Transcript BS-M01 - JET ITER-like ICRH Antenna

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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
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Introduction
Risks
planning
performances
ressources
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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
> 2 W/m (reference
loading 4 W/m)
2 W/m
(at low frequency)
30-55 MHz
30-55 MHz
9 MW/m2
8MW/m2
Efficiency:
95%
90%
Pulse length :
20s
20/10s
Load range
Frequency range:
Coupled power
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In the JET-EP reference design, these performances cannot be achieved.
The tuning network is likely to limit the array operation.
1.
2.
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.
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Limits of CW 3W 400
Power
limit
Pulse length &
duty cycle limit
fc He3
fc H
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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.
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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)
Peak power =2 000 W
Ceramic
Thermal shield = 0 W?
<power> =Phf*(dutycycle)+Pstrap+Prad
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Power transfer efficiency limitation if external matching used
VSWR at band edge single stage transformer is
•
Increase in MTL voltage:
20 kV
•
Increase in MTL losses:
5%
~3
4
Thanformer input VSWR
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f He
3.25
fH
Case
2.5
3/30 W
1.5
1.75
1.0
.
1
30
36.25
42.5
48.75
55
frequency
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)
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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.
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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
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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.
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2.
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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.
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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.
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