C-Mod ICRF Research Program C-Mod Ideas Forum December 2-6, 2004 MIT PSFC Presented by Steve Wukitch Outline: 1. Overview of ICRF program 2. Summary of MP s and proposals
ICRF Highlights Antenna Performance Evaluation and Coupling: Demonstrated high power, phased antenna (4-strap) operation with performance independent of antenna phase. Found the loading variations in C-Mod are dominated changes in the H-mode density pedestal. Mode Conversion Physics: Simultaneously measured the Fast, Ion Bernstein (IBW), and Ion Cyclotron (ICW) waves in the mode conversion region using a phase contrast imaging diagnostic in D( 3 He) plasmas. Initial mode conversion current drive (MCCD) results suggest possible sawtooth control. Energetic Ion Physics: Observed first monster sawteeth in C-Mod. Observed sawtooth period dependence on antenna phase for central H minority heated plasmas. Measured core localized Alfvén modes in both current rise and high power ICRF experiments.
Context of the C-Mod ICRF Program Primary auxiliary heating system on C-Mod ITER initially plans to have 20 MW ICRF heating power. Most critical element is the antenna. Provides means for burn control.» Heat bulk ions no other means available.» Control sawtooth period. Provide peaked on-axis current drive during advanced scenario. Physics understanding of energetic particles is of obvious importance for burning plasma experiments. Core localized Alfvén modes are likely to be the most unstable. Fast particle transport in the presence of Alfvén modes is another important issue.
ICRF Research Themes Reliable antenna coupling with minimum negative impact on the plasma. Antenna performance with Mo and BN protection limiters. Parametric dependence of power and voltage handling. Develop understanding of limits with 3-D TOPICA modeling. Examine weak single pass absorption scenarios. Is H-mode heated by D( 3 He) similar to D(H) scenario? Does the impurity production increase with weak single pass? Investigated mode conversion in ICRF experiments. Compare PCI and power deposition measurements with TORIC in the mode conversion regime.
Research Themes Continued Investigate mode conversion current drive (MCCD). Specifically evaluate the impact of mode converting to ion cyclotron waves in addition to ion Bernstein waves. Experimental exploration of mode conversion flow drive (MCFD). Theoretical calculations are difficult and Experiments could provide important insight. Investigate and develop sawtooth control. Utilize both fast particle pressure and localized current drive to control sawtooth period. Investigate Alfvén modes driven by minority ion population in both current ramp and high power ICRF experiments.
Tasks Matching network: Test and implement prototype fast ferrite matching network. Antennas: Evaluate antenna operation with metallic limiters. Test J- antenna voltage handling with shorter vacuum transmission lines. Diagnostics: Upgrade PCI to higher k and perform proof of principle localization experiment. (DOE Diagnostic Initiative) Test and implement active charge exchange for H minority energy distribution. Increase number of poloidal B-dot coils for Alfvén mode identification (toroidal mode number).
Overview of the ICRF System D &E J antenna Thru 2006 Frequency Power Antenna Phase D & E ~ 80 MHz 2 x 2 MW 2 x 2 Strap fixed J 50,70, MHz 4 MW 4 Strap variable
Summary of Active MPs, Proposals, and Ideas Title MP/Proposal J antenna Freq Comments RF conditioning MP355 All Always needs to be done 50 MHz operation MP355 50 Need to overcome transmitter problems Fast Ferrite matching prototype initial plasma operation new Commission and test units and assess potential use. Piggy back experiment Modified antenna performance Revise MP295 Perform experiments to investigate J antenna with BN tiles and short vacuum transmission lines
Summary of Active MPs, Proposals, and Ideas Title MP/Proposal J antenna Freq Comments Plasma performance with Mo protection tiles Revise MP376 To be compared with performance obtained with BN protection tiles. Investigate D( 3 He) minority and mode conversion heating MP390 50 Direct comparison of D(H) and D( 3 He) minority heating in same discharge. Evaluate MCCD Revise MP356 50 A. Parisot thesis subject Investigate MC poloidal or toroidal flow drive MP3 50 Investigate ICRF MC in D(H), D( 3 He), H( 3 He) discharges Revise MP272 50, Has been done in piggyback New high k and localization will yield further insight.
Summary of Active MPs, Proposals, and Ideas Title MP/Proposal J antenna Freq Comments ICRF minority tails Characterization via Neutral Particle Analysis MP389 Initial data was promising. V. Tang s thesis subject Influence of ICRF on sawtooth behavior MP380 First monster sawteeth on C-Mod were recently achieved Double mode conversion D/ 3 He/H at 6.4-7.4 T recycled Past idea without MP Investigation of RF edge heating recycled New diagnostic necessary TORIC simulation of energetic particle modes new