FEL/Duke University, Durham, North Carolina
SLAC, Menlo Park, California
USTC/NSRL, Hefei, Anhui
Touschek lifetime of an electron beam in a storage ring depends on the beam polarization through the intrabeam scattering effect. Consequently, the electron beam polarization can be determined by comparing the measured Touschek lifetime of a polarized beam and an unpolarized beam. In this paper, we report a systematic experimental procedure to study the radiative polarization of a stored electron beam. Based upon this technique, we have successfully observed the polarization build-up of a 1.15 GeV electron beam in the Duke storage ring. Using the Touchek lifetime data, we are able to determine the equilibrium degree of the electron beam polarization and the time constant for the polarization build-up process.
FEL/Duke University, Durham, North Carolina
Compton scattering of a laser beam with a relativistic electron beam has been used to generate an intense, highly polarized, and nearly monoenergetic gamma-ray beam at several facilities. The ability of predicting the spatial and spectral distributions of a Compton gamma-ray beam is crucial for the optimization of the operation of a Compton light source as well as for the applications utilizing the Compton beam. Based upon the Lorentz invariant Compton scattering cross section, we have derived an analytical formula to study the Compton scattering process. Using this formula, we have developed an integration code to produce the smooth results for the spatial and spectral distributions of the Compton beam. This code has been characterized at the High Intensity Gamma-ray Source (HIGS) facility at Duke University for varying electron and laser beam parameters as well as different gamma-ray beam collimation conditions.
FEL/Duke University, Durham, North Carolina
After years of development, High Intensity Gamma-ray Source (HIGS) at Duke University, the most powerful Compton gamma-ray source in the 1 to 100 MeV region, has recently become a dedicate light source facility for scientific research. Driven by the kW power of a storage ring FEL, the HIGS produces high-intensity gamma-ray beams with an exceptionally high flux, a total flux up to few 1010 g/s and a spectral flux of more than 103 g/s/eV, in the few MeV to 10 MeV region. With the present configuration, the HIGS has a wide energy tuning range from 1 to 100 MeV, a high degree of polarization (nearly 100%) switchable among linear, left-, and right-circular polarizations, and a high energy-resolution as low as 0.8% (FWHM). The planned future upgrades will enable the HIGS to produce high-energy gamma-ray beams up to 160 MeV, providing a precision tool for the photo-pion physics research. With these outstanding capabilities, the HIGS is a world-class Compton gamma-ray source for frontier research in a wide range of scientific areas from nuclear physics to astrophysics, from medicine to industry.
FEL/Duke University, Durham, North Carolina
The Duke FEL and High Intensity Gamma-ray Source (HIγS) are operated with a wide range of electron beam energies (0.24 - 1.2 GeV) and photon beam wavelengths (190 - 1060 nm). Currently, the HIγS provides users with the gamma beams in the energy range from 1 to about 65 MeV, with a near future extension to about 100 MeV. The maximum total gamma-flux produced at the HIγS facility is up to 1010 gammas per second. Production of high level gamma-ray flux, requiring a very high average FEL intra-cavity power and high electron beam current, can cause significant degradation of the FEL mirrors. To ensure the predictability and stability of the HIγS operation for user research program, we have developed a comprehensive program to continuously monitor the performance of the FEL mirrors. This program has 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 and present our estimates of the mirror life time as a function of the FEL wavelength, gamma-ray polarization, and total gamma-flux.
FEL/Duke University, Durham, North Carolina
The light source research program at the Duke Free-Electron Laser Laboratory (DFELL) is focused on the development of accelerator-driven light sources, including storage ring based free-electron lasers (FELs) and Compton gamma-ray source, the High Intensity Gamma-ray Source (HIGS). The HIGS is the most intense Compton gamma-ray source currently available with an energy tuning range from 1 to 100 MeV. The accelerator physics program at the DFELL covers a wide range of activities, from nonlinear dynamics research, to the study of beam instability with advanced feedback systems, to FEL research and development. In this paper, we will report our recent progress in accelerator physics research and light source development to meet new challenges of today's and future accelerators.