Advances In High Harmonic Fast Wave Heating of NSTX H-mode Plasmas P. M. Ryan, J-W Ahn, G. Chen, D. L. Green, E. F. Jaeger, R. Maingi, J. B. Wilgen - Oak Ridge National Laboratory, Oak Ridge, TN, USA R. E. Bell, J. C. Hosea, S. M. Kaye, B. P. LeBlanc, C. K. Phillips, M. Podestá, G. Taylor, J. R. Wilson - Princeton Plasma Physics Laboratory, Princeton, NJ, USA P. T. Bonoli - MIT Plasma Science and Fusion Center, Cambridge, MA, USA R. W. Harvey - CompX, Del Mar, CA, USA • Goal was to bring system voltage limit with plasma (~15 kV) up to its vacuum limit (~25 kV), thus increasing the power limit by a factor of ~2.8. • For a given strap current – Peak strap voltage would be halved. – Peak voltage on vacuum side of feedthrough would be reduced by ~30%. – Peak system voltage in transmission line would remain unchanged. • Tests whether electric fields in strap/Faraday shield region or the strap/antenna frame currents set the limit for plasma operation 12 Antenna Straps 30 MHz RF Power Sources 5 Port Cubes Decoupler Elements HHFW antenna extends toroidally 90º • 12 straps are connected to form two adjacent 6-element arrays, 180º out of phase with each other. • For phase shifts of 30º, 90º, and 150º, it operates as a 12-element array with a single highly directional peak. 3λ/4 (7.5 m) λ/2 (5 m) λ/2 (5 m) Transmitter powe 5λ/4 (12.5 m) Original Upgrade Transmitter powe Original RF Feeds Original RF Feeds Previous Ground Previous Ground New Ground New Ground New Feeds New Feeds Antenna Upgraded To Reduce Peak Voltages on the Straps Extensive Antenna Conditioning Needed For Li Operation Dual Liquid Lithium Evaporators ~ Dual Lithium Powder Droppers Liquid Lithium Divertor Observation of Arcs During Plasma Conditioning • Li deposited on antenna contributed to arcing and had to be cleaned by plasma conditioning • Three visible light cameras (1000, 2000, and >30,000 fps) observing antenna during plasma condtioning in He, L-mode plasma. • Shot 135242 had three transmitter trips during a 200 ms, 2.6 MW pulse at -90º phasing. 0.188s 0.418s RF Power (MW) Transmitter 1 (straps 1 & 7) trips off at 188.1 ms 8 9 10 11 12 12 3 45 6 7 8 9 189.755 ms 191.755 ms 193.755 ms 195.755 ms 189.749 ms 191.751 ms 193.753 ms 195.755 ms 189.742 ms 191.742 ms 193.742 ms 195.742 ms 2000 fps 38,460 fps 1000 fps Standard camera sees straps 6- 12 Fast camera sees straps 8- 12 Additiona l camera sees straps 1- 9 Transmitter 5 (straps 5 & 11) trips off at 418.1 ms 414.655 ms 416.655 ms 419.655 ms 414.649 ms 416.651 ms 419.615 ms Ohmically-Heated Helium Target Plasma Transitions to H-Mode During 2.6 MW HHFW Pulse k = -8 m -1 •GENRAY ray tracing simulation predicts HHFW power deposited on electrons inside ~ 0.5. •Broader power deposition during H-mode. • Negligible damping on He predicted, some H minority heating (1 MW, k = -8 m -1 , He with 3% H minority) H-mode Initiated & Maintained Through ELMs with P RF ~ 2.7 MW During ~ 2 MW D 2 NBI (Shot 135340) • Transition to H-mode occurs after RF turn on and without RF arc. • With reflection coefficient trip level set to 0.7, RF stays on during ELMing plasma. k = - 13 m -1 Li Operation Improves Power Coupling to the Core RECORD T e
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Advances In High Harmonic Fast Wave Heating of NSTX H-mode Plasmas
Original RF Feeds. Decoupler Elements. 30 MHz RF Power Sources. 5 Port Cubes. New Ground. RF Power (MW). 12 Antenna Straps. New Feeds. Previous Ground. Antenna Upgraded To Reduce Peak Voltages on the Straps. 0.188s. 0.418s. HHFW antenna extends toroidally 90º. - PowerPoint PPT Presentation
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Advances In High Harmonic Fast Wave Heating of NSTX H-mode Plasmas
P. M. Ryan, J-W Ahn, G. Chen, D. L. Green, E. F. Jaeger, R. Maingi, J. B. Wilgen - Oak Ridge National Laboratory, Oak Ridge, TN, USAR. E. Bell, J. C. Hosea, S. M. Kaye, B. P. LeBlanc, C. K. Phillips, M. Podestá, G. Taylor, J. R. Wilson - Princeton Plasma Physics Laboratory, Princeton, NJ, USAP. T. Bonoli - MIT Plasma Science and Fusion Center, Cambridge, MA, USAR. W. Harvey - CompX, Del Mar, CA, USA
• Goal was to bring system voltage limit with plasma (~15 kV) up to its vacuum limit (~25 kV), thus increasing the power limit by a factor of ~2.8.• For a given strap current
– Peak strap voltage would be halved.– Peak voltage on vacuum side of feedthrough would be reduced by ~30%.– Peak system voltage in transmission line would remain unchanged.
• Tests whether electric fields in strap/Faraday shield region or the strap/antenna frame currents set the limit for plasma operation
12 Antenna Straps
30 MHz RF Power Sources5 PortCubes
DecouplerElements
HHFW antenna extends toroidally 90º
• 12 straps are connected to form two adjacent 6-element arrays, 180º out of phase with each other.• For phase shifts of 30º, 90º, and 150º, it operates as a 12-element array with a single highly directional
peak.
3λ/4 (7.5 m)
λ/2 (5 m)
λ/2 (5 m)
Transmitter power
5λ/4 (12.5 m)
Original
Upgrade
Transmitter power
Original RF Feeds Original RF Feeds Original RF Feeds Original RF Feeds