Sources and Medium Energy Accelerators
Tech 02: Lepton Sources
Paper Title Page
WEP277 Operational Findings and Upgrade Plans on the Superconducting Electron Accelerator S-DALINAC 1999
 
  • F. Hug, C. Burandt, J. Conrad, R. Eichhorn, M. Kleinmann, M. Konrad, T. Kürzeder, P.N. Nonn, N. Pietralla, S.T. Sievers
    TU Darmstadt, Darmstadt, Germany
 
  Funding: DFG through SFB 634.
The S-DALINAC is a superconducting recirculating electron accelerator with a final energy of 130 MeV. It operates in cw at 3 GHz. It accelerates beams of either unpolarized or polarized electrons and is used as a source for nuclear- and astrophysical experiments at the university of Darmstadt since 1987. We will report on the operational findings, recent modifications and on the future upgrade plans: First results from the new digital rf control system, the injector current upgrade and the improved longitudinal working point will be presented. In addition, an overview of the future plans, namely installing an additional recirculation path and two scraper systems will be given.
 
 
WEP279 Improvements on the Design of an Ultra-Low Emittance Injector for a Future X-ray FEL Oscillator 2002
 
  • X.W. Dong, K.-J. Kim
    ANL, Argonne, USA
 
  Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DEAC02-06CH11357.
The concept of an ultra-low transverse emittance injector for the X-ray Free-Electron Laser Oscillator* was discussed at PAC09**. Two problems come to mind. A dual-frequency rf chopper for reducing the beam rate from 100 MHz to 1 ~ 3 MHz would limit our choice of the beam repetition rate. The electron back-bombardment could be solved by embedding a three-pole wiggler*** in the nose cone of the gun cavity, but that results in increased emittance. Inspired by the concept of a triode gun, the injector now includes a gated 100 MHz rf gun with thermionic cathode to avoid those limitations. The design has been studied and is capable of producing 40 pC bunches with 0.1 micrometer effective transverse rms emittance.
* K.-J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008).
** P.N. Ostroumov et al., Proc. of PAC09, p.461 (2009).
*** M. Borland et al., Proc. of LINAC10, to be published.
 
 
WEP280 Development of an Ultra-Low-Emittance RF PhotoInjector for a Future X-Ray FEL Oscillator 2005
 
  • X.W. Dong, K.-J. Kim, N. Sereno, C.-X. Wang, A. Zholents
    ANL, Argonne, USA
 
  Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DEAC02-06CH11357.
The proposed x-ray free-electron laser oscillator* requires continuous electron bunches with ultra-low normalized transverse emittance of less than 0.1 micrometer, a bunch charge of 40 pC, an rms uncorrelated energy spread of less than 1.4 MeV, produced at a rate between 1 MHz to 10 MHz. The bunches are to be compressed to an rms length of ~1 ps and accelerated to the final energy of 7 GeV. In this paper, we discuss a design for an ultra-low-emittance injector based on a 325-MHz room-temperature rf cavity and a Cs2Te photocathode. The results of initial optimizations of the beam dynamics with a focus on extracting and preserving ultra-low emittance will be presented.
* K.-J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008).
 
 
WEP281 Beam Imaging of a High-Brightness Elliptic Electron Gun 2008
 
  • T.M. Bemis, C. Chen, M.H. Lawrence, J.Z. Zhou
    Beam Power Technology, Inc., Chelmsford, MA, USA
 
  Funding: This work was funded in part by the Department of Energy, Grant No. DE-FG02-07ER84910.
An innovative research program is being carried out to experimentally demonstrate a high-brightness, space-charge-dominated elliptic electron beam using a non-axisymmetric permanent magnet focusing system. Results of the fabrication, initial testing and beam imaging of an elliptic electron gun are reported. Good agreement is found between the experimental measurements and simulation.
 
 
WEP282 Design of the NSLS-II Linac Front End Test Stand 2011
 
  • R.P. Fliller, M.P. Johanson, M. Lucas, J. Rose, T.V. Shaftan
    BNL, Upton, Long Island, New York, USA
 
  Funding: This manuscript has been authored by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
The NSLS-II operational parameters place very stringent requirements on the injection system. Among these are the charge per bunch train at low emittance that is required from the linac along with the uniformity of the charge per bunch along the train. The NSLS-II linac is a 200 MeV linac produced by RI Research Instruments GmbH. Part of the strategy for understanding to operation of the injectors is to test the front end of the linac prior to its installation in the facility. The linac front end consists of a 90 keV electron gun, 500 MHz subharmonic prebuncher, focusing solenoids and a suite of diagnostics. The diagnostics in the front end need to be supplemented with an additional suite of diagnostics to fully characterize the beam. In this paper we discuss the design of a test stand to measure the various properties of the beam generated from this section. In particular, the test stand will measure the charge, transverse emittance, energy, energy spread, and bunching performance of the linac front end under all operating conditions of the front end.
 
 
WEP284 Performance Study of K2CsSb Photocathode inside a DC High Voltage Gun 2017
 
  • T. Rao, J. Smedley
    BNL, Upton, Long Island, New York, USA
  • J.M. Grames, R.R. Mammei, J.L. McCarter, M. Poelker, R. Suleiman
    JLAB, Newport News, Virginia, USA
 
  Funding: The authors wish to acknowledge the support of the U.S. Department of Energy (DOE) under grant DE-FG02-08ER41547.
In the past decade, there has been considerable interest in the generation of tens of mA average current in a photoinjector. Until recently, GaAs:Cs cathodes and K2CsSb cathodes have been tested successfully in DC and RF injectors respectively for this application. Our goal is to test the GaAs:Cs in RF injector and the K2CsSb cathode in the DC gun in order to widen our choices. Since the multialkali cathode is a compound with uniform stochiometry over its entire thickness, we anticipate that the life time issues seen in GaAs:Cs due surface damage by ion bombardment would be minimized with this material. Hence successful operation of the K2CsSb cathode in DC gun could lead to a relatively robust electron source capable of delivering ampere level currents. In order to test the performance of K2CsSb cathode in a DC gun, we have designed and built a load lock system that would allow the fabrication of the cathode at BNL and its testing at JLab. In this paper, we will present the design of the load-lock system, cathode fabrication, and the cathode performance in the preparation chamber and in the DC gun.
 
 
WEP287 Field Emission Measurements from Niobium Electrodes 2020
 
  • M. BastaniNejad
    Old Dominion University, Norfolk, Virginia, USA
  • P.A. Adderley, J. Clark, S. Covert, J. Hansknecht, C. Hernandez-Garcia, R.R. Mammei, M. Poelker
    JLAB, Newport News, Virginia, USA
 
  Increasing the operating voltage of a DC high voltage photogun serves to minimize space charge induced emittance growth and thereby preserve electron beam brightness, however, field emission from the photogun cathode electrode can pose significant problems: constant low level field emission degrades vacuum via electron stimulated desorption which in turn reduces photocathode yield through chemical poisoning and/or ion bombardment and high levels of field emission can damage the ceramic insulator. Niobium electrodes (single crystal, large grain and fine grain) were characterized using a DC high voltage field emission test stand at maximum voltage -225kV and electric field gradient > 10MV/m. Niobium electrodes appear to be superior to diamond-paste polished stainless steel electrodes.  
 
WEP288 Optimizing the CEBAF Injector for Beam Operation with a Higher Voltage Electron Gun 2023
 
  • F.E. Hannon, A.S. Hofler, R. Kazimi
    JLAB, Newport News, Virginia, USA
 
  Recent developments in the DC gun technology used at CEBAF have allowed an increase in operational voltage from 100kV to 130kV. In the near future this will be extended further to 200kV with the purchase of a new power supply. The injector components and layout at this time have been designed specifically for 100kV operation. It is anticipated that with an increase in gun voltage and optimization of the layout and components for 200kV operation, that the electron bunch length and beam brightness can be improved upon. This paper explores some upgrade possibilities for a 200kV gun CEBAF injector through beam dynamic simulations.  
 
WEP289 The Impact of Laser Polarization in Multiphoton Photoemission from a Copper Cathode 2026
 
  • R.K. Li, J.T. Moody, P. Musumeci, C.M. Scoby, H.L. To, M.T. Westfall
    UCLA, Los Angeles, California, USA
 
  Multiphoton photoemission from a copper cathode has been recently demonstrated to be a simple and efficient method to generate high quality electron beams. To further improve this scheme to achieve higher charge yielding efficiency and lower intrinsic emittance, we explored the effects of laser polarization at oblique incidence. Charge yields of s and p polarization from coated and uncoated cathodes were measured. The vectorial photoelectric effect was observed on the uncoated cathode but much less evident on the coated one, suggesting that surface properties are critical to the vectorial effect and in general important in photoemission. The results not only are useful in the optimization of an rf photoinjector, but also allow deeper understanding of the photoemission physics.
* P. Musumeci et al., Phys. Rev. Lett. ZeHn4, 084801 (2010).
** P. Musumeci et al., Phys. Rev. Lett. ZeHn0, 244801 (2008).
 
 
THOCN1 Cathodes for Photoemission Guns 2099
 
  • L. Cultrera
    CLASSE, Ithaca, New York, USA
 
  The last decade has seen a considerable interest in pursuit and realization of novel light sources such as Free Electron Lasers and Energy Recovery Linacs that promise to deliver unprecedented quality x-ray beams. The performance of these machines is strongly related to the brightness of the electron beam generating the x-rays. The brightness of the electron beam itself is mainly limited by the physical processes by which electrons are generated. For laser based photoemission sources this limit is ultimately related to the properties of photocathodes. In this paper an overview of the recent progress on photocathode development for photoemission electron sources is presented.  
 
FROAN4 Femtosecond RF Gun Based MeV Electron Diffraction 2558
 
  • J. Yang, K. Kan, Y. Murooka, N. Naruse, K. Tanimura, Y. Yoshida
    ISIR, Osaka, Japan
  • J. Urakawa
    KEK, Ibaraki, Japan
 
  Ultrafast time-resolved electron diffraction based on a photocathode rf electron gun is being developed in Osaka University to reveal the hidden dynamics of intricate molecular and atomic processes in materials. A new structure rf gun has been developed to generates a low-emittance femtosecond-bunch electron beam, and has been used successfully for the single-shot MeV electron diffraction measurement. The transverse emittance, bunch length and energy spread were measured. The growths of the emittance, bunch length and energy spread due to the rf and the space charge effects in the rf gun were investigated by changing the laser injection phase, the laser pulse width and the bunch charge. The same demonstrations of the electron diffraction measurement were reported.  
slides icon Slides FROAN4 [5.097 MB]  
 
FROAS1
Tutorial on High Brightness Photoinjectors  
 
  • D. Dowell
    SLAC, Menlo Park, California, USA
 
  Photoinjectors are an enabling technology for a number of linac-based accelerators with applications varying from advanced accelerator techniques, such as wake field acceleration to super-bright x-ray light sources, nuclear physics, and others. The speaker will introduce this exciting subject to novices, and discuss the basics of electron production, acceleration, and beam manipulation in photoinjectors.  
slides icon Slides FROAS1 [3.306 MB]