l. zanotto, 13th rfp workshop, stockholm10/10/2008 similarity experiments on rfx-mod and mst...
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L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
Similarity experiments on RFX-mod and MST
standard discharges: magneticsT. Bolzonella, P. Franz, D. Terranova, L. Zanotto and the RFX team
A. Almagri, D.J. Den Hartog, G. Fiksel , J. Reusch, J. Sarff and the MST team
13th RFP Workshop, Stockholm, 9-11 October 2008
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
Motivations & aims
Definition of a general framework and methodology to compare different RFPs (in non-standard discharges also)
Establish standard discharges on both MST and RFX-mod under similar operative conditions and in the same parameters space
Compare results with common “processing” methods
Beginning of an exercise which can be extended to old RFX machine and other RFPs (e.g. T2R). Preliminary results, tools refinement ongoing
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
Machine assembly(1)
MST
R=1.5m, a=0.52m (R/a~3)
Thick (50mm) alluminium shell
b/a=1.04
Vessel = shell
RFX-mod
R=2.0m, a=0.46m (R/a~4)
Thin (3mm) copper shell
b/a=1.17
Vessel ≠ shell ≠ support structure
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
Machine assembly(2)
MST48 separate coils (12 sectors)
RFX-mod
Internal toroidal gap
Support struct.
Thin shell
Shell = single-turn toroidal wind.
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
Machine assembly(3)
RFX-mod
magnetizing wind.
Field shaping wind.
MST
2 poloidal gaps (shell, support structure)1 poloidal gap
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
Mode and error field control
MST
Passive control (thick shell + careful design of passive structure and power supplies)
Active control at poloidal flange
RFX-mod
Active control (4x48 saddle coils independently controlled)
Various real-time control algorithms available. Virtual Shell can mimic a passive MST-like control
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
Magnetic measurements
MST
Internal Rogowski coil for plasma current
Toroidal (ex-vessel) and poloidal (in-vessel) loop voltages, fluxes
Toroidal array of 64 internal pick-up coils @241°P measuring Bt, Bp, Br
2 Polodal arrays of 16 internal pick-up coils @0°T and 180°T measuring Bt, Bp, Br
RFX-mod
Pick-up coil arrays (4x48 + 8x4 ) for Bt, Bp
8 Rogowski probes (plasma current)
Poloidal and toroidal loop voltages and fluxes
Saddle loops for Br (4x48)
Halo probes
In-vessel sensors (ISIS, magnetic+electrostatic arrays)
All probes but ISIS are placed between the vacuum vessel and
the shell (vessel filter)
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
Criteria for comparison and analysis
Perform discharges as close as possible on plasma parameters and machine operation:
Choice of some fixed normalized parameters: F, Ip (Bp(a)), density (norm. I/N)
Mimic operation: ideally, self-reversal, “parallel” operation of toroidal windings, virtual shell operation to mimic thick shell, non-sustained plasmas
Process data with common algorithms: a similarity pulse file is being built and filled up to this purpose
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
Similarity shots: general
Shallow (-0.05) & deep (-0.2) F similarity shots tried, in H2.
RFX-modMST
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
First results: F-Theta plan
For a given F, the flat-top theta value is clearly different in the two machines (Time interval is [0:40]ms for MST and [0:80]ms for RFX-mod)
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
First results: -Theta0
Average profiles flatter in RFX-mod
RFX-modMST
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
First results: dynamo behavior
Discrete dynamo events are very clear in MST for both F values, while in RFX-mod at shallow F large bursts seem to disappear
RFX-modMST
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
First results: modes(shallow F)
QSH can develop more frequently in MST, while in RFX at 400 kA standard plasma is always in MH state.
RFX-modMST
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
First results: modes(deep F)
QSH can develop in MST also at deep F (not in this case). DRE are more evident in the MST case
RFX-modMST
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
First results: modes(deep F)
Only slow rotations can be seen (induced) in RFX-mod
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
First results: modes (deep F)
Fast mode rotations can be seen in MST, at least in the startup phase, with strong variations due to dynamo cycles.
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
First results: modes (shallow F)
The phase locking seems weaker than the deep F case. Less dynamo required?
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
First results: modes(shallow F)
Fast mode rotations can be seen in MST, at least in the startup phase
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
Comments
Standard discharges setup for similarity studies are feasible, exercise just started
It is confirmed that, for a given F, the two machines have different magnetic equilibrium profiles
Dynamo in MST exhibits more discrete behavior
Tearing mode spectrum is more often in MH state (especially in RFX-mod).
TM spontaneous fast rotations are observed in MST while only slow rotations can be induced in RFX-mod.
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
Future work
Add a point at same Theta and different F in the comparison? Maybe more similar dynamo activity
Assess the relevance of startup? More can be done in both machines (e.g. Virtual shell, self-reversal in RFX-mod, new Bt power supply in MST). Comparison also in terms of efficiency (volt-second consumption)
Pulse file “Similarity” created, to be filled up after definition of common calculation procedures
Extend RFX-mod similarity database (few dedicated shots up to now), better mimic of MST is possible
In MST gathering consistent amount of data and accessing measurements seem easier
L. Zanotto, 13th RFP Workshop, Stockholm 10/10/2008
Similarity shots: startup
In RFX-mod deep F discharges normally need higher toroidal voltage
RFX-modMST