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

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

RFX-mod Workshop – Padova, January QSH in the high current regime I p > 1 MA 10  E QSH i SHAx Magnetic topology of dominant mode computed by FLiT[1] Helical plasma configuration [1] R. Lorenzini et al, APS Conference (2008)

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

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

RFX-mod Workshop – Padova, January energy confinement time SHAx QSH i Poloidal scan TS measurements[2]: wider hot region hence higher energy content in SHAxs Energy confinement time  E 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) 2D Te Thomson scattering map:

RFX-mod Workshop – Padova, January Energy diffusion calculation [5] L.Carraro, submitted to Nucl. Fusion  E computed by 1D single fluid approach and solving the power balance equation (symmetric approximation) in SHAx regimes  E 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, January magnetic configuration in QSH – SHAx states improved confinement and energy transport particle confinement: density and impurity behaviour conclusion

RFX-mod Workshop – Padova, January Density behaviour in QSH [2] F. Bonomo et al, submitted to Nucl.Fus. neutral density profile QSH confining region Inverted density profile Average line density 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

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

RFX-mod Workshop – Padova, January pellet injection: additional information The pellet injection experiments show: 1. Asymmetries due to topology 2. Ablated pellet particles are “confined” (flat density time evolution)

RFX-mod Workshop – Padova, January Pellet particle deposition and FLiT (by D. Terranova) 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. Pellet toroidal angle Interferometer toroidal angle Each colour indicates the points corresponding to different time instants. [6] D.Terranova et al, RFP-WS (2008)

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

RFX-mod Workshop – Padova, January Pellet and global particle confinement t pre t2t2 tptp Multiple Helicity  pre = 4.2 ms Pellet ablation Growing QSH (n e diffusion)  2 = 6.9 ms Single Helical Axis (n e sustained)  p = 8.6 ms This could be an alternative way for having QSH or SHAx at high density. We still need more experimental evidence.  [6] D.Terranova et al, RFP-WS (2008)

RFX-mod Workshop – Padova, January 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] [5] L.Carraro, submitted to Nucl. Fusion M. Gobbin presentation

RFX-mod Workshop – Padova, January conclusion Helical magnetic topology observed also on kinetic quantities (T e and n e ) 80% higher energy confinement time in SHAXs than in QSH i Energy diffusion coefficient  e 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, January

RFX-mod Workshop – Padova, January Asymmetries (2/2): enhanced pellet ablation H  emission from the ablation of the pellet increases abruptly as the pellet hits the edge of the island where large T e gradients are present.

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

RFX-mod Workshop – Padova, January 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  has been assumed to be a simple 3-parameter function of  

RFX-mod Workshop – Padova, January Single pulse ruby laser 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  =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 Edge TS /LBO system