1. HEAT TRANSPORT andCONFINEMENTin EXTRAP T2R L. Frassinetti, P.R. Brunsell, M. Cecconello, S. Menmuir and J.R. Drake

2. OUTLINE Device and diagnostics Heat transport model Heat diffusivity and confinement estimations Scaling with plasma current Conclusions

3. EXTRAP T2R – the device R=1.24m a=0.18m I p  80kA (standard current plasma) I p  150kA (High current plasma) n e ≈10 19 m -3 T e ≈200-400eV  pulse ≈20ms (no feedback)  pulse ≈up to 90ms (IS)

4. EXTRAP T2R – the diagnostics PLASMA CURRENT-F-OHMIC POWER standard magnetic diagnostics RADIATED POWER Eight chord bolometric system ELECTRON TEMPERATURE Ruby laser Thomson Scattering diagnostic at a single point, single time. ELECTRON DENSITY line averaged density  two color interferometer core density  Thomson scattering MAGNETIC FLUCTUATIONS 256 coils (4 poloidal x 64 toroidal) m=1 connected toroidal resolution |n|=32 Soft X Ray 10-chord camera with a 9  m Be filter ION TEMPERATURE AND VELOCITY 1m Czerny-Turner grating (2400lines/mm) spectrometer for 278.1nm OV spectral line measurement

5. THE HEAT TRANSPORT MODEL/1 How to determine the heat diffusivity? The usual power balance is not a good choice. We use a heat transport model and the corresponding numerical code developed for RFX-mod [Frassinetti L. et al., Nucl. Fusion 48, 045007 (2008)]  e is estimated using the model (and free parameters) T e (r,t) Using the heat equation Comparison between simulated T e (r,t) and the experimental T e. Determination of the free parameters and validation of the model The code must be adapted to take into consideration the T2R experimental data RFX-mod data

6. a core ≈1.5 [D’Angelo F. and Paccagnella R. Phys. Plasmas 3, 2353 (1996)] [Terranova D. et al., Plasma Phys. Control. Fusion 42, 843 (2000)]  m=1 magnetic fluctuations B  equilibrium magnetic field A- Core 1- RFP plasma core is stochastic 2- In stochastic fields the heat diffusivity can be modeled using the RR formula: B- Reversal 1- the reversal region is probably less stochastic 2- We assume a rev =1 THE HEAT TRANSPORT MODEL/2

7. The model has four free parameters k 1  determine absolute value of  e core k 0  determine absolute value of  e rev r 1  separation between core and reversal region r 0  separation between reversal and edge region Constant radial profile is assumed We need to: (1)verify that the model is valid also in EXTRAP T2R (2)determine the free parameters THE HEAT TRANSPORT MODEL/3

8. T e (r,t) Using the heat equation (a)Z eff profile experimentally determined [Corre Y. et al., Phys Scripta 71, 523 (2005)] (b) Assumption: Z eff has no time evolution (c) Assumption: SXR emissivity is due only to Bremsstrahlung f(T e ) is numerically determined using the transmission function of the Be filter To have a direct comparison with experimental data. THE HEAT TRANSPORT MODEL/4

9. APPLICATION OF THE MODEL Free parameters of the model determined in order to minimize the difference between experimental and simulated data During the flat-top Discharge with Ip≈80kA and NO feedback

10. UNCERTAINTIES Uncertainties can be determined by considering experimental errors on the input data 1- The simulation is repeated by varying the input the data within their error 2- The range of variation of  e and T e can be determined n e profile and  n e Experimental  T e Z eff profile  P in  SXR

11. STANDARD and IS PLASMAS IS std =280  40eV =220  30eV Std and IS plasmas just before a crash Simulation suggests that the higher T e in IS plasma is due mainly to a lower  e in the core region IS = 300  150m 2 /s std =1000  300m 2 /s Average over 10 shots IS = 110  40m 2 /s std = 150  50m 2 /s IS std

12. a rev =2 Example of high Ip plasma HIGH CURRENT PLASMAS

13. SCALING WITH PLASMA CURRENT Experimental results - particles Density increases with current 1.Reduction of particle diffusivity? 2.Increase of the source term? The source increases with Ip Data suggests that the particle diffusivity does not change significantly with current Experimental data

14. SCALING WITH PLASMA CURRENT Experimental results – heat Temperature increases with current 1.Reduction of heat diffusivity? 2.Increase of the input power? The input power increases with Ip But also the density increases with Ip. Data suggests that the increase of the temperature can be due to a reduction of the heat transport Experimental data

15. SCALING WITH PLASMA CURRENT Simulation results – heat Low IpHigh Ip 300  150m 2 /s200  100m 2 /s 110  40m 2 /s85  30m 2 /s <e><e>0.15  0.04ms0.19  0.05ms Improvement of the confinement at high current

16. SCALING WITH PLASMA CURRENT What happens to ions? Ion (OV) temperature steadily increases with Ip Ion (OV) velocity increases with Ip but then saturates. TM velocity (m=1,n=-12) has a trend very similar to ion velocity Good agreement between TM and ion velocity

17. CONCLUSIONS Heat transport and confinement estimated with a model Core heat transport dominated by magnetic fluctuations Heat transport reduced in the core of IS plasma Heat transport reduced in high current plasmas <e><e> No FB Low Ip 220  30eV 1000  300m 2 /s 150  50m 2 /s 0.09  0.03ms IS Low Ip 270  50eV 300  150m 2 /s 110  40m 2 /s 0.15  0.04ms IS High Ip 380  60eV 200  100m 2 /s 85  30m 2 /s 0.19  0.05ms