Technical developments Recent ICRH physics topics on TS

1. ICRH activity on TS • Technical developments • Recent ICRH physics topics on TS

2. Development of RF loads [ er = e’r – j e’’r] H. Bottellier-Curtet M. El-Khaldi Studies are on-going to propose alternative solutions to improve the RF loads used to qualify at low power ICRF array. The studies are considering passive and active loads.

3. Development of RF loads Existing load [ er = e’r – j e’’r] Water : 81 – j 0 Soda water : 81 – j 400 Electrolyte : 81 – j 1700 • Searching loads with high e’’r (2000, e’r= 0) is not a conclusive option with loading resistance not exceeding 2.2 Ohm/m. • The proposed solution is to explore medium with high e’r (>1000 e’’r = 0). Two technological approaches are investigated : • Composite material • Meta-material

4. Development of RF loads • Main characteristics of the passive load : • Isotropic medium • Power stand-off : few W • Volume : < 1 m3 • Electromagnetic properties : • Some candidate of composite material featuring poly-crystalline structure : • Perovskites : PbZrxTx-1O3 (PZT), Ba TiO3 , SrTiO3 (BST) • KTaNbO3 (KTN) (er ~ 1000 – j0) { er = e’r – j e’’r= 1000 – j 0 mr = m’r– jm’’r = 1 – j 0

5. Development of RF loads The TS antenna prototype will be used to test some of these mediums. Several candidates are foreseen : • Absorbing foam loaded with carbon composite • Powder of composite material diluted inside a water load (powder of BST ceramic in water : er ~1000 – j0)

6. Development of RF loads Use of Meta-material * In the meantime, the feasibility of array based on meta-material are explored in collaboration with French laboratories. εr’ = 300 [Ikonen2007], Helsinki U εr’ = 1 000 possible ? * Definition : Macroscopic composites having a manmade, three-dimensional, periodic cellular architecture designed to produce an optimized combination, not available in nature, of two or more responses to specific excitation.

7. RF test of sliding contact Multilam LA-Cut RF test under pressurized N2 have started November 28th and will be followed by vacuum test.

8. RF test of sliding contact

9. Water loop for ITER relevant RF test Pre-design of an ITERrelevant water loop for the qualification of RF components (D. Thouvenin) HV: Hand Valve SV: Switch Valve Demineralised water Expansion tank Buffer tank CV: Control Valve Safety valve Heater Drain off Pump Drain off Filtrer Heat exchanger Drain off Decarbonated water

10. Water loop for ITER relevant RF test Main technical characteristics

11. Water loop for ITER relevant RF test Implantation studies near the TS RF antenna test facility The water loop alone is a rather compact facility, but it require connection to many auxiliary systems, (demineralised filling loop, decarbonated water, nitrogen …) and imply strong constraints related to the safety. The water chemical characteristics and the baking conditions lead to strong constraints for the choice of the components  Impact on the cost. RF test stand TS RF sources

12. Water loop for ITER relevant RF test Cost estimate

13. Prospective study for a new Faraday screen The aging of the B4C coating on TS FS leads to strong operational limits. Different strategies are under consideration to resolve this matter. One of them is to build a new screen based on an innovative structure, that can be used for comparative studies and code benchmarking. All ideas are welcome. ICANT model of a FS with retracted box edge

14. Recent ICRF Physics topics on TS • ICRF wave coupling • Role of local gas injection • « Long distance » coupling • High power scenarios with combined ICRH and LHCD • Development of ICRH scenarios around Bt=2T • 2H, 2.12T- 63MHz • 2H, 1.87T- 57MHz • FWEH, 2.10T- 48MHz • Search for sub-harmonic emission from plasma in ICRF range • Collaboration S. Assas, IPP-Garching • ICRF wall conditioning • Collaboration A. Lyssoivan, ERM-KMS, see D. Douai

15. Experimental protocol ICRH Q5 Q6a Q6b Reflect. V9 outboardlimiter V7 Q2b Q1b • ICRH : Q5 antenna (1MW) • Gas inlet module V9 • Connected to Q5 antenna •  local edge density ? • Feed-forward, prescribed • Gas module V7 • Not connected to Q5 ant. • Control core density • Feedback on interferometry (request nl~4.65×1019m-2) • Edge n profiles • X-mode reflectometry • Not connected to Q5-V9 • Connected to V7 •  antenna-plasma gap

16. Preliminary results From reflectometry (ncutoff=9×1018m-3) • Rstrap-Rcutoff up to 12cm, limits = max. current on capa. ; then matching lost. • Weak effect of local gas injection on RF coupling. • Side-effect of V7 injection on profiles « seen » by reflectometer ?

17. Development of a high RF power scenario at reduced field Plasma parameters • B0 = 2T, circular plasma • Ip = 700kA • nl ≥ 5x1019 m-3 • LH + ICRF power. ICRF operation parameters • 2nd harmonic H heating • f = 63MHz, dipole Preliminary conclusions • Good wave coupling • Efficient plasma heating • Main issue: thermal effects (hot spots) on antennas • Still requires optimization TS Shot #42785

18. High power ICRH +LHCD discharges • sharp transitions of saw teeth amplitude and period • likely related to fast ion tail stabilization • no intermediate values. Threshold ? Ptot (MW) Ptot (MW) PIC (MW) PIC (MW) Te0 (keV) Te0 (keV) ne0 (1019 m-3) ne0 (1019 m-3) PLH (MW) PLH (MW) Ip (MA) Ip (MA) PEC (MW) Bi-stable saw tooth behavior

19. MHD: fast ion modes ICRH driven fast ion tails • 40-70 kHz modes observed by reflectometry during strong ICRH (H minority heating) • Identified as Beta Alfvén Eigenmodes (BAE) • Measured frequencyvs dispersion relation • Experimental vs theoretical threshold (C. Nguyen, PoP, to be published)