Supersonic Wind at Low Pressures Produced by Arc in Magnetic Field

Abstract

T HE properties of a low pressure discharge are greatly modified by the presence of a transverse magnetic field of several thousand gauss. The over-all behavior, here described, is believed to be unique to values of gas concentration for which the mean free time of the electrons is much greater than their cyclotron periodicity, and the mean free time of the ions much less than their cyclotron periodicity. The experiments were performed inside a large vacuum chamber having a volume of approximately one cubic meter. When the arc is in a large unconfined region, wind effects are observed which are not present when the discharge is in a small glass tube. Figure 1 illustrates the general appearance of an arc at 0.5 millimeter pressure, transverse to a magnetic field of 6000 gauss. The voltage gradient is approximately 100 volts/cm, and the power input and the current density are many times larger than when the magnetic field is not present. The arc column, in air or nitrogen, is pale blue and quite transparent. Although the power dissipated in the positive column of the arc is more than one-half kw/cm of arc length, the gas temperature is surprisingly low because of the cooling effect of the wind. This temperature is greatly dependent on the manner in which the wind is circulating inside the chamber, and to what extent it is cooled during the recirculating process. Observations based on the melting point of chemical salts indicate that in most cases the arc temperature is less than 600 degrees centigrade.When the air flow is blocked by placing a ceramic sheet on the ''downwind" side of the discharge, the arc flattens out against the sheet and forms a white hot surface layer. If the sheet is placed on the "upwind" side of the arc, so as to block the air from entering the region, the arc then spreads out in all directions. Under such conditions, manometer pressure measurements show that the discharge is acting like an air pump. The air pressure on the side of the ceramic sheet which is adjacent to the arc is about 20 percent of the pressure on the opposite side of the sheet.

Rotating Plasmas

“…Since x b is likely to be much smaller than the characteristic dimensions L c of cosmical systems, this mechanism may become more pronounced in cosmos than the separation effect by the centrifugal force discussed later in Section 2. 8. The present diffusion process provides a possible explanation of the observed abundance anomalies of some rare elements in magnetized stars and of helium in the solar wind during active events [56][57][58]97].…”

“…Similar arrangements also provide a convenient method of producing rotating plasmas in the laboratory, where an applied electric field generates a radial electric current across the magnetic field. Electromagnetic 'wind generators' of this kind were constructed and investigated by Early et al [8,9], and a number of ion sources were studied by Smith and Luce [10]. Baker and Anderson [11]suggested the use of the same arrangement for the containment and heating of a thermonuclear plasma in the so-called 'Homopolar' device, and Boyer et al [12] designed a modified device called 'Ixion 1 , having a central plasma electrode and magnetic mirrors at its ends.…”

Hydromagnetic Capacitor

“…Aside from the term in g, this is just the equation 3 for a polarizable medium having a dielectric constant K. that is 1 as expected, identical with the K defined by Eq. (5). The effect of the viscosityt~rm (gc 2 /B 2 )E is to provide for a leakage current density through the dielectric medium.…”

Voltage characteristics of a rotating plasma

“…The present paper concerns the situation where the rotation is produced by an electric current which is generated by external sources and which flows across the magnetic field. Arrangements of this kind have earlier been reported by a number of authors [1]- [4] (see also [5]).…”