10th ITPA conference, Avila, 7-10 Jan. 2008 Effects of High Energy Ions Accelerated in front of ICRF Antennas in LHD S. Masuzaki on behalf of the LHD Experimental.

10th ITPA conference, Avila, 7-10 Jan. 2008

Effects of High Energy Ions Accelerated in front of ICRF

Antennas in LHD

S. Masuzakion behalf of the LHD Experimental Group

National Insititute for Fusion Science

10th ITPA conference, Avila, 7-10 Jan. 2008

Fast Wave Antennas (Loop Antenna)

– Installed from top and bottom ports

– Single strap loop• twisted to fit the LHD plasma shape

– Sizes of launcher• length 60cm• total width 46cm• center strap width 30cm

– Most parts are water cooled for steady state operation

– Radial antenna position is movable by 16cm

10th ITPA, Avila, 7-10 Jan. 2008

Fast Wave Antenna (Loop Antenna)

3.5 U&L 4.5 U&L

7.5 U&L

10th ITPA conference, Avila, 7-10 Jan. 2008

Achieved Pulse Length and Injected Power

10th ITPA conference, Avila, 7-10 Jan. 2008

Experimental Condition for Minority Heating

10th ITPA conference, Avila, 7-10 Jan. 2008

Localized heat load on divertor plates are observed during long pulse discharges, and it causes gradual

density increase and termination of discharge.

Hot spot is formed on a bottom divertor plate

Density and radiation power increased with hot spot formation, and discharge was terminated at last.

10th ITPA conference, Avila, 7-10 Jan. 2008

Particle orbit calculation shows that accelerated ions in front of the antennas can slip out from divertor

trace

10th ITPA conference, Avila, 7-10 Jan. 2008

The calculation well reproduces the observed image.

10th ITPA conference, Avila, 7-10 Jan. 2008

Heat load and recycling increase is localized near ICRF antenna.

Toroidal distributions of temperature rise of divertor plates and Ha increase

10th ITPA conference, Avila, 7-10 Jan. 2008

Other Heating Mode for Steady State Operation

10th ITPA conference, Avila, 7-10 Jan. 2008

Summary• In LHD, ion cyclotron resonance for minority ion (prot

on) heating mode cross the ICRF antenna, and protons outside LCFS are accelerated just in front of antenna.

• The accelerated protons hit divertor plates locally, and rise the plates temperature. It causes density rise due to out-gassing, and terminates discharge.

• Particle orbit calculation well reproduce the localized heat load distribution.

• To mitigate the direct ion loss, other heating mode has been examined.

10th ITPA conference, Avila, 7-10 Jan. 2008

Additional viewgraphs

10th ITPA conference, Avila, 7-10 Jan. 2008

Hot spot on side protectors could be caused by RF sheath

10th ITPA conference, Avila, 7-10 Jan. 2008

Damaged divertor plates distribution agree with the distribution of high energy proton dep

osition

Distribution of high energy proton deposition

Distribution of damaged divertor plates