Anomalous resistance of plasmas in sub-critical electric fields

Sizonenko, V.L.; Степанов, К.Н.

doi:10.1088/0029-5515/10/2/008

Cited by 28 publications

(14 citation statements)

References 4 publications

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“…Field penetration into plasma with varying particle temperatures over time has been considered in a number of papers. In [3][4][5][6][7], skin effect is described under conditions of turbulent heating of electrons. Nonlinear penetration of monochromatic field into plasma with ion-acoustic turbulence was studied in [8,9].…”

Section: Introductionmentioning

confidence: 99%

Penetration of a Heating Electromagnetic Pulse into Plasma in Magnetic Field

2022

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Penetration of a heating pulse of quasistationary electromagnetic field into plasma in constant magnetic field directed along its surface was studied. Weakening of electron heat transfer across the magnetic field leads to more efficient heating of electrons near the plasma surface. As a result, the penetration of the field into the plasma decreases, which is accompanied by suppression of the “inverse” skin effect. Inhomogeneous heating of electrons across the magnetic field leads to generation of an electric field strength component orthogonal to both the magnetic field and the direction of temperature gradient. Appearance of the additional field strength component leads to a change in polarization of the reflected pulse. In a sufficiently strong magnetic field, due to suppression of the electron heat flux and less significant effect of the magnetic field on the ion heat flux, a state with large difference of electron and ion temperatures occurs.

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Section: Introductionmentioning

confidence: 99%

Penetration of a Heating Electromagnetic Pulse into Plasma in Magnetic Field

2022

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“…These conditions agree qualitatively with theory, which states that the high-energy ion component arises from linear damping of ion-acoustic waves, 3 and that the ultimate temperature depends directly upon the heating duration T H , when the energy decay time T L is long. 5 We know from previous microwave scattering measurements of the turbulence spectrum that the ion-acoustic wave level is high during the unstable period (between a and c in Fig. I), 2 and from transport measurements that the loss rate during heating is only about the Bohm diffusion rate.…”

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confidence: 94%

“…Using the equation for skin depth 6,5 (jj pe \ 00 / W 0 W the two initial conditions should lead to currentpenetration depths of 10 and 3 cm, respectively, where a> = 2TT(3X10 5 ) = 1.9X10 6 .…”

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confidence: 99%

Skin Effect and Anomalous Resistivity Accompanying Turbulent Heating

1971

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In turbulent heating experiments the electrical resistivity is anomalously large, once turbulence has developed. But before turbulent levels build up in a dense, collisionless plasma, the high conductivity can cause a skin effect that impedes current penetration. We find that this skin effect has an influence on the onset of current-driven instabilities and on the ultimate heating. Low levels of residual turbulence before heating are found to play a role in the rate of current penetration.In this experiment, intense small-scale current-driven instabilities grow to nonlinear levels, producing a rapid heating of ions and electrons to kilovolt temperatures. The electron drift velocity exceeds the ion sound speed and the ion thermal speed, but is always smaller than the electron thermal speed. The apparatus has been described in the literature. 1 " 3 Two conical-pinch guns inject plasma through hollow electrodes into either end of a 2:1 magnetic mirror field of 3000 G, in a vacuum chamber 40 cm in diameter and 200 cm long. The plasma column, 8 cm in diameter and 180 cm long, reaches a maximum density of 8xl0 13 cm" 3 about 30 jusec after injection. Turbulent heating is accomplished by applying a 50-200-kV pulse between the hollow electrodes, driving currents up to 13 000 A along the magnetic field. Voltage 100, PLASMA CURRENT 3 en 2 *1 O 1 > n i -\ HARD X-RAY I SIGNAL N K . i , i 0 1 2 3 4 TIME (JSEC FIG. 1. Voltage, current, and hard x-ray signals. Instability begins at a and ends at c. and current wave forms for typical operation are shown in Fig. 1. Because of series inductance, the initial current is zero, then rises sinusoidally until the electron-drift velocity eventually exceeds the threshold for current-driven instabilities, indicated by dotted line a. This circuit connection gives the "constant-current" mode of operation referred to in computer simulation experiments, 3 in which changes in plasma resistivity produce voltage fluctuations, with little influence on the current. The plasma column inductance of 0.6 MH, which remains nearly constant during the rise and fall of turbulence, combined with the external inductance of 3 p.H gives an oscillation frequency of 300 kHz.At the instant the heating current pulse is applied, the plasma column has an electron density n e between (2 and 8)xl0 13 cm" 3 , and a conductivity a between 10 and 100 mho/m, depending upon settings. 3 ' 4 The conductivity versus time is shown in Fig. 2. Curves A, B and A', B f are 150, SATURATION ;100h O I 5 > 50 O D Q Z o o 60 40 TIME |JSEC FIG. 2. Conductivity versus time. Curves A, B and A'', B' are from data of an rf conductivity probe. Curve C is from analysis of voltage and current traces, removing inductive effects. A: a 0 «50 mho/m. B: a 0 «10 mho/m. 499

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“…T.~(i Jpe t) 3/2 m e u 2 (2 m e /m.) 2 i.e. if t increases the ions start being heated up more quickly than the electrons 2 .…”

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confidence: 99%

“…As the value of v s increases, the ratio T / r becomes greater than unity and increases with time until the value of u c /u approaches unity (the region on the a(E) curve, where a ~ l / E [2,9]). Further heating of the plasma occurs close to the boundary of the stable region (u«u c ).…”

mentioning

confidence: 99%