03 Particle Sources and Alternative Acceleration Techniques
T02 Electron Sources

Paper	Title	Page
TUPPD050	Investigation of Laser-cleaning Process on Lead Photocathodes	1515
	S.G. Schubert, R. Barday, T. Kamps, T. Quast, A. Varykhalov HZB, Berlin, Germany R. Nietubyć The Andrzej Soltan Institute for Nuclear Studies, Centre Świerk, Świerk/Otwock, Poland F. Siewert BESSY GmbH, Berlin, Germany J. Smedley BNL, Upton, Long Island, New York, USA G. Weinberg FHI, Berlin, Germany
	Funding: Work supported by Bundesministerium für Bildung und Forschung and Land Berlin. Metal photocathodes are widely used in electron injectors due to their stability and long life time; unfortunately they exhibit low quantum efficiency. Due to adsorption of contaminants the work function increases and thus the quantum efficiency is further reduced. In order to increase the quantum efficiency of our Pb cathode we performed a cleaning procedure by means of a high power excimer laser as suggested by Smedley*. The process was studied on witness samples in a combined photo emission, SEM and quantum efficiency measurement study. Thin Lead films were arc-deposited on optical polished Mo-substrates**. Before and after irradiation the sample was analyzed at 140 eV photon energy at a XPS/ARPES end station at the synchrotron radiation source Bessy II. We followed the change of the Pb 5d signals. In the initial situation we observed signals originating from metallic Pb and Pb in the oxidized state, respectively. Since the surface roughness is of concern for the injector performance it was examined before and after the irradiation procedure with white-light-interferometry and the surface morphology by means of SEM. *J. Smedley et al, PRST-AB 11, 013502 (2008). ** Rao, T. et al., IPAC 2010, THPEC020 (2010).
TUPPD051	Operational Experience with the Nb/Pb SRF Photoelectron Gun	1518
	T. Kamps, W. Anders, R. Barday, A. Jankowiak, J. Knobloch, O. Kugeler, A.N. Matveenko, A. Neumann, T. Quast, J. Rudolph, S.G. Schubert, J. Völker HZB, Berlin, Germany P. Kneisel JLAB, Newport News, Virginia, USA R. Nietubyć The Andrzej Soltan Institute for Nuclear Studies, Centre Świerk, Świerk/Otwock, Poland J.K. Sekutowicz DESY, Hamburg, Germany J. Smedley BNL, Upton, Long Island, New York, USA J. Teichert HZDR, Dresden, Germany V. Volkov BINP SB RAS, Novosibirsk, Russia I. Will MBI, Berlin, Germany
	SRF photoelectron guns offer the promise of high brightness, high average current beam production for the next generation of accelerator driven light sources such as free electron lasers, THz radiation sources or energy-recovery linac driven synchrotron radiation sources. In a first step a fully superconducting RF (SRF) photoelectron gun is under development by a collaboration between HZB, DESY, JLAB, BNL and NCBJ. The aim of the experiment is to understand and improve the performance of a Nb SRF gun cavity coated with a small metallic Pb cathode film on the cavity backplane. This paper describes the highlights from the commissioning and beam parameter measurements. The main focus is on lessons learned from operation of the SRF gun.
TUPPD052	A New Load Lock System for the Source of Polarized Electrons at ELSA	1521
	D. Heiliger, W. Hillert, B. Neff ELSA, Bonn, Germany
	Funding: supported by DFG (SFB/TR16) Since 2000, an inverted source of polarized electrons at the electron stretcher accelerator ELSA routinely provides a pulsed beam with a current of 100 mA and a polarization degree of about 80%. One micro-second long pulses with 100 nC charge are produced by irradiating a GaAs strained-layer superlattice photocathode (8 mm in diameter) with laser light. Future accelerator operation requires a significantly higher beam intensity, which can be achieved by using photocathodes with sufficiently high quantum efficiency. Therefore, and in order to enhance the reliability and up time of the source, a new extreme high-vacuum (XHV) load lock system was installed and commissioned at the beginning of this year. It consists of three chambers: The activation chamber for heat cleaning of the photocathodes and activation with cesium and oxygen. The storage chamber in which up to five different types of photocathodes with various diameters of the emitting surface can be stored under XHV conditions. The loading chamber in which an atomic hydrogen source is used to remove any remaining surface oxidation. Additionally, tests of the photocathodes’ properties can be performed during operation.
TUPPD054	Research Activities on Photocathodes for HZDR SRF Gun	1524
	R. Xiang FZD, Dresden, Germany A. Arnold, M. Freitag, P. Michel, P. Murcek, J. Teichert HZDR, Dresden, Germany
	Funding: We acknowledge the support of the European Community-Research Infrastructure Activity (EuCARD, contract number 227579), as well German Federal Ministry of Education and Research grant 05 ES4BR1/8. Since 2005 the photocathode laboratory has been in operation at HZDR. The main goal is to prepare Cs2Te photocathodes for the SRF gun. A vacuum transport system with UHV is used to move the cathodes from preparation lab to accelerator hall. Up to now 31 Cs2Te photocathodes have been deposited and eight of them have been used in the SRF gun. Quantum efficiency of 1% and lifetime of months can be maintained during the gun operation. At the same time activities are directed towards new photocathode materials with high Q.E. for high current electron sources. Cs3Sb and GaN(Cs) photocathodes have been tested as new candidates, and the design of a preparation system for GaAs(Cs, O) is ongoing.
TUPPD055	Characterization of ps-spaced Comb Beams at SPARC	1527
	A. Mostacci URLS, Rome, Italy A. Bacci, A.R. Rossi Istituto Nazionale di Fisica Nucleare, Milano, Italy M. Bellaveglia, E. Chiadroni, G. Di Pirro, M. Ferrario, G. Gatti, C. Vaccarezza INFN/LNF, Frascati (Roma), Italy A. Cianchi Università di Roma II Tor Vergata, Roma, Italy C. Ronsivalle ENEA C.R. Frascati, Frascati (Roma), Italy
	SPARC in Frascati is a high brightness photo-injector used to explore advanced beam manipulation techniques. Sub-picosecond, high brightness electron bunch trains (the so called comb beam) can be generated illuminating the cathode of a RF photoinjector with a laser pulse train and via velocity bunching technique. In this paper different aspects of the physics of this advanced beam manipulation technique are discussed combining simulation and measurements. Beam dynamics numerical macroparticle simulations have been compared with the experimental results for model validation; they allow to gain insights on the beam evolution highlighting several aspects which can not be measured. In particular, we focus on the train evolution in the linac sections and in the dog-leg line up to the THz station and on the effective rms length of the single pulses within the train when it becomes shorter than the resolution.
TUPPD056	Development of a Photo-injector Laser System for KEK ERL Test Accelerator	1530
	Y. Honda KEK, Ibaraki, Japan
	As a test accelerator for future light source, Compact Energy Recovery Linac has been constructed in KEK. For its photo-injector, we have been developing a laser system. It requires high repetition rate and high average power at a visible wavelength. Development of an high power fiber amplifier and high efficiency wavelength conversion system utilizing an optical cavity will be reported.
TUPPD057	High Charge Low Emittance RF Gun for SuperKEKB	1533
	T. Natsui, Y. Ogawa, M. Yoshida, X. Zhou KEK, Ibaraki, Japan
	We are developing a new RF gun for SuperKEKB. We are upgrading KEKB to SuperKEKB now. High charge low emittance electron and positron beams are required for SuperKEKB. We will generate 7.0 GeV electron beam at 5 nC 20 mm-mrad by J-linac. In this linac, a photo cathode S-band RF gun will be used as the electron beam source. For this reason, we are developing an advanced RF gun. Now, we are testing a Disk and Washer (DAW) type RF gun. Its photo cathode material is LaB6. Normally, LaB6 is used as a thermionic cathode, but it is suitable for　long-life photo cathode operation. This gun has a strong focusing field at the cathode and the acceleration field distribution also has a focusing effect. We will obtain 3.2 MeV beam energy with the gun. The design of RF gun and experimental results will be shown.
TUPPD058	Development of an RF Electron Gun for Ultra-Short Bunch Generation	1536
	Y. Koshiba, T. Aoki, K. Sakaue, M. Washio RISE, Tokyo, Japan T. Takatomi, J. Urakawa KEK, Ibaraki, Japan
	At Waseda University, various researches are done using a photocathode rf electron gun with a 1.6 cell cavity. Now we are developing a new rf cavity specialized for producing an ultra-short electron bunch, with the collaboration of High Energy Accelerator Research Organization (KEK). We have used SUPERFISH for designing the new rf cavity and PARMELA for beam tracking. The new rf cavity has an extra cell following the 1.6 cell. The extra cell can chirp the energy of electron bunch so we call it ECC (Energy Chirping Cell). ECC chirp the energy because we shortened the length of iris just before the ECC and also the length of ECC itself. Moreover, electric field in ECC is made to be stronger than others. We have confirmed on PARMELA that ECC rf gun can generate an 100pC electron bunch less than 200fsec with the energy of 4.5MeV at about 2.5m away from the cathode. Such an ultra-short electron bunch enables us to generate a coherent terahertz light using ultra-short electron bunch by synchrotron radiation or transition radiation. In this conference, we would like to introduce the detail of the design of this new ECC rf gun, the present progresses and future prospects.
TUPPD061	High-Power RF Test of an RF-Gun for PAL-XFEL	1539
	J.H. Hong, J.H. Han, H.-S. Kang, C. Kim, S.H. Kim, C.-K. Min, S.S. Park, S.J. Park, Y.J. Park PAL, Pohang, Kyungbuk, Republic of Korea M.S. Chae, I.S. Ko, Y.W. Parc POSTECH, Pohang, Kyungbuk, Republic of Korea
	A photocathode RF-gun for the X-ray free electron laser (XFEL) at the Pohang Accelerator Laboratory (PAL) has been fabricated and tested at PAL. This RF-gun is based on a 1.6-cell cavity with dual-feed waveguide ports and two pumping ports. The RF gun was designed by PAL and POSTECH. The RF-gun has been successfully tested with a cathode electric field gradient up to 126MV/m at a repetition rate of 30 Hz. This paper reports the recent results on the beam test of the RF-gun with high power RF at the gun test facility. We present and discuss the measurements of the basic beam parameters such as charge, energy, energy spread, and transverse emittance.
TUPPD062	The Source of Emittance Dilution and photoemission tunneling effect in Photocathode RF Guns	1542
	V. Volkov BINP SB RAS, Novosibirsk, Russia R. Barday, T. Kamps, J. Knobloch, A.N. Matveenko, S.G. Schubert, J. Völker HZB, Berlin, Germany J.K. Sekutowicz DESY, Hamburg, Germany
	Funding: Work supported by Bundesministerium für Bildung und Forschung, Land Berlin, and grants of Helmholtz Association VH-NG-636 and HRJRG-214. Experimental data on HoBiCaT SRF photoinjector give an emittance which is much larger than the predicted thermal emittance. Modeling of photocathode RF gun beams with the different imperfections of experimental setup (alignment errors, inhomogeneity of quantum efficiency and laser power distributions on the cathode) is given. The main reason for the beam emittance dilution is photocathode field imperfections induced by field emitters that change the local electric field. Some field models of such photocathodes are tested in the simulations. The dependence of photocathode beam currents on the surface electric field was measured with the HoBiCaT SRF Photoinjector. The dependence can be explained by the tunneling effect described by Fowler-Nordheim like equation and is difficult to explain by usually applying Schottky effect.
TUPPD063	Interpretation of Dark Current Experimental Results in HZB SC RF Gun	1545
	V. Volkov BINP SB RAS, Novosibirsk, Russia R. Barday, T. Kamps, J. Knobloch, A.N. Matveenko, A. Neumann HZB, Berlin, Germany
	Funding: Work supported by Bundesministerium für Bildung und Forschung, Land Berlin, and grants of Helmholtz Association VH-NG-636 and HRJRG-214. The experimental dark current measurement results are obtained on HZB SC RF gun. The field emitters are considered to be random defects on the back wall of the cavity. Conducting wires with 1 micron length, blobs of 200 micron diameter and ”tip on tip” combination of them are taken as dark current emitters in the cavity. RF fields were calculated with CLANS program. The dynamic simulation of dark currents from these emitters fit experimental data. The emitter heating power by RF induced current is four orders of magnitude larger than by the field emitted dark current. The RF induced emitter temperature is proportional to ω1/2 which explains the accelerating gradient limit of a cavity like Kilpatrik law. The RF processing by high order modes seems to be promising.
TUPPD064	Cathode Insert Design for SC RF Guns	1548
	V. Volkov BINP SB RAS, Novosibirsk, Russia R. Barday, T. Kamps, J. Knobloch, A.N. Matveenko HZB, Berlin, Germany
	Funding: Work supported by Bundesministerium für Bildung und Forschung, Land Berlin, and grants of Helmholtz Assiciation VH-NG-636 and HRJRG-214. The cathode inserts in superconducting (SC) RF guns are normal conducting devices attached to a SC RF gun cavity. They enable the photocathode replacement and, at the same time, preserve high quality factor and high fields in the RF guns. However, the insert may also limit the gun performance because of multipacting etc. The experience gathered in early designs at Wuppertal [1], and, more recently at BNL [2] and HZDR [3] is taken into account. We consider the design structure of the cathode insert worked out by BINP for 1 cell prototype of SC HZDR RF gun [4]. The detailed electric, mechanic, and thermal calculations of the initial [4] and the upgraded design are presented in this paper. * A. Michalke et al., EPAC'92, p. 1014 (1992). ** A. Burrill et al., PAC07, p. 2544 (2007). *** D. Janssen et al., NIM A507, 314 (2003). **** D. Janssen et al., NIM A445, 408 (2000).
TUPPD065	An Electron Gun Test Stand to Prepare for the MAX IV Project	1551
	S. Werin, E. Elafifi, M. Eriksson, D. Kumbaro, F. Lindau, S. Thorin MAX-lab, Lund, Sweden E. Mansten Lund University, Division of Atomic Physics, Lund, Sweden
	The MAX IV facility, currently under construction, will include a 3 GeV linac injector with two RF guns providing beams for the two operations modes: ring injection and the Short Pulse Facility. The ring injection will be done by a thermionic 3 GHz RF gun developing from the current MAX-lab RF gun. The SPF gun will be a laser driven photo cathode 3 GHz RF gun based on the 1.6 cell BNL/SLAC type. The guns will be operated with short (0.7 us) RF pulses from a SLED system. A test stand to fine tune the operation of the two different systems has been assembled at the MAX IV laboratory (former MAX-lab). The experience in RF commissioning and initial measurements of energy, charge and quantum efficiency will be reported and the extension of the test stand for full emittance characterization will be outlined.
TUPPD066	Lifetime Studies of Cs2Te Cathodes at the PHIN RF Photoinjector at CERN	1554
	C. Heßler, E. Chevallay, M. Divall Csatari, S. Döbert, V. Fedosseev CERN, Geneva, Switzerland
	The PHIN photoinjector has been developed to study the feasibility of a photoinjector option for the CLIC (Compact LInear Collider) drive beam as an alternative to the baseline design, using a thermionic gun. The CLIC drive beam requires a high charge of 8.4 nC per bunch in 0.14 ms long trains, with 500 MHz bunch spacing and 50 Hz macro pulse repetition rate, which corresponds to a total charge per macro pulse of 0.59 mC. This means unusually high peak and average currents for photoinjectors and is challenging with respect to the cathode lifetime. In this paper detailed studies of the lifetime of Cs2Te cathodes, produced by the co-evaporation technique, with respect to bunch charge, train length and vacuum level are presented. Furthermore, the impact of the train length and bunch charge on the vacuum level will be discussed and steps to extend the lifetime will be outlined.
TUPPD067	Experimental Facility for Measuring the Electron Energy Distribution from Photocathodes	1557
	L.B. Jones, R.J. Cash, B.D. Fell, J.W. McKenzie, K.J. Middleman, B.L. Militsyn STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom H.E. Scheibler, A.S. Terekhov ISP, Novosibirsk, Russia
	ASTeC have spent several years developing a GaAs Photocathode Preparation Facility (PPF) which routinely produces cathodes with quantum efficiencies (Q.E.) up to 20% at 635 nm*. The goal is to use these cathodes in high-average-current high-brightness injectors for particle accelerators. Electron injector brightness is driven by photocathode emittance, and brightness will be increased significantly by reducing the longitudinal and transverse energy spread. We are constructing an experimental system for measurement of the horizontal and transverse energy spreads at room and LN2-temperature which accepts photocathodes from the PPF. The sample will be illuminated by a small, variable-wavelength light spot. The beam image will be projected onto a detector comprised of 3 grids which act as an energy filter, a micro-channel plate and a phosphor screen. A low-noise CCD camera will capture screen images, and the electron distribution and energy spread will be extracted through analysis of these images as a function of the grid potentials. The system will include a leak valve to progressively degrade the cathode, and thus allow its properties to be measured as a function of Q.E. * Proc IPAC ’11, THPC129 (2011).
TUPPD068	Design of the Production and Measurement of Ultra-Short Electron Bunches from an S-band RF Photoinjector	1560
	J.W. McKenzie, D. Angal-Kalinin, J.K. Jones, B.L. Militsyn STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	The Electron Beam Test Facility (EBTF) is planned for installation in late 2012 at Daresbury Laboratory. An S-band RF photoinjector provides ultrashort, low emittance electron bunches up to 6 MeV. A suite of diagnostics has been designed to fully characterise the bunches. A particular focus has been on producing and measuring bunch lengths less than 100 fs. This can be achieved with a multi-cell standing wave S-band transverse deflecting cavity. Operating such a cavity with low energy electrons provides certain challenges which are discussed in this paper with respect to beam dynamic simulations.
TUPPD069	Schottky-Enabled Photoemission and Dark Current Measurements - Toward an Alternate Approach to Fowler-Nordheim Plot Analysis	1563
	E.E. Wisniewski, W. Gai, J.G. Power ANL, Argonne, USA H. Chen, Y.-C. Du, Hua, J.F. Hua, W.-H. Huang, C.-X. Tang, L.X. Yan, Y. You TUB, Beijing, People's Republic of China A. Grudiev, W. Wuensch CERN, Geneva, Switzerland E.E. Wisniewski Illinois Institute of Technology, Chicago, Illinois, USA
	Field-emitted dark current, a major gradient-limiting factor in RF cavities, is usually analyzed via Fowler-Nordheim (FN) plots. Traditionally, field emission is attributed to geometrical perturbations on the bulk surface whose field enhancement factor (beta) and the emitting area (A) can be extracted from the FN plot. Field enhancement factors extracted in this way are typically much too high (1 to 2 orders of magnitude) to be explainable by either the geometric projection model applied to the measured surface roughness or by field enhancement factors extracted from Schottky-enabled photoemission measurements. We compare traditional analysis of FN plots to an alternate approach employing local work function variation. This is illustrated by comparative analysis of recent dark current and Schottky-enabled photoemission data taken at Tsinghua S-band RF gun. We conclude by describing a possible experimental plan for discrimination of variation of local work function vs. local field enhancement.
TUPPD070	Kelvin Probe Studies of a Cesium Telluride Photocathode for the AWA Photoinjector	1566
	E.E. Wisniewski, K.C. Harkay, Z.M. Yusof ANL, Argonne, USA L.K. Spentzouris, J. Terry, D.G. Velazquez, E.E. Wisniewski Illinois Institute of Technology, Chicago, Illinois, USA
	Cesium telluride is an important photocathode as an electron source for particle accelerators. It has a relatively high quantum efficiency (>1%), is sufficiently robust in a photoinjector, and has a long lifetime. This photocathode is grown in-house for the new Argonne Wakefield Accelerator (AWA) to produce high charge per bunch (~50 nC). Here, we present a study of the "work function" of a cesium telluride photocathode using the Kelvin Probe technique. The study includes an investigation of the correlation between the quantum efficiency and the work function, the effect of photocathode aging, the surprising effect of UV exposure on the work function, and the puzzling behavior of the work function during and after photocathode rejuvenation via heating.
TUPPD071	Development of Cesium Telluride Photocathodes for the AWA Accelerator Upgrade	1569
	Z.M. Yusof, M.E. Conde, W. Gai ANL, Argonne, USA L.K. Spentzouris, E.E. Wisniewski Illinois Institute of Technology, Chicago, Illinois, USA
	Funding: U.S. Department of Energy Office of Science under Contract No. DE-AC02-06CH11357. Cesium telluride photocathodes have been fabricated for the Argonne Wakefield Accelerator (AWA) upgrade. The as-deposited photocathodes have consistently produced quantum efficiency values better than 10% with 254 nm light source and with variation of less than 5% over a circular area of 1.2 inches in diameter. We present various characterizations of the photocathode that have performed, including rejuvenation, lifetime, and performance in the L-band AWA photoinjector.
TUPPD075	Simulated Performance of the Wisconsin Superconducting Electron Gun	1572
	R.A. Bosch, K.J. Kleman UW-Madison/SRC, Madison, Wisconsin, USA R.A. Legg JLAB, Newport News, Virginia, USA
	The Wisconsin superconducting electron gun is modeled with multiparticle tracking simulations using the ASTRA and GPT codes. To specify the construction of the emittance-compensation solenoid, we studied the dependence of the output bunch's emittance upon the solenoid's strength and field errors. We also evaluated the dependence of the output bunch's emittance upon the bunch's initial emittance and the size of the laser spot on the photocathode. The results suggest that a 200-pC bunch with an emittance of about one mm-mrad can be produced for a free-electron laser.
TUPPD076	Photocathode Studies for the SPEAR3 Injector RF Gun	1575
	S. Park, W.J. Corbett, S.M. Gierman, J.R. Maldonado SLAC, Menlo Park, California, USA
	Funding: Work supported by U.S. Department of Energy Contract DE-AC03- 76SF00515 and Office of Basic Energy Sciences, Division of Chemical Sciences. The electron gun for the SPEAR3 injector operates with a warm thermionic dispenser cathode immersed in a 1.5-cell RF structure. At each injection cycle the gun accelerates several thousand electron bunches up to ~3 MeV during a 2.5us rf pulse. The individual bunches are then compressed by an alpha magnet and a traveling-wave chopper selects 3-5 bunches so they don’t cause beam loading to the linac, where the accelerated bunches reach 120 MeV for subsequent capture in a single booster synchrotron bucket. Tests are underway to operate the dispenser cathode as a cold electron photo-emitter driven by an external laser system. Eventually, without the copper, this will enable multi-bunch injections to the Booster and SPEAR3. In parallel, tests are underway to evaluate quantum efficiency and beam emittance for a beam emitted from a CsBr photocathode with ns- and ps-pulses of UV laser light. In this paper we report on both the cold cathode electron gun operation studies for SPEAR3 and the CsBr research aimed at developing advanced cathode materials for future applications.
TUPPD078	A Novel Design of a High Brightness Superconducting RF Photoinjector Gun Cavity	1581
	F. Marhauser, R. Rodriguez MuPlus, Inc., Newport News, USA Z. Li SLAC, Menlo Park, California, USA
	Funding: Work supported under U.S. DOE Grant Application Number 98802B12-I Next generation electron accelerators for research, medical, defense or industrial use are in need of electron sources operating at high repetition rates of 1 MHz and beyond, with normalized emittance of 1 mm-mrad or less and bunch charges as much as one nC or more. A conceptual layout of a novel superconducting RF photoinjector gun cavity (SRF gun) is proposed, which can provide unprecedented flexibility to vary beam pulse patterns in the MHz regime and beyond at average currents around 1 mA. It does not require an opening in the center of the back wall and avoids the complex cathode exchange system, but still allows an exchange or refurbishment of the cathode. The demountable back plate has the major benefit to clean the cavity cells independently from the back wall carrying a superconductive photocathode. This mitigates risks of cavity contamination and eases fabrication and chemical post-processing to achieve high accelerating fields, a key parameter to guarantee high brightness beams.
TUPPD079	Design of an L-Band RF Photoinjector for the Idaho Accelerator Center 44 MeV Linac	1584
	M. Titberidze, A.W. Hunt, D.P. Wells IAC, Pocatello, IDAHO, USA Y. Kim ISU, Pocatello, Idaho, USA
	At the Idaho Accelerator Center (IAC) of Idaho State University, we have been operating a 44 MeV L-band RF (1300 MHz) linear accelerator (LINAC) for various user applications such as medical isotope production, Laser Compton Scattering (LCS), positron annihilation energy spectroscopy, and photo fission. But the LINAC is not optimized properly to supply high quality electron beam for those experiments due to limitations of an existing 85 kV thermionic DC gun. In the near future, we are planning to use the L-band LINAC for new user applications such as Accelerator Driven subcritical nuclear reactor System (ADS), photon tagging facility, Ultrafast Electron Diffraction (UED) facility, and high power coherent Terahertz light source facility. Therefore, recently, we have been studying a future upgrade of the L-band LINAC with an RF photoinjector using ASTRA code. In this paper, we describe ASTRA simulation results and a new layout of the L-band LINAC, which is based on an L-band 1.5 cell RF photoinjector. Then, we describe its expected performance for two different single bunch charges (1 nC and 5 nC).
TUPPD080	Design of Ultrafast High-Brightness Electron Source	1587
	J.H. Park, H. Bluem, J. Rathke, T. Schultheiss, A.M.M. Todd AES, Princeton, New Jersey, USA
	Funding: This work was supported by the U.S. Department of Energy, under Contract No. DE-SC0006210. Generation and preservation of ultrafast electron beams is one of the major challenges in accelerator R&D. Space charge forces play a fundamental role in emittance dilution and bunch lengthening for all high brightness beams. In order to generate and preserve the ultrafast high-brightness electron beam, transverse and longitudinal space charge effects have to be considered. Several approaches to achieving ultra-short bunches have been explored such as velocity bunching and magnetic compression. However, each option suffers drawbacks in achieving a compact ultrafast high-brightness source. We present an alternative scheme to achieve an ultrafast high-brightness electron beam using a radial bunch compression technique in an x-band photocathode RF electron gun. By compensating the path length difference with a curved cathode and using an extremely high acceleration gradient (greater than 200 MV/m), we seek to deliver 100 pC, 100 fsec bunches.
TUPPD081	Development of Carbon NanoTube (CNT) Cathodes at RadiaBeam	1590
	L. Faillace, R.B. Agustsson, S. Boucher, A.Y. Murokh, A.V. Smirnov RadiaBeam, Santa Monica, USA
	RadiaBeam is developing Carbon Nanotube (CNT) cathodes for DC-pulsed and radio frequency (RF) driven electron sources. CNT cathodes, if realized, are capable of producing very high current density with low thermal emittance, due to ambient operating temperature. The initial experimental results of CNT cathodes are presented, including the high-voltage tests, and life time studies. CNT cathodes potential applications in accelerator science and microwave industry are discussed, and near term plans to test the CNT cathodes in the RF environment are presented.
TUPPD082	Simulations of Multipacting in the Cathode Stalk and FPC of 112 MHz Superconducting Electron Gun	1593
	T. Xin, X. Liang Stony Brook University, Stony Brook, USA S.A. Belomestnykh, I. Ben-Zvi, T. Rao, J. Skaritka, E. Wang, Q. Wu BNL, Upton, Long Island, New York, USA X. Chang Far-Tech, Inc., San Diego, California, USA
	Funding: Work is supported at BNL by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. The work at Stony Brook is supported by the US DOE under grant DE-SC0005713. A 112 MHz superconducting quarter-wave resonator electron gun will be used as the injector of the Coherent Electron Cooling (CEC) proof-of-principle experiment at BNL. Furthermore, this electron gun can be used for testing of the performance of various high quantum efficiency photocathodes. In a previous paper, we presented the design of the cathode stalks and a Fundamental Power Coupler (FPC). In this paper we present updated designs of the cathode stalk and FPC. Multipacting in the cathode stalk and FPC was simulated using three different codes, Multipac, CST particle studio and FishPact respectively. All simulation results show no serious multipacting in the cathode stalk structure and FPC.
TUPPD083	Raising Photoemission Efficiency with Surface Acoustic Waves	1596
	A. Afanasev, F. Hassani, C.E. Korman GWU, Washington, USA V.G. Dudnikov, R.P. Johnson Muons, Inc, Batavia, USA M. Poelker, K.E.L. Surles-Law JLAB, Newport News, Virginia, USA
	Funding: Supported in part by DOE STTR Grant DE-SC0006256. Notice: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 We are developing a novel technique that may help increase the efficiency and reduce costs of photoelectron sources used at electron accelerators. The technique is based on the use of Surface Acoustic Waves (SAW) in piezoelectric materials, such as GaAs, that are commonly used as photocathodes. Piezoelectric fields produced by the traveling SAW spatially separate electrons and holes, reducing their probability of recombination, thereby enhancing the photoemission quantum efficiency of the photocathode. Additional advantages could be increased polarization provided by the enhanced mobility of charge carriers that can be controlled by the SAW and the ionization of optically-generated excitons resulting in the creation of additional electron-hole pairs. It is expected that these novel features will reduce the cost of accelerator operation. A theoretical model for photoemission in the presence of SAW has been developed, and experimental tests of the technique are underway.
WEOAB02	Photocathode R&D at Cornell University	2137
	L. Cultrera, I.V. Bazarov, J.V. Conway, B.M. Dunham, Y. Hwang, Y. Li, X. Liu, R. Merluzzi, T.P. Moore, K.W. Smolenski CLASSE, Ithaca, New York, USA S.S. Karkare, J.M. Maxson, W.J. Schaff Cornell University, Ithaca, New York, USA
	Funding: This work has been supported by NSF DMR-0807731 and by DOE DE-SC0003965. A wide R&D program is pursued at Cornell University aimed at preparation and characterization of high efficiency photocathodes for the Energy Recovery Linac photoinjector. The currently investigated photoemitters include both positive and negative electron affinity materials such as respectively bi-alkali antimonide and III-V semiconductors activated with Cs and either O or F. Analysis techniques as Scanning Auger Spectroscopy, Low Energy Electron Diffraction, Reflected High Energy Electron Diffraction and work function measurements are used to characterize the surfaces properties of the specimens. Spectral response, photoemission uniformity, electron energy distributions are used to characterize the quality of the photoelectron beam and to relate it to the measured surface properties.
	Slides WEOAB02 [6.934 MB]
WEEPPB004	Status of the APEX Project at LBNL	2173
	F. Sannibale, B.J. Bailey, K.M. Baptiste, J.M. Byrd, C.W. Cork, J.N. Corlett, S. De Santis, L.R. Doolittle, J.A. Doyle, P. Emma, J. Feng, D. Filippetto, G. Huang, H. Huang, T.D. Kramasz, S. Kwiatkowski, W.E. Norum, H.A. Padmore, C. F. Papadopoulos, G.C. Pappas, G.J. Portmann, J. Qiang, D.G. Quintas, J.W. Staples, T. Vecchione, M. Venturini, M. Vinco, W. Wan, R.P. Wells, M.S. Zolotorev, F.A. Zucca LBNL, Berkeley, California, USA M. J. Messerly, M.A. Prantil LLNL, Livermore, California, USA C.M. Pogue NPS, Monterey, California, USA
	Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231. The Advanced Photo-injector Experiment (APEX) at the Lawrence Berkeley National Laboratory is focused on the development of a high-brightness high-repetition rate (MHz-class) electron injector for X-ray FEL applications. The injector is based on a new concept gun, utilizing a normal conducting 186 MHz RF cavity operating in cw mode in conjunction with high quantum efficiency photocathodes capable of delivering the required repetition rates with available laser technology. The APEX activities are staged in 3 main phases. In Phases 0 and I, the gun will be tested at its nominal energy of 750 keV and several different photocathodes are tested at full repetition rate. In Phase II, a pulsed linac will be added for accelerating the beam at several tens of MeV to reduce space charge effects and measure the high-brightness performance of the gun when integrated in an injector scheme. At Phase II energies, the radiation shielding configuration of APEX limits the repetition rate to a maximum of several Hz. Phase 0 is under commissioning, Phase I under installation, and initial activities for Phase II are underway. This paper presents an update on the status of these activities.