03 Novel Particle Sources and Acceleration Technologies
T02 Electron Sources
Paper Title Page
TUPML006 Updates of the Argonne Cathode Test-stand 1542
 
  • J.H. Shao, M.E. Conde, D.S. Doran, W. Gai, W. Liu, J.F. Power, C. Whiteford, E.E. Wisniewski, L.M. Zheng
    ANL, Argonne, Illinois, USA
  • S.P. Antipov, G. Chen, E. Gomez, C.-J. Jing
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • S.V. Baryshev
    Michigan State University, East Lansing, Michigan, USA
 
  The Argonne Cathode Test-stand (ACT) is a unique testbed to develop cathodes and to conduct fundamental surface study under ultra-high rf field (up to 700 MV/m with pin-shaped cathodes). The test-stand consists of an L-band 1.3 GHz single-cell photocathode rf gun and a field emission (FE) imaging system to locate emitters with a resolution of ∼20 𝜇m. In the recent upgrade, UV laser has been introduced to improve the imaging system and to significantly expand the ACT towards photoemission and laser-assisted field emission research. In addition, a load-lock system has been added to the beam line to expedite the cathode switching period. The paper will present details of the upgrade as well as experiments planned in the near future.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML006  
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TUPML011 Experiments Producing Nanopatterned Electron Beams 1553
 
  • L.E. Malin, W.S. Graves, J. Spence, K. Weiss, C. Zhang
    Arizona State University, Tempe, USA
  • R.K. Li, E.A. Nanni, X. Shen, S.P. Weathersby, J. Yang
    SLAC, Menlo Park, California, USA
 
  Funding: Work supported by NSF awards 1632780 and 1231306, DOE award DE-AC02-76SF00515, and the SLAC UED/UEM Initiative Program Development Fund.
RF photoinjectors are increasingly used to image at the nanoscale in much the same way as a Transmission Electron Microscope (TEM), which are generally sub-MeV energy. We have conducted electron diffraction experiments through a thin membrane of single crystal silicon using both the TEM and photoinjector, and have been able to model and predict the diffraction patterns using the multislice method. A nanopatterned single crystal silicon grating was also imaged in the TEM in the bright field, where all but the direct beam of the diffraction pattern is blocked, giving high contrast spatial modulations corresponding to the 400 nm pitch grating lithographically etched into the silicon. Drawing from our previous multislice calculations, we determined the crystallographic orientation that maximized the contrast in this spatial modulation at the energy of the TEM, giving a bunching factor comparable to a saturated FEL. We report on these key steps toward control of radiation phase and temporal coherence in an FEL.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML011  
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TUPML019 Design of Multi-Alkali Photocathode Preparation System for CTFEL Facility 1571
 
  • D.X. Xiao, M. Li, Q. Pan, H. Wang, X. Yang
    CAEP/IAE, Mianyang, Sichuan, People's Republic of China
 
  The first saturated lasing of the China Academy of Engineering Physics tera-hertz free electron laser (CTFEL) facility has been realized. In order to improve the performance of the CTFEL facility, the multi-alkali photocathode with much longer life-time has been proposed to replace the GaAs photocathode currently used. This paper presents the design of the multi-alkali photocathode preparation system, which consists of three chambers: the suitcase chamber, the preparation chamber, and the loading chamber. The function of each chamber is also discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML019  
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TUPML025 Long Lifetime Spin-Polarized GaAs Photocathode Activated by Cs2Te 1589
SUSPF049   use link to see paper's listing under its alternate paper code  
 
  • J. Bae, L. Cultrera, P. Digiacomo
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • I.V. Bazarov
    Cornell University, Ithaca, New York, USA
 
  Funding: This work was supported by the Department of Energy Grant Nos. DE-SC0016203 and NSF PHY-1461111.
High intensity and highly spin-polarized electron source is of great interest to the next generation Electron Ion Colliders. GaAs prepared by the standard activation method, which is the most widely used spin-polarized photocathode, is notorious for its vacuum sensitivity and short operational lifetime. To improve the lifetime of GaAs photocathodes, we activated GaAs by Cs2Te, a material well known for its robustness. We confirmed the Cs2Te layer forms negative electron affinity on GaAs with a factor of 5 improvement in lifetime. Furthermore, the new activation method had no adverse effect on spin-polarization. Considering Cs2Te forms much thicker activation layer (~ 2 nm) compared to the standard activation layer (~ monolayer), our results trigger a paradigm shift on new activation methods with other robust materials that were avoided for their thickness.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML025  
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TUPML026 Multi-photon Photoemission and Ultrafast Electron Heating in Cu Photocathodes at Threshold 1593
 
  • J. Bae, L. Cultrera
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • I.V. Bazarov, J.M. Maxson
    Cornell University, Ithaca, New York, USA
  • S.S. Karkare, H.A. Padmore
    LBNL, Berkeley, California, USA
  • P. Musumeci, X.L. Shen
    UCLA, Los Angeles, California, USA
 
  Funding: U.S. National Science Foundation under award PHY-1549132, the Center for Bright Beams.
Operating photocathodes near the photoemission threshold holds the promise of yielding small intrinsic emittance, at the cost of significantly reduced quantum efficiency. In modern femtosecond photoemission electron sources, this requires a very high intensity (10s of GW/cm2) to extract a useful quantity of electrons. At this intensity, the electron occupation function is far from equilibrium and evolves rapidly on sub-ps timescales. Thus, ultrafast laser heating and multiphoton photoemission effects may play a significant role in emission, thereby increasing the minimum achievable emittance. In this work, we use a Boltzmann equation approach to calculate the non-equilibrium occupation function evolution in time for a copper photocathode, yielding a prediction of quantum efficiency and mean transverse energy as a function of input intensity.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML026  
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TUPML027 Barium Tin Oxide Ordered Photocathodes: First Measurements and Future Perspectives 1597
 
  • A. Galdi, E. B. Lochocki, H. Paik, C.T. Parzyck, D. G. Schlom, K.M. Shen
    Cornell University, Ithaca, New York, USA
  • G. Adhikari, W.A. Schroeder
    UIC, Chicago, Illinois, USA
  • I.V. Bazarov, L. Cultrera, W. H. Li, J.M. Maxson, C. M. Pierce
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams.
Single crystalline photocathodes with small electron effective mass are supposed to enable ultra-low emittance beams, by taking advantage of the conservation of transverse (crystal) momentum. We present a preliminary study on photoemission from epitaxial films of La-doped BaSnO3 with (100) orientation. We demonstrate here the possibility of generating and characterizing electron beams by exciting photoelectrons solely from the conduction band. We report quantum efficiency and mean transverse energy meaurements as a function of photon energy from the bare and Cs-activated La-doped BaSnO3 surface.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML027  
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TUPML028 Photocathodes R&D for High Brightness and Highly Polarized Electron Beams at Cornell University 1601
 
  • L. Cultrera, J. Bae, A.C. Bartnik, I.V. Bazarov, R. Doane, A. Galdi, C.M. Gulliford, W. H. Li, J.M. Maxson, S.A. McBride, T.P. Moore, C. M. Pierce, C. Xu
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Cornell University is a leader in the development of photocathode materials for the production of high brightness electron beam sources for applications in large scale accelerators and small scale electron scattering experiments. During the last year we have also included Mott polarimetry to investigate long lifetime spin-polarized photocathodes materials. Another thrust of our laboratory is the exploration of ultra low emittance photocathodes at cryogenic temperatures, for which we are building a novel LHe cryogenic electron source. We will review updates from our lab across each of these areas.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML028  
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TUPML029 Novel Photocathode Geometry Optimization: Field Enhancing Photoemission Tips 1605
 
  • W. H. Li, I.V. Bazarov, C.M. Gulliford, J.M. Maxson
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Funding: This work was supported by the U.S. National Science Foundation under award PHY-1549132, the Center for Bright Beams.
For photoemission sources, the extraction electric field defines the maximum achievable emission current, and hence the maximum achievable beam brightness. Recently, interest has been growing in studying photocathodes with non-flat geometries to produce local field enhancements in excess of what can be achieved with large area flat cathodes. However, such geometries cause image charge effects which require self-consistent field solvers to correctly simulate. We present a novel simulation framework which combines a full particle in cell field solver (WARP) with a fast adaptive mesh space charge particle tracker (GPT) and a parallel multi-objective genetic optimizer to explore photocathode geometries for ultra high brightnesses. A first application of this technique is also shown, namely the use of field enhanced photoemission tips to create bright beams for ultra-fast electron diffraction.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML029  
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TUPML031 Characterization of Polarization-Dependent Emittance From an Array of Au Nanorods using Velocity Map Imaging Spectrometer 1612
 
  • H. Ye, F.X. Kärtner, S. T. Trippel
    Deutsches Elektronen Synchrotron (DESY) and Center for Free Electron Science (CFEL), Hamburg, Germany
  • A. Fallahi, J. Küpper, O. Muecke
    CFEL, Hamburg, Germany
  • F.X. Kärtner
    MIT, Cambridge, Massachusetts, USA
  • F.X. Kärtner, J. Küpper, S. T. Trippel, H. Ye
    The Hamburg Center for Ultrafast Imaging, University of Hamburg, hamburg, Germany
  • J. Küpper, G.M. Rossi
    DESY, Hamburg, Germany
  • H. Ye
    University of Hamburg, Hamburg, Germany
 
  Electron beams of high quality, e.g., low emittance, are of crucial importance for cutting-edge scientific instruments, such as x-ray free electron lasers (XFELs) and ultrafast electron diffraction (UED) setups. A velocity-map-imaging (VMI) spectrometer was implemented to characterize the intrinsic root-mean-square (rms) normalized emittance from photocathodes. The spectrometer operated in both, spatial map imaging (SMI) and VMI modes. Therefore, spatial- and velocity-coordinates were recorded independently and quickly. The technique allows for fast complete emittance measurements, within minutes. A 75 μm pitch array of Au nanorods of dimension 100×30~nm, was studied under strong-field-emission regime by 100 fs 1 kHz 1.3 μm laser pulses with a 300×30 μm2 focus spot size on the sample. A patterned electron bunch was observed, each emitted from a single nanorod within the array. A polarization dependent photoemission study was performed showing a smaller rms-normalized divergence of 0.8 mrad with the laser polarization normal to the sample surface, compared to 1.15 mrad for the parallel case.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML031  
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TUPML053 The BERLinPro SRF Photoinjector System - From First RF Commissioning to First Beam 1660
 
  • A. Neumann, D. Böhlick, M. Bürger, P. Echevarria, A. Frahm, H.-W. Glock, F. Göbel, S. Heling, K. Janke, A. Jankowiak, T. Kamps, S. Klauke, G. Klemz, J. Knobloch, G. Kourkafas, J. Kühn, O. Kugeler, N. Leuschner, N. Ohm, E. Panofski, H. Plötz, S. Rotterdam, M.A.H. Schmeißer, M. Schuster, H. Stein, Y. Tamashevich, J. Ullrich, A. Ushakov, J. Völker
    HZB, Berlin, Germany
 
  Funding: The work is funded by the Helmholtz-Association, BMBF, the state of Berlin and HZB.
Helmholtz-Zentrum Berlin (HZB) is currently constructing a high average current superconducting (SC) ERL as a prototype to demonstrate low normalized beam emittance of 1 mm-mrad at 100 mA and short pulses of about 2 ps. To attain the required beam properties, an SRF based photo-injector system was developed and during the past year underwent RF commissioning and was setup within a dedicated diagnostics beamline called Gunlab to analyze beam dynamics of both, a copper cathode and a Cs2KSb cathode as well as their quantum efficiency at UV and green light respectively. The medium power prototype - a first stage towards the final high power 100 mA design - presented here features a 1.4 x λ/2 cell SRF cavity with a normal-conducting, high quantum efficiency CsK2Sb cathode, implementing a modified HZDR-style cathode insert. This injector potentially allows for 6 mA beam current and up to 3.5 MeV kinetic energy, limited by the modified twin TTF-III fundamental power couplers. In this contribution, the first RF commissioning results of the photo-injector module will be presented including dark current analysis as well as measured beam properties with an initially installed Copper cathode.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML053  
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TUPML061 Study of Mean Transverse Energy of (N)UNCD with Tunable Laser Source 1677
SUSPF050   use link to see paper's listing under its alternate paper code  
 
  • G. Chen
    IIT, Chicago, Illinois, USA
  • G. Adhikari, W.A. Schroeder
    UIC, Chicago, Illinois, USA
  • S.P. Antipov, C.-J. Jing, K. Kovi
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • S.V. Baryshev
    ANL, Argonne, Illinois, USA
  • L.K. Spentzouris
    Illinois Institute of Technology, Chicago, Illinois, USA
 
  Funding: NSF grant No. NSF-1739150, DOE SBIR program grant No. DE-SC0013145, NSF grant No. PHYS-1535279, DOE Contract No. DE-AC02-06CH11357.
There is a strong motivation to develop and understand novel materials with the potential to be utilized as photocathodes, as these could have desirable photoemission properties for research and industrial applications. Nitrogen-incorporated ultrananocrystalline diamond ((N)UNCD) photocathodes have potential to become a material of choice for photocathode applications*. (N)UNCD has high quantum efficiency when processed in hydrogen plasma*, low surface roughness, and high electron conductivity through the bulk**. The mean transverse energy (MTE) was calculated for (N)UNCD thin films using the double-solenoid scan method. (N)UNCD thin film with thickness of 160nm was deposited on highly-doped silicon substrate. Studies of the MTE of a (N)UNCD sample were done using a tunable laser source with photon energies of 3.56 eV to 5.26 eV. These results are presented.
* K.J. Pérez Quintero et al., Appl. Phys. Lett. 105, 123103 (2014).
** S. Bhattacharyya et al., Appl. Phys. Lett. 79, 1441 (2001)
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML061  
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THPMF089 Design of a Radial RF Electron Gun 4287
 
  • J.W. Lewellen, F.L. Krawczyk
    LANL, Los Alamos, New Mexico, USA
  • J.R. Harris
    Directed Energy Directorate, Air Force Research Laboratory, Albuquerque, USA
 
  Funding: DOE Accelerator Stewardship Program
Most electron beam sources generate beams that propagate away from the source in a single primary direction, with the overall envelope being either pencil-like or sheet-like. We present the design of a radial RF electron gun, intended to produce a radially propagating electron beam (either towards or away from an axis) with the overall envelope being that of an expanding or contracting annulus. Such a source has several potential advantages for materials processing, and may also be useful as the basis for unique optical elements for hadron machines.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF089  
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THPML007 An Investigation of Electron Beam Divergence from a Single DFEA Emitter Tip 4662
 
  • H.L. Andrews, B.K. Choi, R.L. Fleming, D. Kim, J.W. Lewellen, K.E. Nichols, D.Y. Shchegolkov, E.I. Simakov
    LANL, Los Alamos, New Mexico, USA
 
  Funding: We gratefully acknowledge the support of the U.S. Department of Energy through the LANL/LDRD Program for this work.
Diamond Field-Emitter Array (DFEA) cathodes are arrays of micron-scale diamond pyramids with nanometer-scale tips. DFEAs can produce high emission currents with small emittance and energy spread. At LANL, we have an ongoing program to test DFEA cathodes for the purpose of using them to generate high-current, low-emittance electron beams for dielectric laser accelerators. We have recently upgraded our cathode test chamber to use a mesh anode in place of a solid luminescent anode. In addition to allowing for downstream beam transport, this arrangement may eliminate earlier problems with reduced cathode performance due to ion back-bombardment. We are measuring divergence of the electron beam past the mesh in an effort to characterize the inherent beam divergence off the diamond tip and divergence contribution from the mesh. We will compare these observations with theoretical and modeled values.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML007  
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THPML010 Modeling of Diamond Field Emitter Arrays for Shaped Electron Beam Production 4668
 
  • K.E. Nichols, H.L. Andrews, D.Y. Shchegolkov, E.I. Simakov
    LANL, Los Alamos, New Mexico, USA
 
  We present simulations of shaped electron beam production from diamond field emitter array (DFEA) cathodes. DFEAs are arrays of diamond pyramids with bases of the order of 10 microns that produce high current densities. These arrays can be fabricated in arbitrary shapes such as a triangle or a double triangle, so that they produce an inherently shaped beam. These transversely shaped beams can be put through an emittance exchanger to produce a longitudinally shaped electron beam distribution for use with high-transformer ratio wakefield accelerators. Simulations are conducted with MICHELLE. We design cathodes and focusing systems that preserve the beam's shape while transporting it to the emittance exchanger.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML010  
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THPML025 Operation of an RF Modulated Thermionic Electron Source at TRIUMF 4705
 
  • F. Ames, K. Fong, B. Humphries, S.R. Koscielniak, A. Laxdal, Y. Ma, T. Planche, S. Saminathan, E. Thoeng
    TRIUMF, Vancouver, Canada
 
  ARIEL (Advanced Rare IsotopE Laboratory) at TRIUMF will use a high-power electron beam to produce radioactive ion beams via photo-fission. The system has been designed to provide up to 10 mA of electrons at 30 MeV. The electron source delivers electron bunches with charge up to 16 pC at a repetition frequency of 650 MHz at 300 keV. The main components of the source are a gridded dispenser cathode (CPI - Y845) in an SF6 filled vessel and an in-air HV power supply. The beam is bunched by applying DC and RF fields to the grid. A macro pulse structure can be applied by additional low frequency modulation of the RF signal. This allows adjusting the average beam current by changing the duty factor of the macro pulsing. Unique features of the gun are its cathode/anode geometry to reduce field emission, and transmission of RF modulation via a dielectric (ceramic) waveguide through the SF6. The source has been installed and fully commissioned to a beam power up to 1 KW and tests with accelerated beams have been performed. Measurements of the beam properties and results from the commissioning and operational experiences of the source will be presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML025  
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THPML053 Computational Screening for Low Emittance Photocathodes 4755
 
  • J.T. Paul, R.G. Hennig
    University of Florida, Gainesville, Florida, USA
  • I.V. Bazarov, A. Galdi
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • S.S. Karkare, H.A. Padmore
    LBNL, Berkeley, California, USA
 
  The majority of photocathode materials in use in accelerator applications have been discovered empirically through trial and error with little guidance from material science calculations. Alternatively, one can envision a process which is heavily guided by computational search using latest advances in density functional theory (DFT). In this work, the MaterialsProject database is searched for potential single crystal photocathodes that would be suitable for ultralow emittance beam production. The materials in the database are initially screened on the basis of experimental practicality. Following this, the expected emittance is calculated from the DFT computed band structures for the pre-screened materials using the conservation of energy and transverse momentum during photoemission. Based on such computational screening, we provide a list of potential low emittance photocathode materials which can be investigated experimentally as high brightness electron sources.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML053  
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THPML054 Design Studies of an S-Band Multipacting Electron Gun 4759
SUSPF051   use link to see paper's listing under its alternate paper code  
 
  • C. Henkel, W. Hillert, V. Miltchev
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • K. Flöttmann
    DESY, Hamburg, Germany
 
  A multipacting electron gun (MEG) is a micro-pulse electron source based on secondary electron emission in a resonant microwave cavity structure for the generation of low emittance electron bunches with high repetition rate. By theoretical simulations a suitable radio-frequency gun design at 3 GHz is established, simultaneously meeting the demands of bunch production and amplification process as well as including the effects of space charge and beam loading for the evolution of a stable beam. In this contribution we show detailed simulation studies of the impact of important design parameters like mechanical dimensions and choice of material on the average output current, which is in the order of several mA. For the experimental investigation a test setup is under construction, which may demonstrate the application of MEG's as a serious alternative or addition to commonly used electron sources like thermionic and photocathodes.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML054  
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THPML055 Scaled Studies on Radio Frequency Sources for Megawatt-Class Ionospheric Heaters 4763
 
  • B.L. Beaudoin, T.M. Antonsen, J.A. Karakkad, A.H. Narayan, G.S. Nusinovich, K.J. Ruisard
    UMD, College Park, Maryland, USA
  • R. Fischer
    Naval Research Laboratory (NRL), Washington, USA
  • S.H. Gold, A. Ting
    NRL, Washington,, USA
 
  Funding: Funding for this project and travel is provided by the Air Force Office of Scientific Research under grant FA95501410019.
The ionosphere plays a prominent role in the performance of critical civilian and military communication systems. The key instrument in Ionospheric Modification (IM) research is a powerful, ground-based, High Frequency (HF) source of electromagnetic waves known as a heater. With a mobile heater, investigators would be able to conduct IM research at different latitudes without building a costly permanent installation. A new highly efficient Megawatt class of Radio Frequency sources is required to reduce the overall power demands on a fully deployable system. Such a source has been described previously*. Results of a scaled experiment, using the electron beam produced by a gridded gun to drive an external lumped element circuit for high efficiency radio frequency generation is presented. The IOT gun produces an electron beam bunched at the driving frequency that is then collected by an external circuit for impedance matching to the load. Results showed that effects such as the internal resistance of the inductor and deflection of beam electrons by the induced RF voltages on the beam collector are important considerations to be included in the design of a practical device.
* B.L. Beaudoin, G.S. Nusinovich, G. Milikh, A. Ting, S. Gold, J.A. Karakkad, A.H. Narayan, D.B. Matthew, D.K. Papadopoulos, T.M. Antonsen Jr., Journal of Elec. Waves and Appl.,31,17,pp.1786, 2017.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML055  
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THPML133 Design and Optimization of the Electron Gun 4995
 
  • K. Huang, T.L. He, Z.L. Ren, D.R. Xu, H. Xu
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  • Y. Chen
    Department of Information Engineering , Anhui Economic Management Cadres' Institute, Hefei, Anhui, People's Republic of China
 
  Funding: Work supported by the National Nature Science Foundation of China under Grant Nos.11375176 and 10875118.
Design of an energy-modified electron gun is of significance to do some research on the properties of Diamond-amplified cathode. Based on the design method of the Pierce electron gun, the optimum parameters of the electron gun have been obtained using the Opera-3D program. And the beam waist's position, the beam current, the beam size and the beam emittance related to the electron bean energy was investigated in this paper.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML133  
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