R. Drori

Demonstration of microwave generation by a ferroelectric-cathode tube

A ferroelectric cathode is employed in a cyclotron-resonance maser (CRM). The CRM oscillator device operates at similar to 7 GHz, near the cutoff frequency of a hollow cylindrical cavity. The cathode is made of a PLZT 12/65/35 ceramic with high-dielectric constant (epsilon(r)similar to 4000). Electrons are extracted from the plasma excited on the cathode surface by similar to 1 kV short rise-time pulses. The use of ferroelectric cathodes may advance the microwave tube technology for various applications

Free-electron maser oscillator experiment in the UHF regime

A nonrelativistic electron beam (< 4 keV) travels in this experiment in a non-dispersive waveguide along a planar undulator and an axial magnetic fields. The electron beam has a Gaussian pulse shape with a 1 ms pulse width. Two distinct radiation bursts are observed during the electron energy sweep. Each burst contains a different range of microwave frequencies. One burst corresponds to the FEM interaction, at ∼ 0.8 GHz. The other burst corresponds to the cyclotron resonance interaction, at ∼ 5 GHz. This experiment demonstrates an FEM operation in an extremely long wavelength (37.5 cm) in the UHF regime.

Free-electron-laser-type interaction at 1 meter wavelength range☆

A free-electron-laser (FEL)-type interaction is observed between a low-energy electron beam (∼ 0.7 keV) and a radio wave in the VHF range (λ = 1.1 m). The experimental device consists of a transmission-line (TEM-mode) cavity, and a folded-foil planar wiggler (λw = 4 cm). Coherent oscillations are observed in the fundamental-cavity mode (0.28 GHz) and in higher-order modes. The FEL-type mechanism is demonstrated here in a new regime, λ ⪢ λw.

Carbon-fiber emitter in a cyclotron-resonance maser experiment

Abstract A compact cyclotron-resonance oscillator which employs a carbon-fiber electron-gun is presented in this paper. The maser oscillates at ∼3 GHz frequency near the electron cyclotron-resonance. The 2mm diameter carbon-fiber cathode emits ∼1 A current at ∼1 kV voltage. The electron beam tends to be unstable. Clear bursts of RF oscillations are observed in this experiment.

Cyclotron resonance maser experiment in a non-dispersive waveguide

Abstract A cyclotron-resonance maser (CRM) experiment with a transverse electromagnetic (TEM) wave is presented in this paper. A nonrelativistic electron beam is spiraling in this device in a non-dispersive parallel-line waveguide. The CRM oscillator output frequency is tuned by the axial magnetic field in the range of 3.2–4.8 GHz.

Cyclotron resonance maser experiment in a nondispersive waveguide

A cyclotron-resonance maser (CRM) oscillator experiment in which a spiraling electron beam interacts with a transverse electromagnetic wave in a nondispersive waveguide is presented. The experiment employs a low-energy (<5 keV) low-current (<1 A) electron beam in a two-wire (Lecher type) waveguide. The microwave output frequency is tuned in this experiment by the axial magnetic field in the range 3.5-6.0 GHz. A second harmonic emission is observed at /spl sim/7 GHz. CRM theory shows that in a free-space TEM-mode interaction, the gain might be canceled due to the equal and opposite effects of the axial (Weibel) and the azimuthal bunching mechanisms. This balance is violated in the large transverse velocity regime (V/sub /spl perp///spl Gt/V/sub z/) in which our experiment operates. The tunability measurements of the CRM oscillator experiment in the nondispersive waveguide are discussed in view of the CRM theory.

Low-voltage (750 V) free-electron laser operation at VHF (280 MHz)

A free-electron laser (FEL) type device that operates with a low-energy electron beam (/spl sim/0.7 keV) and a radiowave in the VHF range (/spl lambda/=1.1 m) is presented. The experimental device consists of a transmission-line (TEM-mode) cavity, and a folded-foil planar wiggler (/spl lambda//sub w/=4 cm). Coherent oscillations are observed in the fundamental cavity mode (0.28 GHz) and in higher order modes. This FEL-type device marks a record for an extremely low voltage operation.

Free-electron maser operation at the 1 GHz/1 keV regime

Abstract The paper describes a free-electron maser (FEM) experiment operating in the low-frequency (∼ 1 GHz) low-energy (∼ 1 keV) regime. The table-top FEM device consists of a non-dispersive parallel-stripline waveguide and a planar folded-foil wiggler. The experimental results show a super-regenerative amplification. Oscillations are observed above a threshold of the wiggler field.

Cyclotron-resonance maser experiments in first and second harmonics

Cyclotron-resonance maser (CRM) oscillator experiments in a non-dispersive (TEM-mode) waveguide are reported in this paper. The table-top CRM oscillator constructed in our laboratory operates with a low-energy (<5 keV), low-current (<1 A) electron beam. The electron beam is rotating in the cyclotron frequency due to an axial magnetic field produced by an external solenoid. The large electron transverse velocity, needed to obtain amplification in a TEM-CRM, is achieved by a strong kicker coil. The coplanar waveguide used in this experiment supports odd and even TEM-modes, and enables cyclotron interactions with both first and second harmonics. Microwave output power at the first cyclotron harmonic is observed in the range of 3-6 GHz, where the frequency is tuned by the axial magnetic field in this range. A considerable second harmonic emission is observed around 7 GHz frequency. This experiment may lead to the development of a new compact high-power microwave source.

Observation of a free-electron laser interaction in the UHF regime

A free-electron laser (FEL) oscillator experiment operating with a low-energy (<4 keV), low-current (<0.5 A) pulsed electron beam is presented in this paper. In the table-top FEL oscillator constructed in our laboratory the electrons travel along a planar undulator and an axial magnetic field, and interact with TEM-mode electromagnetic waves. In this experiment, microwave output is observed at /spl sim/40 cm wavelength. This radiation is much longer than the undulator period (2 cm). To the best of our knowledge, this is the first demonstration of an FEL operation in the UHF regime. For electron beam energy of /spl sim/3 keV, we observe also microwave output at /spl sim/5 GHz. This emission is related to the cyclotron resonance due to the axial magnetic field. These experiments may lead to the development of new high-power UHF and microwave radiation sources.