V. S. Burmasov

STATUS AND PROSPECTS OF GOL-3 MULTIPLE-MIRROR TRAP

Abstract The paper reviews recent experimental results from GOL-3. Currently efforts are focused on further development of a physical database for multiple-mirror confinement systems and also on an upgrade of plasma heating systems of GOL-3 device. In general, current GOL-3 parameters demonstrate good prospects of a multiple-mirror trap as a fusion reactor.

Plasma Heating and Confinement in GOL-3 Multi Mirror Trap

Recent results of the experiments at GOL-3 facility are presented. In present configuration of the device, plasma with a density of 1014[divided by]1016 cm-3 is confined in a 12-meter-long solenoid, which comprises 55 corrugation cells with mirror ratio Bmax/Bmin=4.8/3.2 T. The plasma in the solenoid is heated up to 2-4 keV temperature by a high power relativistic electron beam (˜1 MeV, ˜30 kA, ˜8 μs, ˜120 kJ) injected through one of the ends. Mechanism of experimentally observed fast ion heating, issues of plasma stability and confinement are discussed.

Observation of spectral composition and polarization of sub-terahertz emission from dense plasma during relativistic electron beam–plasma interaction

The paper presents results of measurements of sub-terahertz electromagnetic emission from magnetized plasma during injection of a powerful relativistic electron beam of microsecond duration in plasma with the density of 3 × 1014 cm−3. It was found that the spectrum of the radiation concentrated in three distinct regions with high level of spectral power density. The first region is located near f1 = 100 GHz; the second one is in the vicinity of 190 GHz, and the third region is in the frequency interval f3 = 280–340 GHz. Polarization vectors of the emission in the first and third regions (f1 and f3) are directed mainly perpendicular to the magnetic field in the plasma. At the same time, the polarization of the radiation in the vicinity of f2 = 190 GHz is parallel to the magnetic field. The most likely mechanism of electromagnetic wave generation in the frequency regions f1 and f2 is the linear conversion of the plasma oscillations into the electromagnetic waves on strong gradients of the plasma density. Th...

Experiments with “Thin” Electron Beam at GOL-3

Abstract The latest experimental campaign at the GOL-3 multiple-mirror trap was mainly aimed at features of heating and stability of the electron-beam-heated turbulent plasma. The discussed experiments feature a reduced-cross-section electron beam with the current decreased down to 1 ÷ 1.5 kA at the current density of ~1 kA/cm2 (the same as in the “full-scale” experiments). The hot plasma cross-section decreased correspondingly. Lowered current of the electron beam became less than the critical vacuum current. This gives the possibility to make a direct comparison of regimes with the beam injection into a neutral or a preliminary ionized deuterium. New experimental results will be presented on the beam relaxation in the plasma and on heating and stability of the reduced-cross-section plasma with low central safety factor q(0) ~ 0.3. Stabilization of some MHD modes by a controlled coupling of the plasma with an exit receiver plate was demonstrated.

Development of Extended Heating Pulse Operation Mode at GOL-3

Novel technology of electron beam generation for plasma heating in GOL-3 was developed and for the first time used in the experiment. The distinctive features of the new beam are non-relativistic energy, medium power and sub-ms duration. The experiments were done at the following beam and plasma parameters: ~100 keV, ~10 MW, >100 μs, ~1020 m-3. The beam was safely transported through the 13-m-long deuterium-filled multiple-mirror solenoid. The plasma was created and then heated by the beam. Main physical task for the reported experiments was to reach quasi-stationary plasma conditions during the long-pulse beam injection.

Microwave Generation During 100 keV Electron Beam Relaxation in GOL-3

First experimental results on microwave radiation at double plasma frequency from plasma heated by ~100 keV, 2-10 MW electron beam of ~100 μs duration in GOL-3 are presented. Measurements were done in 75-200 GHz band. The spectrum was peaked at ~94 GHz at ~3·1013 cm-3 plasma density, the temporal behavior of radiated power was spiky. The generation efficiency reached ~1% of total beam power.

DYNAMICS OF ELECTRON DISTRIBUTION FUNCTION IN MULTIPLE MIRROR TRAP GOL-3

Abstract Electron distribution function in experiments with intensive beam-plasma interaction is usually non-Maxwellian with high-energy tail. Details of such distribution function can clarify physics of the beam-plasma interaction process. The paper presents new experimental data from Thomson scattering measurements at GOL-3.

EXPERIMENTS WITH LARGE-MIRROR-RATIO CORRUGATION AT MULTIPLE MIRROR TRAP GOL-3

Abstract New operation regime with a high-mirror-ratio corrugation at first 2 meters of GOL-3 plasma was studied. Five corrugation periods of 44 cm length were created with mirror ratio R ≈ 2.7 by means of special configuration of a power feed of existing solenoid coils. First data on the plasma heating, confinement and features of neutron emission from the strongly corrugated plasma in the above conditions are presented.

First Experiments on Neutral Injection in Multimirror Trap GOL-3

Abstract First stage of neutral beam heating system was developed at the GOL-3 facility. Configuration of magnetic field and initial gas distribution were adopted for operation with NBI system. As a result the neutral beam with 0.5 MW power and 0.8 ms pulse duration was achieved and stable regimes suitable for beam injection experiments were found. The neutral beam system was used in first experiment as diagnostic tool for measuring the plasma density. Dynamics of plasma density and its radial distribution were studied in experiments.

MM-wave emission by magnetized plasma during sub-relativistic electron beam relaxation

There are described electromagnetic spectra of radiation emitted by magnetized plasma during sub-relativistic electron beam in a double plasma frequency band. Experimental studies were performed at the multiple-mirror trap GOL-3. The electron beam had the following parameters: 70–110 keV for the electron energy, 1–10 MW for the beam power and 30–300 μs for its duration. The spectrum was measured in 75–230 GHz frequency band. The frequency of the emission follows variations in electron plasma density and magnetic field strength. The specific emission power on the length of the plasma column is estimated on the level 0.75 kW/cm.