scholarly journals Microwave Interferometry for Plasma Studies

1963 ◽  
Vol 16 (3) ◽  
pp. 439 ◽  
Author(s):  
LC Robinson ◽  
LE Sharp
Keyword(s):  
Electron Density ◽  
Microwave Radiation ◽  
Collision Frequency ◽  
Plasma Frequency ◽  
Plasma Temperature ◽  
Electron Plasma ◽  
Optical Path ◽  
Average Electron Density ◽  
Laboratory Plasmas ◽  
Average Electron

A beam of microwave radiation is a powerful and penetrating means of exploring the density and temperature of laboratory plasmas while causing minimal perturbation of the plasma. To a wave of frequency greater than the electron plasma frequency the plasma behaves like a dielectric, causing a change in the "optical" path which, when measured by interference techniques, yields the average electron density. The attenuation of the probing wave can give the collision frequency and hence the plasma temperature.

scholarly journals X-ray phase determination by the principle of minimum charge

1999 ◽  
Vol 55 (3) ◽  
pp. 489-499 ◽  
Author(s):  
Veit Elser
Keyword(s):  
Electron Density ◽  
Diffraction Data ◽  
Global Minimum ◽  
Unit Cell ◽  
Electronic Charge ◽  
Total Charge ◽  
Phase Determination ◽  
X Ray ◽  
Average Electron Density ◽  
Average Electron

When the electron density in a crystal or a quasicrystal is reconstructed from its Fourier modes, the global minimum value of the density is sensitively dependent on the relative phases of the modes. The set of phases that maximizes the value of the global minimum corresponds, by positivity of the density, to the density having the minimum total charge that is consistent with the measured Fourier amplitudes. Phases that minimize the total electronic charge (i.e. the average electron density) have the additional property that the lowest minima of the electron density become exactly degenerate and proliferate within the unit cell. The large number of degenerate minima have the effect that density maxima are forced to occupy ever smaller regions of the unit cell. Thus, by minimization of the electronic charge, the atomicity of the electron density is enhanced as well. Charge minimization applied to simulated crystalline and quasicrystalline diffraction data successfully reproduces the correct phases starting from random initial phases.

A radio method of searching for fine structure in H 11 regions

1967 ◽  
Vol 31 ◽  
pp. 237
Author(s):  
O. B. Slee
Keyword(s):  
Fine Structure ◽  
Radio Emission ◽  
Electron Density ◽  
Path Length ◽  
Low Frequency ◽  
Radio Sources ◽  
Average Electron Density ◽  
Scale Size ◽  
Average Electron ◽  
Radio Method

Fine structure with a scale size of about 10-3pc in the galactic ionized hydrogen may scatter the low-frequency radio emission of extragalactic sources with intrinsically small angular diameters, thus making them apparently large. For example, application of the Chandrasekhar scattering formula to a path length of 100 pc through an H 11 region with an average electron density of 0·1 cm-3, and structure of scale size 10-3pc filling 1% of the volume, results in a scattering to half-brightness points of 8″ (arc) at 38 MHz. Radio sources with apparent angular sizes of this amount should be partially resolved by an interferometer with an effective baseline of about 10 000 wavelengths.

scholarly journals Emission Nebulae as Radio Sources

1956 ◽  
Vol 9 (2) ◽  
pp. 218 ◽  
Author(s):  
BY Mills ◽  
AG Little ◽  
KV Sheridan
Keyword(s):  
Electron Temperature ◽  
Electron Density ◽  
Radio Telescope ◽  
Optical Data ◽  
Radio Sources ◽  
Pencil Beam ◽  
Orion Nebula ◽  
Average Electron Density ◽  
Average Electron ◽  
Bright Emission

Attempts have been made to detect 14 bright emission nebulae at a wavelength of 3?5 m using a pencil-beam radio telescope with a beamwidth of 50 min of arc. Of these nebulae, six were probably observed in emission, seven were undetectable, and one, NGC 6357, was observed in absorption; radio isophotes were obtained for NGC 2237 and NGC 3372. Radio and optical data have been combined to estimate electron densities, masses, and sometimes the electron temperature of many of the nebulae. Values range from an electron density of 3 cm?3 and a mass of 3�10. solar masses for the outer regions of the 30 Doradus complex to an average electron density of 500 cm?3 and a mass of 20 solar masses for the Orion Nebula. Temperatures generally appear to be in the neighbourhood of 10,000 �K, except in the case of NGC 6357, for which 6500 �K is estimated.

scholarly journals Pulsar distances, spiral structure and the interstellar medium

1970 ◽  
Vol 38 ◽  
pp. 178-181 ◽  
Author(s):  
B. Y. Mills
Keyword(s):  
Interstellar Medium ◽  
Electron Density ◽  
Supernova Remnants ◽  
Spiral Structure ◽  
Radio Continuum ◽  
Average Electron Density ◽  
Uniform Medium ◽  
The Mean ◽  
Average Electron

The distances of all pulsars are calculated on the assumption that they are immersed in a uniform medium of average electron density 0.06 cm−3. It then appears that the pulsars are concentrated towards the local and Sagittarius spiral features and that their mean height above the plane is consistent with that of known supernova remnants. The mean distances appear to be approximately correct, but individual distances are uncertain by about a factor of two. Evidence from radio continuum results supports this model of the ionized interstellar medium.

A sensitive microwave interferometer for plasma diagnostics

1969 ◽  
Vol 3 (3) ◽  
pp. 371-375 ◽  
Author(s):  
J. R. Wallington ◽  
J. D. E. Beynon
Keyword(s):  
Phase Shift ◽  
Electron Density ◽  
Plasma Diagnostics ◽  
Collision Frequency ◽  
Plasma Frequency ◽  
Electron Collision ◽  
Microwave Attenuation ◽  
Electron Collision Frequency ◽  
Broad Dimension

More accurate methods of measuring microwave attenuation and phase are constantly being sought, particularly for such applications as plasma diagnostics. The microwave bridge technique described here was developed for the study of a quiescent plasma having an electron density of 1015 to 1018 m−3 corresponding to a plasma frequency of 3 × 108 to 1010 Hz, and an electron collision frequency of 1010 to 1011 s−1. The plasma had a broad dimension of 0·3 m. For such a plasma a probing frequency of 10 GHz was considered to be the most suitable; at this frequency the attenuation α and phase shift δβ expected were 0·1 < α< 50 dB and 1° < δβ < 1000° respectively.

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