Electrostatic Probe Measurements Research Articles

Comparison of cylindrical electrostatic probe measurements on Alouette II and explorer XXXI satellites

The Alouette II and Explorer XXXI satellites were placed in orbit by a single launch vehicle and separated. Cylindrical electrostatic probes of identical design were installed on each satellite in part to test the effects of the long sounder antennas and large radio-frequency power on Alouette II upon direct measurements of the thermal electrons and ions. Comparisons of the early data, taken when the satellites were separated less than 1000 km along their common orbit, suggest that there is no inherent incompatibility between the sounder experiment and direct measurement experiments. The electron temperature T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</inf> and concentration N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</inf> derived from the two experiments generally agree to better than 10 percent, although unexplained differences of up to 15 percent in T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</inf> and 40 percent in N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</inf> have been found on rare occasions.

Electrostatic probe measurements in flowing NaK-seeded argon.

Electrostatic probe measurements in flowing NaK-seeded argon.

A Cesium MHD Arc Jet

A cesium-fueled magnetohydrodynamic arc jet was operated between 4 and 12 kW at magnetic field strengths up to 1000 G. Electrostatic probe, spectroscopic, and microwave measurements were made on the exhaust beam. Beam momentum was determined from the deflection of a downstream sieve. The magnitude and position of Hall currents were determined using magnetic-loop pickup coils. The over-all arc voltage is a linear function of applied axial magnetic-field strength. The thrust is a linear function of the product of the arc current and applied axial magnetic-field strength, and is of a magnitude too great to be produced by the measured Hall currents. A partial theory is developed that describes the functional dependence of the arc voltage and thrust. Data are presented that show mass entrainment was present and that when the arc is operated with mass entrainment the exhaust velocity is predicted by the Alfvén ``critical velocity.''

The ionosphere at 640 kilometers on quiet and disturbed days

Tiros VII electrostatic probe measurements of ionospheric electron density on quiet and disturbed days

Plasma Diagnostics using Electrostatic Probes under Short Mean Free Path Conditions

The properties of a medium pressure plasma were inferred from electrostatic probe measurements using the theory of Zakharova et al. The results were compared with microwave measurements and the agreement was within a factor of 3.

Determination of Resonant Modes in Piezoelectric Plates

The wide usage of piezoelectric plates in ultrasonics and communication systems has stimulated considerable interest in the determination of the resonant modes of vibration of these plates. Experimentally, it is possible to measure the frequency, the reactance, and the loss associated with modes that may occur in a plate of arbitrary geometry. The determination of these parameters are generally not sufficient to identify a particular mode of vibration. The use of electrostatic probe measurements and x-ray diffraction topography can be used to determine the actual particle displacements associated with the resonant modes. All of these measurements may be used to compliment and extend the present approximations to anisotropic-plate vibrations. This paper reviews the techniques for the measurement of frequency, displacement, and electrical parameters in piezoelectric plates. These measurements are compared with the results computed from Mindlin's first-order theory for rectangular AT-cut quartz plates.

Propagation of a Glow Discharge into the Annular Gap between the Discharge Tube Wall and the Cathode

Time-resolved spectroscopic measurements and electrostatic probe measurements were used to study that part of a high-voltage pulsed glow discharge in hydrogen that propagated into the annular gap between the cathode and the Pyrex discharge tube wall. The spectroscopic and probe measurements revealed that a luminous front and a potential wave started to propagate into the annular gap at the same time as the electric field in the cathode fall region at the face of the cathode reached its maximum value. The dependence of the propagation velocity on the discharge parameters is presented and the importance of the secondary emission at the wall of the discharge tube is established as a factor in the propagation of the discharge.

Measurements on a Stable and Unstable Mode Observed in a Lithium Reflex Arc

A powerfull P. I. G. reflex arc in lithium vapour has been studied using spectrographic, mass spectrometric and probe measuring techniques. The Li-vapour has been produced in a special Li-oven; the vapour entered through a small tube directly into the hollow anode cylinder. The residual gas pressure was 10-7 mm Hg with the arc in operation, the density in the plasma column was about 1013 cm-3. The discharge showed two different modes of operation. We observed that at a fixed flow of Li-vapour the discharge can be operated in a stable state (Mode I) only below a certain limit of the applied electrical power. An increase of electrical power (or a decrease of the flow of Li-vapour) causes a strong instability (Mode II). 1. Mode I showed the discharge column to be very well stabilized by the confining magnetic field. Electrostatic probe measurements showed no voltage fluctuations. The electron temperature ranged from 1.8 to 8 eV, depending on the electrical power applied. 2. Mode II showed the plasma column to become diffuse. Large voltage fluctuations of several volts in the megacycle region could be detected on the electrostatic probe. A powerfull flux of ions leaving the plasma column perpendicular to the magnetic lines of force and hitting the walls with energies up to 327 eV has been measured. These energetic ions are responsible for the strong light emission of the walls of the vacuum tube, this light intensity being much higher than the intensity of the plasma column. The experimental results are similar to those observed by NEIDIGH, WEAVER, NEZLIN and SOLNTSEV under different experimental conditions.

Probe Measurement of Electron Density in Magnetized Plasma

Electrostatic probe measurement of electron density in magnetized plasma is discussed. Experiments are made in helium at pressures ranging from 0.3 to 1.6mmHg with 1011-1012/cc of plasma electron density and 0-5000 gauss of magnetic field strength.The influence of magnetic field, pressure and discharge current on the saturation electron current to cylindrical probe is investigated, for which the plasma electron density determined by the following two methods is taken as the true density : one is based on probe characteristic of ion current almost free from the effect of magnetic field, the other is with a microwave cavity devised to become free from the effect of magnetic field. Results of experiment show that the thickness of sink region around the probe perpendicular to the magnetic field is given by Ve/ (ω2p+ω2B) 1/2where Ve is the thermal velocity of electron, and ωP and ωB are respectively the angular frequencies of electron plasma and cyclotron.Use of this region and the theory developed by Dote enables the numerical determination of electron density of magnetized plasma. The electron density calculated by using electron current characteristics of the probe with its axis parallel to the magnetic flux agrees well with the true electron density of magnetized plasma. The electron density measurement with the probe perpendicular to the magnetic line of force is also investigated.

Electrostatic plasma resonances

It is shown that the resonances observed in microwave scattering from a positive column depend on the existence of a radial electron density gradient. Deductions are made about the boundary conditions governing the space charge distribution associated with the resonant scattering. A comparison with electrostatic probe measurements shows that subsidiary resonances exist, their position being a function of number density and probing frequency. The principal resonance, on the other hand, depends also on the external geometry. It is a feature of measurements made in this way that the principal resonance occurs at a frequency somewhat less than the mean plasma frequency.

Microwave Radiation from Plasmas

In the present experiments observations were carried out in a micro-wave region, where the wavelength was comparable to or shorter than a dimension of the discharge tube. Incoherent radiation, namely, noise radiation from plasmas which were semi-opaque or opaque was observed. Comparison between the electron temperature determined from microwave measurement and that from electrostatic probe measurement gives a satisfactory agreement. It is experimentally investigated that the plasma oscillation in a hot cathode discharge tube gives rise to radiation. Obtainable power of this radiation is estimated about 0.1 µW.