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Coaxial helicity injection in open-flux low-aspect-ratio toroidal discharges
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10.1063/1.2800863
/content/aip/journal/pop/14/11/10.1063/1.2800863
http://aip.metastore.ingenta.com/content/aip/journal/pop/14/11/10.1063/1.2800863
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

Maximum marginally stable edge vacuum-region thicknesses (according to PEST analysis) vs toroidal plasma current for a series of EFIT-generated equilibria. Vertical lines indicate the values of corresponding to integer values for the edge safety factor . Reprinted from Ref. 26.

Image of FIG. 2.
FIG. 2.

(Color) Schematic layout of the HIT-II device. The location and shape of each of the 28 poloidal field (PF) coils is indicated in red, and the toroidal insulating breaks at the injector and absorber are indicated in blue. Some of the 34 poloidal locations of surface-mounted magnetic triple probes are also indicated.

Image of FIG. 3.
FIG. 3.

Vacuum magnetic fluxes for three HIT-II injector topologies, superimposed on an outline of the HIT-II vacuum vessel. From left to right, these configurations are: Narrow “HIT-like,” intermediate “NSTX-like,” and “wide-injector.” Diamonds indicate the locations of poloidal flux loops used for feedback control.

Image of FIG. 4.
FIG. 4.

Vacuum magnetic fluxes for single-null (left) and unbalanced double-null (right) HIT-II CHI discharges, superimposed on an outline of the HIT-II vacuum vessel. Diamonds indicate the locations of poloidal flux loops used for feedback control.

Image of FIG. 5.
FIG. 5.

(a) Injector voltage, (b) injector current, (c) poloidal wall current, (d) toroidal plasma current, (e) edge midplane poloidal field fluctuations, and (f) the ratio vs time for typical HIT-like open-flux SND discharge #25247.

Image of FIG. 6.
FIG. 6.

(a) Injector voltage, (b) injector current, (c) poloidal wall current, (d) toroidal plasma current, (e) edge midplane poloidal field fluctuations, and (f) the ratio vs time for typical NSTX-like open-flux SND discharge #25257.

Image of FIG. 7.
FIG. 7.

(a) Injector voltage, (b) injector current, (c) poloidal wall current, (d) toroidal plasma current, (e) edge midplane poloidal field fluctuations, and (f) the ratio vs time for typical wide-injector open-flux SND discharge #25243.

Image of FIG. 8.
FIG. 8.

(a) Injector voltage, (b) injector current, (c) poloidal wall current, (d) toroidal plasma current, (e) edge midplane poloidal field fluctuations, and (f) the ratio vs time for high-current HIT-like open-flux DND discharge #23225.

Image of FIG. 9.
FIG. 9.

Measured poloidal wall current in the HIT-II outboard shell vs poloidal location for (a) six SND HIT-like discharges, including #25247; (b) five SND NSTX-like discharges, including #25257; and (c) six SND wide-injector discharges, including #24243. Each point is the time-average during the discharge steady state. Calculated errors are comparable to the shot-to-shot variations. The vertical dashed lines indicate the locations of the two flux loops defining the injector flux region.

Image of FIG. 10.
FIG. 10.

Measured poloidal fields on the (a) outboard shell and (b) central column for HIT-II CHI discharge #28311 at . This shot has double-null flux boundaries with a HIT-like injector, and a total TF coil current of -turns. Measurements by the poloidal Rogowski coils are indicated with diamonds, and by the two triple-probe arrays with boxes and triangles. The solid curves correspond to a best fit of .

Image of FIG. 11.
FIG. 11.

(a) Injector voltage, (b) injector current, (c) poloidal wall current, (d) toroidal plasma current, (e) edge midplane poloidal field fluctuations, and (f) the ratio vs time for wide-to-HIT dynamic injector SND discharge #25174. The dotted vertical lines at and indicate the start and end of the injector flux topology sweep.

Image of FIG. 12.
FIG. 12.

Autopower fluctuation spectra for measured injector voltages vs frequency, for: (a) HIT-like #25247, (b) NSTX-like #25257, and (c) wide-injector #25243. The spectra are normalized to the maximum value from the HIT-like spectrum.

Image of FIG. 13.
FIG. 13.

(a) Toroidal plasma current, (b) injector current, and (c) current amplification ratio for a set of SND and DND HIT-II discharges, grouped according to injector flux geometry. The average values are shown for each dataset, with error bars calculated from the shot-to-shot variances. Diamonds indicate DND data, boxes represent SND data.

Image of FIG. 14.
FIG. 14.

Measured mode (a) frequency and (b) poloidal-field amplitude vs total TF coil current, for a series of HIT-like SND HIT-II discharges. Diamonds are averages during the steady postformation phase, with error bars calculated from the variances.

Image of FIG. 15.
FIG. 15.

For the HIT-II CHI discharge database (thousands of shots, including both SND and DND discharges), (a) measured injector current every , (b) normalized by , and (c) average , grouped in bins of width , with error bars vs the CHI injector power.

Image of FIG. 16.
FIG. 16.

For open-flux HIT-like CHI time slices, (a) measured plasma current every , (b) normalized by the theoretical maximum , and (c) average , with error bars, grouped in intervals of width 25 V vs the applied CHI injector voltage .

Image of FIG. 17.
FIG. 17.

For a particular SND TF coil current scan, the measured plasma current vs TF coil current .

Image of FIG. 18.
FIG. 18.

For two injector flux scans, measured plasma current vs nominal injector flux . (a) Single-null scan, including #24954–24971, and (b) double-null scan, including shots #23430–23456. The dashed lines correspond to the predicted from the thin current sheet model.

Image of FIG. 19.
FIG. 19.

For HIT-like HIT-II CHI discharges, the measured value of from surface magnetic probes, for each time slice vs the corresponding . The solid line corresponds to .

Image of FIG. 20.
FIG. 20.

For (a) HIT-like and (b) NSTX-like HIT-II CHI discharges, the calculated overestimate for the current-sheet thickness vs the corresponding value of . The dashed lines correspond to , the predicted sheet thicknesses from the thin current sheet model, which are and , respectively.

Image of FIG. 21.
FIG. 21.

(a) Injector voltage, (b) injector current and poloidal wall current, (c) plasma current, (d) poloidal field at the outer midplane wall, (e) internal at , and (f) internal at vs time, for single-null CHI discharge #26070. Shot #26070 has and .

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/content/aip/journal/pop/14/11/10.1063/1.2800863
2007-11-20
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Coaxial helicity injection in open-flux low-aspect-ratio toroidal discharges
http://aip.metastore.ingenta.com/content/aip/journal/pop/14/11/10.1063/1.2800863
10.1063/1.2800863
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