IPAC2017 - Classification: 03 Novel Particle Sources and Acceleration Techniques / T02 Electron Sources

Paper	Title	Page
MOPIK003	Improvement of the Photoemission Efficiency of Magnesium Photocathodes	500
	R. Xiang, A. Arnold, P.N. Lu, P. Michel, P. Murcek, J. Teichert, H. Vennekate HZDR, Dresden, Germany P. Patra IUAC, New Delhi, India
	Funding: The work is supported by the European Community under the FP7 programme (EuCARD-2) and by the German Federal Ministry of Education and Research (BMBF) grant 05K12CR1. To improve the quality of photocathodes is one of the critical issues in enhancing the stability and reliability of photo-injector systems. Presently the primary choice is to use metallic photocathodes for the ELBE SRF Gun-II to reduce the risk of contamination of the superconducting cavity. Magnesium has a low work function (3.6 eV) and shows high quantum efficiency (QE) up to 0.3 % after laser cleaning. The SRF Gun II with an Mg photocathode has successfully provided electron beam for ELBE users. However, the present cleaning process with a high intensi-ty laser (activation) is time consuming and generates unwanted surface roughness. This paper presents the investigation of alternative surface cleaning procedures, such as thermal treatment. The QE and topography of Mg samples after treatment are reported.
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MOPIK004	Demonstration of an All-Optically Driven Sub-keV THz Gun	503
	W.R. Huang, K.-H. Hong, F.X. Kärtner, E.A. Nanni, KR. Ravi MIT, Cambridge, Massachusetts, USA A-L. Calendron, H. Cankaya, A. Fallahi, F.X. Kärtner, X. Wu CFEL, Hamburg, Germany D. Zhang DESY, Hamburg, Germany
	Funding: European Research Council under the European Union Seventh Framework Program (FP/2007-2013)/ERC Grant Agreement no. 609920 Intense ultrashort THz and optical pulses with single-cycle pulse duration became possible after the recent advances in ultrafast technologies. Using such ultrashort pulses for electron acceleration offers advantages in terms of higher thresholds for material breakdown which opens up a promising path towards increased acceleration gradients. In addition, using optically generated THz pulses enable inherently synchronized acceleration schemes, since accelerating field and particle injecting field are excited by a single seed laser. In this contribution, we present the first experimental demonstration of laser-driven THz acceleration of electrons initially at rest. It is shown that strong-field, single-cycle THz fields accelerate electrons with peak energies of up to 0.8 keV in an ultracompact THz gun with bunch charge of 40 fC. The achieved energy spreads are as low as 5.8%.
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MOPIK005	Compact Electron Injectors Using Laser Driven THz Cavities	506
	M. Fakhari, A. Fallahi, F.X. Kärtner, N.H. Matlis, A. Yahaghi CFEL, Hamburg, Germany R.W. Aßmann, U. Dorda, K. Galaydych, B. Marchetti, G. Vashchenko, T. Vinatier, D. Zhang, C. Zhou DESY, Hamburg, Germany
	We present ultra-small electron injectors based on cascaded cavities excited by short multi-cycle THz signals. The designed structure is a 3.5 cell normal conducting cavity operating at 300 GHz. This cavity is able to generate pC electron bunches and accelerate them up to 250 keV using less than 1 mJ THz energy. Unlike conventional RF guns, the designed cavity operates in a transient state which, in combination with the high frequency of the driving field, makes it possible to apply accelerating gradients as high as 500 MV/m. Such high accelerating gradients are promising for the generation of high brightness electron beams with transverse emittances in the nm-rad range. The designed cavity can be used as the injector for a compact accelerator of low charge bunches.
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MOPIK006	Characterization of the Electron Beam from the Thz Driven Gun for AXSIS	509
	G. Vashchenko, R.W. Aßmann, U. Dorda, K. Galaydych, B. Marchetti, T. Vinatier DESY, Hamburg, Germany M. Fakhari, A. Fallahi, F.X. Kärtner, N.H. Matlis CFEL, Hamburg, Germany W. Qiao, C. Zhou University of Hamburg, Hamburg, Germany
	Funding: The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. 609920 The AXSIS (Attosecond X-ray Science: Imaging and Spectroscopy) project aims for development of a compact, fully coherent, THz-driven, attosecond X-ray source. A compact THz driven gun was developed, produced and tested as a source of the ultra-short electron bunches required for the project. To characterize the low energy, low-charge beam produced by such a gun tailored diagnostic devices were developed and commissioned at a test-stand chamber in CFEL (DESY). Results of the first experiments on the production and characterization of the electron beam are presented.
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MOPIK007	THz Driven Electron Acceleration with a Multilayer Structure	512
	D. Zhang, M. Fakhari, W. Qiao, C. Zhou DESY, Hamburg, Germany F. Ahr, A-L. Calendron, H. Cankaya, M. Fakhari, A. Fallahi, F.X. Kärtner, F. Lemery, N.H. Matlis, X. Wu CFEL, Hamburg, Germany W.R. Huang, F.X. Kärtner MIT, Cambridge, Massachusetts, USA C. Zhou University of Hamburg, Hamburg, Germany
	We present first results in THz-based electron acceleration using a novel multilayer structure which we dub a Butterfly LINAC. THz-based accelerators are mm-scale devices that bridge the gap between micron-scale, ultra-compact devices such as laser-plasma accelerators (LPAs) and dielectric laser accelerators (DLAs) and meter-scale conventional accelerators. These intermediate-scale devices are promising because they combine many of the benefits of LPAs and DLAs, such as intrinsic synchronization and high acceleration gradients with the benefits of conventional accelerators such as high charge capacity, tunability as well as the robustness, stability and simple fabrication of static, macroscopic acceleration structures. The Butterfly LINAC allows optimization of electron acceleration using transversely-coupled single-cycle THz pulses by phase-matching electrons with the driving field. Proof-of-concept experiments will be described demonstrating 10 keV energy gain of a 55 keV source, in good agreement with simulation. Scalability of this device to the MeV level and applicability towards free electron lasers and ultrafast electron diffractometers will also be discussed.
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MOPIK008	Numerical Studies on a Modified Cathode Tip for the ELBE Superconducting RF Gun	515
	E.T. Tulu, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany A. Arnold HZDR, Dresden, Germany
	Future light sources such as synchrotron radiation sources driven by an Energy Recovery Linac (ERL), Free Electron Laser (FEL) or THz radiation sources have in common that they require injectors, which provide high-brilliance, high-current electron beams in almost continuous operation. Thus, the development of appropriate highly brilliant electron sources is a central factor. A promising approach for this key component is provided by superconducting radiofrequency photoinjectors (SRF guns) []. Since 2007, the free-electron laser FELBE at HZDR successfully operates such a SRF gun under real conditions and equipped with all components []. Nevertheless, there are limitations caused by multipacting which should be overcome in order to further improve the gun []. One aspect in order to reach this aim lies in studying various modifications of the cathode tip [*]. This contribution will present the effectiveness of isosceles triangular grooves with respect to MP. Arnold, et al., NIM A, 593, 57, (2008). J. Teichert, et al., 2008 NSS/MIC, Dresden, Germany. * J. Teichert, et al., J. Phys.: Conf. Ser. 298(2011), 012008. **** E. T. Tulu, et al., IPAC2014, p652, Dresden, Germany.
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MOPIK009	Characterization of Cold Model Cavity for Cryocooled C-Band 2.6-Cell Photocathode RF Gun at 20 K	518
	T. Tanaka, K. Hayakawa, Y. Hayakawa, K. Nakao, K. Nogami, T. Sakai, K. Takatsuka LEBRA, Funabashi, Japan M.K. Fukuda, D. Satoh, T. Takatomi, N. Terunuma, J. Urakawa, M. Yoshida KEK, Ibaraki, Japan
	Funding: This work was partly supported by the Photon and Quantum Basic Research Coordinated Development Program of the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT). A cryocooled C-band 2.6-cell photocathode RF electron gun has been studied at Nihon University in cooperation with KEK. The cold model cavity with an input coupler was completed in spring 2016. The RF characteristics measured at room temperature were in agreement with the prediction by the CST Studio simulation. The RF characteristics at 20 K have been measured using a rather simple cavity-cooling vacuum system that was built by using existing components for tentative experiments. A thin-wall stainless-steel R48 waveguide with copper-plated inner walls has been used for the RF power transmission from the room-temperature input port to the 20-K cooled coupler waveguide. The unloaded Q-value of 73000 has been obtained by the reflection coefficient measurement at 20 K, which is in agreement with the result of the CST Studio simulation using the cavity surface resistance predicted by the theory of the anomalous skin effect.
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MOPIK011	Electron Beam Generation From InGaN/GaN Superlattice Photocathode	522
	N. Yamamoto KEK, Ibaraki, Japan M. Hosaka, A. Mano, T. Miyauchi, Y. Takashima Nagoya University, Nagoya, Japan M. Katoh UVSOR, Okazaki, Japan
	GaAs-type photocathode (PC) has been used as electron spin polarization (ESP) sources for various applications. Recently, by using a strain-compensated technique for GaAs/GaAsP, the super lattice (SL) thickness of up to 720 nm could be manufactured and the quantum efficiency (QE) improvements with the thickness increases was observed. In the experiments, the ESP degradation was also observed for the thicker thickness samples than 194nm and we considered that electron spin relaxation during diffusion process in the PC caused the degradation. Therefore, we propose developing fcc-GaN based PCs instead of GaAs because a factor of ten longer spin relaxation time compared with GaAs/GaAsP SL was reported. However an fcc-GaN sample with adequate dimensions for PC applications is not available at present due to manufacturing difficulties. Then at the start of GaN-type PC development, an hcp-GaN sample has been studied. In the study, NEA-activation was made for an InGaN/GaN SL sample and QE, surface lifetime and ESP were measured. The QE and ESP values were 1.3% and 2.1% at the pump laser wavelength of 405nm.
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MOPIK013	Design and Simulation of a C-Band Photocathode RF Gun With a Coaxial Coupler for UEM	525
	T. Chen, Y.J. Pei, Y. Song USTC/NSRL, Hefei, Anhui, People's Republic of China
	A ultrafast electron microscope (UEM) has been become much more important research instrument and has been widely used in many fields. As a part of the UEM, a photocathode RF gun working at C-band frequency of 5712MHz is being developed, which provides electron beam with high qualities for UEM. This paper presents the physics and structure design, including optimization of cavity shape parameter for improving shunt impedance and Q factor. We adopt a novel coaxial coupler, which could decrease the multipole field and decrease the focusing coil size, build better accelerating field in the RF gun. In this paper, we discussed the simulation process and results of the RF gun, especially the design of the coaxial input coupler was described.
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MOPIK015	Improvement of Electron Intensity Reduction System at SLRI Beam Test Facility	528
	K. Kittimanapun, N. Chanlek, P. Klysubun, S. Krainara, S. Supajeerapan SLRI, Nakhon Ratchasima, Thailand
	Funding: This work is partly supported by the National Science and Technology Development Agency (NSTDA) under contract FDA-C0-2558-855-TH. Synchrotron Light Research Institute (SLRI) has been commissioning an additional experimental station, a Beam Test Facility (BTF), to the SLRI accelerator complex. SLRI BTF was constructed to provide electron test beams with energy ranging from 40 MeV up to 1.2 GeV and with tunable electron intensity from a few to millions of electrons per burst. In order to obtain low intensity of test beams, an approach using a metal target together with an energy selector has been employed. A combination of a target chamber installed at the high energy beam transport line and the existing 4-degree bending magnet that is used as an energy selector first produced low intensity test beams. However, the test beam profile was not well determined due to the insufficient bending angle of the energy selector and high primary beam energy. Another approach mounting a target chamber at the low energy beam transport line and using the synchrotron booster as an energy selector was implemented to avoid such problems. Once in operation, the facility will have the potential to service calibration and testing of high energy detectors as well as beam diagnostic instrumentations.
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MOPIK016	Sub-Picosecond Beam Production for External Injection Into Plasma Experiments	531
	O. Mete Apsimon, R. Apsimon, G. Burt Cockcroft Institute, Lancaster University, Lancaster, United Kingdom G.X. Xia UMAN, Manchester, United Kingdom
	Funding: This work has been funded by STFC. Applications of plasmas in accelerators benefit from short probe bunches comparable to plasma wavelength due to currently achievable plasma wake profiles. In plasma acceleration case, high capture efficiency within a narrow energy spectrum can be achieved when a sub-picosecond to femtosecond witness bunch injected behind the driver pulse at the high electric field region. A start-to-end simulation study was performed for parametric optimisation of an rf photoinjector to provide a short witness bunch for plasma applications in accelerators. An rf photoinjector is a laser-driven, high brightness and robust electron source that can provide stability and flexibility provided by today's advanced laser and rf technologies.
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MOPIK017	Simultaneous Generation of Drive and Witness Beam for Collinear Wakefield Acceleration	535
	G. Ha POSTECH, Pohang, Kyungbuk, Republic of Korea M.E. Conde, D.S. Doran, W. Gai, J.G. Power ANL, Argonne, Illinois, USA
	Funding: This work is supported by Department of Energy, Office of High Energy Physics, under Contract No. DE-AC02-06CH11357. Generating the drive and witness bunch for collinear wakefield acceleration (CWFA) requires precise control of the longitudinal bunch shape for each bunch as well as the controlling their separation. The emittance exchange (EEX) beamline and a transverse mask can be used to achieve all of these requirements. First, this EEX-based method can independently control the longitudinal bunch shape of each bunches so that the drive bunch is shaped to generate a high transformer ratio while witness bunch is shaped to suppress its energy spread. Second, the timing jitter between the drive and witness bunch poses a serious limitation to the CWFA scheme but the EEX-based method eliminates this since both bunches are generated at the same time and share the exactly same beamline so there are no relative errors. In this paper, we confirm the feasibility of this EEX-based method for simultaneous generation with simulation for CWFA in a dielectric structure.
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MOPIK018	Micro-Scale Electron Beam Generation Using Pyroelectric Crystals	538
	R.B. Yoder, Z. Kabilova Goucher College, Baltimore, Maryland, USA
	Novel laser-powered acceleration structures currently under development, which have dimensions comparable to optical wavelengths and can be constructed on a silicon wafer, require injection of a sub-micron-scale electron bunch to achieve high-quality, monoenergetic output beams. A potential injection mechanism for such micro-scale beams relies on field emission from a nanotip array, followed by acceleration to near-relativistic energies. We demonstrate field emission of electrons from a lithium niobate crystal during heating and cooling, and describe the production of electrons within a hollow channel along the axis of a lithium niobate crystal. Measurements of emitted beam properties are compared with direct measurements of crystal fields under comparable conditions and modeled mathematically.
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MOPIK019	Upgrade Options Towards Higher Fields and Beam Energies for Continuous-Wave Room-Temperature VHF RF Guns	542
	F. Sannibale, J.M. Byrd, D. Filippetto, M.J. Johnson, D. Li, T.H. Luo, C.E. Mitchell, J.W. Staples, S.P. Virostek LBNL, Berkeley, California, USA
	Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231 Science demand for MHz-class repetition rate electron beam applications such as free electron lasers (FELs), inverse Compton scattering sources, and ultrafast electron diffraction and microscopy (UED/UEM), pushed the development of new gun schemes that could generate high brightness beams at such high rates. At the Lawrence Berkeley Lab (LBNL), we proposed a new concept room-temperature RF gun resonating in the VHF frequency range (30-300 MHz) capable of operating in continuous wave mode at the fields required for high-brightness performance. A first VHF-Gun was constructed and tested in the APEX facility at LBNL, which successfully demonstrated all design parameters and the generation of high brightness electron beams. A second version of the APEX VHF-Gun is being built at LBNL for the LCLS-II, the new SLAC X-ray FEL. Recent studies showed that a proposed LCLS-II upgrade and UED/UEM applications would greatly benefit from an increased gun brightness obtained by raising the electric field at the cathode and the beam energy at the gun exit. In this paper, we present and discuss possible upgrade options that would allow extension of the VHF-Gun performance towards these new goals.
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MOPIK021	Generation of Transversely Segmented Beam Using a Nano-Patterned Photocathode	545
	A. Lueangaramwong, P. Piot Northern Illinois University, DeKalb, Illinois, USA G. Andonian RadiaBeam, Santa Monica, California, USA P. Piot Fermilab, Batavia, Illinois, USA
	Funding: Work supported by US Department of Energy (DOE) contract DE-SC0009656 with Radiabeam Technologies and by NSF grant PHY-1535401 with Northern Illinois University. Plasmonic photocathodes – nano-patterned photocathodes with periodicity comparable to the excitation laser – have demonstrated enhanced quantum efficiency. In the present paper we present numerical simulations of the beam dynamics associated to the emission process from this type of cathodes and to the subsequent acceleration to relativistic energies by combining WARP and IMPACT-T programs. We especially consider the possibility to transversely image the cathode surface at high energy and enable the generation of transversely segment beams.
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MOPIK022	Experimental Investigation of Field-Emission From Silicon Nano-Cone Cathodes	548
SUSPSIK041	use link to see paper's listing under its alternate paper code
	A. Lueangaramwong, C. Buzzard, V. Korampally, O. Mohsen, P. Piot Northern Illinois University, DeKalb, Illinois, USA S. Chattopadhyay Northern Illinois Univerity, DeKalb, Illinois, USA R. Divan Argonne National Laboratory, Argonne, Illinois, USA P. Piot Fermilab, Batavia, Illinois, USA
	Funding: This work is supported by the NSF grant PHY-1535401 with Northern Illinois University Field emission cathode are capable of forming electron beam with extreme brightness via strong-field excitation from applied electrostatic, or electromagnetic (radiofrequency and laser) fields. Our group, in collaboration with the Argonne Center for Nanoscale Material, has recently developed nanocone cathode. The present paper reports on the experimental characterization of these cathodes both configured as a single-cone emitter or as large arrays of tightly-packed emitter. The tests carried in a diode setup are capable of measuring IV characteristic curves and beam distributions.
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MOPIK023	Cornell Laboratory for High Intensity, Ultra-Bright and Polarized Electron Beams	551
	L. Cultrera, A.C. Bartnik, I.V. Bazarov, C.M. Gulliford, P. Gupta, H. Lee, S.A. McBride, T.P. Moore Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This work has been funded by the National Science Foundation (Grant No. PHY-1416318) and Department of Energy (Grants No. DE-SC0014338, No. DE-SC0011643 and No. DE-SC0016203). We report on the current activities pursued at Cornell University for the production of electron beams tailored to a wide range of applications. We have developed the expertise to grow many different type of high quantum efficiency photocathode belonging to the alkali antimonide family. Those materials are ideal candidates to produce high intensity beam with average currents in the mA range. When operated near threshold at cryogenic temperature in transmission mode they can also generate the electron beams needed to perform ultrafast electron diffraction of bio molecules. We have recently expanded our facility with a Mott polarimeter to include the capability to measure polarization of the electron beam. The photocathode lab is being complemented by a dedicated photo-gun laboratory to test the photocathode properties in a real environment and to perform measurement of the beam properties under new and yet unexplored operating conditions.
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MOPIK026	Commissioning and Operation of an Ultrafast Electron Diffraction Facility as Part of the ATF-II Upgrade at Brookhaven National Laboratory	554
	M.G. Fedurin, M. Babzien, C. Folz, M. Fulkerson, K. Kusche, J.J. Li, R. Malone, M.A. Palmer, T.V. Shaftan, J. Skaritka, L. Snydstrup, C. Swinson, F.J. Willeke BNL, Upton, Long Island, New York, USA
	Funding: Work supported by the US DOE under contract DE-SC0012704. The Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL) is presently carrying out an upgrade, ATF-II, which will provide significantly expanded experimental space and capabilities for its users. One of the new capabilities being integrated into the ATF-II program is an Ultrafast Electron Diffraction (UED) beam line, which was originally deployed in the BNL Source Development Laboratory. Inclusion of the UED in the ATF-II research portfolio will enable ongoing development and extension of the UED capabilities for use in materials research. We describe the design, operation and future plans for the UED beam line at the ATF-II.
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MOPVA010	Setup and Status of an SRF Photoinjector for Energy-Recovery Linac Applications	865
	T. Kamps, D. Böhlick, A.B. Büchel, M. Bürger, P. Echevarria, A. Frahm, F. Göbel, S. Heling, A. Jankowiak, S. Keckert, H. Kirschner, G. Klemz, J. Knobloch, G. Kourkafas, J. Kühn, O. Kugeler, A.N. Matveenko, A. Neumann, N. Ohm-Krafft, E. Panofski, F. Pfloksch, S. Rotterdam, M.A.H. Schmeißer, M. Schuster, H. Stein, J. Ullrich, A. Ushakov, J. Völker HZB, Berlin, Germany I. Will MBI, Berlin, Germany
	Funding: The work is funded by the Helmholtz-Association, BMBF, the state of Berlin and HZB. The Superconducting RF (SRF) photoinjector programme for the energy-recovery linac (ERL) test facility BERLinPro sets out to push the brightness and average current limits for ERL electron sources by tackling the main challenges related to beam dynamics of SRF photoinjectors, the incorporation of high quantum efficiency (QE) photocathodes, and suppression of unwanted beam generation. The paper details the experimental layout of the SRF photoinjector and the gun test facility GunLab at Helmholtz-Zentrum Berlin.
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MOPVA033	A Compact Thermionic RF Injector with RF Bunch Compression fed by a Quadrupole-Free Mode Launcher	924
	F. Toufexis, V.A. Dolgashev, C. Limborg-Deprey, S.G. Tantawi SLAC, Menlo Park, California, USA
	Funding: This project was funded by U.S. Department of Energy under Contract No. DE-AC02-76SF00515, and the National Science Foundation under Contract No. PHY-1415437. We present a design for a compact X-Band RF thermionic injector consisting of two iris-loaded accelerator structures. Both structures are fed by a single quadrupole-free TM01 mode launcher. In the first structure the electron bunches are extracted from a thermionic cathode. The second structure creates an energy chirp in the bunch for its further ballistic compression. This injector can produce short electron bunches without the need for a magnetic bunch compressor. We are developing this injector as part of a linac-based 91.392 GHz RF power source, which further comprises a booster linac and a mm-wave decelerator structure that extracts 91.392 GHz RF power from the electron beam. This source will be used to power a short-period RF undulator with 1.75 mm period. F. Toufexis and S.G. Tantawi, A 1.75 mm Period RF-Driven Undulator, these proceedings.
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Paper

Title

Page

Improvement of the Photoemission Efficiency of Magnesium Photocathodes

500

R. Xiang, A. Arnold, P.N. Lu, P. Michel, P. Murcek, J. Teichert, H. Vennekate
HZDR, Dresden, Germany
P. Patra
IUAC, New Delhi, India

Funding: The work is supported by the European Community under the FP7 programme (EuCARD-2) and by the German Federal Ministry of Education and Research (BMBF) grant 05K12CR1.
To improve the quality of photocathodes is one of the critical issues in enhancing the stability and reliability of photo-injector systems. Presently the primary choice is to use metallic photocathodes for the ELBE SRF Gun-II to reduce the risk of contamination of the superconducting cavity. Magnesium has a low work function (3.6 eV) and shows high quantum efficiency (QE) up to 0.3 % after laser cleaning. The SRF Gun II with an Mg photocathode has successfully provided electron beam for ELBE users. However, the present cleaning process with a high intensi-ty laser (activation) is time consuming and generates unwanted surface roughness. This paper presents the investigation of alternative surface cleaning procedures, such as thermal treatment. The QE and topography of Mg samples after treatment are reported.

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MOPIK004

Demonstration of an All-Optically Driven Sub-keV THz Gun

503

W.R. Huang, K.-H. Hong, F.X. Kärtner, E.A. Nanni, KR. Ravi
MIT, Cambridge, Massachusetts, USA
A-L. Calendron, H. Cankaya, A. Fallahi, F.X. Kärtner, X. Wu
CFEL, Hamburg, Germany
D. Zhang
DESY, Hamburg, Germany

Funding: European Research Council under the European Union Seventh Framework Program (FP/2007-2013)/ERC Grant Agreement no. 609920
Intense ultrashort THz and optical pulses with single-cycle pulse duration became possible after the recent advances in ultrafast technologies. Using such ultrashort pulses for electron acceleration offers advantages in terms of higher thresholds for material breakdown which opens up a promising path towards increased acceleration gradients. In addition, using optically generated THz pulses enable inherently synchronized acceleration schemes, since accelerating field and particle injecting field are excited by a single seed laser. In this contribution, we present the first experimental demonstration of laser-driven THz acceleration of electrons initially at rest. It is shown that strong-field, single-cycle THz fields accelerate electrons with peak energies of up to 0.8 keV in an ultracompact THz gun with bunch charge of 40 fC. The achieved energy spreads are as low as 5.8%.

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MOPIK005

Compact Electron Injectors Using Laser Driven THz Cavities

506

M. Fakhari, A. Fallahi, F.X. Kärtner, N.H. Matlis, A. Yahaghi
CFEL, Hamburg, Germany
R.W. Aßmann, U. Dorda, K. Galaydych, B. Marchetti, G. Vashchenko, T. Vinatier, D. Zhang, C. Zhou
DESY, Hamburg, Germany

We present ultra-small electron injectors based on cascaded cavities excited by short multi-cycle THz signals. The designed structure is a 3.5 cell normal conducting cavity operating at 300 GHz. This cavity is able to generate pC electron bunches and accelerate them up to 250 keV using less than 1 mJ THz energy. Unlike conventional RF guns, the designed cavity operates in a transient state which, in combination with the high frequency of the driving field, makes it possible to apply accelerating gradients as high as 500 MV/m. Such high accelerating gradients are promising for the generation of high brightness electron beams with transverse emittances in the nm-rad range. The designed cavity can be used as the injector for a compact accelerator of low charge bunches.

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MOPIK006

Characterization of the Electron Beam from the Thz Driven Gun for AXSIS

509

G. Vashchenko, R.W. Aßmann, U. Dorda, K. Galaydych, B. Marchetti, T. Vinatier
DESY, Hamburg, Germany
M. Fakhari, A. Fallahi, F.X. Kärtner, N.H. Matlis
CFEL, Hamburg, Germany
W. Qiao, C. Zhou
University of Hamburg, Hamburg, Germany

Funding: The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. 609920
The AXSIS (Attosecond X-ray Science: Imaging and Spectroscopy) project aims for development of a compact, fully coherent, THz-driven, attosecond X-ray source. A compact THz driven gun was developed, produced and tested as a source of the ultra-short electron bunches required for the project. To characterize the low energy, low-charge beam produced by such a gun tailored diagnostic devices were developed and commissioned at a test-stand chamber in CFEL (DESY). Results of the first experiments on the production and characterization of the electron beam are presented.

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MOPIK007

THz Driven Electron Acceleration with a Multilayer Structure

512

D. Zhang, M. Fakhari, W. Qiao, C. Zhou
DESY, Hamburg, Germany
F. Ahr, A-L. Calendron, H. Cankaya, M. Fakhari, A. Fallahi, F.X. Kärtner, F. Lemery, N.H. Matlis, X. Wu
CFEL, Hamburg, Germany
W.R. Huang, F.X. Kärtner
MIT, Cambridge, Massachusetts, USA
C. Zhou
University of Hamburg, Hamburg, Germany

We present first results in THz-based electron acceleration using a novel multilayer structure which we dub a Butterfly LINAC. THz-based accelerators are mm-scale devices that bridge the gap between micron-scale, ultra-compact devices such as laser-plasma accelerators (LPAs) and dielectric laser accelerators (DLAs) and meter-scale conventional accelerators. These intermediate-scale devices are promising because they combine many of the benefits of LPAs and DLAs, such as intrinsic synchronization and high acceleration gradients with the benefits of conventional accelerators such as high charge capacity, tunability as well as the robustness, stability and simple fabrication of static, macroscopic acceleration structures. The Butterfly LINAC allows optimization of electron acceleration using transversely-coupled single-cycle THz pulses by phase-matching electrons with the driving field. Proof-of-concept experiments will be described demonstrating 10 keV energy gain of a 55 keV source, in good agreement with simulation. Scalability of this device to the MeV level and applicability towards free electron lasers and ultrafast electron diffractometers will also be discussed.

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MOPIK008

Numerical Studies on a Modified Cathode Tip for the ELBE Superconducting RF Gun

515

E.T. Tulu, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
A. Arnold
HZDR, Dresden, Germany

Future light sources such as synchrotron radiation sources driven by an Energy Recovery Linac (ERL), Free Electron Laser (FEL) or THz radiation sources have in common that they require injectors, which provide high-brilliance, high-current electron beams in almost continuous operation. Thus, the development of appropriate highly brilliant electron sources is a central factor. A promising approach for this key component is provided by superconducting radiofrequency photoinjectors (SRF guns) [*]. Since 2007, the free-electron laser FELBE at HZDR successfully operates such a SRF gun under real conditions and equipped with all components [**]. Nevertheless, there are limitations caused by multipacting which should be overcome in order to further improve the gun [***]. One aspect in order to reach this aim lies in studying various modifications of the cathode tip [****]. This contribution will present the effectiveness of isosceles triangular grooves with respect to MP.
* Arnold, et al., NIM A, 593, 57, (2008).
** J. Teichert, et al., 2008 NSS/MIC, Dresden, Germany.
*** J. Teichert, et al., J. Phys.: Conf. Ser. 298(2011), 012008.
**** E. T. Tulu, et al., IPAC2014, p652, Dresden, Germany.

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MOPIK009

Characterization of Cold Model Cavity for Cryocooled C-Band 2.6-Cell Photocathode RF Gun at 20 K

518

T. Tanaka, K. Hayakawa, Y. Hayakawa, K. Nakao, K. Nogami, T. Sakai, K. Takatsuka
LEBRA, Funabashi, Japan
M.K. Fukuda, D. Satoh, T. Takatomi, N. Terunuma, J. Urakawa, M. Yoshida
KEK, Ibaraki, Japan

Funding: This work was partly supported by the Photon and Quantum Basic Research Coordinated Development Program of the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT).
A cryocooled C-band 2.6-cell photocathode RF electron gun has been studied at Nihon University in cooperation with KEK. The cold model cavity with an input coupler was completed in spring 2016. The RF characteristics measured at room temperature were in agreement with the prediction by the CST Studio simulation. The RF characteristics at 20 K have been measured using a rather simple cavity-cooling vacuum system that was built by using existing components for tentative experiments. A thin-wall stainless-steel R48 waveguide with copper-plated inner walls has been used for the RF power transmission from the room-temperature input port to the 20-K cooled coupler waveguide. The unloaded Q-value of 73000 has been obtained by the reflection coefficient measurement at 20 K, which is in agreement with the result of the CST Studio simulation using the cavity surface resistance predicted by the theory of the anomalous skin effect.

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MOPIK011

Electron Beam Generation From InGaN/GaN Superlattice Photocathode

522

N. Yamamoto
KEK, Ibaraki, Japan
M. Hosaka, A. Mano, T. Miyauchi, Y. Takashima
Nagoya University, Nagoya, Japan
M. Katoh
UVSOR, Okazaki, Japan

GaAs-type photocathode (PC) has been used as electron spin polarization (ESP) sources for various applications. Recently, by using a strain-compensated technique for GaAs/GaAsP, the super lattice (SL) thickness of up to 720 nm could be manufactured and the quantum efficiency (QE) improvements with the thickness increases was observed. In the experiments, the ESP degradation was also observed for the thicker thickness samples than 194nm and we considered that electron spin relaxation during diffusion process in the PC caused the degradation. Therefore, we propose developing fcc-GaN based PCs instead of GaAs because a factor of ten longer spin relaxation time compared with GaAs/GaAsP SL was reported. However an fcc-GaN sample with adequate dimensions for PC applications is not available at present due to manufacturing difficulties. Then at the start of GaN-type PC development, an hcp-GaN sample has been studied. In the study, NEA-activation was made for an InGaN/GaN SL sample and QE, surface lifetime and ESP were measured. The QE and ESP values were 1.3% and 2.1% at the pump laser wavelength of 405nm.

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MOPIK013

Design and Simulation of a C-Band Photocathode RF Gun With a Coaxial Coupler for UEM

525

T. Chen, Y.J. Pei, Y. Song
USTC/NSRL, Hefei, Anhui, People's Republic of China

A ultrafast electron microscope (UEM) has been become much more important research instrument and has been widely used in many fields. As a part of the UEM, a photocathode RF gun working at C-band frequency of 5712MHz is being developed, which provides electron beam with high qualities for UEM. This paper presents the physics and structure design, including optimization of cavity shape parameter for improving shunt impedance and Q factor. We adopt a novel coaxial coupler, which could decrease the multipole field and decrease the focusing coil size, build better accelerating field in the RF gun. In this paper, we discussed the simulation process and results of the RF gun, especially the design of the coaxial input coupler was described.

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MOPIK015

Improvement of Electron Intensity Reduction System at SLRI Beam Test Facility

528

K. Kittimanapun, N. Chanlek, P. Klysubun, S. Krainara, S. Supajeerapan
SLRI, Nakhon Ratchasima, Thailand

Funding: This work is partly supported by the National Science and Technology Development Agency (NSTDA) under contract FDA-C0-2558-855-TH.
Synchrotron Light Research Institute (SLRI) has been commissioning an additional experimental station, a Beam Test Facility (BTF), to the SLRI accelerator complex. SLRI BTF was constructed to provide electron test beams with energy ranging from 40 MeV up to 1.2 GeV and with tunable electron intensity from a few to millions of electrons per burst. In order to obtain low intensity of test beams, an approach using a metal target together with an energy selector has been employed. A combination of a target chamber installed at the high energy beam transport line and the existing 4-degree bending magnet that is used as an energy selector first produced low intensity test beams. However, the test beam profile was not well determined due to the insufficient bending angle of the energy selector and high primary beam energy. Another approach mounting a target chamber at the low energy beam transport line and using the synchrotron booster as an energy selector was implemented to avoid such problems. Once in operation, the facility will have the potential to service calibration and testing of high energy detectors as well as beam diagnostic instrumentations.

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MOPIK016

Sub-Picosecond Beam Production for External Injection Into Plasma Experiments

531

O. Mete Apsimon, R. Apsimon, G. Burt
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
G.X. Xia
UMAN, Manchester, United Kingdom

Funding: This work has been funded by STFC.
Applications of plasmas in accelerators benefit from short probe bunches comparable to plasma wavelength due to currently achievable plasma wake profiles. In plasma acceleration case, high capture efficiency within a narrow energy spectrum can be achieved when a sub-picosecond to femtosecond witness bunch injected behind the driver pulse at the high electric field region. A start-to-end simulation study was performed for parametric optimisation of an rf photoinjector to provide a short witness bunch for plasma applications in accelerators. An rf photoinjector is a laser-driven, high brightness and robust electron source that can provide stability and flexibility provided by today's advanced laser and rf technologies.

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MOPIK017

Simultaneous Generation of Drive and Witness Beam for Collinear Wakefield Acceleration

535

G. Ha
POSTECH, Pohang, Kyungbuk, Republic of Korea
M.E. Conde, D.S. Doran, W. Gai, J.G. Power
ANL, Argonne, Illinois, USA

Funding: This work is supported by Department of Energy, Office of High Energy Physics, under Contract No. DE-AC02-06CH11357.
Generating the drive and witness bunch for collinear wakefield acceleration (CWFA) requires precise control of the longitudinal bunch shape for each bunch as well as the controlling their separation. The emittance exchange (EEX) beamline and a transverse mask can be used to achieve all of these requirements. First, this EEX-based method can independently control the longitudinal bunch shape of each bunches so that the drive bunch is shaped to generate a high transformer ratio while witness bunch is shaped to suppress its energy spread. Second, the timing jitter between the drive and witness bunch poses a serious limitation to the CWFA scheme but the EEX-based method eliminates this since both bunches are generated at the same time and share the exactly same beamline so there are no relative errors. In this paper, we confirm the feasibility of this EEX-based method for simultaneous generation with simulation for CWFA in a dielectric structure.

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MOPIK018

Micro-Scale Electron Beam Generation Using Pyroelectric Crystals

538

R.B. Yoder, Z. Kabilova
Goucher College, Baltimore, Maryland, USA

Novel laser-powered acceleration structures currently under development, which have dimensions comparable to optical wavelengths and can be constructed on a silicon wafer, require injection of a sub-micron-scale electron bunch to achieve high-quality, monoenergetic output beams. A potential injection mechanism for such micro-scale beams relies on field emission from a nanotip array, followed by acceleration to near-relativistic energies. We demonstrate field emission of electrons from a lithium niobate crystal during heating and cooling, and describe the production of electrons within a hollow channel along the axis of a lithium niobate crystal. Measurements of emitted beam properties are compared with direct measurements of crystal fields under comparable conditions and modeled mathematically.

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MOPIK019

Upgrade Options Towards Higher Fields and Beam Energies for Continuous-Wave Room-Temperature VHF RF Guns

542

F. Sannibale, J.M. Byrd, D. Filippetto, M.J. Johnson, D. Li, T.H. Luo, C.E. Mitchell, J.W. Staples, S.P. Virostek
LBNL, Berkeley, California, USA

Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
Science demand for MHz-class repetition rate electron beam applications such as free electron lasers (FELs), inverse Compton scattering sources, and ultrafast electron diffraction and microscopy (UED/UEM), pushed the development of new gun schemes that could generate high brightness beams at such high rates. At the Lawrence Berkeley Lab (LBNL), we proposed a new concept room-temperature RF gun resonating in the VHF frequency range (30-300 MHz) capable of operating in continuous wave mode at the fields required for high-brightness performance. A first VHF-Gun was constructed and tested in the APEX facility at LBNL, which successfully demonstrated all design parameters and the generation of high brightness electron beams. A second version of the APEX VHF-Gun is being built at LBNL for the LCLS-II, the new SLAC X-ray FEL. Recent studies showed that a proposed LCLS-II upgrade and UED/UEM applications would greatly benefit from an increased gun brightness obtained by raising the electric field at the cathode and the beam energy at the gun exit. In this paper, we present and discuss possible upgrade options that would allow extension of the VHF-Gun performance towards these new goals.

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MOPIK021

Generation of Transversely Segmented Beam Using a Nano-Patterned Photocathode

545

A. Lueangaramwong, P. Piot
Northern Illinois University, DeKalb, Illinois, USA
G. Andonian
RadiaBeam, Santa Monica, California, USA
P. Piot
Fermilab, Batavia, Illinois, USA

Funding: Work supported by US Department of Energy (DOE) contract DE-SC0009656 with Radiabeam Technologies and by NSF grant PHY-1535401 with Northern Illinois University.
Plasmonic photocathodes – nano-patterned photocathodes with periodicity comparable to the excitation laser – have demonstrated enhanced quantum efficiency. In the present paper we present numerical simulations of the beam dynamics associated to the emission process from this type of cathodes and to the subsequent acceleration to relativistic energies by combining WARP and IMPACT-T programs. We especially consider the possibility to transversely image the cathode surface at high energy and enable the generation of transversely segment beams.

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MOPIK022

Experimental Investigation of Field-Emission From Silicon Nano-Cone Cathodes

548

SUSPSIK041

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

A. Lueangaramwong, C. Buzzard, V. Korampally, O. Mohsen, P. Piot
Northern Illinois University, DeKalb, Illinois, USA
S. Chattopadhyay
Northern Illinois Univerity, DeKalb, Illinois, USA
R. Divan
Argonne National Laboratory, Argonne, Illinois, USA
P. Piot
Fermilab, Batavia, Illinois, USA

Funding: This work is supported by the NSF grant PHY-1535401 with Northern Illinois University
Field emission cathode are capable of forming electron beam with extreme brightness via strong-field excitation from applied electrostatic, or electromagnetic (radiofrequency and laser) fields. Our group, in collaboration with the Argonne Center for Nanoscale Material, has recently developed nanocone cathode. The present paper reports on the experimental characterization of these cathodes both configured as a single-cone emitter or as large arrays of tightly-packed emitter. The tests carried in a diode setup are capable of measuring IV characteristic curves and beam distributions.

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MOPIK023

Cornell Laboratory for High Intensity, Ultra-Bright and Polarized Electron Beams

551

L. Cultrera, A.C. Bartnik, I.V. Bazarov, C.M. Gulliford, P. Gupta, H. Lee, S.A. McBride, T.P. Moore
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This work has been funded by the National Science Foundation (Grant No. PHY-1416318) and Department of Energy (Grants No. DE-SC0014338, No. DE-SC0011643 and No. DE-SC0016203).
We report on the current activities pursued at Cornell University for the production of electron beams tailored to a wide range of applications. We have developed the expertise to grow many different type of high quantum efficiency photocathode belonging to the alkali antimonide family. Those materials are ideal candidates to produce high intensity beam with average currents in the mA range. When operated near threshold at cryogenic temperature in transmission mode they can also generate the electron beams needed to perform ultrafast electron diffraction of bio molecules. We have recently expanded our facility with a Mott polarimeter to include the capability to measure polarization of the electron beam. The photocathode lab is being complemented by a dedicated photo-gun laboratory to test the photocathode properties in a real environment and to perform measurement of the beam properties under new and yet unexplored operating conditions.

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MOPIK026

Commissioning and Operation of an Ultrafast Electron Diffraction Facility as Part of the ATF-II Upgrade at Brookhaven National Laboratory

554

M.G. Fedurin, M. Babzien, C. Folz, M. Fulkerson, K. Kusche, J.J. Li, R. Malone, M.A. Palmer, T.V. Shaftan, J. Skaritka, L. Snydstrup, C. Swinson, F.J. Willeke
BNL, Upton, Long Island, New York, USA

Funding: Work supported by the US DOE under contract DE-SC0012704.
The Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL) is presently carrying out an upgrade, ATF-II, which will provide significantly expanded experimental space and capabilities for its users. One of the new capabilities being integrated into the ATF-II program is an Ultrafast Electron Diffraction (UED) beam line, which was originally deployed in the BNL Source Development Laboratory. Inclusion of the UED in the ATF-II research portfolio will enable ongoing development and extension of the UED capabilities for use in materials research. We describe the design, operation and future plans for the UED beam line at the ATF-II.

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MOPVA010

Setup and Status of an SRF Photoinjector for Energy-Recovery Linac Applications

865

T. Kamps, D. Böhlick, A.B. Büchel, M. Bürger, P. Echevarria, A. Frahm, F. Göbel, S. Heling, A. Jankowiak, S. Keckert, H. Kirschner, G. Klemz, J. Knobloch, G. Kourkafas, J. Kühn, O. Kugeler, A.N. Matveenko, A. Neumann, N. Ohm-Krafft, E. Panofski, F. Pfloksch, S. Rotterdam, M.A.H. Schmeißer, M. Schuster, H. Stein, J. Ullrich, A. Ushakov, J. Völker
HZB, Berlin, Germany
I. Will
MBI, Berlin, Germany

Funding: The work is funded by the Helmholtz-Association, BMBF, the state of Berlin and HZB.
The Superconducting RF (SRF) photoinjector programme for the energy-recovery linac (ERL) test facility BERLinPro sets out to push the brightness and average current limits for ERL electron sources by tackling the main challenges related to beam dynamics of SRF photoinjectors, the incorporation of high quantum efficiency (QE) photocathodes, and suppression of unwanted beam generation. The paper details the experimental layout of the SRF photoinjector and the gun test facility GunLab at Helmholtz-Zentrum Berlin.

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MOPVA033

A Compact Thermionic RF Injector with RF Bunch Compression fed by a Quadrupole-Free Mode Launcher

924

F. Toufexis, V.A. Dolgashev, C. Limborg-Deprey, S.G. Tantawi
SLAC, Menlo Park, California, USA

Funding: This project was funded by U.S. Department of Energy under Contract No. DE-AC02-76SF00515, and the National Science Foundation under Contract No. PHY-1415437.
We present a design for a compact X-Band RF thermionic injector consisting of two iris-loaded accelerator structures. Both structures are fed by a single quadrupole-free TM01 mode launcher. In the first structure the electron bunches are extracted from a thermionic cathode. The second structure creates an energy chirp in the bunch for its further ballistic compression. This injector can produce short electron bunches without the need for a magnetic bunch compressor. We are developing this injector as part of a linac-based 91.392 GHz RF power source, which further comprises a booster linac and a mm-wave decelerator structure that extracts 91.392 GHz RF power from the electron beam. This source will be used to power a short-period RF undulator with 1.75 mm period*.
* F. Toufexis and S.G. Tantawi, A 1.75 mm Period RF-Driven Undulator, these proceedings.

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