Relaxed and partially relaxed magnetic equilibria in tight-aspect-ratio tori

Browning, Philippa; Clegg, Jenny; Duck, R C; Rusbridge, M G

doi:10.1088/0741-3335/35/11/006

Cited by 19 publications

(24 citation statements)

References 26 publications

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“…3,9 As the rod current is increased, r c reduces for each given pair of values, and crit decreases. In other words, the flux amplification is greater at higher rod currents ͑for a fixed profile͒, which is consistent with the two-dimensional equilibria, 28 and also the critical for ejection is lowered. 21 Having a smaller column radius indicates a larger volume for the annulus, and therefore, given the same profile, greater flux amplification.…”

Section: Equilibrium Resultssupporting

confidence: 83%

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Stability studies and the origin of the n=1 mode in the SPHEX spheromak experiment

et al. 1999

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Oscillations with toroidal mode number n=1 are ubiquitous in helicity injected spheromaks and spherical tokamaks, and play a crucial role in current drive. It has been proposed that these arise from a current driven instability of the open flux tube. Stability calculations are presented to confirm this, and they are compared with experimental data from the Spheromak Experiment (SPHEX) [M. Rusbridge et al., Plasma Phys. Control. Fusion 39, 683 (1997)]. The equilibria are modelled as piece-wise constant μ profile force-free plasmas with different values for the μ in the open (μc) and closed (μa) flux regions. A stability map in μc,μa space is then calculated. The SPHEX experimental data is also reduced to the same space both as a culmination of direct single point measurements of μ and as a time history of the reconstructed equilibrium from a particular shot. The results show a favorable comparison of the stability map with experiment, both in magnitude and shape. The effect of inserting a central current-carrying rod on the stability is also discussed.

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Section: Equilibrium Resultssupporting

confidence: 83%

“…If flux crosses the boundary, there is a resonance at the eigenvalues, at which the closed flux becomes infinite. 6,4,28 In the one-dimensional model, with its two valued profile, it is clear that when the closed flux is infinite the annulus will fill the entire volume. From Eqs.…”

Section: The Equilibrium Modelmentioning

confidence: 99%

Stability studies and the origin of the n=1 mode in the SPHEX spheromak experiment

et al. 1999

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“…Summaries of the SPHEX project have recently appeared emphasizing the "rodomak" configuration [46], ion energy measurements [47], general SPHEX operation [48], the structure of the n=l mode [49], and the effects of instabilities in the plasma [SO].…”

Section: Collaborations and Contributors To The White Papermentioning

confidence: 99%

The Spheromak path to fusion energy

Hooper¹,

Barnes²,

Bellan³

1998

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The spheromak is a simple and robust magnetofluid configuration with several attractive reactor attributes including compact geometry, no material center post, high engineering p, and sustained steady state operation through helicity injection. Spheromak physics was extensively studied in the US program and abroad (especially Japan) in the 1980's with work continuing into the 1990s in Japan and the UK. Scientific results included demonstration of self-organization at constant helicity, control of the tilt and shift modes by shaped flux conservers, elucidation of the role of magnetic reconnection in the magnetic dynamo, and sustainment of a spheromak by helicity injection.Several groups attained electron temperatures above 100 eV in decaying plasmas, with CTX reaching 400 eV. This experiment had high magnetic field (>l T on the edge and -3 T near the symmetry axis) and good confinement. More recently, analysis of CTX found the energy confinement in the plasma core to be consistent with Rechester-Rosenbluth transport in a fluctuating magnetic field, potentially scaling to good confinement at higher electron temperatures. The SPHEX group developed an understanding of the dynamo in sustained spheromaks but in a relatively cold device. These and other physics results provide a foundation for a new "concept exploration" experiment to study the physics of a hot, sustained spheromak.If successful, this work leads to a next generation, proof-of-principle program.The new SSPX experiment will address the physics of a large-scale sustained spheromak in a national laboratory (LLNL) setting. The key issue in near term spheromak research will be to explore the possibly deleterious effects of sustainment on confinement.Other important issues include exploring the P scaling of confinement, scaling with Lundquist number S, and determining the need for active current-profile control. Collaborators from universities and other national laboratories are contributing experience from previous work, diagnostics, and physics support. Experiments at PPPL and Swarthmore are being conducted on the physics of magnetic reconnection, yielding physics results which should help advance the confinement work.A spheromak reactor will require steady state operation with the equilibrium fully supported by external coils. Although the present generation of experiments can provide data on the initial stages of the transition from short-pulsed operation, sustainment longer than the wall resistance time will be addressed in the proof-of-principle experiments.-lContents

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“…The equilibrium analysis presented in Ref. [14] on the basis P H Y S I C A L R E V I E W L E T T E R S of the helicity-driven relaxation theory [10] predicts that a flipped ST plasma is formed when the external toroidal flux t:e is negative ( t:e < 0). By using the analytical solution of the force-free equation in a rectangular flux conserver (FC) that was presented in Ref.…”

mentioning

confidence: 99%

“…In order to investigate the generation process of the RFP-like configuration and the subsequent currentreversal process, we have measured the time evolution of modes with toroidal mode number n and the toroidal current density profile J t R. The value is estimated by co 0 I t = t averaged in the central core region (R 0:21-0:34 m) and the q 0 value around the magnetic axis is approximately given by the formula of q 0 2=R co [14], where R is the major radius. We note that the meanings of co and q 0 are not well defined during the relaxation.…”

mentioning

confidence: 99%

Self-Reversal Phenomena of Toroidal Current by Reversing the External Toroidal Field in Helicity-Driven Toroidal Plasmas

et al. 2003

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In order to understand self-organization in helicity-driven systems, we have investigated the dynamics of low-aspect-ratio toroidal plasmas by decreasing the external toroidal field and reversing its sign in time. Consequently, we have discovered that the helicity-driven toroidal plasma relaxes towards the flipped state. Surprisingly, it has been observed that not only toroidal flux but also poloidal flux reverses sign spontaneously during the relaxation process. The self-reversal of the magnetic fields is attributed to the nonlinear growth of the n=1 kink instability of the central open flux.

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Relaxed and partially relaxed magnetic equilibria in tight-aspect-ratio tori

Cited by 19 publications

References 26 publications

Stability studies and the origin of the n=1 mode in the SPHEX spheromak experiment

Stability studies and the origin of the n=1 mode in the SPHEX spheromak experiment

The Spheromak path to fusion energy

Self-Reversal Phenomena of Toroidal Current by Reversing the External Toroidal Field in Helicity-Driven Toroidal Plasmas

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