Author: Douglas, D.
Paper Title Page
MOP094 Development of Advanced Beam Halo Diagnostics at the Jefferson Lab Free-Electron-Laser Facility 274
 
  • S. Zhang, S.V. Benson, D. Douglas, F.G. Wilson
    JLAB, Newport News, Virginia, USA
  • R.B. Fiorito, A.G. Shkvarunets, H.D. Zhang
    UMD, College Park, Maryland, USA
  
  Funding: Many colleagues at JLab FEL provided help with the installation of the present experimental setup. This work is partially supported by DOE Contract DE-AC05-060R23171.
High average current and high brightness electron beams are needed for many applications. At the Jefferson Lab FEL facility, the search for dark matter with the FEL laser beam has produced interesting results*, and a second very promising method for dark matter search using JLab Energy-recovery-linac (ERL) machine has been put forward**. Although the required beam current has been achieved on this machine, one key challenge is the management of beam halo. UMD has demonstrated a high dynamic range halo measurement method using a digital micro-mirror array device. A similar system has been established at JLab FEL facility as a joint effort by UMD and JLab to measure the beam halo on the high current ERL machine***. The experiment and characterization are being performed while the new UV FEL is running for optimization. In this paper, the limitations of the current system will be analyzed and study of other approaches (such as an optimized coronagraph) for further extending measuring dynamic range will be presented. In particular, we will discuss in detail the possibility of performing both longitudinal and transverse (3D) halo measurement altogether on one single system.
* A. Afanasev, et al., PRL. 101 120401 (2008).
** J. Thale, Searching for a New Gauge Boson at JLab, Newport News, VA, September 20-21, 2010
*** H. Zhang, et al., this conference. 		 
 
WEOCN4 Electron Beam Diagnostics of the JLab UV FEL 1446
 
  • P. Evtushenko, S.V. Benson, G.H. Biallas, J.L. Coleman, C. Dickover, D. Douglas, M. Marchlik, D.W. Sexton, C. Tennant
    JLAB, Newport News, Virginia, USA
  
  In this contribution we describe various systems of the electron beam diagnostics of the JLab UV FEL. The FEL is installed on a new bypass beam line of existing 10kW IR Upgrade FEL. Here we describe a set of the following systems. A combination of OTR and phosphor viewers used for measurements of a transverse beam profile, transverse emittance, Twiss parameters. This system is also used for alignment of the optical cavity of the UV oscillator and to ensure the overlap between the electron beam and optical mode in the FEL wiggler. A system of beam position monitors equipped with log-amp based BPM electronics. Bunch length on the order of 120 fs RMS is measured with the help of a modified Martin-Puplett interferometer. The longitudinal transfer function measurements system is used to setup bunch compression in an optimal way such that the LINAC RF curvature is compensated using only higher order magnetic elements of the beam transport. This set of the diagnostics system made its contribution to achieve the first lasing of the FEL after about 60 hours of beam operation.  
slides icon Slides WEOCN4 [8.864 MB]  
 
WEOCN5 Beam Halo Measurements at UMER and the JLAB FEL Using an Adaptive Masking Method 1449
 
  • H.D. Zhang, S. Bernal, R.B. Fiorito, R.A. Kishek, P.G. O'Shea, A.G. Shkvarunets
    UMD, College Park, Maryland, USA
  • S.V. Benson, D. Douglas, F.G. Wilson, S. Zhang
    JLAB, Newport News, Virginia, USA
  
  Funding: US Dept. of Energy Offices of High Energy Physics and Fusion Energy Sciences and by the Dept. of Defense Office of Naval Research and Joint Technology Office.
Beam halo is a challenging issue for intense beams since it can cause beam loss, emittance growth, nuclear activation and secondary electron emission. Because of the potentially low number of particles in the halo compared with beam core, traditional imaging methods may not have sufficient contrast to detect faint halos. We have developed a high dynamic range, adaptive masking method to measure halo using a digital micro-mirror array device and demonstrated its effectiveness experimentally on the University of Maryland Electron Ring (UMER). We also report on similar experiments currently in progress at the Jefferson Lab Free Electron Laser (FEL) using this method. 		 
slides icon Slides WEOCN5 [1.287 MB]  
 
THP171 Demonstration of 3D Effects with High Gain and Efficiency in a UV FEL Oscillator 2429
 
  • S.V. Benson, G.H. Biallas, K. Blackburn, J.R. Boyce, D.B. Bullard, J.L. Coleman, C. Dickover, D. Douglas, F.K. Ellingsworth, P. Evtushenko, C.W. Gould, J.G. Gubeli, D. Hardy, C. Hernandez-Garcia, K. Jordan, J.M. Klopf, J. Kortze, R.A. Legg, M. Marchlik, S.W. Moore, G. Neil, T. Powers, D.W. Sexton, M.D. Shinn, C. Tennant, R.L. Walker, A.M. Watson, G.P. Williams, F.G. Wilson, S. Zhang
    JLAB, Newport News, Virginia, USA
  
  Funding: This work was supported by U.S. DOE Contract No. DE-AC05-84-ER40150, the Air Force Office of Scientific Research, DOE Basic Energy Sciences, the Office of Naval Research, and Joint Technology Office
We report on the performance of a high gain UV FEL oscillator operating on an energy recovery linac at Jefferson Lab. The high brightness of the electron beam leads to both gain and efficiency that cannot be reconciled with a one-dimensional model. Three-dimensional simulations do predict the performance with reasonable precision. Gain in excess of 100% per pass and an efficiency close to 1/2NW, where NW is the number of wiggler periods, is seen. The laser mirror tuning curves currently permit operation in the wavelength range of 438 to 362 nm. Another mirror set allows operation at longer wavelengths in the red with even higher gain and efficiency. 		 
 
THP172 Operation and Commissioning of the Jefferson Lab UV FEL using an SRF Driver ERL 2432
 
  • C. Tennant, S.V. Benson, G.H. Biallas, K. Blackburn, J.R. Boyce, D.B. Bullard, J.L. Coleman, C. Dickover, D. Douglas, F.K. Ellingsworth, P. Evtushenko, C.W. Gould, J.G. Gubeli, F.E. Hannon, D. Hardy, C. Hernandez-Garcia, K. Jordan, J.M. Klopf, J. Kortze, M. Marchlik, S.W. Moore, G. Neil, T. Powers, D.W. Sexton, M.D. Shinn, R.L. Walker, G.P. Williams, F.G. Wilson, S. Zhang
    JLAB, Newport News, Virginia, USA
  • R.A. Legg
    UW-Madison/SRC, Madison, Wisconsin, USA
  
  Funding: Supported by the US Dept. of Energy under DoE contract number DE-AC05-060R23177.
We describe the operation and commissioning of the Jefferson Lab UV FEL using a CW SRF ERL driver. Based on the same 135 MeV linear accelerator as the Jefferson Lab 10 kW IR Upgrade FEL, the UV driver ERL uses a bypass geometry to provide transverse phase space control, bunch length compression, and nonlinear aberration compensation necessitating a unique set of commissioning and operational procedures. Additionally, a novel technique to initiate lasing is described. To meet these constraints and accommodate a challenging installation schedule, we adopted a staged commissioning plan with alternating installation and operation periods. This report addresses these issues and presents operational results from on-going beam operations. 		 
 
THP173 Design of the SRF Driver ERL for the Jefferson Lab UV FEL 2435
 
  • C. Tennant, S.V. Benson, G.H. Biallas, K. Blackburn, J.R. Boyce, D.B. Bullard, J.L. Coleman, C. Dickover, D. Douglas, F.K. Ellingsworth, P. Evtushenko, C.W. Gould, J.G. Gubeli, F.E. Hannon, D. Hardy, C. Hernandez-Garcia, K. Jordan, J.M. Klopf, J. Kortze, M. Marchlik, S.W. Moore, G. Neil, T. Powers, D.W. Sexton, M.D. Shinn, R.L. Walker, F.G. Wilson, S. Zhang
    JLAB, Newport News, Virginia, USA
  
  Funding: Support by DoE Contract DE-AC05-060R23177.
We describe the design of the SRF ERL providing the CW electron drive beam at the Jefferson Lab UV FEL. Based on the same 135 MeV linear accelerator as – and sharing portions of the recirculator with – the Jefferson Lab 10 kW IR Upgrade FEL, the UV driver ERL uses a novel bypass geometry to provide transverse phase space control, bunch length compression, and nonlinear aberration compensation (including correction of RF curvature effects) without the use of magnetic chicanes or harmonic RF. Stringent phase space requirements at the wiggler, low beam energy, high beam current, and use of a pre-existing facility and legacy hardware subject the design to numerous constraints. These are imposed not only by the need for both transverse and longitudinal phase space management, but also by the potential impact of collective phenomena (space charge, wakefields, beam break-up (BBU), and coherent synchrotron radiation (CSR)), and by interactions between the FEL and the accelerator RF system. This report addresses these issues and presents the accelerator design solution that now successfully supports FEL lasing. 		 
 
THP187 Design Concept for a Compact ERL to Drive a VUV/Soft X-Ray FEL 2468
 
  • C. Tennant, D. Douglas
    JLAB, Newport News, Virginia, USA
  
  Funding: Support by US DOE contract #DE-AC05-060R23177
We explore possible upgrades of the existing Jefferson Laboratory IR/UV FEL driver to higher electron beam energy and shorter wavelength through use of multipass recirculation to drive an amplifier FEL. The system would require beam energy at the wiggler of 600 MeV with 1 mA of average current. The system must generate a high brightness beam, configure it appropriately, and preserve beam quality through the acceleration cycle - including multiple recirculations - and appropriately manage the phase space during energy recovery. The paper will discuss preliminary design analysis of the longitudinal match, space charge effects in the linac, and recirculator design issues, including the potential for the microbunching instability. A design concept for the recirculator and a lattice solution will be presented.