V. Skalyga

Plasma creation by terahertz electromagnetic radiation

The results of experiments aimed at the study of the discharge in a focused beam of terahertz waves in argon under near-atmospheric pressures are presented. The range of electric fields and gas pressures, at which a breakdown occurs, is determined. The study of the discharge glow dynamics showed that the discharge starts at the maximum of the terahertz wave beam field and its front moved towards the radiation with the speed of about 105 cm/s into the region of the fields being significantly weaker than the breakdown value. Measurements of the ratio of wave transmission through the discharge allow one to conclude that the density of the plasma produced in the discharge exceeds 1015 cm−3. Some features of the terahertz discharge are discussed.

Scaling for ECR sources of multicharged ions with pumping at frequencies from 10 to 100 GHz

One of the major trends in the development of ECR sources of multicharged ions is an increase of the extracted ion current. The main factor affecting the current of an ion beam produced by such a source is, obviously, the density of the plasma from which ions are extracted. In the present article the mean ion charge, the ion current density, and the minimal microwave power required to sustain needed electron temperature are calculated for a broad range of plasma densities (up to 1014u200acm−3, which corresponds to 90 GHz cutoff frequency of microwave pumping). The electron temperature is taken as granted and no effects due to instabilities are considered. The distinguishing future of the analysis performed is that it takes into account alteration of the regime of plasma confinement, which occurs as the plasma density is increased. If the plasma density exceeds a certain threshold, the classical Pastukhov’s regime of plasma confinement is replaced by the quasi-gas-dynamic regime. It is demonstrated, in particu...

Prospect for a 60 GHz multicharged ECR ion source

The conceptual design of a fourth generation hybrid electron cyclotron resonance (ECR) ion source operated at 60 GHz is proposed. The axial magnetic mirror is generated with a set of three Nb3Sn coils, while the hexapole is made with room temperature (RT) copper coils. The motivations for such a hybrid development are to study further the ECR plasma physics and the intense multicharged ion beams production and transport at a time when a superconducting (SC) hexapole appears unrealistic at 60 GHz. The RT hexapole coil designed is an evolution of the polyhelix technology developed at the French High Magnetic Field Facility. The axial magnetic field is generated by means of 3 Nb3Sn SC coils operated with a maximum current density of 350 A/mm2 and a maximum coil load line factor of 81%. The ECR plasma chamber resulting from the design features an inner radius of 94 mm and a length of 500 mm. The radial magnetic intensity is 4.1 T at the wall. Characteristic axial mirror peaks are 8 and 4.5 T, with 1.45 T minimum in between.

Experimental evidence on microwave induced electron losses from ECRIS plasma

The balance between warm and hot (>1u2009keV) electron density and their losses from the magnetic confinement system of an Electron Cyclotron Resonance Ion Source (ECRIS) plasma is considered to be one of the main factors determining the rate of the high charge state ion production. One of the key loss channels for heated electrons is thought to be induced by the injected microwaves. While this loss mechanism, referred to as rf-induced pitch angle scattering, has been studied theoretically and with computational tools, direct experimental evidence of its significance in minimum-B ECRIS plasmas remains limited. In this work, experimental evidence of microwave induced electron losses in the axial direction is presented in both continuous wave (CW) and pulsed operation of a 14u2009GHz ECRIS. In the CW mode, the experiment was carried out by comparing the characteristic X-ray emission from the plasma volume and from the surface of the biased disc located in the flux of the escaping electron at the axial magnetic mirror. Parametric sweeps of magnetic field, neutral gas pressure, and microwave power were conducted to determine their effect on electron losses. In the pulsed mode, the experiment was conducted by measuring the flux of escaping electrons through aluminum foils of different thicknesses providing some energy resolution. Both diagnostics support the view that rf-induced losses account for up to 70% of total hot electron losses and their importance depends on the source parameters, especially power and neutral gas pressure.

Plasma creation by a powerful electromagnetic radiation of terahertz gyrotrons

Summary from only given. The study of the discharge in a focused beam of terahertz radiation in argon at pressures close to atmospheric was made. The range of breakdown electric fields and gas pressures at which the discharge occurs was determined. Discharge, had started at the focus of the beam, propagated in the region of weak fields, where the value of the intensity was substantially less than the breakdown one. The investigation of the discharge glow dynamics was made and it was shown that its front had moved towards the radiation with the speed of about 105 cm/sec. The estimation of the plasma density was made on the basis of the terahertz wave transmission coefficient measurements, and the value of the density exceeded the value of 1015 cm-3. The features of the discharge excited by radiation of the terahertz frequency range and its possible applications are discussed.

Short pulse ECR ion sources of multicharged ions

Present work is devoted to demonstration of possibility of short pulsed (< 100 µs) multicharged ion beams formation by ECR ion source sustained by millimetre waves. Such investigations were stimulated by “Beta Beam” project¹.