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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.

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D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004

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  1. 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 D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004

  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 Test particle simulationsElectron motion in the “near-field” approximation [Fuchs] PIC simulations(i)Electron time scales [Rantamäki] (ii)Ion time scales [Tskhakaya] Fluid simulations3D fluid model [Petržilka] “Quasi”-PIC simulationsElectron motion in the “exact” field [Tskhakaya] D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004

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

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

  6. Quasi-PIC model 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 TEMfield) Schematic of quasi-PIC simulation of electron acceleration in front of the LH grill. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004

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

  8. 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]. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004

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

  10. DETAILED DESIGN DESCRIPTION LOWER HYBRID HEATING AND CURRENT DRIVE SYSTEM by Ph. BIBET, G. BOSIA (2001) PAM support structure 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 modes TE01+TE02+TE03 Frequency 5 GHz Plasma end Preliminary results for ITER D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004

  11. Preliminary results for ITER ITER PAM Simulation Number of waveguides 24 32 Width of active waveguide mm 9.25 7.5 Width of passive waveguide mm 7.25 0 Width of septa mm 3 3 Frequency GHz 5 3.7 Phasing 270° 90° Maximum final energy vs “rounding” radius, R. Case with E0=4 kV/cm. [Bibet 2001] D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004

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

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

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

  15. Conclusions • The results obtained indicate that the radial width of the high energy beam observed experimentally (2-5mm) 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. D. Tskhakaya, LH SOL Generated Fast Particles Meeting IPP.CR, Prague December 16-17, 2004

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