S. L. Sinitsky

Dynamics and Spectral Composition of Subterahertz Emission From Plasma Column Due to Two-Stream Instability of Strong Relativistic Electron Beam

This paper describes results of GOL-PET experiments on subterahertz (0.1-0.5 THz) emission from a magnetized plasma column during passing of a high-current (~ 10 kA) relativistic (~ 0.6 MeV) electron beam. The subterahertz radiation is generated in the plasma due to high-level turbulence induced by two-stream instability of the electron beam. These experiments are carried out at the specialized GOL-3T device. For the plasma density range 1014 - 1015 cm-3, we have studied emission dynamics from the plasma column in its transverse and longitudinal directions. The spectral composition and polarization of the radiation was also investigated.

Using Two-Dimensional Distributed Feedback for Synchronization of Radiation from Two Parallel-Sheet Electron Beams in a Free-Electron Maser.

A spatially extended planar 75xa0GHz free-electron maser with a hybrid two-mirror resonator consisting of two-dimensional upstream and traditional one-dimensional downstream Bragg reflectors and driven by two parallel-sheet electron beams 0.8u2009u2009MeV/1u2009u2009kA has been elaborated. For the highly oversized interaction space (cross section 45×2.5 vacuum wavelengths), the two-dimensional distributed feedback allowed realization of stable narrow-band generation that includes synchronization of emission from both electron beams. As a result, spatially coherent radiation with the output power of 30-50xa0MW and a pulse duration of ∼100u2009u2009ns was obtained in each channel.

Two Ways for High-Power Generation of Subterahertz Radiation by Usage of Strong Relativistic Electron Beams

This paper describes results of studies on application of high current (1-10 kA) relativistic electron beams to generate millimeter and subterahertz (sub-THz) radiation in two ways. The first one is realized at the ELMI-device where the scheme of a free electron maser (FEM) with a sheet electron beam is applied for the case of a planar two-beam-channel geometry. The second way is based on emission of sub-THz radiation from plasmas with turbulence induced by a strong relativistic electron beam. These experiments are carried out at the GOL-3 facility. We present experimental results obtained at these two devices and briefly describe their theoretical analysis.

GOL-PET experiments on THZ-emission from dense plasma at relativistic electron beam relaxation

Summary form only given. Electromagnetic emission from plasma in the vicinity of the fundamental plasma frequency and at its double value during a relativistic electron beam (REB) relaxation is studied at the GOL-3 facility [1]. In our paper we will present results of experiments carried out on the specialized GOL-PET device for the emission of terahertz radiation from plasma at its density ~ 1015 cm-3 and the magnetic field strength 2-4 T. The plasma column created by a high-voltage discharge in the GOL-PET device has its diameter 6 cm and the length about of 250 cm. The injected electron beam has the following parameters: ~0.8 MeV, ~20 kA, ~10 μs. The beam current density in the plasma is up to 3kA/cm2. The radiation in the frequency interval from 0.1 up to 0.8 THz is analyzed by fast eight-channel polychromator and polarimeter based on frequency selection quasioptical elements.Results of the experimental measurements will be discussed in accordance to theoretical description with taking into account the influence of the magnetic field and high level turbulent in the plasma [2].

Submillimeter generation in intercavity scattering scheme with two sheet relativistic electron beams

In experiments at ELMI-device (BINP, Novosibirsk) the operation of 4-mm free electron maser (FEM) with two dimensional distributed feedback was demonstrated [1, 2]. These results gave a base for development multichannel planar FEM with 2-D distributed feedback [3]. In case of two channels jointed by special waveguide 2-D distributed feedback can be also used for two stage generation of submillimeter radiation exploiting an intercavity scattering scheme [3]. As the first step on studying of two stage generation we performed the experiments on simultaneous generation and transport of two intensive sheet electron beams. We modified the geometry of a ribbon accelerator diode at the ELMI-device and realized simultaneous generation of two sheet beams with the following parameters: the electron energy − 0.8 MeV, the total current of each beam - 3 kA, the cross section 0.4×7 cm and the pulse duration - 3 mcs. These sheet beams were transported on the length 1.3 m in slit vacuum channels with cross section 0.95×9 cm in the guiding magnetic field 1.7 T [4]. Next step of this series of experiments is devoted to realization of the two stage scheme. The paper presents results of the experiments and theoretical analysis of a prospect of the two stage scheme for THz pulses generation.

Experimets on pulse elongation of high-power microsecond e-beam for plasma heating in multi mirror trap GOL-3

Essential progress was achieved in experiments on heating the dense plasma in the multimirror trap GOL-3 by high-power relativistic electron beam in last few years. The beam parameters at the experiments were the following: electron energy ~1 MeV, beam current ~25 kA, beam current density in plasma ~2 kA/cm2, pulse duration 9 mus, total energy of the beam pulse ~150 kJ. Due to the high level of the current density and effect of a novel mechanism of ion heating the temperature of ions reached 2-3 keV at the electron temperature about 3 keV for the plasma density ~1015 cm-3. Energy confinement time of the plasma in these experiments has reached the level of 1 ms. The mechanism of fast ion heating is based on the collective ion acceleration along the magnetic field lines produced by high-gradients of the electron pressure in the plasma due to enhanced heating in the mirrors. The basic condition for such mechanism realization is anomalously low electron thermal conductivity along the trap axis which is provided by small scale Langmuir turbulence developing as result of two-stream instability. In order to analyze fusion prospects of such way of plasma heating in the long solenoid trap it is necessary to investigate experimentally the possibility of further increase of plasma parameters by the elongation of the beam pulse. As the first step on solving this task we have performed the experiments at the accelerator U-2 on 1.5 fold increase of the e-beam duration. Results of these experiments are presented in this paper. Conditions for durable generation in magnetically insulated diode, stable transportation and compression in the magnetic field of intense REB found in the experiments, permit us to increase the beam pulse duration from 9 mus to 14 mus with somewhat less energy of the electrons but with the same level of the energy content in the pulse. In the paper we describe the experiments on the diode voltage shaping for better matching of pulse generator with the accelerator diode as well as the results of measurements of the beam cross section by means of X-ray obscure and sectional calorimeter. Also we discuss the directions of future investigations aimed to the increase of the beam parameters in order to obtain (5-10) keV temperature of the plasma confined in multimirror trap.