Euratom TORE SUPRA

1

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

Euratom TORE SUPRA

2

Introduction

planning

performances

ressources

Risks

Euratom TORE SUPRA

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)

Key target parameters

Phase II proposal June 2000

PB Meeting

July 2001

Load range > 2 /m (reference loading 4 /m)

2 /m

(at low frequency)

Frequency range: 30-55 MHz 30-55 MHz

Coupled power 9 MW/m2 8MW/m2

Efficiency: 95% 90%

Pulse length : 20s 20/10s

Euratom TORE SUPRA

4

1. 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 /m

- Power and/or pulse length de-rating required to access the minimum load (2 /m).

2. Max pulse length (due to temperature rise in fixed capacitor electrode)

- Max pulse length at 4 /m 18 s

- Max pulse length at 2 /m 9.8 s

**This capacitor was qualified by high power tests.

In the JET-EP reference design, these performances cannot be achieved.

The tuning network is likely to limit the array operation.

Euratom TORE SUPRA

5

fc He3 fc H

Limits of CW 3W 400

voltageCurrent

Powerlimit

Pulse length &duty cycle limit

Euratom TORE SUPRA

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.

Euratom TORE SUPRA

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.

Peak power =2 000 W

Constant flux= 10 W typ.or 0 (cooling)

Thermal shield = 0 W?

Average transfert 20 W for T=30 °C

Strap

Ceramic

<power> =Phf*(dutycycle)+Pstrap+Prad

Euratom TORE SUPRA

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)

1.0

1.5

f Hf He

30 36.25 42.5 48.75 551

1.75

2.5

3.25

4

frequency

Tha

nfor

mer

inpu

t VSW

R

.

Case

3/30

Euratom TORE SUPRA

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.

Euratom TORE SUPRA

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

Euratom TORE SUPRA

11

Feasibility / Planning issues

1. 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.

Euratom TORE SUPRA

12

2. 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.

Euratom TORE SUPRA

13

Conclusions

1. 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.