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CEA comments on documents provided by the Project Leader

CEA comments on documents provided by the Project Leader. Introduction I Performance issues II Operation Issues III. Manufacturing aspects IV. Feasibility / Planning issues V. Conclusion. Risks. planning. performances. ressources. Introduction. Performance issues

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CEA comments on documents provided by the Project Leader

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  1. CEA comments on documents provided by the Project Leader IntroductionI Performance issuesII Operation IssuesIII. Manufacturing aspects IV. Feasibility / Planning issuesV. Conclusion

  2. Risks planning performances ressources Introduction

  3. Performance issues The ITER-like Ion Cyclotron antenna is developed to assess whether the performances predicted for the ITER launching structure (or possibly better performances) can be achieved in similar experimental conditions (in particular : high power density and ELMs resilience)

  4. In the JET-EP reference design, these performances cannot be achieved. The tuning network is likely to limit the array operation. • The Operational Domain (Minimum load vs Frequency) is reduced due to CW 3W 400** tuning capacitor power handling limits. • Actual frequency range 33-52 MHz • Minimum plasma load accessible at full power (dependent on frequency) 3 - 3.5 W/m • Power and/or pulse length de-rating required to access the minimum load (2 W/m). • Max pulse length (due to temperature rise in fixed capacitor electrode) • Max pulse length at 4 W/m 18 s • Max pulse length at 2 W/m 9.8 s **This capacitor was qualified by high power tests.

  5. Limits of CW 3W 400 voltage Current Power limit Pulse length & duty cycle limit fc He3 fc H

  6. Notes : Electrical and performance domain calculations are based on a TEM modelling, in general optimistic (e.g. the current distribution on the surface of the structures are assumed to be uniform and losses due to field concentrations are not allowed for). As the margins are small, any deviation from models will result in performance derating.

  7. The thermal analysis in the capacitor area is subject to large error bars, since it relies on small thermal fluxes exchanges, across the ceramic ring and the finger contacts (Ratio: average power/max power < 1%) . Radiation loads supposed to be negligible. Strap Average transfert 20 W for DT=30 °C Constant flux = 10 W typ. or 0 (cooling) Ceramic Peak power =2 000 W Thermal shield = 0 W? <power> =Phf*(dutycycle)+Pstrap+Prad

  8. 3. Power transfer efficiency limitation if external matching used VSWR at band edge single stage transformer is ~3 • Increase in MTL voltage: 20 kV • Increase in MTL losses: 5% Note: The proposed tuning system, if extrapolated to ITER power would require the simultaneous control of 64 variable components (32 capacitors, 16 phase shifters and 16 stubs) Case 3/30 W

  9. Operational Issues Instrumentation: Essential monitors for control and protection not described in the report, VTL unlikely to be used for RF probes because of high order modes, Matching: Matching strategy unclear If external tuning used, matching conditions over determined and presumably controlled by monitors different in type and location.

  10. Manufacturing Issues Some design features appear unnecessarily complex, and this may have implications on cost and planning: • Non symmetric nor modular antenna and tuning system geometry • External capacitor bellows may be unnecessary if an hydraulic or a compact electric drive are adopted • Big bellows and heavy external support structure • VTL odd shape • Curved housing back plate

  11. Feasibility / Planning issues • Strap to capacitor connections The proposed solutions (contact fingers, current carrying capability, pressure requirements …) are not yet qualified, Three different options proposed, to be studied and tested.

  12. A tricky approach proposed to accommodate (computed) high stresses on ceramic brazed joints due to disruption currents. • A re-design of the capacitors is planned to hold the loads on the brazed joint. This is a heavy and possibly long and hazardous development to come: • Any change on a COMET capacitor has always proved to be very long to implement (stainless steel bellows ~4 years). • Concerning the development foreseen on the brazed joint, predictive modelling is only an indicative tool in this field where know-how and experience are essential. • Other remedies (such as transferring the induced currents to a shielding component or to stress relieve the capacitor by flexible elements) should perhaps be considered.

  13. Conclusions • The performances do not meet all requirements. • Design margins are small, • The operational domain could be actually smaller than estimated. However, the projected performances may fulfil power handling and ELMs resilience demonstration at a single frequency (optimisation ?) provided that the coupling is high enough. • Changes in requirements should be formally accepted by the Customer. 2. Doubts on feasibility of critical items (contacts, capacitors). 3. Success of planned R&D hardly achievable in the available time scale.

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