13th IEA/RFP Workshop – Stockholm October 9-11, D characterization of thermal core topology changes in controlled RFX-mod QSH states A. Alfier on behalf of the RFX-mod team (in collaboration with J. Reusch and H. Stephens)

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 Outline 1. Physics issues. 2. Diagnostic set-up & data interpretation. 3. QSH control in experiments. 4. Results on QSH island and SHAx.

13th IEA/RFP Workshop – Stockholm October 9-11, Starting from measurements … During QSH states at Ip>1MA, the localized thermal structure associated to the dominant m=1, n=-7 mode may: 1) become large enough to occupy most of the plasma core (±20cm) 2) have 1keV Te plateau in the plasma core. QSH with island (QSH i )SHAx

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 … some issues have come along together with SHAx How can we compare Te and SXR measurements? Is it a poloidally symmetric structure? (e.g. does the plateau uniformly fill the core?) How does it evolve? How can we compare Te and SXR measurements to magnetic reconstructions?

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 Diagnostic set-up Thomson scattering (TS) 82.5° 40Hz time resol. 1cm spatial resol. [-0.96, 0.84] r/a 84 T e points Soft X Tomography (SXT) 202.5° ~ 10 2 kHz time resol. 78 chords brightness values tomographic reconstr. of emissivity Soft X Multichord Camera (SXMC) 262.5° ~ kHz time resol. 4.5cm spatial resol. outer midplane 10 line-integrated Te values (double filter technique) TS SXMCSXT Top view of RFX-mod vessel

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 Interpretation of measurements during QSH state We exploit the phase relation  n  to determine the poloidal position of the island O-point at the location of the three diagnostics (n=-7 for the m=1 dominant mode)

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 QSH control Temporal phase (i.e.: QSH appearance) The OPCD technique triggers the plasma transition from MH to QSH (i.e applying a 40Hz poloidal current which generates a toroidal field perturbation ). Spatial phase (i.e O-point poloidal position) An external reference of 1mT at the plasma edge for the n=-7 mode rotates at a frequency of 40Hz as a seed for the QSH state. StandardRot. Perturb.Rot. Perturb. + OPCD OPCD cycle

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 Plasma pulses Plasma parameters : I p ~ 1.5MAI/N = A/m F ~  ~ 1.4; OPCD + Rot. perturb. + TS laser trigger control to scan the island Te profile; ~ 30 shots; O-point in the range TS time; Measurements from TS – SXT – SXCM have been correlated, and compared with Poincarè plots obtained with ORBIT (see M. Gobbin presentation this afternoon).

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 RESULTS

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 Localized QSH and SHAx example separatrix SHAx QSH i

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 Island width 1. Defined the magnetic width on Poincarè (sticky region) and thermal width on TS profiles. 2. w mag proportional to w TS QSH i SHAx QSH i SHAx Hint: some discrepancy due to the definition of width.

13th IEA/RFP Workshop – Stockholm October 9-11, D T e reconstruction SHAxQSH i w TS has a poloidal dependence, slightly increasing (QSH l ) or decreasing (SHAx) approaching to the O-point poloidal position Combining TS profiles, with respect to the island O-point position, we can obtain a 2D T e reconstruction for localized QSH i and SHAx SHAx QSH i

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 Comparison between emissivity and T e T e and SXR brightness are related through the Bremsstrahlung formula: const Interferometer inversion 2D map Line integrated measurements from SXT (empty triangles) agree with those simulated in the range 0-20%. Hint: the simulation is based on nested circular surfaces, not helical surfaces! TS measurements T e approximation TS measurements T e approximation Isoemissive ~ Isothermal QSHi #24124SHAx #24598

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 Evolution to a SHAx state 1/2 First example (ext. ref. + OPCD): from a QSH island to a SHAx

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 Evolution to a SHAx state 2/2 Second example (ext. ref.): from a centered wide emissive and thermal structure (not a typical QSH island) to a SHAx

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 Recent analysis on MST Te profiles (thanks to J. Reusch & H. Stephens) During PPCD experiment on MST, Te profiles similar to those found on RFX-mod have been measured. Adapting ORBIT to MST in a very approximate way*, the obtained Poincarè plot shows similar feature to those of RFX-mod * the equilibrium is calculated with the  &p model, reproducing the q-profile produced by MSTFIT. This is a very preliminary analysis done on just 5 shots: it needs to be extended and improved, but it is very promising. All modesn=6 mode RFX-mod (OPCD + Rot. Pert.) I p =1.35MA n e =3.5·10 19 m -3 I/N= 5.5· Am MST (PPCD) I p =400kA n e =10 19 m -3 I/N= 5· Am n=6 n=-7

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 Conclusions During the experimental campaign in 2008 TS, SXT and SXMC have been run simultaneously and measurements combined. OPCD and external rotating reference have been successfully used to trigger QSH/SHAx states and control its position 2D map of electron temperature has been obtained for SHAx and QSH island  SHAx are poloidally asymmetric structure and occupy most of the plasma core Isoemissive surfaces of SXT can be considered isothermal surfaces during both QSH and SHAx islands (discrepancy < 20%). The transition from MH to SHAx may occur with features which are not unique (here we have shown just two examples) Some MST Te profiles during PPCD show features similar to those of Te profiles during SHAx states on RFX-mod at similar I/N (very preliminary analysis).

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 Thanks

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 In QSH thermal profile: 1. Peak T e linearly increased up to 1keV; 2.  T e between eV; 3. ∇ T e increased to 4-7 keV/m; 4. lowest values ever measured on RFX- mod of  E,e (5-15 m 2 /s) on the island gradient. Thomson scattering 75ms T e (keV) I p ~ 1.26MA n e ~ 2.2·10 19 m -3 Best results: T e peak ~ 1 keV at 3.5·10 19 m -3  e,island ~ 10 m 2 /s  E,e ~ 1.3 ms

13th IEA/RFP Workshop – Stockholm October 9-11, 2008

TS and emissivity poloidal and radial profiles

13th IEA/RFP Workshop – Stockholm October 9-11, 2008 Normalized averaged density profiles