Hugh J. Karr
Los Alamos National Laboratory
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Featured researches published by Hugh J. Karr.
Physics of Fluids | 1971
P. R. Forman; A. Haberstich; Hugh J. Karr; J.A. Phillips; Aldred E. Schofield
The effect of high‐frequency linear quadrupole magnetic fields on the m = 1 kink instabilities of a z pinch, as proposed by Osovets, is investigated. Short‐wavelength instabilities of 5‐12 cm are observed to be dominant and are not suppressed by the stabilization fields. This is contrary to the reported result of others that the short‐wavelength instabilities do not develop if the long wavelengths of the order of the interelectrode distance are stabilized. For the experimental conditions used, magnetohydrodynamic theory predicts stabilization of wavelengths of 20‐80 cm and reduced growth rate for the shorter wavelengths. The observed instabilities have a reduced growth rate in agreement with theory.
Physics of Fluids | 1961
Hugh J. Karr; E. Knapp; J. E. Osher
Most high‐temperature plasma devices, and in particular pinch discharges, have energy‐loss rates much larger than can be accounted for in terms of hydrogenic bremsstrahlung or quiescent plasma diffusion. This loss has been investigated for a toroidal pinch discharge machine with longitudinal stabilizing magnetic field, Perhapsatron S‐4. It is found that the major energy dissipation is due to vacuum ultraviolet emission from partially stripped impurity ions. The impurity is predominantly oxygen liberated from the walls of the tube into the discharge after the pinch has been formed. Characteristics of this radiation are discussed, as well as a possible mechanism for the release of the impurity into the discharge. Comparisons between experimental results and theoretical predictions on the rate of radiation loss are given.
Physics of Fluids | 1976
R. B. Howell; Hugh J. Karr
The plasma temperature in the ZT‐1 toroidal pinch as been determined using spectral line Doppler broadening measurements facilitated by the use of analog‐to‐digital converters and an on‐line computer. The ZT‐1 system has been operated in a ’’derated’’ mode with peak toroidal currents of 30 to 110 kA, initial current rise times of 0.5 to 2.5×1011 A/sec, stabilizing toroidal magnetic fields of 0.06 to 0.3 T, and filling pressures of 2 to 30 Pa. Results of the plasma temperature measurements in this mode of operation are reviewed with the objective of determining the effects of scaling the machine parameters on the ion temperature with extension to results obtained in the earlier higher current ’’fast’’ mode operation. An analysis and experimental tests of several possible sources of error in the ion temperature measurements are given in an appendix.
Physics of Fluids | 1963
Hugh J. Karr; E. Knapp; W. B. Riesenfeld
The ion cyclotron resonance interaction of plasma with a rotating transverse magnetic perturbation on a longitudinal magnetic field is investigated experimentally and theoretically. The plasma is injected axially from a coaxial hydromagnetic gun along a longitudinal magnetic field on which there is superimposed a transverse spatially rotating perturbation field. A resonance transfer of ion energy from the longitudinal to the transverse direction is observed when the spatial period or wavelength of the perturbation field and the plasma velocity and ion cyclotron frequency satisfy the relation λz = 2πvz/ΩB. Measurements of plasma diamagnetism and transit time show an increase of up to a factor of two in diamagnetism coupled with a decrease in axial velocity corresponding to a reduction to half the initial longitudinal energy. Resonance may be observed over a range of longitudinal energies by varying the parameters of the system. For the plasma gun and perturbation field helix used in the experiment, optimum...
Physics of Fluids | 1969
L. C. Burkhardt; Joseph N. DiMarco; Hugh J. Karr
A minimum‐average‐B‐stable toroidal magnetic well with high shear is obtained from the combined fields of a solenoid, axial conductors, and an internal ring conductor. Results of measurements of the injection and trapping of high‐energy plasma from a coaxial gun are described. The confinement times are dependent on both particle energy and magnetic field. The density e‐folding time is independent of the ion velocity under conditions of low shear and well depth. As they are increased the e‐folding time varies roughly as 1/vi2. Trapped 0.9‐keV plasma decays with an e‐folding time that increases by a factor of 6 to 110 μsec as shear and magnetic well depth increase. The initial density of the plasma (0.5 to 3 keV) is ∼ 5 × 1011 cm−3 for field magnitudes resulting in a 40‐μsec lifetime of 0.9‐keV deuterons. This lifetime is independent of density over the range from ∼ 5 × 1011 cm−3 to 109 cm−3. The range of magnetic field magnitude is limited by the decreasing amount of plasma injected from the gun with incre...
Physics of Fluids | 1968
L. C. Burkhardt; Joseph N. DiMarco; J. E. Hammel; R. M. Henson; Hugh J. Karr
Experimental tests of the effectiveness of the magnetic shielding of current leads or supports in the form of linear dipoles are described. Results show that this technique may be useful in experimental plasma confinement devices.
Physics of Fluids | 1966
Hugh J. Karr; J. E. Osher
The injection and subsequent behavior of a dense (∼3 × 1013/cm3) fast (V ∼ 108 cm/sec) deuterium plasma jet fired from a coaxial plasma gun into a simple biconical cusped magnetic field has been studied. The experiment shows that for sufficiently high cusp fields up to 90% the plasma jet penetrates the entrance cusp and is lost through the ring cusp without being trapped. In the process of injection a part of the ion energy in the plasma jet is found to be transferred to a group of electrons. X rays of up to 220‐keV energy are observed from these energetic electrons with a characteristic decay time of up to 1 msec for cusp fields of 8.5 kG. These long duration energetic electrons are found to be accompanied by a variety of slow high momenta impurity ions (e.g., Fe, O, Si, etc.) in transit through the field and lower energy ions trapped for times in essential agreement with theoretical values for a low‐β plasma in a simple cusped field. Observations on the plasma potential are also described.
Other Information: Orig. Receipt Date: 30-JUN-76 | 1975
D.A. Baker; L. C. Burkhardt; R.S. Dike; J.N. Di Marco; P. R. Forman; A. Haberstich; Hugh J. Karr; L.W. Mann; J.A. Phillips; A.E. Schofield
Electrical design details are given for a toroidal Z-pinch device named ZT-1 that uses field programming to achieve a stable, reversed field pinch. The plasma is formed in a 4-mm-thick, 10.3-cm-i.d., high alumina, segmented ceramic vacuum chamber. Voltages as high as 70 kV are routinely attained by interrupting with a fuse 800 kA in an inductive store. The current is diverted from the fuse to the primary of a single-turn transformer divided into quadrants. A total of 280 kV at 200 kA can then be applied to the plasma, which forms the secondary circuit of the transformer. This system produces dB/sub theta//dts of up to 8 T/
Pulsed High Beta Plasmas#R##N#Proceedings of the Third Topical Conference Held at Ukaea Culham Laboratory, Abingdon, Oxfordshire, U.K., 9–12 September 1975 | 1976
R.B. Howell; Hugh J. Karr; P.R. Forman
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pp 274-85 of Feedback and Dynamic Control of Plasmas. /Chu, T. K. (ed.). New York American Institute of Physics (1970). | 1970
Jonathan Phillips; P. R. Forman; A. Haberstich; Hugh J. Karr
s; with modifications to the electrical system, dB/sub theta//dts as low as 0.1 T/