ITER ICRF R&D - ERM-KMS proposals P. Dumortier, F. Durodié, R. Koch, P. Lamalle, F. Louche, A. Messiaen, R. Weynants CCFW 37, Brussels, 22 November 2004

Proposed ITER R&D work items for LPP in RF analysis of antenna design 1 ppy  Optimization of straps and feeders re. loading, electric field, mutual coupling [continuation of 2004 Task, with a broader scope]  Optimization of matching circuit (detailed design using 3D modelling results) [continuation of 2004 Task; new study may be required depending on future selection of design options]  Generator control issues related to array phasing and mutual coupling effects.  Alternative matching schemes and options, e.g. (i) using decouplers, (ii) “passive” power splitting scheme with restriction to sym / antisym phasings,...  Document a design option with feedthroughs closest to feeders.  Possible participation in “ELM dump” design; evaluation of ELM-induced reduction of efficiency, etc. NB on the long term we would bid for detailed RF design work (incl. pumping, mechanics, thermal, disruption, ceramics, neutronics aspects…) for the design selected by an appointed ITER ICRF manager… [seems implicit in Europe’s 50% responsibility in the launcher]

2a. RF analysis of Faraday shield 1 ppy Unresolved questions remain, with a high impact on electrical performance and mechanical design. They must be addressed in due time. Faraday shields to be included in MWS antenna models to  Compare different shield types  Investigate the influence of shield opacity on loading and mutual coupling Parallel experimental activity on the scaled mockup:  Compare different shield types  Investigate the influence of shield opacity on loading and mutual coupling Review (again!) theory and experimental results (e.g. dependence of loading and heating efficiency on shield pitch relative to B 0 ), in view of optimization. Do we need more theory / experiments? Can also address analysis and design of antenna private limiters and septa, problem of RF contact between antenna box and first wall. Proposed ITER R&D work items for LPP in

2b. Additional RF analysis 0.5 ppy Sheath effects are systematically invoked to explain unaccounted power in (mainly non-dipole) ICRH experiments. The modelling effort worldwide (CEA + ?) should be increased. We propose to develop RF sheath calculations based on the MWS 3D RF fields, in collaboration with CEA. Antenna RF voltage standoff in presence of ELMs is another key issue requiring more attention. We propose to conduct a study on this topic, including survey of existing RF data & literature, of ELM data and models, appropriate analysis and tentative extrapolation to ITER ICRH. Proposed ITER R&D work items for LPP in

3. Further Prototype development 0.5ppy Line stretcher testing: in collaboration with W7-X, see following slides. Four-port junction: prototype procurement and testing (including cooling issues) Vacuum feedthrough: leave the lead to UKAEA; we need to coordinate RF aspects (different window designs depending where they are located) Scaled mockup: important role in matching algorithm development and testing, and evaluation of mutual coupling effects and load resilience on the phased array. Proposed ITER R&D work items for LPP in

6m-stroke line stretcher at JET Tuning line stretchers for ITER ICRF external matching On ITER: - Installed in port cell - Mounted horizontally in pairs - Mounted on trolley for easy displacement (cask operation) - Existing technology (similar ones delivered to JET) -14”, double trombone, 2 x 2m stroke - Silver contacts (3.33 kA capability) - NB: Space between vacuum windows and line stretchers sufficient to modify tuning layout - Visit to ITER team scheduled for update on space requirements

Transmission lines and line stretchers: Feasability discussed with Spinner Transmission lines Maximum electric field allowed in the lines outside the vacuum region: 8 kV/cm without pressurisation (air, 1 bar) 16 kV/cm with pressurisation (air, 3 bar) Proposed transmission lines: among standard sizes, 14” are the most suitable. This is valid for the different characteristic impedance parts (20 , 20/3 , 30  ) alumina holders with pressurisation with water cooling: the technology exists to introduce the water cooling. Cooling by strong air flow is also a possibility but requires a precise evaluation and needs expensive air blowers. length of a size transition from 270 mm to 345 mm at constant Z0 = 20  : less than 300 mm. Line stretchers Can be constructed with the same technology as the 6 m line stretchers delivered to JET (3 cascaded stages of 2 m stroke). As only 4 m stretchers are needed (2 stages of 2 m stroke) but in 14” (instead of 9” for JET) the volume needed would be comparable (basis of 1.0 x 1.74m2 and height of 2.73 m, motorization included) The line stretchers can be operated with horizontal trombones. The motion mechanism must be manufactured to take this option into account. Maximum current per unit length for the sliding contacts with the robust technology of massive silver ball contacts: 30 A per contact, the width of a contact is 7 mm. These sliding contacts do not require additional cooling. Tests have been performed on 9” lines in CW operation with 2 kA in the sliding contacts. With 60 balls for the inner sliding contact (i.e. more than 30 A per ball) and 96 balls for the outer sliding contact, the temperature increase of the contact was of only 0.3 K. The transmission line needs of course active cooling (see above).

Milestones JET-EP ICRF antenna planning  End June / early July 2005: low power RF measurements, probe assembly and calibration.  July 2005: installation on testbed.  Early August 2005: pumping.  August – September: commissioning on testbed, incl. at high power.  Matching studies  end October.  November 2005: installation on JET.  2006: commissioning and usage in JET campaigns  ERM to initiate work on ITER Design + R&D tasks in 2005, keeping main thrust in 2006 (after technical commissioning of IL antenna on JET) Decision on ITER ICRF design needs to await results from JET-EP antenna: not before end 2006!