V. D. Stepanov

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.

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.

Energy Spectrum of Electrons in Flow from Plasma Column Heated by REB at GOL-3 Facility

Abstract Efficiency of the beam–plasma interaction was investigated for the case of small radial size intense E-beam on the base of the energy spectrum measurements with multifoil analyser. This shows good prospects of such beams for reactor applications.

Submillimeter radiation production by intercavity stimulated scattering in planar FEM at the ELMI-device

This paper describes main features of a project on two- stage generation of submillimeter radiation pulses at ELMI-device. In this project one sheet beam will drive 2D Bragg planar FEM in which intensive 4-mm radiation accumulated in the FEM resonator, is used for stimulated scattering on the another sheet beam.

Experimental and Theoretical Investigations of High Power Sub-Millimeter Wave Emission at Two-Stream Instability of High-Current REB

Sub-mm radiation can be generated by conversion of plasma waves into electromagnetic (EM) radiation at strong Langmuir turbulence (LT) via the two-stream instability induced by a high current relativistic electron beam (REB). A plasmon scattering on plasma density fluctuations produces EM emission at the plasma frequency ωp (“ωp process”). Nonlinear plasmon-plasmon merging results in the generation of photons nearby the 2nd harmonic of the plasma frequency 2ωp (2ωp process”). For plasma densities 1020-1021 m-3, these frequencies are in the range of sub-mm waves: 180-566 GHz. The power density of sub-mm-wave emission from plasmas in the multi-mirror trap GOL-3 (BINP) during injection of a 10-μs-REB at plasma densities ne ≈ (1-5)·1020 m-3, electron temperatures Te ≈ 1-3 keV and magnetic field B ≈ 4 T was measured to be up to 1 kW/cm3 in the frequency band above 100 GHz. To calculate the second harmonic emission power from turbulent magnetized plasma we use the model of coalescence of two upper-hybrid waves. Results of these calculations and measured power are in good coincidence in the investigated area of plasma density.

Study of Plasma on the GOL-3 Facility by Imaging VUV Spectroscopy

Abstract The series of experiments on plasma heating by the electron beam of reduced diameter was carried out at the GOL-3 facility. To define the size of a high-temperature plasma region the imaging VUV spectrometer was used in these experiments. In the paper the description of the diagnostic system, the results of measurements, the comparison with simulation data of the ionization balance are presented. Estimations of transverse diffusion and macroscopic movements of the beam are discussed.

Theory of a planar free-electron maser with transverse electromagnetic flux circulation in a 2D Bragg mirror

A planar free-electron maser with a resonator consisting of a 2D entrance Bragg mirror and a 1D exit Bragg mirror is theoretically studied in the framework of a nonstationary 2D model. In such a configuration, the 2D Bragg mirror provides synchronization of the radiation emitted by a wide (compared with the wavelength) ribbon-shaped electron beam. The transverse electromagnetic energy fluxes arising in this mirror are closed through an additional coupling waveguide, which provides a single-mode single-frequency masing regime insensitive to variation of the beam parameters over wide limits.

4 MM wave generation in two-channel planar FEM at strong electrodynamic coupling of channels

Two-dimensional (2-D) distributed feedback gives the opportunity to construct generators of a coherent electromagnetic wave flux with very wide cross-section. We study such mechanism of spatial synchronization of electromagnetic oscillations for the case of a planar free electron maser (FEM) at the ELMI-device (INP, Novosibirsk)1. The FEM-oscillator consists of two channels driven by two sheet electron beams (1 MeV/ 1 kA/ 5 μs). Each channel contains a hybrid two-mirror cavity that is composed of upstream 2-D and downstream 1-D Bragg reflectors. The transverse sizes of the reflectors essentially exceed the radiation wavelength. Nevertheless, we have experimentally demonstrated well reproducible single-mode mm-wave generation regime of each channel due to the 2-D distributed feedback. In the first experiments at weak interchannel diffraction coupling the radiation pulses with the following parameters: frequency ~75 GHz, close to one of the cavity eigenmodes, spectrum width ~20 MHz, pulse duration ~200 ns and power-few tens of MW were obtained1.

Formation of high-brightness REB to generate THz radiation in beam-plasma system

Summary form only given. Terahertz emission from plasma with strong Langmuir turbulence excited by high current relativistic electron beam (REB) is experimentally studied at the GOL-3 facility (BINP). The typical parameters of the beam used in the experiments, were the following: 0.6÷0.8 MeV/20 kA/10 μs. In recent experiments the beam current density was about 1÷2 kA/cm2 in a plasma column with the density ~ 2·1014 cm-3 that allowed us to get sub THz-emission with a power of a few kW/cm3 in the frequency range 100÷400 GHz. To extend our experiments on emission to the range of 1 THz we have to inject the beam into the plasma column of higher density 1÷2·1015 cm-3. This level of the plasma density requires the substantial increase of the beam brightness in the plasma. To solve this problem we have performed 2-D self-consistent simulations by numerical code POISSON-2 for the beam formation at different geometries of a magnetically insulated ribbon diode. In addition, the transformation of the generated ribbon beam to a circular one and its compression to the radius ~2 cm in the magnetic field ~4 T in which the plasma column is placed, were also considered in the computer simulations. To determine the brightness of the beam we have measured the beam current density and the angular spread of the beam electrons after the transformation and compression of the beam cross-section. The comparison of the experimental and simulation data has been done. The obtained results are used for the design of a new diode configuration with high brightness of the beam.