Exploration of HHFW coupling via modulation.

1. Exploration of HHFW coupling via modulation. HHFW XP-2 Presented by Stefano Bernabei for the RF group

2. 1 Overview of planned experiment We would like to devote this year’s experimentation to clarifying and understanding coupling of the waves to the plasma, which we believe is the most important parameter for the success of HHFW. XP 1 proposes experiments with different configurations of magnetic field and current directions. (already presented) XP 2 is designed to continue and complete last year’s runs of pulsed RF power to obtain heating effectiveness.

3. 2003-2004 results best heating with 180° (high n||, ~symmetric spectrum). heating for +90° (counter-CD) usually a little better than for -90° (co-CD), but: -90° exhibits higher Da, higher radiated power and better loading: this suggests excitation of surface waves. Power lost in excitation of surface waves and parametric instabilities at the edge (detected) can explain the lower heating for -90°

4. modulation experiments yield percentage of absorbed power and confinement time. definitely 180° heats best in spite of lower confinement time Is coupling playing a major role? Is it due to outer radius damping for 180° (and +90°) because of higher n||?

5. 2 justification The results of last year were incomplete. First of all the discharges in Deuterium were not as good as those in Helium, so we lack a comparison between the two (see next slide). As indicated, we have no good explanation for the difference in confinement time for different phases. We did not explore other parameters which could (should) affect coupling, such as plasma-antenna distance, Kappa….. MMM But over all, the point is that we have incomplete understanding of RF coupling.

6. The problem with 60 Hz Plasma exhibited a noise at 388 Hz caused by a power supply: it did not greatly jeopardize the analysis. Noise at 60 Hz also was present almost all the time, but the level varied a lot from day to day. It was rather big on June 24 2004 when we run the pulsed RF experiment in deuterium, altering the results. For this reason we would like to have the right not to run if the 60 Hz noise is too high on that day.

7. 3 experimental run plan We want to start with 2 shots varying the level of RF power between the single pulses. The reason being that, since we cannot obtain a complete 0-power for technical reasons, we need to know if the small power left between pulses causes error in the calculation of t-confinement. 3 RF pulses starting at t=0.2 sec Each pulse 33 ms long, separated by 33 msec Power level between shots: 150 and 300 kW Phase = 180° Machine conditions as in shot 112705

8. experimental run plan (continued) After checking the validity of the 2004 scans, we will change the shape of the RF pulses to the following: 0.15 MW

9. experimental run plan (continued) Same conditions as follows, 2 shots at 600kA, with phase = 180° to compare and confirm 2004 results ________________________________________________________________________ Ip = 300kA B = -4.4 kG Helium K = K = 1.7 desired DND Prf = 3 MW Outer gap = 0.04 Density = 10^19 2 shots @ -90° 2 shots @ +90° 2 shots @ 180° 1 shot no-RF ________________________________________________________________________ Ip = 900kA ------------------ (if 900kA cannot be achieved, then 800kA) B = -4.4 kG Helium K = K = 1.7 desired DND Prf = 3 MW Outer gap = 0.04 this 3 conditions constitute a current scan Density = 10^19 which corresponds to a scan of the field pitch angle. 2 shots @ -90° 2 shots @ +90° 2 shots @ 180° 1 shot no-RF

10. experimental run plan (continued) Different Kappa • Ip = 900 kA • B = -4.4 kG • Helium • K = K = 1.9 • desired DND • Prf = 3 MW • Density = 10^19 • Outer gap = 0.04 • 2 shots @ -90° • 2 shots @ +90° • 2 shots @ 180° • 1 shot no-RF Total 27 good shots TS should fire at t-to= 0.011 and 0.022, during each shot. Where to is either the shut off or the turn on of the single pulse Fast EFIT can be run between shots, so that it can be decided if the shot is suitable for analysis or not.

11. Requirements: we definitely need the machine, RF power and diagnostics. 5. Planned analysis What analysis of the data will be required: EFIT, TRANSP, etc. Fast EFIT will be our primary tool 6. Planned publication of results What will be the final disposition of the results; where will results be published and when? These data, combined with the data obtained in the last few years, will be suitable for a publication summarizing the HHFW experiment (no CD).