1. Effects of ICRF conditioning on the first wall in LHD N. Ashikawa, K. Saito, T. Seki, M. Tokitani, Y. Ohtawa 1), M. Nishiura, S. Masuzaki K. Nishimura and A.Sagara 9th ITPA meeting on SOL/divertor physics, May 8, 2007 IPP Garching, Germany National Institute for Fusion Science, Japan Kyushu University, Japan 1)

2. Introduction Resonance layer with Bt=2.75T, Rax=3.6m, f=38.47MHz (LHD) 1.Investigation of effective area using material probes 2.Mode Conversion experiment with different frequency ICRF conditioning (ICC) for recycling control / deducing impurities and T removal using He, D,O2 gasses For Investigation of high energy tails, mode conversion experiment was done in 2006. As Heating efficiency of ICRF system, it was done in JET, C-mod and LHD. – –M.-L. Mayoral et al., NF 46 (2006) S550. – –Y. Lin, et al., POP 11 (2004) 2466. – –K. Saito, et al., NF 41 (2001) 1021. It is important for antenna design in ITER. In Helical device such as LHD, a confinement magnetic field during ICC is different in tokamaks. But a comparison between different operation scenarios using relative ratio can be possible.

3. Experimental setup in LHD Hydrogen removal rate with He gasses by GDC is 10 times larger than ICC in LHD. B t =2.75T, R ax =3.6m ICRF heating antennas at 3.5 and 7.5 port Working gas was He (10 -3 -10 -1 Pa) f=38.47MHz ， 85MHz Duration time is 3 second (on), and interval time is 2 second (off). P icrf =8-149kW (2004FY ） -287 kW(2006FY)

4. Material probes setup From experiences (LHD, AUG, others), effective cleaning area by ICRF conditioning is considered smaller than by glow discharge From damages area of material probes, effective cleaning area by ICRF conditioning was estimated. Material holder was installed at the first wall level. It have three kinds of facing. Plasma １． Plasma Facing Area ３． Gap （ slit 1.5mm) Demonstration between divertor tiles ２． Vertical direction

5. Plasma facing Vertical Gap ×2 B Bright field images,SS316L ICRF conditioning (about 4000s) Transmission Electron Microscopy （ TEM ） Analysis Damages with He bubbles are observed only plasma facing area - Vertical : small - Gap : non Number of damages is depend on direction － － it is suggested effective particles come to the wall straight － ICC is difficult for shadow area. 200nm

6. Mode Conversion Exp.(1) High energy distributions were measured by Si fast neutron analyzer (FNA). 38MHz,1.5T38MHz,1.5T 38MHz, 2.75T : He 2 nd harmonics38MHz, 2.75T : He 2 nd harmonics 85MHz, 2.75T : electron accelerated mode85MHz, 2.75T : electron accelerated mode 85MHz(30%)+38MHz(70%) : mix85MHz(30%)+38MHz(70%) : mix High energy tails are observed on He 2 nd harmonics mode (38MHz, 2.75T) High energy ion particles were not observed at electron accelerated mode.High energy ion particles were not observed at electron accelerated mode. Tail distribution does not depend on an input power.Tail distribution does not depend on an input power. Natural Diamond Detector measured particle flux by ICC.Natural Diamond Detector measured particle flux by ICC. 1.6 – 3.2 x 10 5 at #70825 (38MHz, 2.85T, 287kW).

7. Mode Conversion Exp. (2) 38MHz,1.5T : Low removal rate38MHz,1.5T : Low removal rate Comparison of 38MHz and 85MHz with 2.75T : ?? (difficult)Comparison of 38MHz and 85MHz with 2.75T : ?? (difficult) 85MHz 38MHz 38MHz, 1.5T From comparison of modes with 1.5T, 38MHz w/o tails and 2.75T, 38MHz with tails, with high energy distribution mode have higher hydrogen removal rate.

8. Function of power density, P in /(pV) 1) V; Volume of vacuum camber P in ; Input power of ICRF antenna. p; He partial pressure Powers: -800kW(TEXTOR) He Pressures: 0.55 Pa( HT-7) Minimum estimation for ITER, about 100 kW/Pa m 3 is shown using 0.01 Pa and 3MW (using pulse mode). Function of power density is used as a function of accelerating power to particles Power density related to hydrogen removal rate 1) E. de la Cal PPCF(2005)

9. Summary Using material probes, damaged area is observed in LHD. On the first wall level, only plasma facing area have damages with helium bubbles. A shadowed area have no damage. In future, we have a planning the same experiment in EAST. From mode conversion experiment, different high energy distributions were measured during ICC. From comparison of modes with 1.5T, 38MHz w/o tails and 2.75T, 38MHz with tails, with high energy distribution mode have higher hydrogen removal rate. Particle flux measured by NDD is 1.6 – 3.2 x 10 5. Comparison of hydrogen removal rate and power density of ICC shows a good relation. Using new design parameters of -3 MW with 0.01 Pa for ICRF antenna, a power density of ICC in ITER is same level in current devices.