Compact toroid formation, compression, and acceleration

Degnan, J.H.; Peterkin, R.E.; Baca, G.; Beason, J.D.; Bell, D.; Dearborn, M.E.; Dietz, D.; Douglas, M. R.; Englert, S.E.; Englert, T.J.; Hackett, K. E.; Holmes, J. H.; Hussey, T. W.; Kiuttu, G.F.; Lehr, F.M.; Marklin, G.J.; Mullins, B. W.; Price, D.W.; Roderick, N. F.; Ruden, E.L.; Sovinec, C. R.; Turchi, P. J.; Bird, Gareth Adam; Coffey, S.K.; Seiler, S. W.; Chen, Y. G.; Gale, D.; Graham, J.D.; Scott, M.; Sommars, W.

doi:10.1063/1.860681

Cited by 64 publications

(45 citation statements)

References 30 publications

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“…Except for the work during the 1950s and 1960s when the research was associated with applications to fusion, most of the research on these accelerators in the past four decades has been associated with applications to space propulsion. During the 1980s and 1990s, plasma accelerators were en-countered in several other applications, including dense plasma focus and the acceleration of relatively large compact toroids ͑MARAUDER of the Air Force Research Laboratory, 18 RACE of Lawrence Livermore Laboratory, 19 CTIX of UC-Davis 20 ͒ for fusion and x-ray generation, and in accelerating solid projectiles to hypervelocity for impact fusion and a variety of defense applications. For space propulsion, these accelerators are called pulsed plasma thrusters ͑PPTs͒.…”

Section: A Backgroundmentioning

confidence: 99%

A contoured gap coaxial plasma gun with injected plasma armature

Witherspoon

Case

Messer

et al. 2009

Review of Scientific Instruments

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A new coaxial plasma gun is described. The long term objective is to accelerate 100-200 microg of plasma with density above 10(17) cm(-3) to greater than 200 km/s with a Mach number above 10. Such high velocity dense plasma jets have a number of potential fusion applications, including plasma refueling, magnetized target fusion, injection of angular momentum into centrifugally confined mirrors, high energy density plasmas, and others. The approach uses symmetric injection of high density plasma into a coaxial electromagnetic accelerator having an annular gap geometry tailored to prevent formation of the blow-by instability. The injected plasma is generated by numerous (currently 32) radially oriented capillary discharges arranged uniformly around the circumference of the angled annular injection region of the accelerator. Magnetohydrodynamic modeling identified electrode profiles that can achieve the desired plasma jet parameters. The experimental hardware is described along with initial experimental results in which approximately 200 microg has been accelerated to 100 km/s in a half-scale prototype gun. Initial observations of 64 merging injector jets in a planar cylindrical testing array are presented. Density and velocity are presently limited by available peak current and injection sources. Steps to increase both the drive current and the injected plasma mass are described for next generation experiments.

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Section: A Backgroundmentioning

confidence: 99%

A contoured gap coaxial plasma gun with injected plasma armature

Witherspoon

Case

Messer

et al. 2009

Review of Scientific Instruments

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“…To examine this issue, a number of 2-dimensional magnetohydrodynamic (MHD) calculations were performed using the MACH2 [22] code. In these calculations, the injected gas distribution was simulated by a uniform density, right circular cylinder, with a concave outer surface and height of 2.0 cm.…”

Section: Effect Of Sheath Curvature On Rayleigh-taylor Mitigation In mentioning

confidence: 99%

Effect of Sheath Curvature on Rayleigh-Taylor Mitigation in High-Velocity Uniform-Fill,Z-Pinch Implosions

1997

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Recent gas puff experiments on the 7-MA Saturn machine identified a curved surface at the plasma-vacuum interface during the run-in phase of the implosion. Incorporating this topology into a corresponding two-dimensional magnetohydrodynamic calculation revealed that this curvature plays a surprisingly dominant role in mitigating Rayleigh-Taylor (RT) growth prior to stagnation. Calculations with both Saturn and representative PBFA-Z parameters show that sheath curvature contributes to the reduction in RT growth by convecting the instability to the edges of the pinch faster than it can grow.[S0031-9007 (97)03377-2] PACS numbers: 52.35.Py, 52.55.Ez, 52.65.KjTraditional Z-pinch implosions are known to be susceptible to the Rayleigh-Taylor (RT) instability [1,2], especially for thin foil loads [3]. To improve the implosion quality, gas puff loads with thicker shells were subsequently developed. However, experiments have never demonstrated acceptable radiation performance with large diameter, high-velocity annular implosions [3,4]. For example, Saturn [5] data with annular gas puffs have shown significant instability growth and poor radiation emission at diameters of 4.5 cm [6,7]. Many techniques have been suggested to reduce RT development in conventional loads without substantially degrading the compression ratio of the pinch. Such techniques include uniform fills [8,9], puff on puff [10-12], B z or shear stabilization [13][14][15], and tailored density profiles [16,17]. Uniform fills, in particular, have been investigated both experimentally and theoretically.In a recent set of experiments on the 8-MA Saturn generator, the effect of uniform fill loads on stability was examined using neon-argon and krypton-argon gas mixtures [18]. These experiments demonstrated an improvement in implosion quality compared to corresponding annular loads. In addition, a unique feature associated with the uniform-fill loads was identified. Based on images from a high resolution, space-and time-resolved pinhole camera, a curved sheath was clearly seen at the plasma-vacuum interface during the observable portion of the implosion phase. This "hourglassing" [19] effect is shown in the experimental pinhole camera images of Fig. 1 and is attributed to the divergence of the gas flow coupled with an axial mass gradient. This is similar to the long wavelength effects that produce zippering [20,21]. It is evident from the figure that the hourglassing is fairly severe, and is maintained throughout the implosion.The detection of hourglassing in this set of experiments has led to speculation concerning the role, if any, that sheath curvature may play in instability growth or reduction. To examine this issue, a number of 2-dimensional magnetohydrodynamic (MHD) calculations were performed using the MACH2 [22] code. In these calculations, the injected gas distribution was simulated by a uniform density, right circular cylinder, with a concave outer surface and height of 2.0 cm. Imposing the curved outer surface of the load as an initial condition prov...

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“…Various models for the plasma resistivity are available. The simulations utilized the classical electron-ion SpitzerHärm formulation with contributions from electron-neutral collisions applicable to weakly ionized gases [3]. In many engineering applications the source of magnetic flux is applied currents produced from externally applied voltage differentials.…”

Section: Numerical Modelmentioning

confidence: 99%

Modeling and Performance Analysis of the Pulsed Inductive Thruster

Mikellides

Neilly

2007

Journal of Propulsion and Power

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Numerical modeling of the pulsed inductive thruster exercising a time-dependent, two-dimensional, axisymmetric magnetohydrodynamics code provides bilateral validation of the thruster's measured performance and the code's capability of capturing the pertinent physical processes. Computed impulse values for helium and argon propellants demonstrate excellent correlation to the experimental data for a range of energy levels and propellant-mass values. Quantitative energy deposition analysis confirms the thruster's approximately constant-efficiency operation and captures the experimentally observed, critical-mass phenomenon. An idealized model produced a simple impulse expression for this energy range that expands the validity of the aforementioned insights to other propellants and corroborates the thruster's singular operation with ammonia propellant. The simple impulse expression produced compares well with experimental trends and can be used to guide design and optimization of operating conditions. Nomenclaturenumber of same atoms L = inductance ' = number of different atoms M = atomic mass m = propellant mass n = number of electrons Q = ionization energy R = resistance r, , z = cylindrical dimensions r i = inner radius r o = outer radius t = time V = voltage Z = impedance = diffusion depth = efficiency o = 4 10 7 H=m = energy fraction Subscripts c = critical e = electron or external H = heavy particle o = stored or initial

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Compact toroid formation, compression, and acceleration

Cited by 64 publications

References 30 publications

A contoured gap coaxial plasma gun with injected plasma armature

A contoured gap coaxial plasma gun with injected plasma armature

Effect of Sheath Curvature on Rayleigh-Taylor Mitigation in High-Velocity Uniform-Fill,Z-Pinch Implosions

Modeling and Performance Analysis of the Pulsed Inductive Thruster

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