Measurement of potential variations in a dense oscillating plasma

When temperature fluctuations are large in a plasma, the floating potential cannot be used to calculate electric fields. This note describes a method which allows the calculation of the plasma potential as a function of time from measured values of the electron temperature and the floating potential. An application of this technique to the evaluation of electric fields in a reflex discharge is briefly outlined.

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A study on the modification of density and plasma potential in presence of electron temperature fluctuations (abstract)

Review of Scientific Instruments ◽

10.1063/1.1323473 ◽

2001 ◽

Vol 72 (1) ◽

pp. 465-465

Author(s):

C. Riccardi ◽

G. Longoni ◽

G. Chiodini ◽

M. Fontanesi

Keyword(s):

Electron Temperature ◽

Temperature Fluctuations ◽

Plasma Potential

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Observation of a Critical Gradient Threshold for Electron Temperature Fluctuations in the DIII-D Tokamak

Physical Review Letters ◽

10.1103/physrevlett.110.045003 ◽

2013 ◽

Vol 110 (4) ◽

Cited By ~ 34

Author(s):

J. C. Hillesheim ◽

J. C. DeBoo ◽

W. A. Peebles ◽

T. A. Carter ◽

G. Wang ◽

...

Keyword(s):

Electron Temperature ◽

Temperature Fluctuations

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Effect of the gas puff location on the divertor plasma properties in COMPASS tokamak

Journal of Physics Conference Series ◽

10.1088/1742-6596/1492/1/012003 ◽

2020 ◽

Vol 1492 (1) ◽

pp. 012003

Author(s):

M Dimitrova ◽

M Tomes ◽

Tsv Popov ◽

R Dejarnac ◽

J Stockel ◽

...

Keyword(s):

Electron Temperature ◽

Vacuum Chamber ◽

Plasma Potential ◽

Saturation Current ◽

Langmuir Probes ◽

Plasma Parameters ◽

Plasma Properties ◽

Low Field ◽

Saturation Current Density ◽

Deuterium Gas

Abstract Langmuir probes are used to study the plasma parameters in the divertor during deuterium gas puff injection on the high- (HFS) or low-field sides (LFS). The probe data were processed to evaluate the plasma potential and the electron temperatures and densities. A difference was found in the plasma parameters depending on the gas puff location. In the case of a gas puff on the LFS, the plasma parameters changed vastly, mainly in the inner divertor – the plasma potential, the ion saturation-current density and the electron temperature dropped. After the gas puff, the electron temperature changed from 10-15 eV down to within the 5-9 eV range. As a result, the parallel heat-flux density decreased. At the same time, in the outer divertor the plasma parameters remained the same. We thus concluded that using a gas puff on the LFS will facilitate reaching a detachment regime by increasing the density of puffed neutrals. When the deuterium gas puff was on the HFS, the plasma parameters in the divertor region remained almost the same before and during the puff. The electron temperature decreased with just few eV as a result of the increased amount of gas in the vacuum chamber.

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The occurrence frequency of auroral potential structures and electric fields as a function of altitude using Polar/EFI data

Annales Geophysicae ◽

10.5194/angeo-22-1233-2004 ◽

2004 ◽

Vol 22 (4) ◽

pp. 1233-1250 ◽

Cited By ~ 5

Author(s):

P. Janhunen ◽

A. Olsson ◽

H. Laakso

Keyword(s):

Electric Field ◽

High Altitude ◽

Electric Fields ◽

Radial Distance ◽

Plasma Potential ◽

Potential Structure ◽

New Finding ◽

Low Altitude ◽

Field Lines ◽

Auroral Arcs

Abstract. The aim of the paper is to study how auroral potential structures close at high altitude. We analyse all electric field data collected by Polar on auroral field lines in 1996–2001 by integrating the electric field along the spacecraft orbit to obtain the plasma potential, from which we identify potential minima by an automatic method. From these we estimate the associated effective mapped-down electric field Ei, defined as the depth of the potential minimum divided by its half-width in the ionosphere. Notice that although we use the ionosphere as a reference altitude, the field Ei does not actually exist in the ionosphere but is just a convenient computational quantity. We obtain the statistical distribution of Ei as a function of altitude, magnetic local time (MLT), Kp index and the footpoint solar illumination condition. Surprisingly, we find two classes of electric field structures. The first class consists of the low-altitude potential structures that are presumably associated with inverted-V regions and discrete auroral arcs and their set of associated phenomena. We show that the first class exists only below ~3RE radial distance, and it occurs in all nightside MLT sectors (RE=Earth radius). The second class exists only above radial distance R=4RE and almost only in the midnight MLT sector, with a preference for high Kp values. Interestingly, in the middle altitudes (R=3–4RE) the number of potential minima is small, suggesting that the low and high altitude classes are not simple field-aligned extensions of each other. This is also underlined by the fact that statistically the high altitude structures seem to be substorm-related, while the low altitude structures seem to correspond to stable auroral arcs. The new finding of the existence of the two classes is important for theories of auroral acceleration, since it supports a closed potential structure model for stable arcs, while during substorms, different superposed processes take place that are associated with the disconnected high-altitude electric field structures. Key words. Magnetospheric physics (electric fields; auroral phenomena) – Space plasma physics (electrostatic structures)

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Theoretical Study of Plasma Using Different Dimension of Hollow Cathode

Journal of Nepal Physical Society ◽

10.3126/jnphyssoc.v5i1.26880 ◽

2019 ◽

Vol 5 (1) ◽

pp. 30-34

Author(s):

L. N. Mishra ◽

K. Khanal

Keyword(s):

Glow Discharge ◽

Hollow Cathode ◽

Theoretical Study ◽

Plasma Processing ◽

Theoretical Work ◽

Plasma Potential ◽

Gas Pressure ◽

Floating Potential ◽

Discharge Behavior

This article deals about the theoretical study on DC hollow cathode glow discharge using different hollow cathode geometry. The mechanism of discharge is analyzed at various gas pressure and radial configuration. The dependence of temperature on gas pressure has been elucidated with the help of Scotty limit. Discharge behavior with radius has also been explained. It is revealed that floating potential increases as gas pressure increases whereas plasma potential decreases as gas pressure increases. This theoretical work resembles with the experimentally measured results. This work might be useful for the plasma processing for industrial purposes.

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Cosmic radio noise absorption events associated with equatorward drifting arcs during a substorm growth phase

Annales Geophysicae ◽

10.5194/angeo-22-1675-2004 ◽

2004 ◽

Vol 22 (5) ◽

pp. 1675-1686 ◽

Cited By ~ 8

Author(s):

J. R. T. Jussila ◽

A. T. Aikio ◽

S. Shalimov ◽

S. R. Marple

Keyword(s):

Electron Temperature ◽

Electric Fields ◽

Growth Phase ◽

Energetic Electron ◽

Cosmic Radio ◽

Radio Noise ◽

Particle Precipitation ◽

Noise Absorption ◽

D Region ◽

E Region

Abstract. Cosmic radio noise absorption (CNA) events associated with equatorward drifting arcs during a substorm growth phase are studied by using simultaneous optical auroral, IRIS imaging riometer and EISCAT incoherent scatter radar measurements. The CNA is generally attributed to energetic particle precipitation in the D-region. However, it has been argued that plasma irregularities or enhanced electron temperature (Te) in the E-region could also produce CNA. Both of the latter mechanisms are related to intense electric fields in the ionosphere. We present two events which occur during a substorm growth phase in the evening MLT sector. In both of the events, an auroral arc is drifting equatorward, together with a region of CNA (auroral absorption bay) located on the equatorward side and outside of the arc. Both of the events are associated with enhanced D-region electron density on the equatorward side of the auroral arc, but in the second event, a region of intense electric field and enhanced electron temperature in the E-region is also located on the equatorward side of the arc. We show that in the studied events neither plasma instabilities nor enhanced Te play a significant role in producing the measured CNA, but the CNA in the vicinity of the equatorward drifting arcs is produced by D-region energetic electron precipitation. Key words. Ionosphere (auroral ionosphere; particle precipitation; electric fields and currents)

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The generation of radio-frequency radiation in the sun

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1948.0104 ◽

1948 ◽

Vol 195 (1040) ◽

pp. 82-97 ◽

Cited By ~ 12

Keyword(s):

Radio Frequency ◽

Electron Temperature ◽

Electric Fields ◽

Solar Atmosphere ◽

Solar Disk ◽

Black Body ◽

The Sun ◽

Radio Frequency Radiation ◽

Circularly Polarized ◽

Frequency Radiation

Measurements of the radiation emitted by the sun at radio-frequencies have shown that the intensity greatly exceeds the value associated with a surface temperature of 6000° K. Under normal conditions the radiation, which appears to be randomly polarized, has an intensity which corresponds to the radiation from a black-body source subtending the same solid angle as the solar disk and at a temperature of about 10 6 °K. During the presence of sunspots very much more intense radiation is emitted by small areas of the solar disk; the intensity at these times corresponds to radiation from a source at a temperature of 10 9 to 10 10 °K, and the radiation is circularly polarized. The experimental results are considered theoretically in this paper, and it is concluded that the radiation in both cases arises from the acceleration of electrons in the solar atmosphere. It is suggested that by the action of the permanent magnetic field of the sun and the non-uniform rotation of the surface matter, a high potential difference is developed between the poles and the equator. Under normal conditions this potential can only produce small discharge currents through the solar atmosphere, although the electric field produced may be sufficient to maintain a mean electron temperature of 10 6 to 10 8 °K in the levels likely to emit radio-frequency radiation. During the presence of sunspots much more intense electric fields can be made available in the solar atmosphere, and in the neighbourhood of the sunspots electron temperatures of the order of 1010 °K should be maintained. A high-temperature electron gas can only radiate appreciably at those frequencies at which it absorbs well. An application of the magneto-ionic theory to the solar atmosphere above a sunspot shows that there are several regions capable of absorbing radiation at each frequency. For one of these regions the absorption (and therefore the radiating power) is very great, but radiation emitted by the region can only be propagated towards the centre of the sun. This region cannot therefore be responsible for the high-intensity radiation associated with sunspots, although the asymmetrical flow of energy from the region must produce an outward radiation pressure; this pressure may be of importance in accounting for the elevation of matter in the solar atmosphere above sunspots. Two other regions have a high absorption (each region absorbing one of the two circularly polarized components) and radiation from both regions can escape from the sun. Owing to the differences of radiating power and electron temperature in the two regions, it is likely that the intensities of the two emitted waves will be different. The radiation which is observed on the earth will therefore appear circularly polarized, the sense of the polarization corresponding to that of the most intense wave.

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