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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.

Summary form only given. Fast plasma heating in a multi-mirror magnetic trap by a high-current beam of relativistic electrons is a promising way to achieve fusion-grade plasma parameters. A high-level Langmuir turbulence develops during the beam-plasma interaction. These high-energy-density plasma oscillations can generate electromagnetic (EM) radiation in a wide frequency range extending from the plasma frequency to its 2nd harmonic. Thus the spectrum of EM emission can achieve 1 THz at 3·1015 cm−3 plasma density. The first experiments on the generation of sub-mm waves by a beam-heated plasma carried out at the GOL-3 facility were presented in [1]. Here we present results on sub-mm wave generation for plasma densities 1014–1015 cm−3 during injection of a relativistic electron beam (≤ 0.8 MeV, 30 kA, ∼10 ms).

One of possible ways to generate submillimeter wave and THz radiation is to use transformation of plasma waves into electromagnetic radiation at strong Langmuir turbulence [1]. We had already described some implementation of such method at the GOL-3 experiments [2–4], wherein the mechanism of plasma heating was recognized as the excitation of strong Langmuir turbulence (LT) via a two-stream instability induced by the propagating high current beam. The detailed theoretical consideration of LT-induced electromagnetic emission from turbulent plasmas distinguishes two main processes responsible for electromagnetic radiation emission during the beam-plasma interaction at GOL-3. First, plasmon scattering on plasma density fluctuations yields electromagnetic emission at the plasma frequency ω p (“ω p -process”). Second, plasmon-plasmon merging results in production of photons in the vicinity of the double plasma frequency 2ω p (“2ω p -process”). For plasma densities of 1014–1015 cm−3, corresponding output radiation frequencies are located in the range from mm to sub-mm waves, ω P /2π ≌ 90–283 GHz, 2ω P /2π ≌ 180–566 GHz.

Paper presents results of investigations of electromagnetic radiation emission in a submillimeter range at strong Langmuir turbulence pumped by a relativistic electron beam. Radiation at double plasma frequency is generated due to plasmon-plasmon merging. Results of radiation power measurements are compared with theoretical estimations.

Study of Langmuir turbulence (LT) in plasma and LT-induced nonlinear phenomena remains an important topic of the fundamental plasma science. A distinctive LT's feature is possibility of electromagnetic radiation emission on plasma frequency (ν p ) and dual plasma frequency (2ν p ) due to processes of plasmon conversion on plasma density fluctuations and plasmon-plasmon merging respectively. Well-identified in solar radio-flares, these processes remained weakly studied in laboratory plasmas.

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 about 10 ms, total energy of the beam pulse ∼150 kJ [1]. 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 [1]. Energy confinement time of the plasma in these experiments has reached the level of 1 ms. The basic condition of such parameters achievement is anomalously low electron thermal conductivity along the trap axis which is provided by small scale Longmuir turbulence developing as a result of two-stream instability [2]. In order to analyze a prospect of further increase of plasma parameters for reaching a fusion area, to elongate the beam pulse duration was decided. As the first step on solving this task we are performing the experiments at the accelerator U-2 on 1.5 fold increase of the E-beam duration. To investigate in more details the process beam-plasma interaction we carry out measurements on temporal dynamics of the plasma electron distribution function in the range of 0–5 keV and on evolution of energy distribution functions of the beam electrons as well. We also measure an electromagnetic radiation gone out from the plasma column as result of transformation of two Langmuir waves in electromagnetic one in strong turbulent plasma. This electromagnetic radiation is measured in the frequency band 210−550 GHz. Results of the pointed experiments and their discussion are presented in this paper.

Collective interactions of a microsecond electron beam with a plasma and its fast heating is being investigated at the GOL-3-II facility. This activity is mainly directed for production of a hot dense (10/sup 15/-10/sup 17/ cm/sup -3/) plasma in long open trap in order to study the multimirror and "wall" confinement of such a plasma. The plasma that is already obtained and can in principle be obtained in this facility is of interest for a broad spectrum of applications, like controlled fusion, a pulsed neutron source, X-ray flash lamps, UV laser etc. Recent results performed at the GOL-3-II facility are presented. These are beam energy losses, plasma heating and electron and ion temperature measurements.