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Operation of Alcator C-Mod with high-Z plasma facing components and implicationsa)
a)Paper FI1 3, Bull. Am. Phys. Soc. 50, 103 (2005).
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View: Figures


Image of FIG. 1.
FIG. 1.

(Color online) The amount of ICRF power required to obtain vs campaign period. The estimated boron layer thickness and date when the BN antenna protection tiles were added and subsequently removed are shown.

Image of FIG. 2.
FIG. 2.

(Color online) The sawtooth reheat rate for a set of discharges where the ICRF power launched and general plasma characteristics were held constant while the ratio was varied. The sawtooth reheat rate is then a measure of the local absorbed power and therefore the heating efficiency as well. The shaded region is the range in considered optimal for minority heating efficiency.

Image of FIG. 3.
FIG. 3.

(Color online) Cross section of the Alcator C-Mod vessel. The molybdenum tiles are shown in blue. The inner wall is located at . The largest major radius edge of the inner divertor is at . The smallest major radius edge of the outer divertor, or outer divertor nose is at . The largest major radius location on the outer divertor is at . The smallest/largest major radii of the outer limiter tiles are 81.8 and , respectively. Finally, the outer vessel wall is at . The vertical line is at .

Image of FIG. 4.
FIG. 4.

(Color online) The history of the hydrogen fraction in the plasma, , as a function of discharge number following a vacuum vent. The grey band spanning 3%–5% is the ideal level for efficient H-minority ICRF heating. Three cases are shown: 1999, before BN tiles were installed and the boron layer thickness on molybdenum tiles was thin (1–2 ); 2003-2004, when the boron layer thickness was largest ( microns); and 2005, when the boron layers were removed.

Image of FIG. 5.
FIG. 5.

(Color online) Examples of discharges from pre-boronization (black), post-first-boronization (red), and post-second-boronization (green). The traces for a number of parameters are given: (a) line-averaged density; (b) stored energy; (c) rf power (source); (d) radiated power from the plasma inside the separatrix (not the divertor); and (e) brightness of a Mo XXXI line .

Image of FIG. 6.
FIG. 6.

(Color online) Comparison of confinement characteristics before (black), post-first-boronization (red), and post-second-boronization (green). -mode points are unfilled, -mode points are filled. (a) vs the radiated power fraction; (b) vs the pedestal electron pressure .

Image of FIG. 7.
FIG. 7.

(Color online) Plotted is the stored energy vs discharge sequence number after an overnight boronization for two ICRF power levels.

Image of FIG. 8.
FIG. 8.

(Color online) The effect of boronization on impurities vs discharge sequence. Only steady state -mode discharges where the VUV instrument was tuned to the proper wavelength to cover iron and molybdenum are included. Boronizations are indicated as solid vertical lines. (a) Radiated power for molybdenum (circles) and iron (squares); (b) impurity fraction for molybdenum (circles) and iron (squares).

Image of FIG. 9.
FIG. 9.

(Color online) Power radiated by molybdenum (circles) and iron (squares) vs total radiated power. Same color coding as for Fig. 6. The molybdenum and iron radiation are generally lower after boronization (second).

Image of FIG. 10.
FIG. 10.

(Color online) The variation in neutral gas characteristics on a day following overnight boronization vs discharge number. Missing data are either due to problems with the measurement or problems with the discharge (did not breakdown, terminated early, …). (a) Gas injected; (b) retained. The two data points with open squares are obtained using method 1 as described in the text; (c) midplane pressure; (d) line-averaged density.

Image of FIG. 11.
FIG. 11.

(Color online) Effect of between-discharge boronization. (a) Variation of total neutrons during the -mode vs boronization period. These boronizations were all done with 50% duty cycle and utilized a 10% diborane, 90% He gas mixture. (b) Variation in radiated power just prior to the -mode transition vs the boronization scan center. These boronization scans were wide (pause at the center of scan) and utilized a 20% diborane, 80% He gas mixture, and a 50% duty cycle except the one point with 100% duty cycle.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Operation of Alcator C-Mod with high-Z plasma facing components and implicationsa)