Experimental QSH confinement and transport

1. Experimental QSH confinement and transport Fulvio Auriemma on behalf of RFX-mod team Consorzio RFX, Euratom-ENEA Association, Padova, Italy RFX-mod Workshop – Padova, 20-22 January 2009 1

2. Outline • magnetic configuration in QSH – SHAx states • improved confinement and energy transport • particle confinement: density and impurity behaviour • conclusion RFX-mod Workshop – Padova, 20-22 January 2009 2

3. 10 tE QSHi SHAx QSH in the high current regime Ip > 1 MA Helical plasma configuration Magnetic topology of dominant mode computed by FLiT[1] [1] R. Lorenzini et al, APS Conference (2008) RFX-mod Workshop – Padova, 20-22 January 2009 3

4. magnetic configuration in QSH – SHAx states • improved confinement and energy transport • particle confinement: density and impurity behaviour • conclusion RFX-mod Workshop – Padova, 20-22 January 2009 4

5. diagnostics for thermal properties of QSH state • TS: 84 points for local Te along an equatorial line of sight • SXT: 78 chords for SXR tomographic reconstruction • SXMC: 10 chords for time resolved Te profile evolution RFX-mod Workshop – Padova, 20-22 January 2009 5

6. QSH [3] SXT provides good experimental approximation of the poloidal map of central hot region L. Marrelli presentation thermal structures in RFX-mod • steep Te gradient in radial profile 1/LTe20 m-1 • Thermal structures related to magnetic topology both for QSHi and SHAx[2] • SXMC (triangles) accords to TS at different toroidal position: Te constant on helical flux surfaces [2] F. Bonomo et al, submitted to Nucl.Fus [3] R.Lorenzini et al. accepted by PoP RFX-mod Workshop – Padova, 20-22 January 2009 6

7. SHAx QSHi energy confinement time 2D Te Thomson scattering map: • Poloidal scan TS measurements[2]: wider hot region hence higher energy content in SHAxs • Energy confinement time tE increases by 50-80% when the plasma transits to the SHAx: • this is both due an increase of the thermal energy content and a reduction of the Ohmic input power[4] [2] F. Bonomo et al, submitted to Nucl.Fus [4] P. Piovesan et al, EPS Conference (2008) RFX-mod Workshop – Padova, 20-22 January 2009 7

8. Energy diffusion calculation • cE computed by 1D single fluid approach and solving the power balance equation (symmetric approximation) • in SHAx regimes cE strongly decreases in the gradient region: thermal transport barrier • In SHAxs regimes the magnetic turbulence could become so small that other transport mechanisms could act [5] RFX-mod Workshop – Padova, 20-22 January 2009 8 [5] L.Carraro, submitted to Nucl. Fusion

9. magnetic configuration in QSH – SHAx states • improved confinement and energy transport • particle confinement: density and impurity behaviour • conclusion RFX-mod Workshop – Padova, 20-22 January 2009 9

10. Inverted density profile neutral density profile Average line density Density behaviour in QSH QSH confining region Average density profiles still flat during QSH/SHAx [2]: lack of particle source (about 0.1%) inside the confining structures, as predicted by NENE code [2] F. Bonomo et al, submitted to Nucl.Fus. RFX-mod Workshop – Padova, 20-22 January 2009 10

11. Mapping electron density ne on helical flux • The ne profile shape, which is modified injecting solid Hydrogen pellets[1] • Homologous interferometer chords show asymmetries that are well matched assuming ne constant on helical flux surfaces. More information also from ne TS measurement with new calibration procedure [7] [1] R. Lorenzini et al, APS Conference (2008) [7] A. Alfier et al. proposal #91 TF3 (2009) RFX-mod Workshop – Padova, 20-22 January 2009 11

12. pellet injection: additional information The pellet injection experiments show: • Asymmetries due to topology • Ablated pellet particles are “confined” (flat density time evolution) RFX-mod Workshop – Padova, 20-22 January 2009 12

13. Pellet particle deposition and FLiT (by D. Terranova) Each colour indicates the points corresponding to different time instants. Pellet toroidal angle Interferometer toroidal angle We follow magnetic field lines for a chosen number of turns starting at the pellet positions in time and see where these lines hit the poloidal cross section of the interferometer. [6] D.Terranova et al, RFP-WS (2008) RFX-mod Workshop – Padova, 20-22 January 2009 13

14. Pellet particle deposition and FLiT Ha from the pellet entering the plasma Pellet toroidal angle Interferometer toroidal angle The time evolution of the chords’ signals is compatible with the reconstructionof the path of the internal magnetic field lines by means of the FLiT code. [6] D.Terranova et al, RFP-WS (2008) RFX-mod Workshop – Padova, 20-22 January 2009 14

15. Multiple Helicity tpre = 4.2 ms Pellet ablation Growing QSH (ne diffusion) t2 = 6.9 ms D Single Helical Axis (ne sustained) tp = 8.6 ms Pellet and global particle confinement tpre t2 tp This could be an alternative way for having QSH or SHAx at highdensity. We still need more experimental evidence. [6] D.Terranova et al, RFP-WS (2008) RFX-mod Workshop – Padova, 20-22 January 2009 15

16. M. Gobbin presentation Impurities injection experiments: LBO Ni XVII 249 Å and Ni XVIII 292 Å observed: impurity reaches the hot helical structure but 1D collisional-radiative impurity transport -> no evidence of improved impurity confinement, according with ORBIT simulation[5] RFX-mod Workshop – Padova, 20-22 January 2009 16 [5] L.Carraro, submitted to Nucl. Fusion

17. conclusion • Helical magnetic topology observed also on kinetic quantities (Te and ne) • 80% higher energy confinement time in SHAXs than in QSHi • Energy diffusion coefficient ce damped by one order of magnitude in SHAxs • Particle confinement in SHAx structures seen in pellet injection experiments: improved global particle confinement time by a factor 2 • No improved impurities confinement in SHAx structure due to their high collisionality • TO DO: • Perform transport simulation in helical geometry both for energy and for particles (new tools to be developed) • New efforts to inject particle source in QSH confining structures • New LBO experiments with other impurities RFX-mod Workshop – Padova, 20-22 January 2009 17

18. RFX-mod Workshop – Padova, 20-22 January 2009 18

19. Asymmetries (2/2): enhanced pellet ablation Ha emission from the ablation of the pellet increases abruptly as the pellet hits the edge of the island where large Te gradients are present. RFX-mod Workshop – Padova, 20-22 January 2009 19

20. Asymmetries (1/2): line integrated density Homologous chords do show a different time evolution [5]. [5] D.Terranova et al, RFP-WS (2008) RFX-mod Workshop – Padova, 20-22 January 2009 20

21. Pellet and global particle confinement (2) Plasma electron density profiles (in flux coordinates) for three pellets with increasing penetration length. tp = 7.9 ms (SHAx) tp = 2.4 ms (diffusion) tp = 12.5 ms (SHAx) tp = 8.0 ms (SHAx) Clear evidence ofimproved global particle confinement time (by a factor 2 to 3)when the internal magnetic field configuration changes from MH to QSH and to SHAx. RFX-mod Workshop – Padova, 20-22 January 2009 21

22. Mapping soft X-ray measurements on helical flux • The soft X-rays tomography is the diagnostic with the highest space resolution in RFX-mod • The emissivity e has been assumed to be a simple 3-parameter function of r • e = e(r) RFX-mod Workshop – Padova, 20-22 January 2009 22

23. Edge TS /LBO system • Single pulse ruby laser (7J @ 694nm, 30ns at FWHM) focused on a 3mm pin-hole in vacuum. • Sapphire lens & prism deflect beam by 30° and image the pin-hole in vacuum vessel. • A camera lens (f=83mm / F#1.2) collects light at ~150°from 16 positions over f=1mm fibers: • 12 scattering volumes for Te, ∼10mm resolution; • 4 measuring points for detecting background plasma light. • The entrance port hosts the input system & the collection window  stable alignment. • Fibers are arranged in a 4x4 pattern and fed into a 4 spectral channels spectrometer. • An Intensified CCD (ICCD) acquires the Thomson and the Background signal RFX-mod Workshop – Padova, 20-22 January 2009 23