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Litvak, B.

Paper Title Page
MOPPH037 Characterization of a New High-Q Talbot Effect Confocal Resonator for mm-Wave FEL  
 
  • J. Dadoun, Kh. Garb, A. Gover, O. Faingersh
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
  • B. Yu. Kapilevich, B. Litvak
    CJS, Ariel
 
  A new FEL resonator for mm- wave range was assembled and characterized before installation into the high voltage terminal of the Tandem electrostatic FEL accelerator. The measured unloaded Q-factor of the new resonator is Q=30,000. Accordingly, the round-trip losses are ~18% for the total length of the resonator about 1.5m The reflector of the new resonator utilizes in one transverse dimension the Talbot effect for imaging and splitting the radiation mode field for the purpose of the laser radiation. In the other transverse dimension optical imaging is realized by means of two confocal mirrors. A 3-wire grid assembly, remotely controlled, provides fine tuning of the laser frequency and control over the resonator out-coupling coefficient. The new resonator includes an integral e-beam profile diagnostics means installed on the safety shield. All e-beam diagnostics and tuning motors are remote controlled in a Lab View environment.  
MOPPH057 Development of mm-Wave TDR Technique for Direct Estimating of the Quality of the FEL’s Resonator Mirrors  
 
  • M. Einat, B. Litvak, B. Yu. Kapilevich
    CJS, Ariel
  • O. Faingersh, A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
 
  Radiated power of the Israeli FEL is greatly dependent on the quality of input/output mirrors of the quasi-optical resonator, where an interaction between electron beam and EM fields is taken placed. Since they are located in the close proximity to the electron beam transport area, the probability of their damaging is increased and regular diagnostics of mirror's quality is urgently required. However, such a diagnostic is time consuming due to the required vacuum-opening. The time domain reflectometry (TDR) method allows estimating the mirror’s quality by means of direct measurements of its power reflectance. We have developed the TDR's experimental set-up in 90-105 GHz permitting to perform such measurements. The key element of this setup is the pulse modulated pin-switch with a rise time of 1-2 ns. The forward and backward signals have been recorded independently using the two separated detectors and Tektronix digital scope. We have investigated the TDR's patterns of various damaged mirrors and conclude that the suggested technique can be recommended for remote diagnostics and estimating their quality without vacuum opening.

Israeli Ministry of Science

 
THBAU04 Millimeter Waves Sensing Behind Walls - Feasibility Study with FEL Radiation 501
 
  • M. Einat, M. Kanter, B. Litvak, A. Yahalom, B. Yu. Kapilevich
    CJS, Ariel
  • A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
 
  The existing through-wall imaging (TWI) systems operate in 1 – 10 GHz, basically, in order to reduce an attenuation caused by building material. However, the spatial resolution is drastically degraded when the operating frequency is relatively low. On the other hand, a majority of building materials demonstrate increased losses as the frequency increases. As a result, higher RF power from the source is required. The Israeli mm-wave FEL provides unique opportunity to solve the above TWI problem permitting to deliver output power 100-1000W at 85-105 GHz. Design of TWI system operating on mm-waves needs comprehensive study of constitutive parameters of different building materials. This paper describes systematic measurements of effective attenuation constant of typical building materials such as concrete bricks, wood, tiles, sand, gypsum, etc. on mm-waves using powerful FEL radiation. Since the Rayleigh criterion for surface roughness cannot be satisfied for some of measured materials, scattering and depolarization effects lead to increasing measured attenuation in comparison with bulky material. Additional experiments were performed to estimate a contribution of these effects into the measured attenuation.  
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