Critical voltage of a rotating plasma

Abstract

The accessible voltage levels have been determined for a rotating plasma device in which the confinement region surrounds a ring-shaped coil that is suspended by a single rod. (i) There exists a sharply defined critical voltage and a corresponding velocity limit which cannot be exceeded by a moderately large power input. This is clearly shown with the present apparatus where the plasma voltage slowly approaches the critical level from below and where the insulator consists only of a narrow rod. (ii) The critical voltage increases with the mean radial ratio r 0/r w in the plasma. This ratio is defined by a magnetic field line which intersects the midplane of the device at a radial distance r 0 from the axis of symmetry, and cuts the end insulator at the corresponding distance r w. (iii) The results can be explained by an interaction between the plasma and a neutral gas layer at the insulator surface that limits the velocity to the critical value v c earlier introduced by Alfvén. As a consequence, the velocity limit becomes (r 0/r w)v c in the equatorial plane. Deductions of the corresponding voltage limit agree with the experiments, (iv) The plasma is heavily disturbed even by a very small obstacle which is introduced in the equatorial plane. This indicates that the losses of the system are small under normal operation, (v) So far the stability, is not influenced by the fact that most of the field lines pass freely around the confinement region and do not end upon an insulator surface.

Alfvén ionization in an MHD-gas interactions code

“…This limit can only be exceeded once the plasma is almost entirely ionized meaning total ionization is associated with a sharp rise in plasma velocity. Many other similar laboratory experiments subsequently verified the presence of a critical velocity in several different kinds of discharges (Angerth et al, 19 Lehnert et al; 20 or reviews by Danielsson 21 and Sherman, 22 for example) and also in industrial discharges, such as thin film deposition magnetron plasmas. 23 There is also a number of results from astrophysical observations that show the existence of a critical velocity ionization process.…”

Wave–particle interactions in rotating mirrors

“…7,12 Because of the electrodes, there must be sufficient conductivity along the field lines to carry power and maintain the rotation. If instead the rotation is produced by waves, the plasma density could be reduced where the field line intersects the containment vessel.…”

An asymptotic state of the critical ionization velocity phenomenon

“…In 1954, Alfv6n postulated that rapid ionization of a neutral gas occurs when it moves through a magnetized plasma with a velocity whose component perpendicular to the magnetic field exceeds a critical value v c. Alfv6n [1954] suggested that v c is given by equating the kinetic energy of the neutral atoms to their ionization energy •bi, i.e., Vc = (2cki/m) •/2. Since then the critical ionization velocity (CIV) phenomenon has been confirmed by laboratory experiments (e.g., by Fahleson [1961], Lehnert et al [1966], Himreel et al [1976], and Mb'bius et al [1979]) and by neutral gas release experiments in the auroral ionosphere [Haerendel, 1982]. It has been discussed in connection with the shuttle glow [Papadopoulos, 1984] and as a means of providing rapid ionization in various astrophysical situations [Galeev, 1981;Formisano et al, 1982].…”