Itzhak Schnitzer

Study of electron diodes with a ferroelectric plasma cathode

We present results of studies of time- and space-resolved energy distributions of electrons and ions emitted from the plasma formed on the surface of poled and unpoled ferroelectric samples. Results of lifetime tests of different ferroelectric cathodes are also described. We studied the operation of a planar electron diode and a relativistic magnetron, both with a ferroelectric cathode under the application of a high-voltage pulse of /spl les/300 kV with a repetition rate of /spl les/5 Hz. In the planar diode, the energy of electrons, the uniformity of the extracted electron beam, and the potential distribution were studied. The obtained experimental data agree well with the model of plasma formation on the surface of the ferroelectric. Successful repetition rate operation of the magnetron with a PZT ferroelectric cathode was demonstrated.

Evolution of spectral power density in grounded-cathode relativistic magnetron

A novel, rep-rated, relativistic magnetron design is demonstrated. Unlike other relativistic magnetrons, the high voltage pulse is positively charged, feeding the anode block, while the cathode is grounded. Moreover, the anode- cathode interaction space is centered in a larger buffer cavity that serves as an electric insulator and electromagnetic impedance matching between the anode block and the exit waveguide(s). The grounded cathode geometry eliminates the axial current (improving efficiency) and enables the use of compact, CW, U-shaped electromagnet. It may also be utilized for frequency tunability through the buffer cavity in a way similar to coaxial magnetrons. Operation with peak power of 50 MW (100 MW) and pulse length of 150 ns (70 ns) has been achieved. Employing metal- dielectric cathodes led to repetitive operation up to 10 Hz. The analysis emphasizes time-resolved spectral power density of both in-cavity and emitted microwaves in regard to the undesirable occurrence of pulse shortening.

Israeli tandem FEL: first-lasing results and future plans

Results of first operation of the Israeli Electrostatic- Accelerator Tandem Free-Electron Laser (EA-FEL) are reported. This EA-FEL utilizes a 1.4 Amp electron beam obtained from a parallel flow Pierce-type electron gun. The e-beam is transported through a resonator located inside a plane Halbach configuration wiggler, both located at the high voltage terminal of the van de graaf accelerator. The high voltage terminal is charge to a positive plates waveguide and two Talbot effect quasioptical reflectors. It exhibited a quality factor of Q approximately equals 30,000. Millimeter wave radiation pulses of 2 microsecond(s) ec duration were obtained at a frequency of 100.5 GHz, as predicted, at a power level above 1 kW.

Design and development of the TAU Tandem FEL

This paper presents a status report on Tandem electrostatic FEL which has been developed based on the 5 MeV linear accelerator at the Weizman Institute. The FEL is designed to operate near 100 GHz and is comprised of the following basic components: (1) an injector based upon a Pierce e-gun which provides a 1.8 amp beam at 50 keV. (2) an electrostatic accelerator that accelerates the beam to 1.4 MeV at the high voltage terminal (in the middle of the accelerator tank) where the wiggler mm-wave cavity is placed. (3) a depressed collector at ground potential. The electron beam is transported towards the wiggler with the aid of magnetic focusing coils, which inject the beam into the electrostatic accelerator tube and then is focused into the wiggler by means of 4 quadruple lenses. The beam transport is corrected by use of steering magnets at the entrance and at the exit of the wiggler, and is monitored with the aid of 3 fluorescent screens (S1-S3) and CCD cameras.