FEL 2006 - List of Keywords (cathode)

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cathode

Paper	Title	Other Keywords	Page
MOBAU05	Status of Japanese XFEL Project and SCSS Test Accelerator	emittance, electron, undulator, radiation	33
	T. Shintake RIKEN Spring-8 Harima, Hyogo
	Japanese XFEL based on SASE, aming at generating 1 A X-ray with 8 GeV e-beam, has been funded. Construction 2006-2010, beam comissioning is scheduled in 2010. In order to estabilish technology for XFEL, SCSS test accelerator, e-beam 250 MeV, 60 nm minimum wavelength, has been constructed, now under beam comissioning. We hope to be able to report the first lasing.
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	Talk

MOPPH008	A Beam Shaper for the Optical Beamline of RF Photoinjectors	laser, radiation, electron, controls	53
	G. Klemz MBI, Berlin I. Will FZR, Dresden
	The transversal beam profile of a laser beam irradiating the photocathode has a significant influence on the emittance of the generated electron beam. Achieving the lowest emittance requires a flat-top beam profile. A typical laser, however, produces an intensity profile which is close to a Gaussian. That is why a special optical element, the so-called beam shaper, is required. We compare different technical solutions for the critical beam-shaping element. The demands on the design of the beamline resulting from the insertion of the beam shaper will be outlined. An aspherical lens pair of the Galilean type seems to be a favourable solution. It permits to precisely control the final intensity profile, it maintains both the temporal shape of the pulse and the coherence of the laser beam. Simulation of the propagation of the beam profile are presented. The described refractive beam-shaper significantly improves the energy efficiency of the complete beamline. It therefore allows to reduce the requirements regarding the energy of the laser pulses. Consequently, the application of an appropriately designed beam shaper can lead to a significant reduction of the overall costs of the laser.

MOPPH072	Ultra High Brightness Accelerator Design	emittance, electron, linac, acceleration	214
	R. J. Bakker, A. Adelmann, A. Anghel, M. Dehler, R. Ganter, S. C. Leemann, K. L. Li, M. Pedrozzi, J.-Y. Raguin, L. Rivkin, V. Schlott, F. Q. Wei, A. F. Wrulich PSI, Villigen
	The Low Emittance Gun (LEG) Project at the Paul Scherrer Institute (PSI) in Switzerland incorporates the development of an ultra low emittance electron-source to drive a cost-effective X-ray FEL. For this purpose the source is based on field-emitter technology followed by high gradient (1 MV, 0.25 GV/m) acceleration. However, even with such a design the emerging electron beam is fragile and it is not evident that the low emittance can be preserved in the following acceleration process. Here we present a concept to achieve this goal, i.e., the status of the electron source development and an overview of the acceleration concept. Emphasis is given to a 250 MeV accelerator design, which is suited to serve as an injector for an X-ray FEL at 0.1 nm (12.4 keV) and boosts the electron beam into a regime where space-charge forces become less dominant. K. Li et al., Proceedings of the FEL2005 Conference, Stanford, CA, USA, p. 483 (2005)

MOCAU04	Focal Point Laser-Field as Optical Seeder	laser, electron, radiation, coupling	242
	T. Shintake RIKEN Spring-8 Harima, Hyogo
	Focusing optical laser into its wavlength size, and crossing the electron beam through the focal point, interaction of electron with laser field becomes non zero, as a result, creates velocity modulation. In contrast with modulation scheme using undulator, this method does not require energy resonance condition to the electron beam, thus works all energy, even with energy chirp. Using it in front of the bunch compressor, with energy chirp, the wavelength can be compressed by large factor with bunch length compression.
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TUPPH022	Development of a Compact Cherenkov Free-Electron Laser in Terahertz Spectral Range	electron, focusing, radiation, laser	364
	M. R. Asakawa, N. Miyabe Kansai University, Osaka M. Kusaba, K. Nakao, Y. Tsunawaki OSU, Daito, Osaka
	A Cherenkov free-electron laser (CFEL) generating terahertz radiation is now being developed under the joint research of Osaka Sangyo university and Kansai university. The main feature of this CFEL is its compactness. Electron beamlets emitted by a Spindt cathode are accelerated up to 60 keV in a D. C. electron gun and then are injected into 100μm-gaps between stacked plates of silicon, which acts as radiator. The radiation frequency will be ranged from 0.8 to 2 THz according to the acceleration voltage. In order to suppress diverging of the beamlet with a high current density about 1kA/cm², the electron gun and the radiator section are immersed in a longitudinal magnetic field produced by a super-conducting (SC) coil. The total length of the CFEL section, i.e., the distance between the cathode and beam dumper, is 4 cm and the diameter of this section is less than 2 cm. Such compact laser module is placed in the bore of SC coil. In spite of the large size of the cryostat and the power supply of the SC coil, the total footprint is about 1×1 m².

TUPPH028	The Research of FIR-FEL in CAEP	electron, gun, wiggler, brightness	386
	X. Yang, X. Jin, M. Li, W. Li, Z. Xu CAEP/IAE, Mianyang, Sichuan
	The research of FIR-FEL has been undertaken about 10 years in CAEP and first lasing at center wavelength 115·10^-6 m was observed in March 2005. The facility consists of RF-gun, alpha magnet, L-band SW accelerator, beam transport line, wiggler, optical cavity and measurement system. At present, a high brightness photo cathode RF-gun is commissioning, the cathode material is Cs2Te. This injector will be used in the FIR-FEL project in the second half of this year. In this paper, the design consideration, the system layout, some experimental results are introduced.

TUPPH036	Optimization of the Injection System for Microtron-Based Terahertz FEL	microtron, electron, injection, beam-loading	403
	G. M. Kazakevich, G. I. Kuznetsov, V. M. Pavlov BINP SB RAS, Novosibirsk Y. U. Jeong, B. C. Lee, S. H. Park KAERI, Daejon
	A compact widely-tunable microtron-based terahertz Free Electron Laser (FEL) has been developed and during last few years operates for users. The laboratory-size, stable facility, at the macro-pulse power of tens of W is attractive for application in research laboratories and universities. Reliability in operation and stability of such microtron-based FEL is determined generally by the microtron injection system. Main parameters of the injection system were studied on the base of a 2-D tracking considering the frequency drift of the accelerating cavity as a result of variation of the beam loading caused by cathode overheating due to back bombardment with non-resonance electrons. The obtained results show that the injection system based on a thermionic single crystal LaB6 2.5 mm-in diameter emitter provides operation of the microtron-based FEL with standard deviation of the macro-pulse lasing power less than 10% during long-time work. Experimental check of the FEL during more than five years confirmed stable and reliable operation of the microtron-based FEL with the macro-pulse power of tens of W in the terahertz range.

TUPPH038	Commissioning of S-band RF GUN and Linac for the Mark-III FEL Facility at Duke University	gun, linac, electron, emittance	411
	Y. Kim, G. Edwards, M. Emamian, J. Gustavsson, S. M. Hartman, G. Swift, P. W. Wallace, P. Wang FEL/Duke University, Durham, North Carolina
	At the Free Electron Laser (FEL) Laboratory of Duke University, there is an S-band linac based Mark III FEL facility which can supply coherent FEL photon beam in the infrared wavelength range. To supply high quality electron beams and to have excellent pulse structure, we installed a new S-band RF GUN with the LaB6 cathode for the Mark III FEL facility in 2005. Since maximum repetition rates of macropulse and micropulse are 15 Hz and 2856 MHz, respectively, our new RF GUN can generate 17142 bunches within a 6 us long bunch train, and maximum 257130 bunches within one second. In this paper, we describe recent commissioning experiences of our newly installed S-band RF GUN and Linac for the Mark III FEL facility.

TUPPH039	Bright Electron Beams and Smith-Purcell Free-Electron Lasers	electron, laser, space-charge, radiation	415
	C. H. Boulware, H. L. Andrews, C. A. Brau, J. D. Jarvis Vanderbilt University, Nashville, Tennessee
	We have continued to develop the theory of Smith-Purcell free-electron lasers * by including the effects of losses in the grating and reflections of the evanescent wave at the ends of the grating. We estimate the magnitude of the reflection coefficient to be about 15 % based on published simulations*, and compute the effect on the start current and the frequency shift. Experiments to observe these effects are underway. H. L. Andrews, C. H. Boulware, C. A. Brau, and J. D. Jarvis, Phys. Rev. ST-AB 8, 050703 (2005). ** D. Li, Z. Yang, K. Imasaki, and G.-S. Park, Phys. Rev. ST-AB 9, 040701 (2006).

THPPH007	First RF-Measurements at the 3.5-Cell SRF-Photo-Gun Cavity in Rossendorf	gun, electron, coupling, simulation	567
	A. Arnold, H. Buettig, D. Janssen, 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 G. Klemz DESY Zeuthen, Zeuthen W.-D. Lehmann IfE, Dresden A. Matheisen, B. van der Horst DESY, Hamburg J. Stephan IKST, Drsden V. Volkov BINP SB RAS, Novosibirsk I. Will MBI, Berlin
	At the Forschungszentrum Rossendorf the development and the setup of the 2nd superconducting radio frequency photo electron injector (SRF-Photo-Gun) is nearly finished. One of the main attention was focussed at the treatment of the cavity. Their RF properties were measured at room temperature. The warm tuning was carried out considering pre-stressing and tuning range of both tuners (half cell and full cells). The adjusted field profiles and pass band frequencies of the four fundamental modes met the requirements. An external Q study of the main coupler yielded to an optimal antenna length and showed very good agreement between simulation and measurement. Furthermore the characteristics of the choke filter and both HOM filters were simulated, measured and tuned at the pi-mode frequency. The preparation (etching and rinsing) and the cold test were successfully done at DESY. The poster presents the setup for the measurements as well as a comparison of the simulated and measured results. Submitted as poster to the 2006 FEL conference

THPPH008	High Peak Current Design of a Superconducting Cavity for a SRF Photoinjector	emittance, gun, laser, booster	571
	D. Janssen FZR, Dresden F. Marhauser BESSY GmbH, Berlin V. Volkov BINP SB RAS, Novosibirsk
	In collaboration between BESSY, DESY, FZR, MBI and BINP a SRF electron gun is under development. The progress obtained in the last year is reported on this conference. The motivation for the design of a new gun cavity is the FEL project at BESSY. The electron injector of the linac should produce bunches with a charge of 2.5 nC and a transverse emittance of 1.5 mm mrad. In order to compensate the emittance expansion by space charge effects a large electric field on the cavity axis and a strong magnetic field near the cathode are necessary. The strengths of these fields are limited by the maximum magnetic surface field in superconducting cavities. We have designed a 1.5 cell gun cavity, where the magnetic field is realized by an additional RF mode (TE mode). In order to reduce third order effects of the RF fields, for the accelerating field a frequency below the linac frequency is used. The laser pulse, which creates the electron bunch, has a length of 20ps and a rise time of 2ps. In the tracking calculation the electrons start with an average energy of 1eV. For a bunch charge of 2.5 nC a transverse emittance of 1.8 mm mrad has been obtained. The maximal surface field is 160 mT.

THPPH009	Cryomodule and Tuning System of the Superconducting RF Photo-Injector	gun, vacuum, acceleration, emittance	575
	J. Teichert, A. Arnold, H. Buettig, R. Hempel, D. Janssen, U. Lehnert, P. Michel, K. Moeller, P. Murcek, Ch. Schneider, R. Schurig, F. Staufenbiel, R. Xiang FZR, Dresden T. Kamps, D. Lipka BESSY GmbH, Berlin G. Klemz DESY Zeuthen, Zeuthen W.-D. Lehmann IfE, Dresden J. Stephan IKST, Drsden I. Will MBI, Berlin
	We present the designs and report on the progress in construction and testing of the cryomodule and the tuning system for the SRF gun. The SRF gun project, a collaboration of BESSY, DESY, MBI and FZR, aims at the installation of a high average current CW photo injector at the ELBE linac with a Nb cavity. The cryostat consists of a stainless steel vacuum vessel, a warm magnetic shield, a liquid N cooled thermal shield, and a He tank with two-phase supply tube. A heater pot in the He input port will be used for He level control. The 10 kW power coupler is adopted from ELBE module. A cooling and support system for the NC photo cathode has been developed and tested. It allows the adjustment of the cathode with respect to the cavity from outside. The cryomodule will be connected with the 220 W He refrigerator of ELBE and will operate at 1.8 to 2 K. The static thermal loss is expected to be less than 20 W. Two tuners will be installed for separate tuning of the three TESLA cells and the half-cell. The tuners are dual spindle-lever systems with step motors and low-vibration gears outside the cryostat. Functionality, tuning range and accuracy have been tested in cryogenic environment.

THPPH012	Dark Current Collimation and Modified Gun Geometry for the European X-Ray FEL Project	gun, electron, emittance, acceleration	579
	J. H. Han, K. Floettmann DESY, Hamburg
	An rf field of 60 MV/m will be applied at the L-band gun of the European X-ray FEL project. Such a high rf gradient will allow to achieve a transverse emittance lower than 1 mm mrad for 1 nC electron bunches but will also produce dark current up to the order of mA. The dark current generated at the gun shows a comparable dynamics to the electron beam because the same acceleration will be furnished from the gun to the last acceleration module. The dark current might accumulate high radiation dose at the undulator and limit the long pulse operation of the SASE. To reduce dark current before the first acceleration module, a new design of gun cavity and collimator is proposed.

THPPH013	Impact of the Cathode Roughness on the Emittance of an Electron Beam	emittance, electron, space-charge, gun	583
	M. Krasilnikov DESY, Hamburg
	An RF photo injector for the European XFEL should produce electron beams with normalized transverse emittance under 1 mm mrad. In order to achieve this high performance of the electron source the electric field at the photo cathode has to be increased up to 60 MV/m. The emittance budget of the optimized XFEL photo injector contains a significant part of thermal (intrinsic) emittance. A roughness of the cathode could lead to an additional uncorrelated divergence of the emitted electrons and therefore to an increased thermal emittance. The cathode roughness has been modeled using an analytical approximation and numerical simulations. The influence of the roughness parameters and the increase of the electric field have been studied.

THPPH017	Experience with the Photoinjector Laser at FLASH	laser, electron, controls, free-electron-laser	590
	S. Schreiber, M. Görler, K. Klose, M. Staack DESY, Hamburg L. Fröhlich Uni HH, Hamburg I. H. Templin, I. Will MBI, Berlin
	The photoinjector laser system of FLASH is a key element for the generation of high quality electron beams required for a stable and reliable operation of the facility. FLASH is the VUV and soft X-ray FEL user facilitry at DESY. FLASH is based on superconducting accelerating structures allowing to accelerate electron bunch trains of a length of up to 800 us with a repetition rate of 10 Hz. Based on the standard 1 MHz pattern, the laser provides to some extend a flexible bunch train structure. We report on operational issues and on the performance of the laser system with emphasis on its transverse and longitudinal properties, energy and timing stability.

THPPH023	Tuning, Conditioning, and Dark Current Measurements of a New Gun Cavity at PITZ	gun, resonance, electron, laser	609
	A. Oppelt, K. Abrahamyan, O. A. Aldrian, G. Asova, J. W. Baehr, G. Dimitrov, H.-J. Grabosch, L. Hakobyan, Y. Ivanisenko, S. Khodyachykh, S. A. Korepanov, M. Krasilnikov, V. Miltchev, B. Petrosyan, R. I. Spesyvtsev, L. Staykov, F. Stephan DESY Zeuthen, Zeuthen K. Floettmann, J. H. Han, C. Martens, R. Meyer, F. Tonisch DESY, Hamburg O. Kalekin Humboldt Universität zu Berlin, Berlin F. Marhauser, R. Richter, E. Weihreter BESSY GmbH, Berlin P. Michelato, L. Monaco, D. Sertore INFN/LASA, Segrate (MI) J. R. Roensch Uni HH, Hamburg
	In December 2005, a new gun cavity for the Photo Injector Test Facility at DESY in Zeuthen (PITZ) was tuned at Hamburg with the help of a specially designed tuning device. The tuning processus and its results as well as RF measurements will be presented. Meanwhile, the cavity was installed in the PITZ facility and conditioned. Dark current measurements with different cathodes were undertaken and will be described in the paper. Comparisons to former measurements will be made.

THPPH027	Ramping Longitudinal Distribution Studies for the FERMI@ELETTRA Injector	space-charge, emittance, electron, linac	621
	G. Penco, M. Trovo ELETTRA, Basovizza, Trieste S. M. Lidia LBNL, Berkeley, California
	In the Fermi Linac optimization studies it comes out the request to have at the exit of the photoinjector a linear ramp in the current distribution along the bunch as alternative option with respect to the flat-top. This requirement is translated in the photoinjector optimization in a big issue. In fact the longitudinal bunch profile at the exit of the photoinjector is affected by the strong non linearity of the space charge fields at the cathode and in the drift between the gun and the first booster. The knowledge of the space charge fields at the cathode plays in important role in finding the optimum driven laser pulse shape. At this purpose an analytical description of the space charge fields produced by a bunch with an arbitrary current distribution at the cathode is provided. Space charge codes (GPT and ASTRA) have been used to evaluate the evolution of several ramping profiles from the cathode to the entrance of the first booster and the results are presented in this paper.

THPPH030	Main High Voltage Solid State Gyrotron Power Supply 60kV / 80A	power-supply, simulation, controls, electron	633
	M. P.C. Pretelli, L. Rinaldi, V. R. Rossi, L. Sita, G. Taddia O. C.E. M. S.p. A., Bologna T. Bonicelli, P. L. Mondino EFDA, Garching R. Claesen, M. Santinelli ENEA C. R. Frascati, Frascati (Roma) D. Fasel EPFL, Lausanne
	This paper describes the design of a 4.8MW Main High Voltage Power Supply, rated 60kV/80A, conceived to supply the voltage between Cathode and grounded Collector of a Gyrotron. The PS is being procured for the EC Test Facility in Lausanne for the development and testing of CPD type 170GHz Gyrotrons. The PS specifications include the requirement of fast and repetitive switch on and off of the current up to 5kHz in order to reduce the average power dissipation on the Collector during modulation of the RF power. A full solid state technology, named SWM (Stair-Way Modulation) has been adopted. The 60kV output voltage is reached by adding 128 high voltage modules in series connection, with ad hoc control criteria to allow a regulation at full performances in the range of 45-60kV, a square wave modulation and a fast switch-off in less than 10us. This solution can be extended to several applications in the High Voltage domain and is aimed to enhance the reliability, decrease costs, provide redundancy and plug-in modularity. In the paper, the technical implications of extending similar topologies to the ITER EC system as alternative to the present ITER reference design will be considered.

THPPH032	Free Electron Laser Triggered Photo-Cathode	emittance, laser, radiation, electron	641
	E. Sabia, A. Dipace ENEA Portici, Portici (Napoli) G. Dattoli ENEA C. R. Frascati, Frascati (Roma)
	The possibility of realizing a FEL triggered photocathode has been proposed long time ago and the advantages have been pointed out. In these devices the FEL can be exploited to extract electrons from a photocathode to provide a high quality e-beam. The device becomes even more appealing if photo-thermoionic cathodes can be exploited in two different phases. In the first the electrons are extracted from the cathode working as thermoionic and are used to drive a FEL oscillator, the FEL light is then used to flash the cathode which operates as a photo thermal assisted device. We comment on the possibility of using FEL triggered photocathodes to produce high quality e-beams for SASE or oscillator FEL devices. The use of the same e-beam driving the photocathode and the FEL makes the system naturally free of any synchronization problem arising when an external laser is used. Examples of interplay between the generation of electron and optical bursts are also investigated.

THPPH036	Design Study of RF Triode Structure for the KU-FEL Thermionic RF Gun	gun, emittance, simulation, electron	656
	K. Masuda, T. Kii, K. Kusukame, H. Ohgaki, T. Shiiyama, T. Yamazaki, K. Yoshikawa, H. Zen Kyoto IAE, Kyoto
	Thermionic rf guns show advantageous features compared with photocathode ones such as easy operation, low cost and high averaged current, which are suitable for their application to FELs for various uses. They however suffer from the back-bombardment effect, resulting in limited macro-pulse duration of severalμseconds. Against this adverse effect, we plan to introduce the triode structure,* in the 4.5-cell rf gun for the KU-FEL by replacing the thermionic cathode by an assembly of a cathode with an additional coaxial cavity. Two-dimensional simulations have predicted a significant reduction of the back-bombardment power by 99% with a moderate rf power of several tens kW fed to the additional extraction cavity. Moreover an improved energy spread and peak current are expected at the same time with an optimal geometry and operating conditions. * E. Tanabe et al., Proc. of 27th Linear Accelerator Meeting in Japan (2002) 57, in Japanese. ** K. Masuda et al., Proc. of 27th Intnl. FEL Conf. 2005 (2006) 588.

THPPH038	Production of Electron Beam with Constant Energy by Controlling Input Power into a Thermionic RF Gun	electron, gun, beam-loading, simulation	664
	N. Okawachi, T. Kii, K. Masuda, M. Nakano, H. Ohgaki, T. Yamazaki, K. Yoshikawa, H. Zen Kyoto IAE, Kyoto
	We have studied on performance of a thermionic RF gun. Though a thermionic RF gun is a compact and economical electron gun, a backbombardment effect makes it difficult to produce electron beam with constant energy. The backbombardment effect depends on cavity voltage of the RF gun (Vc) and cathode current density (Jc). We tried to keep beam energy constant in macro pulse duration by feeding modulated RF power in experiment. We have succeeded to produce a 4 μs macro pulse electron beam. We also tried to perform transient analysis with equivalent circuit including the time evolution of beam loading depending on the Vc and Jc, By using this analysis we have succeeded to reproduce the measured time evolution of electron beam energy and the pulse shape of reflected RF power in case a constant RF power was fed and a modulated RF power was fed. Moreover we found the condition in which we could produce a 6 μs macro pulse electron beam. In this conference we will discuss the comparison between the experimental results and the calculation results.

THPPH042	A Compact Low Emittance DC Gun Employing Single Crystal Cathode of LaB6	emittance, electron, gun, simulation	680
	K. Kasamsook, K. Akiyama, H. Hama, F. Hinode, M. Kawai, T. Muto, K. Nanbu, T. Tanaka, M. Yasuda Laboratory of Nuclear Science, Tohoku University, Sendai
	Development of an electron gun capable of producing low emittance is in the interests of further applications of high brightness electron beam such as Smith-Purcell radiation for examples. A prominent point of this DC gun is that operation high voltage is very low and the emittance is, however, sufficiently low because of a short distance between the wehnelt and the anode. A pulsed high voltage of 50 kV is supplied, and pulse duration is variable from 1 to 5 sec. Since a higher beam current of the macropulse is required in general, a cathode should have higher current density, while the smaller size of the cathode is preferred for lower emittance. Consequently we have chosen single crystal LaB6 as the cathode, which can provide higher current with good homogeneity emission. In additon, a floating bias voltage can be applied between the cathode and the wehnelt to optimize the electric field for achieving the lowest emittance. Numerical calculations using EGUN shows a better normalized rms emittance is expected to be less than 5 mm mrad. A state-of-the-art electron source will possibly open new scientific opportunities in the many fields.

THPPH046	Preliminary Measurement of Emittance Evolution Using Emittance Meter at the PAL	emittance, laser, gun, space-charge	695
	J. H. Park, J. Y. Huang, C. Kim, I. S. Ko, Y. W. Parc, S. J. Park PAL, Pohang, Kyungbuk X. Dao TUB, Beijing X. J. Wang BNL, Upton, Long Island, New York
	A high-brightness electron beam is emitted from a RF photocatoode gun with 1.6 cell cavity from October 2005 at the Pohang Accereator Laboratory (PAL). The project of 4th Generation Light Source (4GLS) with the Spontaneous Amplification Sponteneous Emission Free-electron Laser (SASE FEL) in the PAL is called Pohang Accereator Laboratory X-ray Free-electron Laser (PAL-XFEL). In order to success of the PAL-XFEL project, it is necessary to research the high-brightness electron beam at the injector. A emittance meter (E-Meter) is installed for the high-brightness research in GTS (Gun Test Stand). The measurement of transverse emittance and beam size profile along the longitudinal direction was done by the E-Meter. Precise measurement of the emittance profile will provide powerful tool for the commissioning of the 4GLS injectors based on the emittance compensation principle. We are going to achieve this with the use of slit-based E-Meter that can be moved along the longitudinal direction. In this article, we present a preliminary measurement of the emittance evolution with the E-Meter for the commissioning of the RF photocathode gun.

THPPH063	In-Situ Cleaning of Metal Photo-Cathodes in RF Guns	gun, ion, laser, electron	732
	J. F. Schmerge, J. Castro, J. E. Clendenin, E. R. Colby, D. Dowell, S. M. Gierman, H. Loos, M. Nalls, W. E. White SLAC, Menlo Park, California
	Cu cathodes installed in rf guns typically exhibit much lower quantum efficiency than the theoretical limit. Experimenters often use some sort of in situ technique to "clean" the cathode to improve the QE. The most common technique is laser cleaning where the laser is focused to a small spot and the laser is scanned across the cathode. However, this can also damage the cathode since the laser is operated near the damage threshold and the QE degrades over days and must be cleaned regularly. Alternatively Hydrogen ion beams can be used to clean the cathode and improve the QE but this cleans only the area exposed to the ion beam. In this paper we measure the QE and the dark current emitted from a cathode before and after exposing the gun to a hydrogen plasma created with an rf discharge. With this technique the entire surface of the gun is cleaned simultaneously with no apparent detrimental effects.

THPPH069	Experimental Progress Toward Low Workfunction Controlled Porosity Dispenser Photocathodes	ion, laser, electron, photon	748
	N. A. Moody, D. W. Feldman, P. G. O'Shea IREAP, College Park, Maryland K. Jensen, J. L. Shaw, J. E. Yater NRL, Washington, DC
	High efficiency, long-lived photocathodes are crucial for continued development of high power FELs. Most photocathodes with high quantum efficiency in the visible range suffer from short lifetime, due to chemical instability of the photosensitive surface layer that evaporates or is contaminated during operation in a RF-injector environment. We propose a controlled porosity dispenser (CPD) concept as a means of rejuvenating photosensitivity and performance. In many high-QE photocathodes, degradation over time is due to the loss of a surface coating of cesium. In CPD cathodes, cesium is replaced at near-room temperature via diffusion, maintaining high QE and extending effective lifetime. Measurements of increasingly complex photoemitting surfaces were performed, yielding QE as a function of cesium coating thickness, temperature, and photon wavelength. These measurements validate a photoemission model* that allows calculation of emission distribution, photocathode performance, and surface conditions of the cathode. Techniques for room-temperature cleaning of the CPD surface were determined and a prototype CPD photocathode based on cesiated sintered tungsten was evaluated. * K. L. Jensen, et al., (this conference)

THCAU03	Operational Experience with the Emittance-Meter at SPARC	emittance, laser, gun, simulation	777
	L. Catani, E. Chiadroni, A. Cianchi INFN-Roma II, Roma M. Bellaveglia, R. Boni, M. Boscolo, M. Castellano, L. Cultrera, G. Di Pirro, A. Drago, M. Ferrario, D. Filippetto, V. Fusco, A. Gallo, G. Gatti, F. Tazzioli, C. Vaccarezza, M. Vescovi, C. Vicario INFN/LNF, Frascati (Roma) M. Migliorati, L. Palumbo Rome University La Sapienza, Roma P. Musumeci, M. Petrarca INFN-Roma, Roma C. Ronsivalle ENEA C. R. Frascati, Frascati (Roma)
	We report the operational experience of the movable emittance meter at SPARC. This device is based on the well-known technique of pepper pot (1-D slits in our case) but it allows moving the measuring device along the beam line from about 840 mm to 2200 mm from the cathode, following the emittance oscillations. More than a simple improvement over conventional, though non-trivial, beam diagnostic tools this device defines a new strategy for the characterization of high performance photoinjectors, providing a tool for detailed analysis of the beam dynamics, over a section of the accelerator where emittance compensation take place. With this device we performed detailed and systematic studies on beam dynamics with particular attention to the transverse parameters as well as longitudinal. We report also the operating experience at the PITZ facility.
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