• A. Gover, E. Dyunin
  University of Tel-Aviv, Faculty of Engineering, Tel-Aviv

The conventional analytical descriptions SASE-FEL do not take into account the electron velocity noise and collective effects. We use the general gain-dispersion relation for pre-bunched FEL in the linear regime [1] to define the FEL transfer function response to density and velocity modulation (initial condition problem) allowing for possible collective effect. This is used to derive expressions for SASE radiation line to velocity noise (random velocity modulation which exists even in the cold beam regime), in addition to the conventional shot noise (random density modulation). We find out for the realizable SASE FEL parameters [2] that the contribution of the velocity noise is not negligible relative to the shot noise. Also unexpectedly, collective effects may not be negligible in FELs even at short (UV) wavelength because the high beam current is being used.

[1] I.Schnitzer, A.Gover Nucl.Inst&Meth. Vol.A237. n.1-2, pp.124-140, 1985. [2]. R.Treusch, J.Feldhaus Eur. Phys. J. D, 26 pp.119-122, 2003

• A. Yahalom, Yu. Lurie, Y. Pinhasi
  CJS, Ariel
• A. Eliran, A. Gover
  University of Tel-Aviv, Faculty of Engineering, Tel-Aviv

We have measured spontaneous FEL radiation in the Israeli Electrostatic Accelerator FEL (EA-FEL) . The measurements were repeated numerous times in order to get information of statistical significance. The distribution of the radiation power measurements and various statistical moments derived from this distribution contain information on the electron beam statistics and its interaction with the wiggler magnetic field and the resonator that contain the radiation. In this work we present both the measured radiation power statistical data and its connection to the statistics of the electron beam through numerical and analytical models.

• A. Gover, A. Faingersh, M. Kanter, B. Kapilevich, B. Litvak, S. Peleg, Y. Socol, M. Volshonok
  University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
• M. Einat, Yu. Lurie, Y. Pinhasi, A. Yahalom
  CJS, Ariel

The Israeli Electrostatic Accelerator FEL (EA-FEL) is now being upgraded towards long pulse (1005s) operation and ultra-high resolution (10(-6)) single pulse coherent spectroscopy. We present quantitative estimations regarding the applications of controlled radiation chirp for spectroscopic applications with pulse-time Fourier Transform limited spectral resolution. Additionally, we describe a novel extraction-efficiency-improving scheme based on increase of accelerating voltage (boosting) after saturation is achieved. The efficiency of the proposed scheme is confirmed by theoretical and numerical calculations. The latter are performed using software, based on 3D space-frequency domain model. The presentation provides an overview of the upgrade status: the high-voltage terminal is being reconfigured to accept the accelerating voltage boost system; a new broad band low-loss resonator is being manufactured; multi-stage depressed collector is assembled.

• D. Kipnis, E. Dyunin, A. Gover
  University of Tel-Aviv, Faculty of Engineering, Tel-Aviv

Smith-Purcell radiation is the emission of electromagnetic radiation by an electron beam passing next to an optical grating. Recently measurement of relatively intense power of such radiation was observed in the THz-regime [1]. To explain the high intensity and the super-linear dependence on current beyond a threshold it was suggested that the radiating device operated in the high gain regime, amplifying spontaneous emission (ASE) [1,2]. We contest this interpretation and suggest an alternative mechanism. According to our interpretation the device operates as a distributed feedback (DFB) laser oscillator, in which a forward going surface wave, excited by the beam on the grating surface, is coupled to a backward going surface wave by a second order Bragg reflection process. This feedback process produces a saturated oscillator. We present theoretical analysis of the proposed process, which fits the reported experimental results, and enables better design of the radiation device, operating as a Smith-Purcell DFB laser.

[1] A.Bakhtyari, J.E.Walsh, J.H.Brownell, Phys.Rev. ·10⁶⁵ 006503 (2002). [2] H.L. Andrews, C.A. Brau, Phys.Rev. ST-AB 7, 070701 (2004).

• A. Gover
  University of Tel-Aviv, Faculty of Engineering, Tel-Aviv

A unified analysis for Superradiant emission from bunched electron beams in various kinds of radiation scheme is presented. Radiation schemes that can be described by the formulation include Pre-bunched FEL (PB-FEL), Coherent Synchrotron Radiation (CSR), Smith-Purcell Radiation, Cerenkov-Radiation, Transition-Radiation and more. The theory is based on mode excitation formulation - either discrete or continuous (the latter - in open structures). The discrete mode formulation permits simple evaluation of the spatially coherent power and spectral power of the source. These figures of merit of the radiation source are useful for characterizing and comparing the performance of different radiation schemes. When the bunched electron beam emits superradiantly, these parameters scale like the square of the number of electrons, orders of magnitude more than spontaneous emission. The formulation applies to emission from single electron bunches, periodically bunched beams, or emission from a finite number of bunches in a macro-pulse. We have recently employed the formulation to calculate a ne kind of coherent radiation from electron beam: enhanced Electron Spin Resonance Emission from a polarized electron beam. Estimates of the characteristics and possible applications of this effect will be presented.