Elkuno A. Perelshtein

Sub-millimeter Bragg FEM based on moderately relativistic electron beam: project and first experiments

Sub-mm Bragg FEM (free-electron maser) is developed based on 0.8 MeV / 200 A linac. Present paper describes recent design and key elements of the oscillator. Results of the first experiments, which proved operability of novel FEM scheme, are described.

FEM with high-selective Bragg resonator based on coupling of propagating and cutoff waves

Bragg FEM with a two-mirror resonator including advanced Bragg structure based on coupling of propagating and quasi-cutoff waves was studied. Implication of the cutoff wave into the feedback loop improves selectivity of the Bragg resonators over transverse coordinates and allows advance of FEM into short wavelengths up to THz-band. Operability of Bragg resonator of a novel type has been demonstrated in Ka-band JINR-IAP FEM.

Powerful 30-GHz JINR-IAP FEM: Recent results, prospects and applications

Summary form only given as follows. The JINR-IAP FEM-oscillator was elaborated during the last few years based on 0.8 MeV/200 A/250 ns linac LIU-3000 (JINR, Dubna). This 30-GHz FEM generates currently 20 MW/200 ns pulses with spectrum width of ~6 MHz and repetition rate of up to 1 Hz. The high efficiency and stability of the FEM was achieved by using reversed guide magnetic field regime and advanced type of Bragg resonator, i.e. resonator with a step of phase of corrugation. The parameters achieved allow the FEM to be used in several applications. A test facility to study surface heating effects at 30 GHz was constructed based on the FEM. Information about the life time of the metals in strong RF-fields would be beneficial, in particular, when designing high-gradient accelerating structures for future linear colliders. The special cavity was made for modeling temperature regime of a high-Q accelerating structure. The experimental set-up was verified in 105 pulses with the necessary temperature rise in the test cavity of up to 150degC during each pulse. The experiment in consequence of ~106 pulses is in progress currently. One more important application of the powerful FEM is testing of RF breakdown strength of different materials. The experiment on studying volume and surface (multipactor) breakdown at a silicon disc is under development. This work is aimed to elaborate the control systems for powerful microwave flows and fast switches for microwave pulse compressors. Investigation of possibility to use JINR-IAP FEM in medical and biological applications was also started. The effect of the powerful 30-GHz pulses on the biological tissue and, in particular, on the cancer cells was studied. Project to advance JINR-IAP FEM into sub-mm wavelengths is developed. We propose to use a two-wave regime when the backward mm-wave (forming in the Bragg resonator) is used as an electromagnetic wiggler to provide stimulated scattering into a sub-mm forward wave at a multiple frequency. A 360 GHz generator was designed based on the linac LIU-3000 to operate with a 100-kW power at 12th frequency harmonic of the pumping wave. In the first experiments the operability of novel FEM scheme was demonstrated and radiation with the wavelength shorter than 1 mm was registered with the power estimated at 10-kW level.