Socol, Y.
(Yehoshua Socol)

WEAOS04 Study of Coherence Limits and Chirp Control in Long Pulse FEL Oscillator
Avraham Gover, Alon Eliran, Yehoshua Socol, Mark Volshonok (University of Tel-Aviv, Tel-Aviv), Moshe Einat, Miki Kanter, Boris Yu Kapilevich, B. Litvak, Yuri Lurie, Yosef Pinhasi, Asher Yahalom (The College of Judea and Samaria, Ariel)

Electrostatic Accelerator FELs have the capacity to generate long pulses of tens microseconds and more, that in principle can be elongated indefinitely (CW operation). This allows the generation of very coherent radiation. The fundamental linewidth is extremely narrow [1], and in practice the spectral width is limited by the pulse duration (Fourier transform limit) and e-beam stability. Practical problems such as the accelerator terminal voltage drop due to a non-ideal electron beam transport may reduce the length of the radiation pulse and hence create a limiting factor for coherence measurement. The current status of the Israeli Tandem Electrostatic Accelerator FEL allows the generation of pulses of tens microseconds duration. It has been operated recently past saturation, and produces single mode coherent radiation of relative linewidth ~Δf/f=10-5 at frequencies near 100GHz. A clear frequency chirp is observed during pulses of tens of microseconds (0.1-1 MHz/mS), and is directly proportional to the voltage drop rate of the High-Voltage terminal. We will report experimental studies of the spectral linewidth and chirp characteristics of the radiation, along with theory and numerical simulations, carried out using space-frequency model [2], matching the experimental data.