Measurement Of Plasma Conductivity Research Articles

Visible light emission measurements from a dense electrothermal launcher plasma

Measurements of the visible light emission from dense, weakly nonideal plasmas have been performed on the experimental electrothermal launcher device SIRENS. The plasma is created by the ablation of a Lexan insulator in the source, which then flows through a cylindrical barrel which serves as the material sample. Visible light emission spectra have been observed both in-bore and from the muzzle flash of the barrel, and from the flash of the source. Recent measurements along the axis of the device indicate time-averaged plasma temperatures in the barrel of about 1 eV for lower energy shots, which agree with experimental measurements of the average heat flux and plasma conductivity along the barrel. Measurements of visible emission from the source indicate time-averaged temperatures of 1 to 2 eV which agree with the theoretical estimates derived from ablated mass measurements and calculated estimates derived from plasma conductivity measurements. >

Radio-frequency probe for plasma conductivity measurements. II. Application to an electron beam created plasma in oxygen

Calculations establishing the principles of a radio-frequency coil to measure the electron characteristics of a plasma column have been discussed in the previous article. They are illustrated by an application to a low-pressure oxygen plasma created by an electron beam of some keV. Original experimental apparatus and methodology are described. Electron densities of the order of 1011 cm−3 and electron temperatures around 0.15 eV are readily measured.

Directional rf probe for measurement of conductivity of flowing plasmas

An electrodeless immersible rf probe for measurement of plasma conductivity in the range 0.01 to 100 mho/m has been designed and fabricated. The probe, with an overall diameter of 11 mm, employs unidirectional electromagnetic field lines which reduce the inaccuracies caused by insertion of the probe in a flowing plasma. In the range studied the probe output shows a linear relationship with the conductivity of the medium. Such probes are of interest in the study of MHD and reentry plasmas.

Pulsed spherical probe measurements of plasma conductivity in a flowing continuum plasma

Measurements have been made of the electron conductivity in an atmospheric pressure flowing plasma using a pulsed spherical probe. The method involves measuring the peak electron current flowing to the probe in response to a positive pulsed change in the probe potential. It is shown that for many circumstances the pulse technique effectively eliminates the very large potentials which are usually generated at plasma electrode interfaces during plasma resistance measurements.

Measurement of Plasma Conductivity for Electric Fields Larger than the Runaway Field

The electrical conductivity parallel to a magnetic field of a hot ion hydrogen plasma with n ≃ 109cm−3, Ti ≃ 50 eV, and Te ≃ 5 eV was measured for electric fields larger than the runaway field. The conductivity was found to be proportional to the plasma density with a value much less than Spitzer's conductivity but larger than Buneman's turbulent conductivity. When the current became comparable to the electron thermal current, the conductivity was found to decrease.

Magnetohydrodynamic generator measurements in argon and helium plasmas

Using an electrically driven shock tube as a plasma source, measurements of plasma conductivity have been made using two cold tungsten probes and a magnetohydrodynamic interaction. Complete load characteristics for the generator system were determined and from these conductivity values were estimated. The measurements in argon with a transverse magnetic field of 3100 gauss were as expected yielding conductivity values of the same order as the ionic conductivity predicted theoretically. In the cases of helium for applied magnetic fields of 3100 gauss, 5500 gauss and 7500 gauss, and argon for the two higher field values, the conductivity values for low values of probe current corresponded to the expected ionic conductivities. At a particular current there was an abrupt change of conductivity which for even greater currents remained constant and was of the same order as the theoretical estimates of electronic conductivity.

A technique for the experimental determination of the electrical conductivity of plasmas

A technique is presented which permits the measurement of the electrical conductivity of a plasma by means of observing a diminution of radio frequency magnetic flux through the plasma. This techique has found application in the measurement of conductivity of stationary plasmas, flowing steady-state plasmas, and plasmas produced in the electromagnetic shock tube. The rudiments of the theory of operation of a device using this technique are presented, and a measurement of plasma conductivity is described for the case of the hot exhaust gas of a deflagrating sample of solid rocket fuel expanding in a vacuum.

A Method of Measurement of Plasma Conductivity. II. –Example of Measurement–

A measurement of plasma conductivity is described, which is based on the method theoretically discussed in the previous note. The plasma tube is inserted in a single turn coil of a LC oscillator, and the shift in the resonance frequency, Δf, due to the insertion is observed. From Δf the change in the magnetic flux penetrating the coil can be evaluated, and from the latter the plasma conductivity can be determined. The results are in satisfactory agreement with the conductivity values obtained by the usual probe method.

A Method of Measurement of Plasma Conductivity. I. –Theoretical Approach–

It is shown that the plasma conductivity can be evaluated from the change in magnetic flux in the plasma of an applied electromagnetic field. The evaluation requires no detailed knowledge of the electron collision frequency. This method, not being based on the usual conductor approximation will prove useful if a method of determining the magnetic flux change is established successfully.

Flow of a Hydrogen Plasma through a Transverse Magnetic Field

A study has been conducted of the phenomena occurring when a hydrogen plasma is caused to flow through a transverse magnetic field. Plasma polarization effects were studied as well as the deceleration processes which occurred when large currents were extracted from the plasma. Standing ``wedge-shaped'' shock waves were observed when sufficient current was extracted to permit the deceleration phenomena to be manifested. The effective plasma resistance between electrodes was determined, and a correlation made with plasma conductivity measurements, including boundary layer effects. Finally, a determination was made of the power and energy extracted from the plasma.

Electron-Ion Recombination in Dense Plasmas

The rate of recombination and the characteristics of the afterglow line emission have been measured in magnetically confined plasmas of helium and hydrogen, with electron densities of the order of ${10}^{13}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and degree of ionization initially of the order of 50%. Electron densities and temperatures are deduced from absolute intensity measurements of spectrum line intensities originating from highly excited states, in good agreement with those obtained from microwave phase shift and plasma conductivity measurements. The results are explained in terms of an electron-electron-ion three-body recombination process. The recombination coefficient for this process is calculated as a function of electron temperature and density.