The direct determination of the current density and mu profiles of a spheromak

Martin, R.C.; Gee, S J; Browning, P. K.; Rusbridge, M G

doi:10.1088/0741-3335/35/2/012

Cited by 21 publications

(24 citation statements)

References 9 publications

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“…22 Figure 7 shows the typical temporal evolution of the toroidal current I t , gun voltage V g , and current density J t for the high-q ST operation (I TF ϭ220 kA͒ with bias flux ⌿ bias ϭ2.2 mWb. Note here that the toroidal current is driven around the magnetic axis (R axis Х0.32 m).…”

Section: B Time Evolution Of Toroidal Current Density Profilementioning

confidence: 99%

The internal magnetic field structures and current density profiles in the Helicity Injected Spherical Torus plasma driven by coaxial helicity injection

et al. 2003

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In the Helicity Injected Spherical Torus device [Nagata et al., Proceedings of the 17th International Atomic Energy Agency Fusion Energy Conference, Yokohama, 1998 (International Atomic Energy Agency, Vienna, 1998) CD-ROM, EXP4/10], internal magnetic field and current density structures of spherical torus (ST) plasmas sustained by coaxial helicity injection (CHI) have been revealed via intensive internal magnetic measurements. The internal magnetic configuration of the ST plasma formed by CHI is in good agreement with the results of numerical equilibrium fitting calculations. The generation of closed poloidal flux of ST has been verified by varying the external toroidal field strength in the same device. Interestingly, the transition of the current profile from hollow to peaked has been observed during the sustainment phase, which could be explained by inductive effects of currents on open field lines winding the central conductor.

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Section: B Time Evolution Of Toroidal Current Density Profilementioning

confidence: 99%

The internal magnetic field structures and current density profiles in the Helicity Injected Spherical Torus plasma driven by coaxial helicity injection

et al. 2003

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“…Only spheromak operation is considered, since no data is available for gettered operation with the rod in place. Presented here are surveys within the equatorial plane using an insertable probe called the probe, 8 consisting of three orthogonal field coils together with a small Rogowski coil which measure the value of at any one point in the machine during a shot. The probe was rotated such that it was aligned to the local mean field, thereby measuring J ʈ , and radial profiles of using this probe were built up shot by shot.…”

Section: Comparison With the Sphex Datamentioning

confidence: 99%

“…The result is a nonuniform profile, which during sustainment is higher on the driven open flux and lower on the closed flux. 7,8 A major goal of the SPHEX program has been to identify the relaxation mechanism, which has also been the subject of intensive research for Reverse Field Pinches ͑RFPs͒. SPHEX, described fully by Ref.…”

Section: Introductionmentioning

confidence: 99%

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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“…Careful measurements were performed of the current density and h profiles in SPHEX using a novel Rogowski/magnetic probe [44]. They found a discontinuity in the profiles at the interface between the column and the annulus.…”

Section: Appendix 2 Recent Results From the Sphex Experimentsmentioning

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 direct determination of the current density and mu profiles of a spheromak

Cited by 21 publications

References 9 publications

The internal magnetic field structures and current density profiles in the Helicity Injected Spherical Torus plasma driven by coaxial helicity injection

The internal magnetic field structures and current density profiles in the Helicity Injected Spherical Torus plasma driven by coaxial helicity injection

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

The Spheromak path to fusion energy

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