKST, Drsden V. Volkov BINP SB RAS, Novosibirsk I. Will MBI, Berlin
	In this paper we report the status and the progress of the superconducting RF gun project in Rossendorf. The gun is designed for cw operation mode with 1 mA current and 10 MeV electron energy. The cavity consists of three cells with TESLA geometry, a special designed half-cell in which the photo cathode will be inserted and a choke filter, which prevents the leakage of RF power by the coaxial line between the cathode and the cavity cell. A double tuner allows the tuning of the half-cell and the TESLA cells separately. In 2005 the fabrication of two cavities with RRR300 and RRR40 was finished. We present the results of the field measurement and the warm tuning of the cavity cells as well as the tuning and performance measurement of the choke filter. The fabrication of the double tuner has been also finished. In a test bench we measured the properties of the tuner (tuning range, resolution) at LN2 temperature. Further activities concern the diagnostic beam line of the gun, the new cathode preparation and cathode transfer system, the driver laser and the LHe transfer line.
WEPLS044	Design of a Superconducting Cavity for a SRF Injector	2472
	D. Janssen FZR, Dresden V. Volkov BINP SB RAS, Novosibirsk
	In a collaboration between BESSY, DESY, FZR, MBI and BINP a 3-1/2 cell superconducting RF electron gun is under development at the FZ - Rossendorf. The status of the project and the progress obtained in the last year is reported on this conference. The motivation for the design of a new gun cavity, presented in this paper, is the new FEL project at BESSY. This FEL is designed for a bunch charge of 2.5 nC and the transverse emittance should be comparable with that of the current SRF gun project. In order to compensate the high bunch charge a high electric field on the cavity axis is necessary. In the present paper we will present the design of a 1-1/2 cell cavity for a superconducting RF gun. The active length of the cavity (without beam tube) is 14.4 cm. For the magnetic peak field the conservative value of 130 mT is assumed. The obtained particle energy is 6.6 MeV, corresponding to an accelerating field strength of 45.6 MV/m . In the TESLA cavity the same magnetic peak field is connected with an accelerating field strength of approximately 31 MV/m. Tracking calculation of electron bunches are in progress and will be also reported.
WEPLS045	Study on Low-energy Positron Polarimetry	2475
	A. Schaelicke, K. Laihem, S. Riemann, A. Ushakov DESY Zeuthen, Zeuthen R. Dollan, Th. Lohse Humboldt University Berlin, Institut für Physik, Berlin
	For the design of the International Linear Collider (ILC) a polarised positron source based on a helical undulator system has been proposed. In order to optimise the positron beam, i.e., to ensure high intensity as well as high degree of polarisation, a measurement of the polarisation close to the positron creation point is envisaged. In this contribution methods to determine the positron polarisation at low energies are investigated. These studies are based on simulations with an extended version of Geant4, which allows the tracking of polarised particles taking into account the spin effects.
WEPLS046	Radiation Levels and Activation at the ILC Positron Source	2478
	A. Ushakov, S. Riemann DESY Zeuthen, Zeuthen Eckhard. Elsen, K. Floettmann DESY, Hamburg K.N. Sanosyan CANDLE, Yerevan
	An undulator-based positron source is recommended as baseline design for the International Linear Collider (ILC). Photons generated by electrons passing an undulator hit a rotating target and create electron-positron pairs. The positrons are captured and accelerated. An advantage of this source is the significantly lower radiation level in comparison to a conventional positron source which uses the electron beam directly to produce electron-positron pairs. The fluxes of neutrons and photons have been calculated with the particle transport code FLUKA. The activation of the positron source components has been estimated depending on the parameters of the source. The results for undulator-based and conventional positron sources are compared and presented.
WEPLS047	3-1/2 Cell Superconducting RF Gun Simulations	2481
	C.D. Beard, J.H.P. Rogers CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire F. Staufenbiel, J. Teichert FZR, Dresden
	A 3-1/2 cell superconducting RF photocathode gun is being developed at Forschungszentrum Rossendorf to produce a high peak current, low emittance electron beam. This technology is essential to the realisation of many large scale facilities. The gun is designed for CW operation mode with 1 mA current and 9.5 MeV electron energy, and it will be installed at the ELBE superconducting electron linear accelerator. The gun will have a 3-1/2 cell niobium cavity operating at 1.3 GHz. The cavity consists of three cells with TESLA geometry and a specially designed half-cell in which the photocathode will be placed. Typical ERL-based projects require ~100 mA average current, and therefore suitable upgrade paths are required. Simulations have been carried out to evaluate the design and to determine suitable upgrades for higher current operation. Simulations of alternative cathode surface shapes are presented. Several couplers have been identified that can provide higher power to the cavity, whose integration and suitability has been verified. All the investigations that have identified possible solutions to higher current operation are discussed in this report.
WEPLS048	Development of a Positron Production Target for the ILC Positron Source	2484
	I.R. Bailey, I.R. Bailey, J.B. Dainton, D.J. Scott Cockcroft Institute, Warrington, Cheshire V. Bharadwaj, J. Sheppard SLAC, Menlo Park, California P. Cooke, P. Sutcliffe Liverpool University, Science Faculty, Liverpool J.G. Gronberg, D.J. Mayhall, W.T. Piggott, W. Stein LLNL, Livermore, California
	The future International Linear Collider (ILC) will require of order 10¹⁴ positrons per second to fulfil its luminosity requirements. The current baseline design produces this unprecedented flux of positrons using an undulator-based source. In this concept, a collimated beam of 10MeV photons produced from the action of an undulator on the main electron beam of the ILC is incident on a conversion target. Positrons produced in the resulting electromagnetic shower can then be captured, accelerated and injected into a damping ring. The international community is pursuing several alternative technologies to develop a target capable of long-term operation in the intense photon beam. In the design being developed jointly by the Cockcroft Institute, LLNL and SLAC, a thin (0.4 radiation length) water-cooled Titanium alloy target wheel of diameter 4m is rotated at approximately 1000rpm to spread the incident power of each pulse over a wide area. We present the latest target design, report on the status of the target prototypes and computer models, and review the interplay between the target technology, capture optics, photon collimator and remote-handling systems.
WEPLS049	The Design of a Hybrid Photoinjector for High Brightness Beam Applications	2487
	D. Alesini, M. Ferrario, V. Fusco, B. Spataro INFN/LNF, Frascati (Roma) L. Ficcadenti, A. Mostacci, L. Palumbo Rome University La Sapienza, Roma B. O'Shea, J.B. Rosenzweig, G. Travish UCLA, Los Angeles, California
	In this paper, we illustrate the electromagnetic and beam dynamics design procedure of a new class of photoinjector, a hybrid standing/traveling wave structure. In this device a standing wave RF gun section is integrated with a downstream traveling wave structure through a coupling cell that feeds simultaneously the two sections. We discuss the advantages in RF and beam performance of the hybrid photoinjector compared to conventional systems. The electromagnetic design has been performed using the 2D and 3D electromagnetic codes Superfish and HFSS. Results of beam dynamics simulations in different operating conditions are also discussed.
WEPLS050	Experiments with Electron Cloud and Sources	2490
	M. Cavenago INFN/LNL, Legnaro, Padova G. Bettega, F. Cavaliere, D. Ghezzi, A. Illiberi, R. Pozzoli, M. Rome INFN-Milano, Milano
	The Penning-Malmberg trap ELTRAP installed at University of Milano can provide electron clouds of several sizes for study of non-linear physics: length ranges from 0.15 to 1 m, while diameter is varied between 25 mm and 70 mm by changing the electron source: filament or planar spiral. Vortices develop both in trapped and flowing electron beams. Slow instabilities, due to the accumulation of ions inside the trap are observed and cured by clearing fields. Results as a function of plasma size are described. Plan to install a third laser modulated electron source and additional diagnostic are also summarized.
WEPLS051	Dark Current Investigation of TTF and PITZ RF Guns	2493
	L. Monaco, P. Michelato, C. Pagani, P. Pierini, D. Sertore INFN/LASA, Segrate (MI) J.H. Han, S. Schreiber DESY, Hamburg M. Krasilnikov, F. Stephan DESY Zeuthen, Zeuthen
	The dark current is one of the limiting factor in the operation of RF guns at high gradient. The continuous request of higher brilliance sources and further emittance minimization, leads to apply higher gradients in the RF gun cavity, with the consequence of a significant dark current production. In this context we set up a collaborative effort to identify the dark current sources in the gun, in order to discriminate between the gun and cathode contribution. A critical analysis and organization of dark current measurements, taken during the operation of TTF and PITZ guns, with several cathodes operated at different accelerating fields and solenoids focusing, is presented. Potential areas of improvement are also discussed, together with a possible associated program.
WEPLS052	High QE Photocathode at FLASH	2496
	D. Sertore, P. Michelato, L. Monaco, C. Pagani INFN/LASA, Segrate (MI) J.H. Han, S. Schreiber DESY, Hamburg
	The RF gun-based photoinjector of the VUV-FEL/TTF at DESY continues to use high quantum efficiency (QE) photocathodes produced at LASA, Milano. To study the photocathode behavior during beam operation, an online QE monitoring tool has been installed. In this paper, we present the hardware and software setup for the online QE measurement and the results so far obtained. The measured QEs are usually higher than at TTF phase 1. We compare the QE values taken in the RF gun with data measured just after production with a continuous UV light source.
WEPLS053	RF Design of a Cartridge-type Photocathode RF Gun in S-band Linac	2499
	H. Moritani, Y. Muroya, A. Sakumi, T. Ueda, M. Uesaka UTNL, Ibaraki H. Hanaki, N. Kumagai, S. Suzuki, H. Tomizawa JASRI/SPring-8, Hyogo-ken J. Sasabe Hamamatsu Photonics K.K., Hamakita, Shizuoka J. Urakawa KEK, Ibaraki
	A cartridge-type photocathode RF gun is under development in collaboration with SPring-8 and Hamamatsu Photonics. Each type of cathode (Cs2Te, Mg, diamond, Ag-Cs-O) is sealed in a cartridge-type vacuum tube. Several tubes can be installed in a vacuum chamber. The cathode in the tube is inserted into a center hole in the back plate of the RF gun by a vacuum manipulator. These cartridge-type photocathodes with high QE or sensitivity for visible lights, which are prepared in a factory, can be used for a long time without vacuum breaking. Since a load-lock system for forming a new high QE film is not needed, the cartridge-type RF gun becomes compact. We are going to introduce this cartridge-type system to our linac with the BNL-GUN-IV RF gun this summer. Now, we are calculating the gun parameters of the transmission cavity which has a back plate with a center hole 8mm in diameter with SUPERFISH and simulating the beam dynamics after modifying the beam line to install the system with PARMELA. We aim to use reliable Mg and high-QE Cs2Te and try diamond and Ag-Cs-O for radiation chemistry applications. The detailed numerical design and construction will be presented.
WEPLS054	Higher-order Effect Compensation in Magnetic Compressor for < 50 fs Electron Bunch Generation	2502
	K. Kan, T. Kondoh, J. Yang, Y. Yoshida ISIR, Osaka
	An ultrashort electron bunch is essential for pulse radiolysis, which is a pump-probe measurement based on an ultrashort electron beam and an ultrashort light. In Osaka University, a laser photocathode electron linear accelerator with a magnetic compressor has been constructed for the femtosecond electron bunch generation. An electron beam with bunch length of 98 fs was successfully generated and used in pulse radiolysis. However, an electron beam with bunch length of < 50 fs is required for development of pulse radiolysis with time resolution of 100 fs. To generate such a short bunch, higher order disadvantage effects, which are caused by the fringing fields of the magnets in the compressor, should be compensated. In this paper, a compensation technique of higher-order effects was proposed by using a nonlinear energy modulation in the bunch produced in the linear accelerator by re-phasing the linac away from the zero-crossing of the rf (i.e., away from the linear slope). In the simulation, we compressed the electron bunch into 48 fs at bunch charge of 0.1 nC.
WEPLS055	Development of Double-decker Electron Beam Accelerator for Femto/attosecond Pulse Radiolysis	2505
	Y.K. Kuroda, T. Kondoh, J. Yang, Y. Yoshida ISIR, Osaka
	The study of electron-induced reactions in femto/attosecond time region is very important for the next electron beam nanofabrication. Pulse radiolysis with time resolution of sub-picosecond, as a powerful method to study such reactions in materials, has been developed by using radio-frequency electron accelerators and ultrashort lasers. In Osaka University, a new concept of double-decker electron beam accelerator is proposed for opening next pulse radiolysis on femto/attosecond time scale. The double electron beams with time delay of 1.4ns (350ps x 4) and bunch charge of 0.5-0.6 nC were generated in a photocathode electron accelerator by injecting two laser pulses into the photocathode. The beam energy of the two beams was 31.7MeV. The transverse normalized emittance was 3~6 mm-mrad for both the beams. The front of them is converted to Cherenkov light and used as a probe light source, and the back is used as a pump source. Both electron pulses are generated by one accelerator, resulting in no time jitter between the pump electron bunch and the probe laser pulse.
WEPLS056	R&D Status of the High-intense Monochromatic Low-energy Muon Source: PRISM	2508
	A. Sato, M. Aoki, Y. Arimoto, I. Itahashi, Y. Kuno, K. Kuriyama, T. Oki, T. Takayanagi, M. Yoshida Osaka University, Osaka M. Aiba, C. Ohmori, T. Yokoi, K. Yoshimura KEK, Ibaraki Y. Iwashita Kyoto ICR, Uji, Kyoto S. Machida CCLRC/RAL/ASTeC, Chilton, Didcot, Oxon Y. Mori KURRI, Osaka
	PRISM is a project of a future intense low-energy muon source, which combines monochromaticity and high purity. Its aimed intensity is about $10¹¹-10¹² muons per second. The muon beams will have a low kinetic energy of 20MeV so that it would be optimized for the stopped muon experiments such as searching the muon lepton flavor violating processes. PRISM consists of a pion capture section, a pion/muon transfer section and a phase rotation ssection. An FFAG is used as the phase rotator to achieve the monochromatic muon beams. This paper will describe design status of these sections as well as construction status of PRISM-FFAG.
WEPLS057	Equivalent Velocity Spectroscopy Based on Femtosecond Electron Beam Accelerator	2511
	S. Takemoto, T. Kondoh, J. Yang, Y. Yoshida ISIR, Osaka
	A new femtosecond pulse radiolysis system, which is called as "Equivalent Velocity Spectroscopy (EVS)" based on a photocathode rf linear accelerator and a femtosecond laser, is developed in ISIR for the study of primly process and ultrafast electron-induced reactions for the nanofabrication. In order to achieve a high time resolution on femtosecond scale, a femtosecond electron beam bunch produced by a photocathode accelerator and a synchronized femtosecond laser were used. The electron bunch and laser pulse were injected with an angle determined by the refractive index of the sample. The electron bunch was also rotated with a same angle, resulting in the time resolution degradation due to the velocity difference between light and the electron in the sample is thus avoided. A jitter compensation technique with a femtosecond streak camera was used to reduce the time jitter between the electron bunch and laser pulse. Moreover, in EVS, a technique of double laser pulse injection was used to improve the signal to noise ratio due to the fluctuation of the laser intensity during the measurement.
WEPLS058	Femtosecond Single-bunch Electron Linear Accelerator Based on a Photocathode RF Gun	2514
	J. Yang, K. Kan, T. Kondoh, A. Yoshida, Y. Yoshida ISIR, Osaka
	A femtosecond single-bunch electron linear accelerator based on a photocathode rf gun was developed in Osaka University for the study of radiation-induced ultrafast physical and chemical reactions. A 32 MeV single electron bunch with a bunch length of 98 fs in rms was generated successfully in the linear accelerator with a magnet bunch compressor. The dependences of the bunch length and the transverse emittance on the bunch charge were investigated experimentally and theoretically. The higher-order effects in the magnetic field were studied and compensated successfully by using a nonlinear energy-phase correlation in the bunch produced in the linear accelerator. By using the femtosecond electron bunch, an equivalent velocity spectroscopy with a synchronized femtosecond laser, as a new method with femtosecond time-resolution, was developed for study of the ultrafast reactions or phenomena on the femtosecond time scale.
WEPLS059	The PHIN Photoinjector for the CTF3 Drive Beam	2517
	R. Losito, H.-H. Braun, N. Champault, E. Chevallay, V. Fedosseev, A. Kumar, A.M. Masi, G. Suberlucq CERN, Geneva G. Bienvenu, B.M. Mercier, C.P. Prevost, R. Roux LAL, Orsay M. Divall, G.J. Hirst, G. Kurdi, W. E. Martin, I. O. Musgrave, I. N. Ross, E. L. Springate CCLRC/RAL, Chilton, Didcot, Oxon
	A new photoinjector for the CTF3 drive beam has been designed and is now being constructed by a collaboration among LAL, CCLRC and CERN within PHIN, the second Joint Research Activity of CARE. The photoinjector will provide a train of 2332 pulses at 1.5 GHz with a complex timing structure (sub-trains of 212 pulses spaced from one another by 333 ps or 999 ps) to allow the frequency multiplication scheme, which is one of the features of CLIC, to be tested in CTF3. Each pulse of 2.33 nC will be emitted by a Cs2Te photocathode deposited by a co-evaporation process to allow high quantum efficiency in operation (>3% for a minimum of 40 h). The 3 GHz, 2 1/2 cell RF gun has a 2 port coupler to minimize emittance growth due to asymmetric fields, racetrack profile of the irises and two solenoids to keep the emittance at the output below 20 pi.mm.mrad. The laser has to survive very high average powers both within the pulse train (15 kW) and overall (200 W before pulse slicing). Challenging targets are also for amplitude stability (<0.25% rms) and time jitter from pulse to pulse (<1ps rms). An offline test in a dedicated line is foreseen at CERN in 2007.
WEPLS060	CLIC Polarized Positron Source Based on Laser Compton Scattering	2520
	F. Zimmermann, H.-H. Braun, M. Korostelev, L. Rinolfi, D. Schulte CERN, Geneva S. Araki, Y. Higashi, Y. Honda, Y. Kurihara, M. Kuriki, T. Okugi, T. Omori, T. Taniguchi, N. Terunuma, J. Urakawa KEK, Ibaraki X. Artru, R. Chehab, M. Chevallier IN2P3 IPNL, Villeurbanne E.V. Bulyak, P. Gladkikh NSC/KIPT, Kharkov M.K. Fukuda, K. Hirano, M. Takano NIRS, Chiba-shi J. Gao IHEP Beijing, Beijing S. Guiducci, P. Raimondi INFN/LNF, Frascati (Roma) T. Hirose, K. Sakaue, M. Washio RISE, Tokyo K. Moenig DESY Zeuthen, Zeuthen H.D. Sato HU/AdSM, Higashi-Hiroshima V. Soskov LPI, Moscow V.M. Strakhovenko BINP SB RAS, Novosibirsk T. Takahashi Hiroshima University, Higashi-Hiroshima A. Tsunemi SHI, Tokyo V. Variola, Z.F. Zomer LAL, Orsay
	We describe the possible layout and parameters of a polarized positron source for CLIC, where the positrons are produced from polarized gamma rays created by Compton scattering of a 1.3-GeV electron beam off a YAG laser. This scheme is very energy effective using high finesse laser cavities in conjunction with an electron storage ring. We point out the differences with respect to a similar system proposed for the ILC.