1. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004 Quasi-PIC modelling of electron acceleration in front of the ITER LH antenna D. Tskhakaya Plasma and Energy Physics Group, Association Euratom – ÖAW, Department * Permanent address: Institute of Physics, Georgian Academy of Sciences,Tbilisi, Georgia

2. Outline of the Talk Introduction “Quasi”-PIC model for electron acceleration Results for CASTOR and Tore-Supra Preliminary results for ITER Conclusions D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004

3. Introduction Different models of particle acceleration in front of LH antennas “Quasi”-PIC simulations Electron motion in the “exact” field [Tskhakaya] Test particle simulations Electron motion in the “near-field” approximation [Fuchs] PIC simulations (i) Electron time scales [Rantamäki] (ii) Ion time scales [Tskhakaya] Fluid simulations 3D fluid model [Petržilka]

4. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004 The near-field approximation only inside the Rayleigh zone The experimentally observed electron beam width: 2-5 mm. Introduction

5. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004 Quasi-PIC model Simulation area In the cold plasma approximation, neglecting coupling between the slow and fast waves we have

6. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004 Quasi-PIC model Schematic of quasi-PIC simulation of electron acceleration in front of the LH grill. i) can be obtained from a self-consistent plasma – slow wave coupling code (e.g., SWAN) ii) A simple analytic approximation can be used (for example the TEM field)

7. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004 Results for CASTOR and TS CASTOR: Near-field approximation CASTOR: exact field

8. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004 Results for CASTOR and TS The time needed to reach the stationary state after “switching on” the LH grill is defined by the average electron fly time in front of the grill, and can be from 60 (CASTOR) to 500 (TS) Time evolution of the number of simulation particles [Tskhakaya 2002].

9. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004 Results for CASTOR and TS Radial profiles of the average energy carried by electrons having been accelerated in front of the grill. Energy absorbed in the “first peak”: CASTOR Tore Supra

10. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004 Preliminary results for ITER PAM support structure Plasma end DETAILED DESIGN DESCRIPTION LOWER HYBRID HEATING AND CURRENT DRIVE SYSTEM Number of launchers 2 Power per launcher 20 MW Power density (active wg) 33 MW/m2 Working electric field < 6.2 kV/cm Number of PAM (per launcher) 4 Number of active/passive wg per PAM 24/25 Width of active/passive wg (mm) 9.25/ 7.25 Type of the modesTE 01 +TE 02 +TE 03 Frequency5 GHz by Ph. BIBET, G. BOSIA (2001)

11. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004 Preliminary results for ITER Maximum final energy vs “rounding” radius, R. Case with E 0 =4 kV/cm. [Bibet 2001] 3.75 Frequency GHz 33 Width of septa mm 07.25 Width of passive waveguide mm 7.59.25 Width of active waveguide mm 3224 Number of waveguides SimulationITER PAM 90°270° Phasing

12. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004 Preliminary results for ITER The “exact” toroidal electric field in front of ITER LH antenna. n || < 500. n || < 40 (corresponds to R=1.5 mm)

13. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004 Preliminary results for ITER Average energy of electrons vs timeNumber of simulated electrons vs time Results for near-field approximation

14. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004 Preliminary results for ITER Electron distribution function

15. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004 Conclusions The results obtained indicate that the radial width of the high energy beam observed experimentally (2-5 mm) can be explained as a combined effect of the radial structure of the ”electric field in front of the grill and of the damping of high n || modes by accelerated electrons For studying of electron acceleration time periods of a few hundreds of LH wave periods are required The average energy of electrons accelerated in front of the ITER LH antenna (with a sharp septa) should not exceed 400 eV. Future plan: To complete simulations with the “exact” field and study effect of rounding of the septa.