R. A. Pitts et al., O-161 of 12PSI17, Heifei Anhui, China, 22-26/05/2006 Parallel SOL flow in TCV R. A. Pitts, J. Horacek, W. Fundamenski 1, A. Nielsen 2, O. E. Garcia 2, V. Naulin 2, J. Juul Rasmussen 2, M. Wischmeier Centre de Recherches en Physique des Plasmas, Association EURATOM-Confédération Suisse, École Polytechnique Fédérale de Lausanne, CH-1015, Switzerland 1 UKAEA/Euratom Fusion Association, Culham Science Centre, Abingdon, UK 2 Association-Euratom Risø National Laboratory, Roskilde, Denmark Centre de Recherches en Physique des Plasmas Brief introduction to flows Experimental arrangement Parallel flow in FWD-B and REV-B  density variation Effect of location in the outboard midplane vicinity Understanding the flows Conclusions Outline

R. A. Pitts et al., O-162 of 12PSI17, Heifei Anhui, China, 22-26/05/2006 BB Bx  B E r xB,  pxB Ballooning Pfirsch- Schlüter Divertor sink ExBExB Simplified – flow components in poloidal plane only Poloidal Parallel Motivation – understanding SOL flows FWD B  BB Bx  B REV B  More in Review paper by N. Asakura, Fri. morning

R. A. Pitts et al., O-163 of 12PSI17, Heifei Anhui, China, 22-26/05/2006 Magnetic configurations #26092#27585#27582#27588 Bx  B Only ohmic diverted plasmas, with emphasis on direction of B , configuration and density (|B  | = 1.43 T) B  and I p always reversed together to preserve helicity Mach probe

R. A. Pitts et al., O-164 of 12PSI17, Heifei Anhui, China, 22-26/05/2006 Mach probe Fast reciprocating probe with Mach probe head mounted on the machine midplane Mach No. defined in the usual way: Postive flow defined UPWARDS All data mapped to outer midpl mm Two separate heads used to account for differing poloidal contour as plasma displaced downwards 1 2 Non-Mach pins used to measure profiles of n e, T e, V plasma

R. A. Pitts et al., O-165 of 12PSI17, Heifei Anhui, China, 22-26/05/2006 Case: REV-B, SNL, +340 kA, n e scan Flow always towards outer target in REV-B High flow (M || ~ 0.6) near separatrix at low density Flow decreases with increasing density Very similar in He OUTER divertor (10 19 m -3 ) And in ohmic H-mode (Type III) OUTER divertor (10 19 m -3 ) OUTER divertor (10 19 m -3 )

R. A. Pitts et al., O-166 of 12PSI17, Heifei Anhui, China, 22-26/05/2006 Case: FWD-B/REV-B,  260 kA, n e scan OUTER divertor (10 19 m -3 ) REV-B  Very similar to 340 kA in REV-B Switch direction with B  Always co-current Decrease with increasing n e Behaviour consistent with Pfirsch-Schlüter Slight negative offset (i.e. towards outer divertor) OUTER divertor (10 19 m -3 ) OUTER divertor INNER divertor (10 19 m -3 ) REV-B  FWD-B 

R. A. Pitts et al., O-167 of 12PSI17, Heifei Anhui, China, 22-26/05/2006 Field independent component (260 kA) Assume flow made up of two components: B  dependent B  independent  mean of flows in FWD/REV-B gives B  independent term OUTER divertor (10 19 m -3 ) TCV data support small, offset term (M || ~0.05 – 0.1) with indication of density dependence Good candidate for “ballooning” driven flow

R. A. Pitts et al., O-168 of 12PSI17, Heifei Anhui, China, 22-26/05/2006 Case: REV-B, SNL, z-scan, 260 kA OUTER divertor = 4.2 x m -3 Change in M || with z consistent with a ballooning drive Probe to outer target connection length increases as plasma is lowered vertically +10 cm0 cm-10 cm OUTER divertor

R. A. Pitts et al., O-169 of 12PSI17, Heifei Anhui, China, 22-26/05/2006 Case: REV-B, SNL, z-scan, 260 kA = 4.2 x m -3 Good match in local SOL p e and V p profiles Ion pressure and E r main drivers for neoclassical flows  Not the cause of the flow offset +10 cm0 cm-10 cm

R. A. Pitts et al., O-1610 of 12PSI17, Heifei Anhui, China, 22-26/05/2006 Return to previous 260 kA density scan in FWD/REV-B: Main flow drive is Pfirsch-Schlüter OUTER divertor INNER divertor (10 19 m -3 ) REV B  OUTER divertor INNER divertor (10 19 m -3 ) REV B  FWD B  Choose radial band in the main SOL: 8 < r-r sep < 12 mm Take mean exptl. M || and plot versus density OUTER divertor INNER divertor OUTER divertor INNER divertor Compare with predicted Pfirsch-Schlüter flow 

R. A. Pitts et al., O-1611 of 12PSI17, Heifei Anhui, China, 22-26/05/2006 Return to 260 kA REV-B, high density case: What drives the offset component? Strong candidate is enhanced parallel pressure due to cross-field motion of interchange driven filaments in the outboard midplane region SOLPS5 modelling without drifts shows T i gradients develop above the X-pt. which can drive flows – open divertor geometry OUTER divertor ESEL #115, Density Separatrix Wall O. E. Garcia et al., PPCF 48 (2006) L1 See also P3-8, Thurs. afternoon Estimate M || with simple Ansatz relating the transient filament overpressure to parallel flow (ESEL code 2D only) W. Fundamenski et al., submitted to NF OUTER divertor

R. A. Pitts et al., O-1612 of 12PSI17, Heifei Anhui, China, 22-26/05/2006Conclusions First parallel particle flow measurements in the outboard midplane region of TCV have shown: Flows can be large (M || = ) at low density Decrease as density increases – almost stagnant at high n e Reverse nearly symmetrically with B  reversal Are consistent with Pfirsch-Schlüter return as main drive Clear, small (M || ≤ 0.1) residual offset component towards outer target below and above midplane is consistent with enhanced, interchange driven transport in the midplane region Further experiments necessary to eliminate divertor sink as a possible contributor

R. A. Pitts et al., O-1613 of 12PSI17, Heifei Anhui, China, 22-26/05/2006 Reserve slides

R. A. Pitts et al., O-1614 of 12PSI17, Heifei Anhui, China, 22-26/05/2006 Case: REV-B, SNL z = 0, 260 kA, n e scan (10 19 m -3 ) OUTER divertor Flows on the midplane same direction and similar magnitude to those between midplane and X-point Only REV-B  data available Very sensitive to n e

R. A. Pitts et al., O-1615 of 12PSI17, Heifei Anhui, China, 22-26/05/2006 Example probe and edge TS profiles Good quality measurements for estimates of drift flows Clear flattening of density profile as density increased Probe and edge TS scattering agree well in T e (not n e – understood)

R. A. Pitts et al., O-1616 of 12PSI17, Heifei Anhui, China, 22-26/05/2006 Return to 260 kA REV-B, high density case: What drives the offset component? Strong candidate is enhanced parallel pressure due to cross-field motion of interchange driven filaments in the outboard midplane region SOLPS5 modelling without drifts shows T i gradients develop above the X-pt. which can drive flows – open divertor geometry OUTER divertor ESEL #115, Density Separatrix Wall O. E. Garcia et al., PPCF 48 (2006) L1 See also P3-8, Thurs. afternoon Estimate M || with simple ansatz:  0.5 t(p >  )/  t assuming a “sub-sonic” transient flow of M || = 0.5 W. Fundamenski et al., submitted to NF OUTER divertor