Author: Popov, V.
Paper Title Page
TUOCS6 An VUV FEL for Producing Circularly Polarized Compton Gamma-ray Beams in the 70 to 100 MeV Region 778
 
  • Y.K. Wu, J.Y. Li, S.F. Mikhailov, V. Popov, G. Swift, P.W. Wallace, W. Wu
    FEL/Duke University, Durham, North Carolina, USA
  • S. Huang
    PKU/IHIP, Beijing, People's Republic of China
 
  Funding: This work is supported in part by the US DOE grant no. DE-FG02-97ER41033.
Recently, the Duke optical klystron FEL (OK-5 FEL) has been commissioned to produce lasing in the VUV region (191 - 193 nm), overcoming substantial laser cavity loss due to low reflectivity of the VUV FEL mirrors. With two OK-5 FEL wigglers separated by more than 20 meters in a non-optimal configuration, an adequate FEL gain was realized by operating the Duke storage ring with a high single-bunch current (30 to 50 mA). This VUV FEL has enabled us to produce circularly polarized Compton gamma-ray beams in the 70 to 100 MeV region at the High Intensity Gamma-ray Source (HIGS), Duke University. This high energy gamma-ray beam capability will create new opportunities for both fundamental and applied research at HIGS. In this work, we report our experience of VUV FEL lasing with a high single-bunch current and first production of gamma-ray beams in the 70 to 100 MeV region.
 
slides icon Slides TUOCS6 [2.768 MB]  
 
THP153 Manipulating the FEL gain process with an In-cavity Aperture System 2405
 
  • J.Y. Li, B. Jia, S.F. Mikhailov, V. Popov, Y.K. Wu
    FEL/Duke University, Durham, North Carolina, USA
  • S. Huang
    PKU/IHIP, Beijing, People's Republic of China
 
  Funding: This work is supported in part by the US DOE grant no. DE-FG02-97ER41033.
The 53.73 meters long free-electron laser (FEL) resonator at Duke University consists of two concave mirrors with the similar radius of curvature. The downstream mirror receives not only the fundamental but also higher order harmonic radiation (typically in the UV and VUV range) emitted by relativistic electrons in the magnetic field of wigglers. The power load of wiggler radiation on this mirror can thermally deform and permanently damage the multi-layer coating of the mirror, therefore, limiting the maximum power of the FEL operation and reducing the mirror lifetime. To mitigate these problems, a water-cooled aperture system has been installed inside the FEL resonator. This aperture system has been used to prevent most of off-axis helical wiggler radiation from reaching the downstream FEL mirror. It has also been used to manipulate the FEL gain process by increasing the FEL beam diffraction loss inside the resonator. In principle, this aperture system can be used as an independent FEL gain control device for FEL operation. This paper reports our preliminary study of the FEL operation using the in-cavity apertures to manipulate the FEL gain process.
 
 
THP155 Experience of FEL Mirror Degradation at the Duke FEL and HIGS Facility 2408
 
  • S.F. Mikhailov, J.Y. Li, V. Popov, Y.K. Wu
    FEL/Duke University, Durham, North Carolina, USA
 
  Funding: This work is supported by the US DoE grant #DE-FG02-97ER41033
The Duke FEL and High Intensity Gamma-ray Source (HIγS) are operated in the range of electron beam energies of 0.24 - 1.2 GeV and photon beam wavelengths of 190-1060 nm. The range of gamma-beam energies currently produced by HIγS facility is from 1MeV to about 100 MeV, with the maximum total gamma-flux of up to 3*1010 gammas per second around 10 MeV. Production of this high level gamma-ray flux requires an average FEL photon beam power inside the FEL resonator at one kilowatt or more. The high power FEL operation causes degradation of the FEL mirrors, especially when operating the FEL in the UV and VUV region at a high electron beam energy. To ensure reliable HIγS operation, we developed a comprehensive program to continuously monitor the performance of the FEL mirrors. This program enabled us to use a particular set of FEL mirrors for a few hundreds hours of high gamma-flux operation with predictable performance. In this work, we discuss sources and consequences of the mirror degradation for a variety of wavelengths. We also present estimates of the mirror life time as a function of the FEL wavelength, photon and gamma-ray polarization, and total gamma-flux.
 
 
THP198 Upgrade of the RF Photo-Injector for the Duke Storage Ring 2489
 
  • V. Popov, J.Y. Li, S.F. Mikhailov, P.W. Wallace, P. Wang, Y.K. Wu
    FEL/Duke University, Durham, North Carolina, USA
 
  Funding: This work is supported in part by the US DOE grant no. DE-FG02-97ER41033.
The accelerator facility for the Duke FEL and High Intensity Gamma-ray Source (HIGS) consists of a linac pre-injector, a top-off booster injector, and the storage ring. The S-band RF gun with the LaB6 cathode was initially operated in the thermionic mode, producing a long electron beam pulse and a large radiation background. In 1997, the thermionic RF gun was converted to a photo-cathode operation using a nitrogen drive laser for single bunch injection into the storage ring. The photo-cathode operation typically delivers 0.1 nC of charge in a 1 ns long pulse to the linac. Since 2006, substantial improvements have been made to the photo-cathode and the linac, including improvements of the nitrogen drive laser, development of driver laser optical transport and beam monitoring system, and optimization of the cathode heater current to minimize the thermionic emission. In addition, two electron beam charge measurement systems using Faraday cup detectors and sample and hold electronics have been developed. In this work, we will present these new developments and discuss the impact of these upgrades on everyday operation of the linac pre-injector.