Equilibrium and Stability of Current‐Carrying Discharges in the Non‐Axisymmetric CTH Experiment

Hanson, J.D.; Knowlton, S.; Stevenson, B. A.; Hartwell, G.J.

doi:10.1002/ctpp.200900059

Cited by 5 publications

(5 citation statements)

References 10 publications

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“…One opportunity to find the most important diagnostics for plasma equilibrium reconstruction was recently proposed [12]. A quantity which is referred to as signal effectiveness was introduced.…”

Section: Signal Effectiveness Studymentioning

confidence: 99%

“…The first equilibrium reconstruction of an ohmically driven current profile in a torsatron was demonstrated in the Compact Toroidal Hybrid (CTH) device [12].…”

Section: Introductionmentioning

confidence: 99%

“…Hanson describes the method of signal effectiveness to determine which signals are most important in determining the profile parameters [12].…”

Section: Introductionmentioning

confidence: 99%

“…V3FIT [9] relies on the variational moments equilibrium code (VMEC) [10,11] which assumes nested flux surfaces. The first equilibrium reconstruction of an ohmically driven current profile in a torsatron was demonstrated in the compact toroidal hybrid (CTH) device [12]. In the helically symmetric experiment (HSX), equilibrium reconstruction was used to demonstrate that the Pfirsch-Schlüter current is reduced in magnitude and rotates helically due to the lack of toroidal curvature in the device [13].…”

Section: Introductionmentioning

confidence: 99%

“…An analysis of magnetic diagnostics for equilibrium reconstruction using principal component analysis concluded that it was difficult to extract profile information for Wendelstein 7-X [22]. Hanson describes the method of signal effectiveness to determine which signals are most important in determining the profile parameters [12].…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Magnetic diagnostic optimization for plasma equilibrium reconstruction in the HSX stellarator

Chlechowitz¹,

Talmadge²,

Hanson³

et al. 2015

Nucl. Fusion

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Abstract. A new set of 80 optimized magnetic diagnostics has been designed, built and installed in the HSX stellarator to enable a more accurate reconstruction of the plasma equilibrium compared to a previously installed unoptimized set. The optimization of the positions of the diagnostic coils was based on two different methods. The first technique searches for diagnostics with a high signal effectiveness. This quantity is determined by how much the variance of the reconstructed parameters, which are used to describe the equilibrium, changes depending on a change in the variance of the measurement. The results of this method are combined with a study that determines which diagnostics have the largest signal change if only a single parameter is varied. Calculations show that the new set of diagnostics reduces the uncertainty in the reconstructed plasma pressure and plasma current profile compared to the previous magnetic diagnostics and a virtual internal diagnostic set which was not optimized. With a reduction in the signal uncertainties, a further improvement can be achieved for the optimized diagnostic set, demonstrating the advantage of a careful diagnostic design process. It is shown that it is possible to design diagnostic coils which are only sensitive to either the bootstrap current or the Pfirsch-Schlüter current.

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Section: Signal Effectiveness Studymentioning

confidence: 99%

“…The first equilibrium reconstruction of an ohmically driven current profile in a torsatron was demonstrated in the Compact Toroidal Hybrid (CTH) device [12].…”

Section: Introductionmentioning

confidence: 99%

“…Hanson describes the method of signal effectiveness to determine which signals are most important in determining the profile parameters [12].…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Magnetic diagnostic optimization for plasma equilibrium reconstruction in the HSX stellarator

Chlechowitz¹,

Talmadge²,

Hanson³

et al. 2015

Nucl. Fusion

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Development of a new virtual diagnostic for V3FIT

et al. 2014

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The determination of plasma equilibria from diagnostic information is a fundamental issue. V3FIT is a fully three-dimensional reconstruction code capable of solving the inverse problem using both magnetic and kinetic measurements. It uses VMEC as core equilibrium solver and supports both free- and fixed-boundary reconstruction approaches. In fixed-boundary mode VMEC does not use explicit information about currents in external coils, even though it has important effects on the shape of the safety factor profile. Indeed, the edge safety factor influences the reversal position in RFP plasmas, which then determines the position of the m = 0 island chain and the edge transport properties. In order to exploit such information a new virtual diagnostic has been developed, that thanks to Ampère's law relates the external current through the center of the torus to the circulation of the toroidal magnetic field on the outermost flux surface. The reconstructions that exploit the new diagnostic are indeed found to better interpret the experimental data with respect to edge physics.

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Low edge safety factor operation and passive disruption avoidance in current carrying plasmas by the addition of stellarator rotational transform

et al. 2015

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Low edge safety factor operation at a value less than two (q(a)=1/ι̷tot(a)<2) is routine on the Compact Toroidal Hybrid device with the addition of sufficient external rotational transform. Presently, the operational space of this current carrying stellarator extends down to q(a)=1.2 without significant n = 1 kink mode activity after the initial plasma current rise phase of the discharge. The disruption dynamics of these low edge safety factor plasmas depend upon the fraction of helical field rotational transform from external stellarator coils to that generated by the plasma current. We observe that with approximately 10% of the total rotational transform supplied by the stellarator coils, low edge q disruptions are passively suppressed and avoided even though q(a) < 2. When the plasma does disrupt, the instability precursors measured and implicated as the cause are internal tearing modes with poloidal, m, and toroidal, n, helical mode numbers of m/n=3/2 and 4/3 observed on external magnetic sensors and m/n=1/1 activity observed on core soft x-ray emissivity measurements. Even though the edge safety factor passes through and becomes much less than q(a) < 2, external n = 1 kink mode activity does not appear to play a significant role in the disruption phenomenology observed.

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Equilibrium and Stability of Current‐Carrying Discharges in the Non‐Axisymmetric CTH Experiment

Cited by 5 publications

References 10 publications

Magnetic diagnostic optimization for plasma equilibrium reconstruction in the HSX stellarator

Magnetic diagnostic optimization for plasma equilibrium reconstruction in the HSX stellarator

Development of a new virtual diagnostic for V3FIT

Low edge safety factor operation and passive disruption avoidance in current carrying plasmas by the addition of stellarator rotational transform

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