L-H Transition in addition to Pedestal Studies on MAST H Meyer1, MFM De Bock1,2, NJ Conway1, SJ Freethy1,3, K Gibson3, J Hiratsuka4, A Kirk1, CA Michael1, T Morgan1,3, R Scannell1, G. Naylor1, S Saarelma1, AN Saveliev5, VF Shevchenko1, W Suttrop6, D Temple1,7, RGL Vann3 in addition to the MAST in addition to NBI Teams

L-H Transition in addition to Pedestal Studies on MAST H Meyer1, MFM De Bock1,2, NJ Conway1, SJ Freethy1,3, K Gibson3, J Hiratsuka4, A Kirk1, CA Michael1, T Morgan1,3, R Scannell1, G. Naylor1, S Saarelma1, AN Saveliev5, VF Shevchenko1, W Suttrop6, D Temple1,7, RGL Vann3 in addition to the MAST in addition to NBI Teams www.phwiki.com

L-H Transition in addition to Pedestal Studies on MAST H Meyer1, MFM De Bock1,2, NJ Conway1, SJ Freethy1,3, K Gibson3, J Hiratsuka4, A Kirk1, CA Michael1, T Morgan1,3, R Scannell1, G. Naylor1, S Saarelma1, AN Saveliev5, VF Shevchenko1, W Suttrop6, D Temple1,7, RGL Vann3 in addition to the MAST in addition to NBI Teams

Eller, Claudia, Film Business Reporter has reference to this Academic Journal, PHwiki organized this Journal L-H Transition in addition to Pedestal Studies on MAST VI. Edge current density H Meyer1, MFM De Bock1,2, NJ Conway1, SJ Freethy1,3, K Gibson3, J Hiratsuka4, A Kirk1, CA Michael1, T Morgan1,3, R Scannell1, G. Naylor1, S Saarelma1, AN Saveliev5, VF Shevchenko1, W Suttrop6, D Temple1,7, RGL Vann3 in addition to the MAST in addition to NBI Teams 1EURATOM/CCFE Fusion Association, Culham Science Centre, Oxon, OX14 3DB 2Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherl in addition to s 3University of York, Heslington, York, YO10 5DD, UK 4The University of Tokyo, Kashiwa 277-8561, Japan 5Ioffe Institute, Politekhnicheskaya 26, 194021 St. Petersburg, Russia 5Max-Planck-Institute as long as Plasma Physics, Boltzmannstr. 2, Garching, Germany 7Imperial College of Science, Technology in addition to Medicine, London, UK I. Motivation ITER success relies on H-mode operation with high confinement in addition to tolerable ELMs Limited theoretical underst in addition to ing of H-mode access in addition to pedestal width in addition to stability. H-mode access in non-activation phase (hydrogen) questionable helium operation. Global access conditions studied in He in addition to as long as different X-point height. Change of vertical position in single null (SN), change in elongation in double null (DN). Evolution of local parameters at the low field side mid-plane studied during the L-H transition in addition to the ELM cycle. Evolution of Er, Te, ne, Er, Te in addition to ne measured on 0.2ms time scale through L-H transition. Evolution of pe in addition to j studied during ELM cycle peeling-ballooning model seems incomplete. Novel measurement of Ti shows Ti depends on collisionality on MAST. VII. Conclusions: On MAST PLH is about (5030)% higher in dominant 4He than in D plasmas. The reduction of PLH observed with the X-point closer to the targets can hardly be explained by changes in the SOL connection length, Lc. In SN a change of PLH by a factor of two is observed with only 8% change in Lc. Changes of the mean (equilibrium) Er don’t correlate with changes in PLH. Er seems to be a sufficient condition, but not a necessary. No changes of Er, Er, Te, Te, ne, ne prior to the L-H transition with t < 0.2ms. Ti profile on MAST reflect the fact that entropy is conserved over the whole pedestal at low . Edge current density measurements indicate that the peeling-ballooning model is incomplete. II. H-mode access in helium: Righi et.al.: PLH Aeff-1 (Aeff=aMana/ana) [1] PLH on ITER in hydrogen difficult. New measurements at AUG: PLHHe = PLHD [2] High priority ITER task to improve database. Compare PLH in D in addition to 4He at similar parameters. Ip = 0.7 MW, Spl= 24 m2, =2.41019m-3, Bt=0.5 T PLHHe = (2.10.2)MW compared to PLHD = (1.40.2)MW Aeff~3.7 (85% He), detailed TRANSP analysis since D-NBI in addition to fast-ion redistribution DFI~1 m2/s. Ploss = Pabs+P-dW/dt-Prad (PabsHe~0.8 PNBI, PabsD~PNBI) Similar pedestal at Ploss-PLH~0.3 MW Different atomic physics; 2 ion species, no molecules different velocity distribution. Fit suggests narrower in He (caution). L-H transition dynamics differ between He in addition to D D: Dithering H-mode over wide power range. He: Sharp transition after modest power increase. III. Effect of X-point height on H-mode access: JET: PLH decreases with decreasing X-point height [3] Only if strike point (SP) is on horizontal plates With in addition to without septum – even septum limited. MAST: previously SP close/far from X-point in SN [4] H-mode/L-mode. (2m < Lc< 4m). New: PLH increases by factor of 2 with Zx~ + 10 cm (SN). No significant change in Lc (Lc~ -1m; different direction.) Increased Zx ~ 8 cm better H-mode access. No change in edge Te or ne prior to L-H transition Critical Te or Te favoured by many L-H transition theories no evidence as long as this on slow time scale. IV. Changes in the L-mode Er Er measured using active Doppler spectroscopy on He. L-mode Er averaged over 20ms of the dithering phase (average over many dithers). Little change in mean Er during power scan as Ploss approaches PLH No change in mean Er with increase of from 1.8 to 1.9. n=3 field Er more positive: No H-mode But, increased power (80%) to regain H-mode no change in Er. Mean Er does not correlate with PLH EB > max: sufficient, but not necessary as long as the transition V. Pedestal as long as mation Measured Er at 4 radial points with t = 0.2ms Synchronous bursts of Thomson scattering. t 10ns, every 0.2ms. Sequence of L-H, H-L in addition to L-H transitions as long as ced using the magnetic configuration [4] Improved statistics, jitter of a few ms. Prior to L-H transition: No change in Er, Er, Te, Te, ne or ne. After L-H transition: Shear layer develops at R-Rsep~ -1 cm Increase of ne in addition to ne. Er = Er/tEr ~ 0.6 ms, n ~ 3 ms; L-mode filaments vanish in less than 0.1ms. visible light acts as proxy as long as Note tLH is defined slightly differently in these graphs: Te, ne: top of last dither (reproducibility). Er: top of first dither. vis. light: bottom of last dither. [1] E. Righi et.al., Nucl. Fusion 39 (1999) 309 [2] F. Ryter et.al., Nucl. Fusion 49 (2009) 062003 [3] Y. Andrew et.al., Plasma Phys. Control. Fusion 46 (2004) A87 [4] H. Meyer et.al. Plasma Phys. Control. Fusion 50 (2008) 015005 [5] G. Kagan et.al. Plasma Phys. Control. Fusion 50 (2008) 085010

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