B drift dependence of fluctuations and turbulent transport in DIII-D

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Thomas Casey
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with J.A. Boedo, D. Rudakov, T.N. Carlstrom, R.J. Groeber, M.J. Schaffer, T.L.

1 B drift depedece of fluctuatios ad turbulet trasport i DIII-D preseted by Rick Moyer Fusio Eergy Research Program Uiversity of Califoria, Sa Diego i collaboratio with J.A. Boedo, D. Rudakov, T.N. Carlstrom, R.J. Groeber, M.J. Schaffer, T.L. Rhodes, C. Rettig, C. Fezi, G. McKee, ad X.Q. Xu QTYUIOP 42d APS Aual Mtg. Quebec City 1/ 1

2 ABSTRACT The B drift directio ca chage the H-mode power threshold by factors of 2-8. Reversig the B drift directio alters the divertor coditios ad directio of flows i the boudary. Such boudary flow chages are predicted i BOUT simulatios to chage the boudary turbulece levels due to chages i the effectiveess of the magetic shear dampig associated with the X-poit. Edge fluctuatio measuremets idicate that whe the B drift is toward the domiat X-poit, a regio of sheared fluctuatio propagatio forms i the edge. Whe the B drift is away from the domiat X-poit, the fluctuatio propagatio is relatively uiform across the edge. Probe measuremets of the desity ad potetial fluctuatios i the far edge o the outboard midplae are reduced (desity) or costat (potetial) whe the drift is away from the domiat X-poit, the cofiguratio with lower sheared propagatio ad predicted by BOUT to have higher fluctuatio levels. These fluctuatio levels will be compared with measuremets i the lower divertor for each magetic field directio. Despite the differeces i fluctuatio levels, the turbulet trasport o the outboard midplae is similar for the two magetic field directios, cosistet with the edge plasma profiles. Results will be discussed i terms of the possible impact o the H- mode power threshold, ad will be compared with results from BOUT simulatios. 42d APS Aual Mtg. Quebec City 1/ 2

3 Motivatio The B drift directio ca chage the H-mode power threshold by factors of 2 8. Importat issue for H-mode access Opportuity for uderstadig the physics of the power thrshold for the L to H trasitio The B drift alters the boudary (edge, scrape-off layer, ad divertor) plasma coditios Opportuity to uderstad the role of boudary plasma coditios o the L to H trasitio The BOUT 3-D boudary turbulece code has the uique capability to hadle realistic, diverted (Xpoit) tokamak boudary geometry Opportuity for detailed experimet-simulatio comparisos 42d APS Aual Mtg. Quebec City 1/ 3

4 Summary Neutral beam modulatio ca be bad ews at low duty cycles: For some reaso, the plasma is robust to the NBI perturbatio whe the B drift is toward the X-poit The B drift depedece of the H-mode power threshold is t due to icreases i turbulece ad/or turbulet trasport ear the outboard midplae. Outboard midplae fluctuatio levels ad turbulet trasport are similar or a bit lower Evidece for icreased fluctuatio levels ear the X-poits whe the B drift is away from the X-poit as predicted by BOUT The fluctuatios propagate with a more highly sheared profile whe the B drift is toward the X-poit May be the origi of the lower power threshold sice E B shear layer already partly established. Begs the questio why the propagatio profile is differet 42d APS Aual Mtg. Quebec City 1/ 4

T directios (forward & reversed B T ) I oe day, fix B T directio ad shift plasma

5 Compare discharges at similar power levels with the B drift toward ad away from the (domiat) X-poit O separate days, study lower sigle ull plasmas with opposite B T directios (forward & reversed B T ) I oe day, fix B T directio ad shift plasma vertically from upper sigle ull to lower sigle ull 42d APS Aual Mtg. Quebec City 1/ 5

6 Reproducibility for B drift away from the X- poit was poor i LSN reversed B T shape. Edge E r ad v phase varied durig off part of NBI duty cycle (plasma does t average out the otches). 42d APS Aual Mtg. Quebec City 1/ 6

7 Improved reproducibility of edge coditios whe B drift away from X-poit i USN Higher P threshold allowed higher eutral beam duty cycle but still a perturbatio o edge φ durig otch 42d APS Aual Mtg. Quebec City 1/ 7

8 May edge plasma parameters are well matched with both approaches See Carlstrom et al. Poster GP1.129 this sessio. Example at left of edge electro profiles forward B T = B drift toward the X-poit reverse B T = B drift away from the X-poit. Also similar: edge T i profiles electro pressure P recyclig (Owe et al. Poster GP1.13 this sessio; Colchi et al., oral talk MO1.12 Wed. morig) radiated power e ( 1 12 /cm3 ) T e (ev) e separatrix 9674 forward B T reverse B T reverse B T d APS Aual Mtg. Quebec City 1/ 8

9 But there are some differeces i the edge E r E r (kv/m) E r from T e (r) & d.c. V fl (r) by midplae probe: E r reproducible for B drift toward X-poit, but ot for B drift away from X-poit CER E r chaged sig with B drift directio: B drift toward X-pt B drift away fr X-pt separatrix V float (V) plasma (V) (V/cm) E V r separatrix 9674 forward b T reverse B T reverse B T 9674 forward B T reverse B T reverse B T d APS Aual Mtg. Quebec City 1/ 9

10 I earliest experimets, edge fluctuatio amplitudes were similar (Ψ ) ad Te(Ψ ) are idetical for the two B drift directios, so the ormalized amplitude profiles here idicate absolute rms amplitude differeces. ñ 2 lower with B drift away from X-poit That s right, outboard midplae fluctuatios are lower for the case with the higher H-mode power threshold! ~ ~ Φ ad E θ similar ñ/ E rms (V) flrms /Te ñ/ =1% vs. 5% at separatrix 9674 forward B T reverse B T reverse B T d APS Aual Mtg. Quebec City 1/ 1

11 The two B drift directios have similar turbulet particle trasport o the outboard midplae Cosistet with the similarity i edge profiles (particles/cm 2 s) forward B T 9674 reverse B T reverse B T (particles/cm 2 s) turb forward B 9674 T reverse B T reverse B T frequecy (Hz) turb separatrix Particle flux may be radially iward ear the separatrix whe the B drift is away from the X-poit. 42d APS Aual Mtg. Quebec City 1/ 11

12 Forward B T is bi-modal while reverse B T propagates i either directio depedig upo time from beam otch Blue > forward B T B drift toward X-poit Red > reverse B T B drift away from X- poit 5 ms after NBI otch (96357) k (cm -1 ) v gr = 5.2e5 cm/s v gr = -8.3e5 cm/s Gree > reverse B T B drift away from X- poit 3 ms after NBI otch (96358) Edge relaxatio after NBI tur-off (cm/s) (radias) v phase d APS Aual Mtg. Quebec City 1/ frequecy (khz)

13 Edge profiles matched for the two B drift directios o oe day without reversig B T See Carlstrom Poster GP1.129 this sessio. Ex: edge electro profiles LSN = B drift toward the X-poit USN = B drift away from the X-poit. Also similar: edge T i profiles recyclig (Owe Poster GP1.13 this sessio; Colchi oral talk MO1.12 Wed. morig) radiated power desity ( 1 12 /cm 3 ) T e (ev) separatrix desity B toward X-pt B away from X-pt separatrix R = R - R sep (cm) T e d APS Aual Mtg. Quebec City 1/ 13

14 E r differs betwee B drift directios: some differeces betwee probe ad CER. E r (kv/m) Probe sees opposite sigs of E r betwee cofigs. CER sees small icrease i E r shear CER result E r (kv/m) R-R sep (cm) volts volts E r (V/cm) separatrix V float B drift toward X-pt B drift away fr X-pt V plasma R (cm) E r 42d APS Aual Mtg. Quebec City 1/ 14

15 The poloidal velocity of the fluctuatios is more sheared with the B drift toward the X-poit probe V phase v E B usig probe E r V poloidal (BES; probe) differet from v E B usig CER E r V poloidal (km/s) BES: C. Fezi, G. McKee, UW-Madiso Poster GP B away from X-pt B away from X-pt 5-5 BES B toward X-pt B probe toward X-pt R = R - R (cm) sep? 42d APS Aual Mtg. Quebec City 1/ 15

16 V poloidal measuremets from dispersio reflectometry agree qualitatively with BES. Dispersio reflectometry by T.L. Rhodes, UCLA v θ (a.u.) USN power sca, msec LSN, 145 msec USN, 145 msec R (cm) major shots d APS Aual Mtg. Quebec City 1/ 16

17 Fluctuatio amplitudes o outboard midplae are similar. volts ev ~ fl separatrix ~ T e B toward X-pt B away fr X-pt Homodye reflectometry idicates ñ o more tha 2% lower i USN B drift away from the X-poit. Probe φ, T e ad E θ rms amplitudes similar. V/m E ~ R (cm) 42d APS Aual Mtg. Quebec City 1/ 17

18 The turbulet coducted heat fluxes Q cod o the outboard midplae are similar. See Rudakov Poster GP1.132 this sessio for more iformatio separatrix W/m B drift toward X-pt B drift away fr X-pt R (cm) 42d APS Aual Mtg. Quebec City 1/ 18

19 Strog E B covectio circulates aroud the X-poit for both B drift directios. Due to local maximum i T e, φ plasma at X-poit: Schaffer ivited BI1.5 Mo morig; Boedo Poster GP1.137 B drift toward the X-poit plasma (V) plasma (V) Upstream Private Ier SOL Closed (orm. flux) 25 Upstream 2 Private Outer SOL 15 Closed (orm. flux) plasma (V) plasma (V) Upstream Private Outer SOL Closed (orm. flux) 25 Upstream 2 Private Outer SOL Closed (orm. flux) 42d APS Aual Mtg. Quebec City 1/ 19

20 Circulatio i opposite rotatio sese i each B drift directios. B drift breaks circulatio symmetry, with icreased particle, mometum & heat trasport whe B drift is away from the X-pt. plasma (V) B drift away from the X-poit plasma (V) Upstream Private Ier SOL Closed (orm. flux) Upstream Private Outer SOL Closed plasma (V) plasma (V) Upstream Private Outer SOL Closed (orm. flux) Upstream Private Outer SOL Closed (orm. flux) (orm. flux) 42d APS Aual Mtg. Quebec City 1/ 2

21 volts Potetial fluctuatios are higher ear the X- poit for B drift away from X-poit. ~ φ higher i SOL & core whe B drift is away from X-poit ~ For both B drift directios, SOL & core φ peak o low field side of X-pt midpl. ier SOL midpl. X-poit midpl. SOL midpl. SOL 1 B drift volts midpl. ier SOL HFS core midpl. X-poit core midpl. SOL LFS core midpl. SOL LFS core B drift d APS Aual Mtg. Quebec City 1/ 21

22 Compariso with BOUT modelig results. BOUT code predicts that the H-mode power threshold is higher whe the B drift is away from the X-poit due to icreased fluctuatios ad turbulet trasport ear the X-poits for this drift directio. Cosistet with experimet BOUT code predicts similar fluctuatio levels ad turbulet trasport at the outboard midplae with both drift directios. Cosistet with experimet BOUT code predicts that the fluctuatios propagate with a phase velocity that differs sigificatly from v E B. Need to resolve the E r profiles measured by CER, probe 42d APS Aual Mtg. Quebec City 1/ 22

23 Summary Neutral beam modulatio ca be bad ews at low duty cycles: For some reaso, the plasma is robust to the NBI perturbatio whe the B drift is toward the X-poit The B drift depedece of the H-mode power threshold is t due to icreases i turbulece ad/or turbulet trasport ear the outboard midplae. Outboard midplae fluctuatio levels ad turbulet trasport are similar or a bit lower Evidece for icreased fluctuatio levels ear the X-poits whe the B drift is away from the X-poit as predicted by BOUT The fluctuatios propagate with a more highly sheared profile whe the B drift is toward the X-poit May be the origi of the lower power threshold sice E B shear layer already partly established. Begs the questio why the propagatio profile is differet 42d APS Aual Mtg. Quebec City 1/ 23

ADITIONS TO THE METHOD OF ELECTRON BEAM ENERGY MEASUREMENT USING RESONANT ABSORPTION OF LASER LIGHT IN A MAGNETIC FIELD.

ADITIONS TO THE METHOD OF ELECTRON BEAM ENERGY MEASUREMENT USING RESONANT ABSORPTION OF LASER LIGHT IN A MAGNETIC FIELD. Melikia R.A. (YerPhI Yereva) 1. NEW CONDITION OF RESONANT ABSORPTION Below we ca