L. N. Vyacheslavov

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 3u2009×u20091014u2009cm−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 f1u2009=u2009100u2009GHz; the second one is in the vicinity of 190u2009GHz, and the third region is in the frequency interval f3u2009=u2009280–340u2009GHz. 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 f2u2009=u2009190u2009GHz 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...

Temporal structure of double plasma frequency emission of thin beam-heated plasma

In the work presented here dynamics of spiky microwave emission of a beam-heated plasma near the double plasma frequency in ∼100 GHz band was studied. The plasma is heated by 80u2009keV, ∼2u2009MW, sub-ms electron beam that is injected into the multiple-mirror trap GOL-3. The beam-heated plasma diameter is of the order of the emitted wavelength. Modulation of individual emission spikes in the microwave radiation is found. The radiation dynamics observed can be attributed to a small number of compact emitting zones that are periodically distorted.

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.

Heating of tungsten target by intense pulse electron beam

A test facility for experimental simulation of transient heat loads in ITER divertor with the use of high power electron beam is developed at the Budker Institute of Nuclear Physics. This report presents an experimental study of the absorption of the electron beam with an incident heat power flux of 10-50 GW/m2 on the area of about 2 cm2 of a tungsten target. The electron beam has duration of 0.1-0.3u2005ms and electron energy of 80-95 keV, Diagnostics for measuring of the beam parameters on the target are briefly discussed. Results of measurement of the beam profile and calorimetry of beam energy deposited in tungsten sample at ELM-like heat load are presented.

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.

Observation of dust particles ejected from tungsten surface under impact of intense transient heat load

A test facility for experimental simulation of transient heat load expected for ELMs type I events in ITER is developed at BINP SB RAS. Dynamics of tungsten particles in the ablation plume is investigated by small-angle light scattering technique and using fast CCD and ICCD cameras. The threshold of intense particle generation, sizes and velocities of particles ejected from the surface are estimated.

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.

Observation of the tungsten surface damage under ITER-relevant transient heat loads during and after electron beam pulse

Wide-area (2u2005cm2) high-power (up to 7 MW) submillisecond electron beam source was applied for generation of intense pulsed heat loads on tungsten sample. Various diagnostics sets were used for in-situ research of the surface damage: IR imaging of the front view of the target, capturing of the reflection pattern of continuous wave laser radiation, recording of intensity of thermal radiation from several spots of the surface. Sample was exposed to a various heat loads near and above melting threshold. Formation of the crack network on the surface and its development with successive pulses was observed. Two-dimensional temperature distribution was obtained after heating at the cooling stage. Melting and spalling of material were shown on severe damaged target. Propagation of the cracks along the surface at a depth of 0.1 – 0.2u2005mm was revealed with transverse microsections. Circular motion of the molten layer was found with subsequent exposures.