Hα Radiation Research Articles

What are the mass-loss rates of O stars?

Empirical mass-loss rates of 28 luminous galactic OB stars are derived from thermal radio emission and from Hα recombination radiation. The velocity fields of all stars had previously been analyzed in the IUE ultraviolet spectral region. The results of these ultraviolet line-profile analyses (shape of the velocity law and terminal velocity) are combined with the radio and Hα data for a precise and consistent determination of the stellar mass-loss rates. It is found that radio and Hα rates agree within the observational errors. This suggests that significant clumping in the wind is unlikely due to the very different radius of origin of radio and Hα radiation within the wind

Neutral hydrogen density measurement in TMSPP

Resonance fluorescence of neutral hydrogen illuminated by Hα (656.3 nm) radiation provides a technique for spatially and temporally resolved density measurements of neutral hydrogen in high temperature plasma. Experiments have been performed in the exhaust of a tandem mirror space propulsion device. The laser fluorescence signal from plasma has been separated successfully by eliminating the Hα radiation from plasma and laser stray light using differential method of two optical paths. The resolution of signal is greatly enhanced. The radial distribution of hydrogen decreases from edge toward the center.

Improved confinement and edge plasma fluctuations in the STOR-M tokamak

An improved Ohmic confinement phase has been observed in the STOR-M tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1988 (International Atomic Energy Agency, Vienna, 1989), Vol. 1, p. 323] after application of a turbulent heating (TH) pulse. This improved Ohmic confinement phase is characterized by (a) increased n̄e, (b) reduced Hα radiation from the edge, (c) reduced density and magnetic fluctuations at the edge, (d) a steeper density profile at the edge, and (e) a more negative radial electric field. Almost complete suppression of sawtooth oscillations during the improved confinement phase has also been observed. A linear dispersion relation describes the density and magnetic fluctuations in the frequency range up to 350 kHz. In the region r<a (r≳a) the propagation direction of the density fluctuations is in the electron (ion) diamagnetic direction. The reduction of rms density and magnetic fluctuations after the TH pulse is largely due to suppression of relatively high frequency (≤500 kHz) components. The density fluctuations (ñ/ne) in the scrape-off layer remain intact after the pulse.

Hα laser fluorescence diagnostic on the Tara Tandem Mirror experiment

A laser fluorescence diagnostic has been used for measuring the neutral hydrogen density in the central cell of the Tara thermal barrier tandem mirror. Experiments have been performed using laser-induced, resonance fluorescence detection of Hα (6563-Å) radiation. Measurements were made at a number of radial positions with 1-cm resolution, from the magnetic axis to near the plasma limiter. Stray laser light contributions to the signal were eliminated with a double-pulse technique. For comparison, the chord-averaged plasma Hα radiation was analyzed under the identical conditions for which laser fluorescence data were taken.

A study of particle confinement properties in ohmically and neutral beam heated hydrogen plasmas in the JT-60 tokamak

The characteristics of particle confinement and recycling of ohmically and neutral beam (NB) heated hydrogen plasmas in the JT-60 tokamak are investigated by using the global particle balance equation. The total number of ionization events is estimated by employing a simple formula for the Hα radiation profile, and the gas fuelling efficiency is determined from the time derivatives of the electron density before and after gas feed termination. The global particle confinement time in the Ohmic heating divertor plasma decreases nearly inversely proportionally to the electron density, because of the enhancement of recycling in the plasma periphery. NB injection deteriorates the particle confinement time by a factor of about two. The effective particle confinement time closely related to the density control increases proportionally to the electron density in the Ohmic plasma. In contrast, the effective particle confinement time of the NB heated plasma is independent of the electron density although it decreases with the NB injection power. These results show that the plasma density can be controlled by the gas puff in both ohmically and NB heated hydrogen discharges.

HAIFA: A modular, fiber-optic coupled, spectroscopic diagnostic for plasmas

HAIFA is a modular, multichannel, fiber-optically coupled spectroscopy diagnostic for tokamak plasmas. It operates in the visible, measuring Hα radiation, the visible continuum from thermal bremsstrahlung, and selected impurity lines. HAIFA is characterized by high modularity and flexibility, good radiation resistance, high noise immunity, and low cost. Details of design, construction, and calibration are given. The analysis of visible bremsstrahlung radiation measurements to deduce the effective ionic charge in a plasma is discussed.

Tomography of neutral beams

This paper describes a new diagnostic technique to decode information contained in the spectral and spatial distribution of photons emitted by fast neutral beam particles and provide an estimate of the 2-D beam density distribution function in a cross-sectional slice. By scanning Doppler-shifted Hα radiation from the fast beam particles at a number of peripheral locations around the beam axis, tomographic reconstructions of the beam distribution with spatial resolution Δx≂2 cm and time resolution Δt≂10 ms can be made. Using a maximum entropy reconstruction algorithm (making no symmetry assumptions), experimental reconstructions are presented of the 2-D profile of the beam generated by the prototype JET source for each of the Doppler-shifted line radiation components. Applications of this image processing technique in other areas of high-temperature plasma diagnostic development are discussed briefly.

On the excitation of Lyman β and Balmer α radiation by electron-impact dissociation of methane

The cross sections for the excitation of Lyβ and Hα when methane is dissociated by electron impact have values of 17.1 × 10 −19 cm 2 and 26.0 × 10 −19 cm 2 respectively at an electron impact energy of 100 eV. These results are in disagreement with the implications of recent polarization measurements of Hα radiation that suggest negligible H(3p) excitation in the dissociation of CH 4 by electron impact.

Spatial distribution of soft X-ray and EUV emission associated with a chromospheric flare of importance 1B on August 2, 1972

Soft-X-ray and extreme ultraviolet spectroheliographs carried by the OSO-7 (Orbiting Solar Observatory) have been used to record the development of XUV emission associated with a flare of importance 1b on August 2, 1972. Spatial resolution was 20″ and spectral resolution was adequate to select emission lines originating within well-defined ranges of electron temperature between 5 × 104 and 30 × 106K. The data show that heating only the pre-existing coronal material adjacent to the flare site cannot account for the soft X-ray emission measure observed during the event. The flare emission originating at Te ⩽ 2.3 × 106K exhibits an impulsive component coincident with an impulsive microwave event. This radiation appears to coincide spatially with Hα radiation emitted at that time and is centered on the neutral line separating magnetic fields of opposite polarity. One soft X-ray-emitting feature, estimated to have an initial electron temperature of 2–10 × 106K, forms during the impulsive phase immediately over the Hα flare. A second, arch-like feature observed at wavelengths near 1.9 A and estimated to have Te≅30 × 106K is located approximately 35000 km above the Hα event. Both regions have lengths of about 27000 km but transverse dimensions small compared to the spatial resolution of the spectroheliograph, i.e., less than 14000 km. The region with highest electron temperature exhibits the greatest stability in position. This region cools to approximately 10 × 106K in 6 to 12 min which is compatible with cooling by conduction to the chromosphere. The best association with a dark surge is found in an emission line of Fe xiv.

Formation of the solar H? profile

A series of non-LTE radiative transfer solutions for Hα was computed using the integrodifferential equation technique of Athay and Skumanich (1967). A model hydrogen atom consisting of three bound levels and a continuum was assumed. It was found that increasing the temperature of the chromosphere at the height of line formation decreases the central intensity of the line. The density structure of the atmosphere primarily affects the optical depth scale rather than the source function. The temperature minimum region of the atmosphere was found to be transparent to Hα radiation, so that the radiation in some part of the line will arise from two distinct layers of the atmosphere, one above the temperature minimum and one below it. The computed Hα profile was found to be highly sensitive to the assumed 2–3 collisional cross-section.

Studies in spectral line formation: III. Non-linear multi-level atom problems

Solutions are presented for some non-linear multi-level atom line transfer problems. These include the transfer of Lyα, Lyβ, and Hα radiation through plane parallel atmospheres of three-level model hydrogen atoms, and the transfer of magnesium b-line radiation using four-level model magnesium atoms. The physical meaning of some characteristics of the solutions is emphasized in the discussion.

The electromagnetic radiation associated with the energy dissipated by cosmic rays in interstellar hydrogen

Evidence is presented for an interstellar cosmic-ray spectrum that arises from a source function which is a power law in kinetic energy per nucleon (αE−2.5) and which gets modified by the energy degradation of particles that traverse an average of 3–6 g/cm2 of interstellar matter, with paths distributed according to a steady-state model (Cowsik et al. 1966).For the interstellar spectrum inferred, the Coulomb interactions of cosmic rays with the hydrogen atoms of HI clouds are found to supply the correct energy input for maintaining at equilibrium the observed gas temperature of 102 °K. These interactions give rise to a high electron concentration (~10−1 cm−3), consistent with observations. The galactic backgrounds of X rays and Hα radiation are shown to be measures of the electromagnetic interactions of cosmic rays with the hydrogen atoms of HI clouds.

Ionospheric Effects associated with the Solar Flare of September 28, 1961

THE purpose of this communication is to direct attention to some ionospheric phenomena observed during the period of the above flare and during the early part of the associated geomagnetic storm that ensued on September 30, 1961. The flare, which was of importance 3+, was first detected around 2200 U.T., and the intensity of the Hα radiation reached a peak near 2224 U.T. all on September 28. The magnetic sudden commencement over North America occurred between 2108 and 2109 U.T. on September 30.

The Hα radiation from solar flares in relation to sudden enhancements of atmospherics on frequencies near 27 Kc/s

The development curves of 10 solar flares observed in Hα light are compared with the sudden enhancements of atmospherics (S.E.A.s) generated by them. In confirmation of earlier work (1950), an average time lag of 7 minutes is established between the maximum of the flare and the maximum of the resulting S.E.A. This is interpreted as an effect of “sluggishness” in the response of the D-layer (at a height of about 75 km) to the ionising radiation from the flare. An analysis is made of the association of S.E.A.s with 413 flares of Classes 1, 2 and 3 during a period of 4 years. In the hours between 0900 and sunset 51 per cent of Class 1 flares, 88 per cent of Class 2 flares and all Class 3 flares had associated S.E.A.s. The percentage association is higher during the middle of the day and in the afternoon than in the early morning hours. It is also higher in winter than in summer. It is emphasised that three or four 27 Kc/s recorders well distributed in longitude would give almost complete coverage for the recording of major flares; the method might profitably be used during the International Geophysical Year of 1957.

Hydrogen Atmospheres in the Absence of Thermodynamic Equilibrium. IV. The Solar Chromosphere

A discussion of the observational data shows that in the range 0<z<2.5 x 108 cm. the electron concentration in the lower chromosphere may be expressed as Ne=5x 1011 exp(-6 x 10-9z) per cc., where z cm. is the height measured from a level 500 km. above the base of the chromosphere. It is shown that above the 500-km. level hydrogen atoms are almost completely ionized, and that with hydrostatic equilibrium the observed density gradient corresponds to a temperature of 2.7 X 104 �K . This is in good agreement with the temperature derived by Redman from line profile measurement, so that the lower chromosphere appears to be effectively in thermal and hydrostatic equilibrium. Estimates of lower accuracy are given for the electron concentrations at some higher levels in the chromosphere. A discussion is given of the mechanism of absorption of Hα radiation by a chromosphere whose temperature is well above that of the photosphere.