Avner Rosenberg

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.

Development of a tandem electrostatic accelerator quasi-cw FEL

Abstract The EN tandem electrostatic accelerator at the Weizmann Institute of Science has been converted into an electron accelerator with beam power recovery. We report on the design and performance of the accelerator as well as on a new approach to stable, long-pulse operation of this class of machines. The long-pulse model of operation offers interesting possibilities for the operation of free electron lasers, in particular the study of high-coherence, single-mode operation.

Studies of a high-power nonresonant virtual cathode oscillator

We report the studies of a free running virtual cathode oscillator radiating in the S-band. Although this vircator is acting as a nonresonant device, the radiation bandwidth is relatively narrow (< 2%), almost comparable to the results obtained when a high Q cavity is used (<EQ 1%). The customary chirping behavior of the RF pulse is absent in our measurements. The virtual cathode oscillator is radiating in a single mode identified as TM01 mode by using microwave-gas breakdown techniques. The measured peak power is approximately 300 MW. The mode pattern is strongly affected by the presence of electrons inside the waveguide.

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.

Status of the Rehovot en tandem accelerator free electron laser

Abstract The EN tandem electrostatic accelerator at the Weizmann Institute of Science has been converted into an electron accelerator with a source intensity of 2 A and with beam current recovery. The tandem FEL configuration, in which the wiggler is located in the high voltage terminal, allows for stable, long pulse operation. Two wire-mesh diagnostic systems for monitoring of the beam shape have been installed; one between the electron gun and the entrance to the accelerating tube, the other between the exit from the decelerating tube and the beam collector. We believe to be able to operate our machine with pulse lengths of the order of 1 ms without terminal voltage droop during such a pulse. At present, when operating with 5 μs pulses, only after 10–20 ms there is a noticeable terminal voltage droop. A beam current of 0.8–1.0 A enters the acceleration tube and 75% of it can be presently recovered at the collector. We expect to improve on this figure considerably. The long pulse operation mode, for which we are striving, offers interesting possiblities for the operation of free electron lasers, in particular demonstrating high coherence, single mode operation. A three year FEL experimental study program based on the tandem accelerator was recently proposed.

Development Of A Tandem Electrostatic Accelerator Quasi-CW FEL

The EN tandem electrostatic accelerator at the Weizmann Institute of Science has been converted into an electron accelerator with beam power recovery. We report on the design and performance of the accelerator as well as on a new approach to stable, long-pulse operation of this class of machines. The long-pulse model of operation offers interesting possibilities for the operation of free electron lasers, in particular the study of high-coherence, single-mode operation.