Benson, S. V.

Paper	Title	Page
TUAAU04	On the Design Implications of Incorporating an FEL in an ERL	273
	G. Neil, S. V. Benson, D. Douglas, P. Evtushenko, T. Powers Jefferson Lab, Newport News, Virginia
	Encouraged by the successful operation of the JLab Demo in 1998, many high current ERLs are now being designed with not only short pulse synchrotron beamlines but also FELs. Such inclusion has major implications on magnet quality, rf feedback requirements, wiggler design, srf cavity QL, halo, etc. Measurements on the JLab ERL FEL have identified new challenges. The JLab Upgrade was designed with a 160 MeV beam of 10 mA in 75 MHz, 300 fs bunches. FEL designers set transverse emittance and longitudinal bunching, but to accommodate an FEL in our ERL also means setting stringent phase stability requirements of (<6x10-9/fm rms) based on a desired FEL detuning tolerance of 1.2 microns. Recovered beam RF loading on the subsequent accelerated beam complicates satisfying these requirements. Gain in the rf feedback limits the accuracy of energy stability when loaded Qs are ~107 . Energy recovery to <10 MeV sets magnetic field tolerances at 10-4. We present measurements on the JLab ERL showing how to set system requirements to tolerate such FEL lasing.
	Slides
	Talk
TUPPH008	Harmonic Lasing Characterization at Jefferson Lab	323
	S. V. Benson, M. D. Shinn Jefferson Lab, Newport News, Virginia
	Harmonic lasing is normally suppressed because of lasing at the fundamental wavelength. It can, however, be achieved by using any of several methods that suppress fundamental lasing. In this paper we discuss two methods used at Jefferson Lab. The first is to use the characteristics of dielectric coatings to allow harmonic lasing at cavity lengths longer than the synchronous length for the fundamental. The second is to use a dielectric coating that has little reflectivity at the fundamental. This allows us to directly compare fundamental and harmonic lasing with the same optical resonator and electron beam. We present measurement carried out at Jefferson Lab using the IR Upgrade FEL operating at 0.54, 0.93, 1.04, 1.6, and 2.8 microns in which both schemes are used to produce lasing at both the 3rd and 5th harmonic of the fundamental.
TUPPH061	Phase Noise Comparision of Short Pulse Laser Systems	466
	S. Zhang, S. V. Benson, J. Hansknecht, D. Hardy, G. Neil, M. D. Shinn Jefferson Lab, Newport News, Virginia
	This paper describes the phase noise measurement on several different mode-locked laser systems that have completely different gain media and configurations including a multi-kW free-electron laser. We will focus on the state of the art short pulse lasers, especially the drive lasers for photocathode injectors. A comparison between the phase noise of the drive laser pulses, electron bunches and FEL pulses will also be presented.
TUPPH071	Simulation of Mirror Distortion in Free-Electron LASER Oscillators	477
	H. Freund SAIC, McLean S. V. Benson, M. D. Shinn Jefferson Lab, Newport News, Virginia
	Thermal distortion in cavity mirrors in high-power FELs can alter mode quality and degrade performance. Hence, it is important to be able to predict the character of the distortions to model their effect on FEL performance. To this end, we address these key issues by developing modeling and simulation tools that can accomplish these goals, and then benchmarking the simulation against observations on the 10 kW-Upgrade experiment at the Thomas Jefferson National Accelerator Facility. The modeling and simulation will rely on the MEDUSA code, which is a 3-D FEL simulation code capable of treating both amplifiers and oscillators in both the steady-state and time-dependent regimes. MEDUSA employs a Gaussian modal expansion, and treats oscillators by decomposing the modal representation at the exit of the wiggler into the vacuum Gaussian resonantor modes and then analytically propagating these modes through the resonator back to the entrance of the wiggler in synchronism with the next electron bunch. Knowledge of the power loading on the mirrors allows us to model the mode distortions using Zernicke polynomials and this technique has been incorporated into MEDUSA.
THPPH066	Longitudinal Phase Space Characterization of Electron Bunches At the JLab FEL Facility	740
	S. Zhang, S. V. Benson, D. Douglas, D. Hardy, G. Neil, M. D. Shinn Jefferson Lab, Newport News, Virginia
	We report the latest measurement of the longitudinal phase space of electron bunches on our 10kW free-electron laser facility. The design and construction of an all reflective optical transport has made it possible to make full use of broadband synchrotron radiation and perform a high-efficiency dispersion-free measurement with a remote fast streak camera. The evolution of the longitudinal phase space can be observed live when the accelerating RF phase is tuned. The results for different beam setups including low and high current will be presented.