E.A. Perelstein

Problems of autobunching and phase stability for the TBA-driver: calculations and design for a modeling experiment

Abstract Problems of stability and phase correlation of the TBA-driver radiation are studied on the basis of nonstationary spatio-temporal equations, applied to the model of discrete driver cells without RF connection between them. The design for the modeling experiment is described.

Progress in development of powerful sub-mm Bragg FEM based on moderately relativistic electron beam

A project to generate powerful sub-mm pulses in JINR-IAP FEM-oscillator driven by 0.8 MeV / 200 A linac is in progress. Present paper describes recent design and key elements of the oscillator.

High-power broadband 30-GHz FEM amplifier operated in the grazing incident regime

A high-power broadband free electron maser (FEM) amplifier has been realized in collaboration between JINR (Dubna) and IAP RAS (Nizhny Novgorod) based on the linac LIU-3000 (0.8 MeV/200 A/250 ns). To achieve a wide frequency amplification band, the regime characterized by grazing of the dispersion curves of the beam electrons to the operating wave (the so-called grazing regime) was studied in the FEM. According to the simulations, such an operating regime allows an instant amplification band of up to 5%–7% with output power at the level ∼20 MW and a gain of about 30–35 dB to be obtained in the Ka band. The proof-of-principle experiments examined this scheme in the 30-GHz frequency range and confirmed the simulations. As a result, the predicted power level with design parameters has been achieved, and fast frequency tuning within the feeding magnetron band ±0.5 GHz has been demonstrated.

New scheme of two beam accelerator driver based on linear induction accelerator

The two beam accelerator (TEA) drivers based on a linear induction accelerator were discussed previously. In these schemes the driver electron beam moves through alternating discrete row of microwave generators (free electron lasers (FEL), relativistic klystrons, etc.) and reaccelerator sections. The microwave power is totally extracted from the driver after every generation section. The continuous microwave power extraction along the whole driver length was designed in CLIC. A new scheme of TEA driver based on a linear induction accelerator is suggested. The scheme is quite uniform and has the following characteristic properties: a) the electron beam bunching occurs at a rather low initial energy; b) the bunched beam is accelerated in the accompanying of the microwave that provides the steady longitudinal beam bunching along the whole driver; c) there is no total microwave power extraction anywhere in the driver; d) a waveguide is used along the driver.

Mode splitting effect in FEMs with oversized Bragg resonators

Splitting of the fundamental mode in an oversized Bragg resonator with a step of the corrugation phase, which operates over the feedback loop involving the waveguide waves of different transverse structures, was found to be the result of mutual influence of the neighboring zones of the Bragg scattering. Theoretical description of this effect was developed within the framework of the advanced (four-wave) coupled-wave approach. It is shown that mode splitting reduces the selective properties, restricts the output power, and decreases the stability of the narrow-band operating regime in the free-electron maser (FEM) oscillators based on such resonators. The results of the theoretical analysis were confirmed by 3D simulations and “cold” microwave tests. Experimental data on Bragg resonators with different parameters in a 30-GHz FEM are presented. The possibility of reducing the mode splitting by profiling the corrugation parameters is shown. The use of the mode splitting effect for the output power enhancemen...

Powerful short wavelength fems operated at harmonics of bounce frequency: Recent results and prospects

Summary form only given. High-efficiency narrow-band 30-GHz Bragg FEM-oscillator was elaborated during the last few years in JINR-IAP collaboration based on 0.8 MeV / 200 A / 250 ns LINAC LIU-3000 (JINR). An attractive solution to prospect FEM into short wave-lengths keeping beam energy and geometry of electron-optical system is operation at harmonics of bounce-frequency. Two FEM schemes exploiting this idea are under development at LIU-3000.

Starting mode regime in an FEM oscillator with a Bragg resonator

In an FEM oscillator with a Bragg resonator excitation of an additional starting mode can be exploited as a source of an initial signal for the operating mode. In such a regime the starting mode has a rather small detuning from synchronism resulting in a high temporal gain but a rather small electron efficiency. With the starting mode growth the situation becomes favorable for excitation of the operating mode. Afterwards due to a non-linear competition mechanism the operating mode suppresses the starting mode and a single-mode regime of oscillations is realized with a rather high efficiency.

Development of frequency-tunable FEM-oscillator with Bragg resonator for testing high-gradient accelerating structures

This paper is devoted to progress in the JINR-IAP FEM experiment based on a 1 MeV/200 A/250 ns LINAC. This FEM generates 30 GHz pulses of 150 - 200 ns pulse duration and 20 - 30 MW power with an efficiency on the level of 20

Design considerations of source of synchrotron hard X-ray and coherent infrared radiation at JINR

25%. The high efficiency together with high stability of single-mode single-frequency operation is provided by the use of a reversed guide magnetic field and a novel Bragg resonator with a step of phase of corrugation. At the present stage of the experiments precise tuning of the oscillation frequency was performed by mechanical variation of the value of the phase shift in the Bragg resonator. As a result, the FEM was tuned in the frequency range of 6% with a precision of about 0.1%. Both the spectrum width and the dependence of the frequency tuning value on the corrugation phase shift are in good agreement with the results of simulations. The project to use this high power FEM source for studying surface heating effects in 30 GHz accelerating structures is discussed. A special cavity has been designed to enhance magnetic fields at the cavity surface. The cavity will be studied with regard to 200 - 500/spl deg/C surface pulsed heating stress of the cavity as a consequence of 10/sup 6/ RF-pulses, which are planned to be produced at a repetition rate of 1 Hz.

Experiment on pulse heating and surface degradation of a copper cavity powered by powerful 30 GHz free electron maser

Abstract The review on a source of synchrotron hard X-ray and coherent infrared radiation at JINR is presented. The requirements on the SR source and on the accelerating complex are given. The structure scheme of the SRS is described. The preliminary calculations of the QBA lattice of the main ring are performed.