1. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 Similarity experiments on RFX-mod and MST standard discharges: magnetics T. 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

2. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 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

3. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 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

4. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 Machine assembly(2) MST 48 separate coils (12 sectors) RFX-mod Internal toroidal gap Support struct. Thin shell Shell = single-turn toroidal wind.

5. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 Machine assembly(3) RFX-mod magnetizing wind. Field shaping wind. MST 2 poloidal gaps (shell, support structure) 1 poloidal gap

6. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 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

7. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 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)

8. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 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

9. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 Similarity shots: general  Shallow (-0.05) & deep (-0.2) F similarity shots tried, in H 2. RFX-modMST

10. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 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)

11. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 First results: -Theta0  Average profiles flatter in RFX-mod RFX-modMST

12. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 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

13. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 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

14. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 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

15. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 First results: modes(deep F)  Only slow rotations can be seen (induced) in RFX-mod

16. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 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.

17. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 First results: modes (shallow F)  The phase locking seems weaker than the deep F case. Less dynamo required?

18. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 First results: modes(shallow F)  Fast mode rotations can be seen in MST, at least in the startup phase

19. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 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.

20. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 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

21. L. Zanotto, 13th RFP Workshop, Stockholm10/10/2008 Similarity shots: startup  In RFX-mod deep F discharges normally need higher toroidal voltage RFX-modMST