Studies of Turbulence and Transport in Alcator C-Mod Ohmic Plasmas with Phase Contrast Imaging and Comparisons with GYRO*

Size: px

Start display at page:

Download "Studies of Turbulence and Transport in Alcator C-Mod Ohmic Plasmas with Phase Contrast Imaging and Comparisons with GYRO*"

Oswin Richardson
5 years ago
Views:

Tsujii 1 1 Plasma Scinc and Fusion Cntr, MIT, Cambridg, MA 02139 2 Princton Plasma Physics Laboratory, Princton, Nw Jrsy 08543 50th APS-DPP,

1 Studis of Turbulnc and Transport in Ohmic Plasmas with Phas Contrast Imaging and Comparisons with GYRO* L. Lin 1, M. Porkolab 1, E.M. Edlund 1, J.C. Rost 1, M. Grnwald 1, D.R. Mikklsn 2, N. Tsujii 1 1 Plasma Scinc and Fusion Cntr, MIT, Cambridg, MA Princton Plasma Physics Laboratory, Princton, Nw Jrsy th APS-DPP, Dallas, TX, Nov 18, 2008 Acknowldgmnts: Th authors want to thank Jff Candy and Ron Waltz (Gnral Atomics) for providing th GYRO cod and hlp with th GYRO simulations. *Work supportd by U. S. DOE undr DE-FG02-94-ER54235 and DE-FC02-99-ER54512.

2 Introduction Th xprimnts prsntd hr study turbulnc and transport in th "no-" rgim (linar confinmnt tim scaling with dnsity) and th "saturatd ohmic" rgim in and ar compard with gyrokintic simulations τ Ε [msc] BT=5.2 T Ip=0.8 MA Linar rgim Saturatd rgim _ n [20 m -3 ] Our studis includ xprimntal masurmnts of turbulnc by mans of phas contrast imaging (PCI) diagnostic, numrical simulations by GYRO and dirct comparisons btwn cod prdictions and xprimnts through a synthtic diagnostic mthod

3 A phas contrast imaging (PCI) diagnostic is usd to masur turbulnc. 0.6 PCI B PCI masurs dnsity fluctuations along 32 vrtical chords. z [m] i+ Wavnumbr Rang: 0.5cm -1 < k R < 55 cm -1 Frquncy Rang: 2kHz~5MHz Th localization upgrad allows PCI to rsolv th dirction of propagation of th masurd turbulnc in ITG and TEM rang R [m] k<0 k>0 Th improvd calibration also allows for th intnsity of th obsrvd fluctuations to b dtrmind absolutly.

4 GYRO* is usd to prdict fluctuations and associatd transport. GYRO is an initial valu Eulrian (continuum) 5D gyrokintic cod GYRO is blivd to contain all th ncssary ingrdints for quantitativly accurat transport prdictions taks masurd xprimntal profils as inputs ralistic gomtry (Millr formulation) trappd and passing lctrons finit bta (magntic fluctuations) quilibrium shard ExB *

5 Synthtic PCI diagnostic tchniqu is usd for a quantitativ comparison of xprimntal rsults with cod prdictions A synthtic PCI diagnostic has bn dvlopd to post-analyz GYRO output and mulat th PCI masurmnts.[1] [1] J.C. Rost, M. Porkolab, J.R. Dorris t al, Bull. Am. Phys. Soc. 52 (16), 334 (2007).

6 PCI has rsolvd th fluctuations abov ~80 khz ar dominatd by th mod propagating in th ion diamagntic dirction and from r/a<0.85 Saturatd ohmic n = 0.93 m PCI B 250 Shot: i+ Positiv k Ngativ k Frquncy [khz] Wavnumbr [cm -1 ] [ 32 m - 4 /cm -1 /Hz]

7 PCI has rsolvd th fluctuations abov ~80 khz ar dominatd by th mod propagating in th ion diamagntic dirction and from r/a<0.85 Saturatd ohmic n = 0.93 m Localization dpnds on th magnitud of th magntic pitch angl ζ PCI B 250 Shot: z [m] ζ [ ο ] i+ Positiv k Ngativ k Frquncy [khz] Wavnumbr [cm -1 ] [ 32 m - 4 /cm -1 /Hz]

8 Assuming v E B ~ 2 km/sc for th Dopplr shift, th synthtic and xprimntal spctra ar similar. Saturatd ohmic n = 0.93 m Exprimntal PCI Synthtic PCI (b) 250 Shot: Shot: PCI B i+ Positiv k Ngativ k Frquncy [khz] Wavnumbr [cm -1 ] [ 32 m - 4 /cm -1 /Hz] Frquncy [khz] Wavnumbr [cm -1 ] [ 32 m - 4 /cm - 1 /Hz] Simulations covr and 0.4 < r/ a< 0.8 with mi / m = k θ ρ s

9 Th wavnumbr spctrum of dnsity fluctuations in th frquncy rang of khz quantitativly agrs with GYRO simulation. Saturatd ohmic n = 0.93 m Autopowr [ 32 m - 4 /cm -1 ] Convrgnc (a) Studis PCI Masurmnt: GYRO Simulation: Nn: 16; n: Nn: ; n:12 Nn: 20; n: Shot: [80, 250] khz Autopowr [ 32 m - 4 /cm -1 ] Diffrnt (b) Ti Profils PCI Masurmnt: GYRO Simulation: (Nn: 16; n: ) Ti = Ti (Transp) Ti = 0.8 T Ti = T Shot: [80, 250] khz Wavnumbr [cm -1 ] Wavnumbr [cm -1 ] Th uncrtaintis ar mainly from th absolut calibration ~50 %.

10 Dnsity fluctuation intnsitis in th khz frquncy rang quantitativly agr with GYRO for a rang of dnsitis Fluctuation Intnsity [ 32 m - 4 ] [ 80, 250] khz PCI Masurmnt: GYRO Simulation: _ n [20 m -3 ]

11 TRANSP analysis indicats that lctron and ion channls ar mor strongly coupld as th dnsity incrass 2.0 Linar ohmic n Transition Saturatd ohmic = 0.34 m n = 0.62 m n = 0.93 (a) (b) (c) 2.0 χ 2.0 χ χ i χ i χ ff χ ff m χ χ i χ ff χ [m 2 /sc] 1.0 χ χ ff χ i χ [m 2 /sc] 1.0 χ χ ff χ i χ [m 2 /sc] 1.0 χ χ ff χ i r/a n r/a incrass r/a As n incrass, χ dcrass, but χ i incrass slowly, χ ff also dcrass. In th linar ohmic rgim, χ i is much smallr than χ. In th saturatd ohmic rgim, χ i bcoms comparabl to χ.

12 Agrmnt btwn xprimnt and thory in χ ff is obtaind aftr rducing Ti by 20% χ ff [m 2 /sc] Fluctuation Intnsity [ 32 m - 4 ] _ n [20 m -3 ] Effctiv Thrmal Diffusivity TRANSP: GYRO: ε= ε=0.1 Fluctuation Intnsity PCI Masurmnt: GYRO Simulation: ε= ε=0.1 ε=0.2 ε=0.3 ε=0.2 ε=0.3 [ 80, 250] khz _ n [20 m -3 ] Simulation covrs with Diffusivitis ar avragd ovr Th stimatd uncrtainty of Ti is abov 30% in ohmic plasmas ε is th rduction factor of Ti a T a Ti ( 1 ε) T r T r i = i < k θ ρ s < 1.0 m / m = 3600 i 0.4 < r/ a< 0.8 sim Simulatd fluctuation intnsitis still agr with xprimnts within th xprimntal uncrtainty aftr th Ti rduction i

13 At highr dnsitis, agrmnt btwn xprimnt and cod prdictions of χ and χ i is obtaind aftr th Ti rduction; howvr, at th lowst dnsity, th xprimntal valus of χ and χ i disagr with cod rsults Elctron Thrmal (a) Diffusivity TRANSP: GYRO: ε= ε=0.1 ε=0.2 ε= Ion Thrmal Diffusivity TRANSP: GYRO: ε= ε=0.1 ε=0.2 ε=0.3 χ[m 2 /sc] 2.0 χi[m 2 /sc] _ n [20 m -3 ] ε is th rduction factor of Ti: a T i a Ti = ( 1 ε) T r T r i sim _ n [20 m -3 ] i

14 At th lowst dnsity, inclusion of high-k turbulnc in th ETG rang k θ ρ s =1-4, accounts for only 12% of total simulatd lctron transport; it is not known if including vn highr valus of k θ ρ s would significantly chang this rsult. fractional contribution pr mod Linar ohmic n = Elctron (a) Elctron Thrmal Enrgy Diffusion Diffusivity Contribution from k θ ρ s <1 : 87.4% k θ ρ s >1 : 12.5% k θ ρ s >2 : 4.9% x m k θ ρ s Th short wavlngth turbulnc in th rang of 4.0>k θ ρ s >1.0 only can contribut to th lctron thrmal transport by 12.5%. Aftr adding E B shar supprssion and/or rducing Ti, to match χ i, th lctron transport from high-k turbulnc is not significantly affctd. Masurmnts to dat by PCI indicat vry low lvls of high-k turbulnc, falling into th background nois lvl.

15 Summary Th ky rol playd by th ITG turbulnc in th saturatd ohmic rgim has bn vrifid in ths studis. - Propagation of turbulnc is found to b dominantly in th ion diamagntic dirction. - Intnsity of th ITG turbulnc incrass with dnsity, in agrmnt btwn simulation and xprimnts. - Th absolut fluctuation intnsity agrs with simulation within xprimntal rror (+/-60%). -Simulatd χ ff, χ, and χ i agr with xprimnts aftr rducing th ion tmpratur gradint within 20%. At th low dnsitis in th linar ohmic rgim, whr th lctron transport dominats (χ >> χ i ), GYRO shows χ i > χ. -TEM is found to b stabl for th masurd dnsity and tmpratur profils -ETG simulation with k θ ρ s up to 4 did not rais χ to th xprimntal lvl - At th prsnt tim w ar unabl to dtrmin th caus of th lctron transport in th linar ohmic rgim.

Studies of Turbulence and Transport in Alcator C- Mod H-Mode Plasmas with Phase Contrast Imaging and Comparisons with GYRO*

Studies of Turbulence and Transport in C- Mod H-Mode Plasmas with Phase Contrast Imaging and Comparisons with GYRO* M. Porkolab 1, L. Lin 1, E.M. Edlund 1, J.C. Rost 1, C.L. Fiore 1, M. Greenwald 1, Y.