The work reports the achievement of an energy content of 10 J per microsecond pulse in a directed flux of electromagnetic radiation in the frequency range of ~ 0.2–0.3 THz. The flux is generated by a fundamentally new method, which is realized through the pumping of upper-hybrid plasma oscillations in a magnetized plasma column with a relativistic electron beam (REB) and their subsequent transformation into a flux of electromagnetic radiation. In the described experiments at the GOL-PET facility, this method to generate THz radiation is implemented in the following way a beam of electrons with energy E ~ 0.5 MeV with a current density of (1–2) kA/cm2 is passing through a magnetized (4 T) plasma column with a density of 1014–1015 cm–3. By comparing the experimentally measured spectral composition of the radiation flux with the calculated spectrum, it is proved that this process is realized through resonant pumping of the branch of upper-hybrid plasma waves by such beam. A coordinated increase in plasma density and beam current density opens up the prospect of advancement in the generation of multi-megawatt radiation fluxes in the region of one terahertz.

One of the possible applications of high-current relativistic electron beams (REBs) is to generate electromagnetic waves at plasma frequencies due to the propagation of a beam through a magnetized plasma column. Research work in this direction, aimed at creating terahertz radiation sources at the BINP, is underway using the GOL–PET facility. We study the relaxation of a REB beam with a current density of (1–2) kA/cm2 in a magnetized plasma column with a density of 5 · 1014 cm–3. The purpose of these studies is to create a pulse radiation source with a power of tens of megawatts in the frequency range 0.1–1 THz. To date, a radiation flux with a power level of 10 MW and a maximum power spectral density in the frequency range 150–200 GHz has been achieved in the experiments. Further progress in these studies was related to the experimental establishment of the dependence of the power and spectral composition of the radiation flux on the parameters of the injected beam, in particular, its current density. The current density of the injected beam was varied due to the different compression of the beam cross section by the magnetic field. The results of measuring the characteristics of the radiation flux are presented in correlation with the results of measurements of the beam current density and plasma density.

This paper reports on the generation of a directed flux of electromagnetic radiation with an energy content of 10 J in the frequency range of 0.2–0.3 THz at a microsecond pulse duration in a beam–plasma system. The flux is generated when a relativistic electron beam (REB) pumps electron plasma waves in a magnetized plasma column. In the described experiments, this fundamentally new approach to generate terahertz radiation was carried out at the GOL-PET facility in the conditions of varying the beam current density and the plasma density in the appropriate ranges of 1–2 kA/cm2 and 1014–1015 cm–3. From the comparison of the flux energy spectrum measured experimentally in the frequency range 0.15–0.45 THz with the calculated one obtained using the previously proposed model of radiation generation in a beam–plasma system it was shown that this process occurs through resonant pumping by REB of precisely the branch of upper-hybrid plasma waves. Mastering this new method to generate terahertz radiation opens the prospect of its use to obtain multi-megawatt radiation fluxes in the frequency range up to 1 terahertz and higher. For such a development approach the most promising beam for pumping plasma oscillations seems to be a kiloampere REB generated in a linear induction accelerator.

Research on one of the methods for generation of high-power radiation flows in the subterahertz/terahertz frequency range using the GOL–PET facility is underway at the G. I.Budker Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences (BINP SB RAS). This method consists in using the mechanisms of conversion of the plasma waves excited by a relativistic electron beam (REB) into an electromagnetic radiation flow. In the course of research, a number of mechanisms by which plasma oscillations are converted into radiation were revealed, and a power level of 10 MW was experimentally achieved in a directed submillimeter radiation flow with a duration of a few microseconds. This paper is devoted to the study of radiation generation as a function of the degree of compression of the REB cross section. The compression degree was varied in the experiments by varying the magnetic field distribution along the axis of the facility. The magnetic field was varied uniformly along the entire facility axis. In addition, the configuration with an increased ratio of fields in the accelerator diode and in the plasma section of the facility was considered. As a result of the experiments, it was shown that a decrease in the strength of the guiding magnetic field by a factor of 1.6 does not lead to a change in the radiation generation mechanism.

In Budker Institute of Nuclear Physics (BINP), experimental and theoretical studies of generation of submillimeter electromagnetic radiation with characteristic frequencies 0.1–0.5 THz under conditions of intense plasma–beam interaction are carried out. Generation of radiation occurs in the specialized G-OL‑PET facility during collective relaxation of pulsed relativistic electron beam (REB) with the following parameters: electron energy 0.6 MeV, beam current 15 kA, and pulse duration 5 µs in a plasma column with plasma density (0.5–1) × 1015 cm–3, under conditions of its confinement in a vacuum chamber with a corrugated magnetic field (the ratio of the maximum and minimum values of magnetic induction in the corrugations is Bmax/Bmin = 4.5/3.2 T). An important feature of the carried out studies is the presence of specifically created inhomogeneities both in its cross section and along its length. In experiments carried out earlier under the same conditions, a high level of power (about 10 MW) was reached in the flux of submillimeter radiation going out into the atmosphere. Radiation energy of 7 J was reached at pulse duration of 0.5 µs, which is limited by the high-frequency breakdown at the vacuum side of the output window. This article is devoted to the problem of increasing the duration of the pulse of generated submillimeter radiation of such a high power. This is attained by suppressing high-frequency (HF) breakdown near the surface of the window through which the radiation flux is going out into the atmosphere and by increasing the duration of megavolt radiation pulse applied to the accelerator diode in which REB is generated.

Experiments on pulse generation of submm electromagnetic waves are carried out at GOL-PET facility in Budker Institute of Nuclear Physics. The generation is realized in the process of relativistic electron beam interaction with a plasma column. Recently, the experiments have demonstrated the multi-megawatt power generation of 1 mm wavelength radiation at pulse duration up to 3 µs [1] . Evolution of the energy distribution function of the beam electrons as a result of the beam-plasma interaction is very important characteristic of this process. Firstly, measuring this function permits to evaluate the efficiency of the beam energy deposition in plasma. Secondly, analyzing the evolution of the function in correlation with the time behavior of the power and the spectral composition of the radiation outgoing from the plasma column during the E-beam pulse at various experimental conditions allows one to understand the physics mechanism of the wave generation.

Studies on the generation of electromagnetic radiation during beam-plasma interaction are of considerable scientific interest from the standpoint of analyzing the results of astrophysical observations [1] . Such studies look no less important from the standpoint of solving a wide range of practical problems using high-powerful submillimeter radiation. Experimental and theoretical studies on multimegawatt power submillimeter wave generation due to intense interaction of a relativistic electron beam (REB) with a magnetized plasma column are carried out in BINP SB RAS [2] . In the experiments performed at the GOL-PET facility, the beam with parameters 0.5 MeV/15 kA/6 μs was propagated in a magnetized (induction up to 4.7 T) plasma column with the diameter 6 cm, length 2 m and density (1÷2)x10 15 cm -3 . A radiation flux generated due to beam-plasma interaction was extracted in atmosphere through an output fluoroplastic window of 18 cm diameter. We measured the power and the spectral power density of this flux in the frequency band 0.1÷0.8 THz for various plasma density distributions. The radiation angular distribution of the output flux propagated in the hall atmosphere was also measured. The experiments have shown that the maximal spectral power density of the flux power is located in the frequency range 0.2÷0.35 THz that is the area of the upper-hybrid frequency of plasma oscillations. The value of the spectral power density in this frequency interval depends on the plasma density distribution over the plasma column diameter and on the law of density decrease along the axis at the beam output from the column. The experimental results are discussed in comparison with analytical and computer modeling.

Project of powerful submillimeter wave generator based on intense interaction of a relativistic electron beam with a magnetized plasma is developed at BINP RAS in collaboration with NSU. In presented experiments at the GOL-PET facility, the beam with parameters 0.8 MeV/15 kA/6 μs is injected into a magnetized (induction up to 4.7 T) plasma column with diameter 6 cm, length 2.5 m and the density 8x1014 ÷2 x1015 cm−3 [1]. Experiments showed that at this plasma density, the emission from the beam-plasma system is concentrated in a flux directed along the axis of the column. We measured the power and the spectral composition of this flux in the frequency band 0.1÷0.8 THz. Our studies were focused on the role of strong plasma density gradients in generation of the flux.

The system is described for the preliminary plasma creation in the GOL-PET facility. Currently, after this system was considerably reconstructed, it is based on a high-voltage discharge system with pulsed gas injection. The new system was studied on the subject of whether, with its help, it is possible to create preliminary plasma with different longitudinal and transverse density distributions. The results obtained are presented which seem to be encouraging.

The power of electromagnetic emission near the plasma frequency during collective electron beam-plasma interaction is found to be significantly increased in a plasma with preformed large-amplitude density perturbations. Laboratory experiments at the GOL-PET facility show that injection of a kiloampere relativistic electron beam into a magnetized plasma with strong radial density gradients is accompanied with an order of magnitude more intense generation of sub-millimeter waves than in the case of smooth density profile. As a possible mechanism for the enhanced generation of the longitudinal radiation flux observed in these experiments, we discuss the direct beam pumping of longitudinally propagating electromagnetic plasma modes due to their coupling with the Doppler shifted beam branch in the presence of oblique modulation of plasma density.

Based on the regularities of the electron absorption in the ring collectors a new method for reconstructing the angular distribution function of the magnetized electrons has been worked out. To realize it the angular spread detector with a cylindrical channel of a variable cross-section was developed and applied in an experiment with a high-current electron beam. The results of the measurements with this detector have demonstrated the possibility to achieve an angular spread of 0.1 rad level in microsecond high-current beams generated in a magnetically insulated diode with an explosive-emission cathode at a voltage of similar to 1 MV.

Introduction The beam-plasma interaction system allows one to generate high-power sub-mm waves (frequency interval 0.1÷1 THz) by usage of mechanism of plasma wave transformation [1]. This way gives possibility to achieve multi megawatt power with the promptly varying frequency that can be necessary for various practical applications. The original project of a sub-mm wave based on transformation of plasma waves pumped by a kA-current relativistic electron beam is developed at the GOL-PET facility. We present novel results on the study of mechanisms of sub-mm wave emission by the processes of plasma wave transformation in electromagnetic one in case of the strong beam-plasma interaction.

Results of spectral and magnetic diagnostics of plasma differential rotation in the GOL-3 multiplemirror trap are presented. It is shown that the maximum frequency of plasma rotation about the longitudinal axis reaches 0.5 MHz during the injection of a relativistic electron beam into the plasma. The data of two diagnostics agree if there is a region with a higher rotation frequency near the boundary of the electron beam. Plasma differential rotation can be an additional factor stabilizing interchange modes in the GOL-3 facility.

In the problem on motion of magnetized relativistic electrons in a cylindrical channel with the radius comparable with characteristic Larmor radius of the electrons, a distribution of electrons with arbitrary initial angular spread absorbed in the channel wall along its axis is found. The solution is obtained by 3D modelling taking into account the reflection of electrons from the cylindrical surface of the channel. Basing on the received solution the multichannel detector of the electron angular spread in the form of sequential absorbing collimators with gradually decreasing diameter is constructed and tested in a real experiment. Mathematical procedure to find the angular distribution function of the electron velocities from the measurements of the collimator currents is described.