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Bengtson, R. D.

Publications and source records attributed to Bengtson, R. D..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Investigation of a Light Gas Helicon Plasma Source for the VASIMR Space Propulsion System

An efficient plasma source producing a high-density (approx.10(exp 19/cu m) light gas (e.g. H, D, or He) flowing plasma with a high degree of ionization is a critical component of the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) concept. We are developing an antenna to apply ICRF power near the fundamental ion cyclotron resonance to further accelerate the plasma ions to velocities appropriate for space propulsion applications. The high degree of ionization and a low vacuum background pressure are important to eliminate the problem of radial losses due to charge exchange. We have performed parametric (e.g. gas flow, power (0.5 - 3 kW), magnetic field , frequency (25 and 50 MHz)) studies of a helicon operating with gas (H2 D2, He, N2 and Ar) injected at one end with a high magnetic mirror downstream of the antenna. We have explored operation with a cusp and a mirror field upstream. Plasma flows into a low background vacuum (<10(exp -4) torr) at velocities higher than the ion sound speed. High densities (approx. 10(exp 19/cu m) have been achieved at the location where ICRF will be applied, just downstream of the magnetic mirror.

Squire, J. P.↗
NASA NTRS1999

Plasma Flow During RF Discharges in VASIMR

The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) plasma source consists of a helical antenna, driven at frequencies of 4 to 19 MHz with powers up to 1 kW, in a magnetic field up to 3 kG. Helium is the current test gas, and future experiments with hydrogen are planned. Plasma density and temperature profiles were measured by a reciprocating Langmuir probe, and plasma flow profiles were measured with a reciprocating Mach probe. Both probes were located about 0.5 m downstream from the helical antenna. The plasma source operated in capacitive and inductive modes in addition to a helicon mode. During capacitive and inductive modes, densities were low and plasma flow was < 0.5 Cs. When the plasma operated in a helicon mode, the densities measured downstream from the source were higher [10(exp 12) / cubic cm ] and plasma flow along the magnetic field was of the order Mach 1. Details of the measurements will be shown.

Jacobson, V. T.↗
NASA NTRS1980

Oscillator strength trends in group IV homologous ions

Shock-tube data are used to examine systematic f-value behavior in prominent visible transition arrays for the homologous emitter sequence Si-II, Ge-II, Sn-II, and Pb-II. Regularities found in these data are compared with trends in lighter elements. Agreements and disparities with theoretical and experimental oscillator strengths from existing literature are noted.

Miller, M. H.↗
NASA NTRS1979

Experimental transition probabilities and Stark-broadening parameters of neutral and single ionized tin

Strengths and Stark-effect widths of the Sn I and Sn II lines prominent between 3200 and 7900 A are measured with a spectroscopic shock tube. Absolute strengths of 17 ionic lines are obtained with estimated (22-50)% accuracy and conform to appropriate quantum-mechanical sum rules. Relative transition probabilities for nine prominent neutral tin lines, normalized to radiative-lifetime data, are compared with other experiments and theoretical predictions. Parameters for Stark-effect broadening are measured over a range of plasma electron densities. Broadening data (with accuracies of 15-35%) for one neutral and ten ionic lines of tin are compared to theoretical predictions.

Miller, M. H.↗
NASA NTRS1978

Oscillator strength trends in group IVb homologous ions

Shock tube data are used to examine the systematic f value behavior in prominent visible transition arrays (ns-np, np-(n+l)s, np-nd) for the homologous emitter sequence Si 11, Ge 11, Sn 11, and Pb 11. Regularities found for these data are compared with trends in lighter elements. Agreements and s disparities with theoretical and experimental oscillator strengths from the literature are noted.

Miller, M. H.↗
NASA NTRS1977

Stark shift in ionized boron

Stark shift of the B II line at 3451 A due to plasma microfields was measured in a luminous shock tube. Line profiles, photographically recorded in second order, were compared with closeby wavelength fiduciaries from low-pressure rare-gas lamps. Electron densities for each exposure were found by fitting H-beta profiles to theoretical line shapes. Results, estimated reliable to 25-30%, are compared with theoretical predictions.

Miller, M. H.↗
NASA NTRS1976

Transition probabilities of Br II

Absolute transition probabilities of the three most prominent visible Br II lines are measured in emission. Results compare well with Coulomb approximations and with line strengths extrapolated from trends in homologous atoms.

Bengtson, R. D.↗
NASA NTRS1976

Stark broadening of Balmer lines in the density range /2-8/ x 10 to the 14/cu cm

Experimental profiles of the hydrogen Balmer lines (H gamma-H sub 10) have been measured over the density range (2-8) x 10 to the 14/cu cm and compared with theoretical profiles. Electron densities were measured using a multipass interferometer, while plasma homogeneity was demonstrated using a Langmuir probe. Electron temperatures were in the range 1-2.0 eV. The electron density as deduced from line profiles tended to be as much as 10% lower than that from the interferometer at higher densities. At lower densities, the two methods agreed to within experimental error. Evidence for asymmetries on the line wings was noted.

Bengtson, R. D.↗
NASA NTRS1974

Absolute line strengths for carbon and sulfur

Work has been conducted to reduce substantially uncertainties concerning the line strengths for carbon and sulfur. Two or more independent methods were used to measure thermodynamic variables and to calibrate detectors for absolute sensitivity and spectral response. The absolute transition probabilities of 124 visible and infrared lines of C I, S I, and S II were measured in a consistent way.

Miller, M. H.↗
NASA NTRS1972

Relative transition probabilities for krypton.

First experimental line strength data for the visible Kr II lines and for several of the more prominent Kr I lines are given. The spectroscopic light source used is the thermal plasma behind the reflected shock wave in a gas-driven shock tube. A 3/4-m spectrograph and a 1-m spectrograph were employed simultaneously to provide redundant photometry. The data are compared with other measurements and with theoretical calculations.

Miller, M. H.↗
NASA NTRS1971

Absolute transition probabilities of phosphorus.

Use of a gas-driven shock tube to measure the absolute strengths of 21 P I lines and 126 P II lines (from 3300 to 6900 A). Accuracy for prominent, isolated neutral and ionic lines is estimated to be 28 to 40% and 18 to 30%, respectively. The data and the corresponding theoretical predictions are examined for conformity with the sum rules.-

Miller, M. H.↗