Electron energy confinement in field reversed configuration plasmas

Rej, D.J.; Barnes, G.A.; Baron, M.H.; Chrien, R.E.; Okada, S.; Siemon, R.E.; Taggart, D. P.; Tuszewski, M.; Webster, Robert B.; Wright, B.L.

doi:10.1088/0029-5515/30/6/010

Cited by 17 publications

(5 citation statements)

References 19 publications

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“…This is only a few times the classical value for condition 2. This Xe would represent more than an order of magnitude improvement in confinement than previously observed [13], and is comparable to that observed in smaller tokamak experiments. For a rigid-rotor equilibrium, the poloidal flux decay time ip can be related to a field null resistivity r](R) as r <p^L 5x\0-1 R 2 /n(R).…”

Section: -P T =Jnk Dt E Ldt = P {N -P R -(F-25)nkt Es /R N supporting

confidence: 87%

“…No electron temperature decay, other than that expected from adiabatic cooling, was observed for these data. This is consistent with measurements made on other FRC devices [13].…”

supporting

confidence: 93%

“…The electron temperature measured was found to be significantly higher than previous experiments even with the same pressure balance temperature. This implies a major change in the cross-field thermal transport from that observed previously [13].…”

mentioning

confidence: 55%

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Confinement and stability of plasmas in a field-reversed configuration

et al. 1992

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Experiments have been conducted on the LSX device where plasmas confined in a field-reversed magnetic geometry have exhibited record energy, particle, and configuration lifetimes. The scaling from previous smaller devices showed a very positive confinement scaling with J, the number of ion gyroradii inside the field-reversed configuration. These plasmas were observed to have gross stability to global loworder modes such as the internal tilt. The growth of tilt instabilities was not observed during the equilibrium decay of plasmas up to s~8.PACS numbers: 52.55.Pi A new experimental device (LSX) has been constructed to explore the confinement and stability of magnetically confined plasma known as a field-reversed configuration (FRC). An FRC has a compact toroidal confinement geometry where induced toroidal diamagnetic currents generate the confining poloidal field [1]. Since the toroidal field is typically small inside the FRC, the configuration has an intrinsically high plasma p (the magnetic field vanishes at the plasma core). This feature together with the simple cylindrical geometry, the natural diverter nature of the external magnetic field, and the ease of translation [2] give the FRC unique advantages as a fusion reactor-particularly for advanced fuels [3].From a theoretical point of view, the key issue has been the gross stability of the configuration. For several years it has been known that the FRC equilibrium, as a result of the unfavorable curvature of the closed field lines (see Fig. 1), is unstable in the magnetohydrodynamic (MHD) limit. In particular, the FRC is unstable to the internal tilt instability [4]. This global mode consists of a rotation of the FRC orthogonal to the symmetry axis with only a small distortion to the separatrix shape, and thus cannot be suppressed by the application of an external magnetic field. The mode has a growth rate that would annihilate the configuration on the shortest possible MHD time FIG. 1. Schematic of the LSX experiment. Equilibrium flux contours are shown from a 2D numerical calculation for an FRC in LSX. scale, the time for an Alfven wave to propagate the half length of the FRC.Stability for many Alfven transit times has been observed in several FRC experiments [1,5]. The FRCs formed in these experiments, however, had a strong kinetic particle component. This component can be characterized by the parameter s, the average number of ion gyroradii between the null and separatrix of the FRC, and s was typically 2 or less. It was shown that for s < 2, kinetic effects significantly increased the MHD tilt growth time [6] to as long as the FRC configuration lifetimes obtained at that time. Subsequent experiments on the TRX device, however, indicated stability to the tilt at moderate s (2 to 4) for many kinetically increased tilt growth times [5]. The confinement did not improve with increasing s as had been observed in previous low-j, kinetic-regime experiments. It was not determined what limited confinement; however, the equilibria produced in these large-.? experim...

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Section: -P T =Jnk Dt E Ldt = P {N -P R -(F-25)nkt Es /R N supporting

confidence: 87%

“…No electron temperature decay, other than that expected from adiabatic cooling, was observed for these data. This is consistent with measurements made on other FRC devices [13].…”

supporting

confidence: 93%

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Confinement and stability of plasmas in a field-reversed configuration

et al. 1992

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“…This is because ion-electron thermal relaxation time is faster than the time scale of decreasing T t . The time evolution of the ion or electron temperature up to thermal equilibrium is shown as below [12]:…”

Section: Discussionmentioning

confidence: 99%

Soft X-Ray Measurement on the Collisional Merging Process in a Field-Reversed Configuration

Sekiguchi

Asai

Takahashi

2019

Plasma and Fusion Research

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To investigate excited shockwaves in a collisional-merging field-reversed configuration (FRC), soft X-ray (SXR) measurement was initiated on the FRC amplification via translation collisional merging (FAT-CM) instrument. Since the FRCs collide at a relative speed of 300-400 km/s on the FAT-CM, which is faster than the Alfvén velocity in the separatrix, shockwaves are assumed to be excited in the colliding FRCs. These excited shockwaves would play an important role in energy conversion during the collisional merging formation process of the FRC. The relation between the global behavior of the FRC in the collisional merging process and the time evolution of SXR signals are discussed herein.

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“…The electrons are heated primarily by collisional equilibration with the hotter ions. Within the separatrix, cross-field electron thermal conduction is highly anomalous (factors of 35 to 140 were seen on FRX-C/LSM [29]) and T e profiles tend to be flat.…”

Section: Confinementmentioning

confidence: 99%

Field reversed configurations and spheromaks

Wright

1990

Nucl. Fusion

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The status of controlled nuclear fusion research is reviewed for two major compact toroidal confinement concepts: the field reversed configuration (FRC) and the spheromak. The FRC is an inherently high beta concept offering the advantages of a cylindrical geometry, a natural divertor and the possibility of axial movement of the confined plasma during the formation/burn cycle. The essential techniques of FRC formation, translation and magnetic compression heating have been successfully demonstrated, and gross instabilities driven by plasma rotation have been controlled. Emphasis of present FRC research is on formation symmetry, and on the effects of reducing the large gyroradii of the ions on stability and confinement. The spheromak, like the reversed field pinch, embodies a nearly force-free equilibrium whose evolution is governed significantly by the principle that magnetic helicity is conserved during relaxation processes that minimize magnetic energy. Recent spheromak research has shown how improved edge conditions can enhance global confinement by reducing relaxation and turbulence. Attention to this issue has led to major gains in spheromak energy confinement and plasma beta, and to the discovery of new pressure driven effects.

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Electron energy confinement in field reversed configuration plasmas

Cited by 17 publications

References 19 publications

Confinement and stability of plasmas in a field-reversed configuration

Confinement and stability of plasmas in a field-reversed configuration

Soft X-Ray Measurement on the Collisional Merging Process in a Field-Reversed Configuration

Field reversed configurations and spheromaks

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