Benson, S. V.

Paper	Title	Page
TUCAU04	Second Harmonic Lasing with Storage Ring Based FELs	459
	Y. K. Wu, J. Li, S. F. Mikhailov, V. Popov FEL/Duke University, Durham, North Carolina S. V. Benson, G. Neil JLAB, Newport News, Virginia
	The study of forbidden processes in many types of physical systems is critical for understanding the underlying symmetry breaking. The FEL second harmonic lasing of provides a unique opportunity to study the "forbidden" FEL gain mechanisms which are otherwise not allowed under normal operation conditions of an FEL. Because of its very low gain, the sole study of second harmonic lasing in the optical region was reported by the JLab using its high-gain IR FEL (PRL, 084801, 2001). This work reports the first second harmonic lasing results at Duke University with the storage ring based optical klystron and distributed optical klystron FELs. Several different mechanisms have been proposed for the second harmonic lasing, including relative misalignments between electron and optical beams, transverse field gradients, and longitudinal coupling (NIM A483, p. 527, 2002). Different gain mechanisms can also lead to preferred polarization states. In order to understand and distinguish various gain mechanisms, our work focuses on measurements of the gain and polarization of the second harmonic lasing under various optical and electron beam conditions and for a variety of FEL configurations.
	Slides
THCAU03	Electron Beam Timing Jitter and Energy Modulation Measurements at the JLab ERL	517
	P. Evtushenko, S. V. Benson, D. Douglas, D. W. Sexton JLAB, Newport News, Virginia
	When operating JLab high current ERL a strong reduction of the FEL efficiency was observed when increasing the average electron beam current. Investigating the FEL efficiency drop-off with the electron beam average current we also have measured the electron beam phase noise and the fast energy modulations. The so-called phase noise is essentially a variation of the time arrival of the electron bunches to the wiggler. That could be a very effective way of reducing the FEL efficiency if one takes in to account that the accelerator is routinely operated with the RMS bunch length of about 150 fs. Under a fast energy modulation we mean a modulation which can not be followed by the FEL due to its time constant, defined by the net gain. Such a modulation also could be a possible cause of the efficiency drop-off. Having the measurements made we could rule out the FEL efficiency drop-off due to either the fast energy modulation or the phase modulation. We also have learned a lot about instrumentation and techniques necessary for this kind of beam study. In this contribution we describe the used instrumentation and present results of the measurements.
	Slides