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Fast response of the divertor plasma and PWI at ELMs in JT-60U 1. Temporal evolutions of electron temperature, density and carbon flux at ELMs (outer divertor)

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Presentation on theme: "Fast response of the divertor plasma and PWI at ELMs in JT-60U 1. Temporal evolutions of electron temperature, density and carbon flux at ELMs (outer divertor)"— Presentation transcript:

1 Fast response of the divertor plasma and PWI at ELMs in JT-60U 1. Temporal evolutions of electron temperature, density and carbon flux at ELMs (outer divertor) by T. Nakano 2. Evolutions of ELM plasma and carbon flux at HFS SOL by N. Asakura

2 Introduction (Part 1)  Impurity generation and deposition by ELMs can dominate in ITER even if target lifetime is OK  0.15 g-C/ELM  150 g-C per shot. ( by A. Loarte in Toronto ITPA DSOL meeting ) => new proposal: DSOL19 (impurity generation & transport during ELMs) Preparation for impurity study during ELM :  quantitative evaluation of carbon flux, plasma parameters are required.  time resolution (<100  s ) is required to determine the plasma parameters  Measurements with synchronized clock as well as trigger during ELM: three He I lines to determine T e and n e, D  to determine recycling flux C II line to determine impurity influx (here, minimum probe voltage sweep is slower: 1-2 ms)

3 5 spectral lines measured with synchronized clock in steady-state ELMy H-mode Discharge condition: I p = 1.0 MA, B t = 1.9 T, P NB = 20 MW T e ped = 1.0 keV, T i ped = 1.3 keV, n e ped = 1.6x10 19 m -3 f ELM = 120 Hz, W dia ped = 0.5 MJ,  W dia = 20 kJ 134 ELMs averaged with D  intensity + 10% + 10% 3 He I lines : 50  s C II : 50  s D  : 4  s Spectroscopy Diagnostics:

4 T e and n e determination from three He I lines T e sensitive n e sensitive T e & n e determination with He I CR model Averaged ELM

5 Temporal evolution of T e and n e at outer target S/XB for D  & C + T e & n e  D &  C+->C++ Before D  peak: ELM convective flux increases T e in divertor plasma ionization of recycled & desorbed neutrals After D  peak: rapid decrease of T e due to reduction in ELM heat flux Flux peak 5 s

6 Neutral density/ionization flux becomes dominant at ELM At D  peak, carbon yield (Y C =  C+->++ /  D0->+ ) is the lowest:  D0->+ increase >  C+->++ increase. ・ Significant D flux => enhances surface recombination of D into D 2. ・ Large n D L at D  peak shows high recombination rate of D/neutral source, suggesting Physical sputtering is not so significant => Chemical sputtering becomes large 6 4 2 0 x10 22 3 2 1 0 x10 13 ( 10 22 m -2 s ) Ionization flux Line-neutral density n D L  D C + ->C ++ x 40 YCYC ( 10 17 m -2 )

7 Evolutions of ELM plasma at HFS SOL (Part 2) Upper plasma boundary in extended and gap decreased to  R mid ~2.8cm (1) Flat far SOL decreased above HFS baffle, while LFS SOL profile was comparable (similar to C-MOD double null exp.: Nucl. Fus. 44 (2004) 104) (2) ELM ion flux and large V f peak are reduced at far SOL. suggesting both ELM flux and flat far SOL plasma are mostly produced at LFS.

8 ELM propagation in HFS SOL D  & CII increases start almost simultaneously both at HFS and LFS divertors. Enhancement of j s HFS base-level and SOL flow towards HFS divertor are observed after parallel convection time from LFS to HFS:  // conv = L c LFS-HFS (50m)/C s ped ~185  s  Parallel convection towards HFS divertor Only near separatrix (  r mid < 0.4cm), fast j s HFS and/or heat load to Mach probe is measured: heat flux may be carried by fast el./ conduction ?  neutrals are released due to large T target rise. chemical process of C generation increases.  "flow reversal " (SOL flow away from divertor).

9 ・ Large multi-peaks (filaments) are observed in upstream-side j s HFS (peak) only near separatrix (  r mid < 0.4cm ): fast SOL flow (sonic level) is produced towards HFS divertor. ・ For the large plasma case, j s HFS was measured near separatrix. L // LFS-HFS /C s ~180  s Filaments may extend to HFS SOL as well as LFS, and is exhausted: faster than characteristic time of parallel convection: L // HFS /C s ~180  s Multi-peaks (filaments) structure appeares at HFS SOL

10 Summary (1) Three He I, D  and C II lines were measured at LFS diveror: Plasma T e and n e (He I lines, 50  s smpl.), ionization flux (D , 2  s smpl.), C + -> C ++ ionization flux (C II, 50  s smpl.) 1-1) Temporal evolution of T e and n e at ELM was determined: During ELM heat loading (~200  s), T e was increase => then, T e was decreased due to ionization of recycled neutrals & reduction in heat flux. 1-2) Impurity generation: At the peak of D , carbon yield was the lowest, suggesting chemical sputtering is increased due to large neutral sources. (2) ELM plasma transport at HFS SOL was further investigated: 2-1) ELM and SOL plasmas at the far SOL were mostly transported from LFS. 2-2) Large multi-peak flux with fast flow towards the HFS divetor was measured near separatrix (  R mid <0.4cm where  R<1.2cm at probe): transport time was shorter than convection time from LFS (~180  s) 2-3) Impurity generation: both CII and D  was increased simultaneously at HFS and LFS divertors.

11 Radial distribution of ELM plasma in HFS SOL ・ Large peaks are observed occasionally: j s HFS (peak) and  V f (~100V) are smaller than those in LFS SOL. Fast SOL flow (M // up to 0.4) is produced towards HFS divertor. Parallel convection from LFS to HFS. ・ j s HFS (base) enhancement near separatrix is comparable to that in LFS SOL, while HFS base (~2cm) is smaller than LFS base (~3.5cm). "SOL flow reversal" is generated over wide area in HFS SOL (  r mid <3.5cm). ・ Conductive heat flux/ fast electrons may be transported near separatrix.  Flow reversal will play an important role in particle and impurity transport/ re-deposition (potentially, Tritium retention) at HFS divertor.

12 Laser flash device (LFA427/G, NETZSCH ) Nd GGG1.064  m Pulse width 0.3 〜 1.2ms Laser power 〜 10mJ IR detectorInSb Sample Pulsed laser IR-detector Furnace Ref.1 Thermal diffusivity measurement was performed (2004) Ishimoto et al. PSS (2005) Laser Flash method

13 Comparison with previous measurements Heat conductance "heat transmission coefficient" was used heat conductance: k : thermal conductivity d: thickness Deviceh ( kW/m 2 K )Reference ASDEX Upgrade100A. Herrmann, EPS2001 JET3~300* ) P. Andrew et al., PSI15 JET15~50E. Gauthier et al., PSI16 JT-60U10This study In the case of JT-60U, *) lower value of h is needed on the inner target.

14 Estimation of ELMs heat loads (  W ELM IR vs  W ELM dia ) W/O considering thermal property:  W ELM IR was 6.8x  W ELM dia Difference was dominant at HFS Assuming thermal conductivity at HFS target (using lowest value):  W ELM IR was 1.7x  W ELM dia where thermal properties of LFS divertor (erosion dominant) are equal to those of CFC. - poloidal/ toroidal distribution of deposition layer should be considered. The loss of the plasma stored energy (kJ) Not considering redeposit Considering redeposit Net divertor heat loads estimated from the IR-camera as a function of the loss of the stored energy by ELMs. Net divertor heat load (kJ)  W ELM IR  W ELM dia


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