NSTX 2010 Experimental Proposal:NSTX 2010 Experimental Proposal:Peeling-Ballooning Stability Dependence on Peeling-Ballooning Stability Dependence on

Plasma TriangularityPlasma Triangularity

Aaron Sontag, Oak Ridge National Lab

FY2010 NSTX Research ForumDec. 1-3, 2009

College W&MColorado Sch MinesColumbia UComp-XGeneral AtomicsINELJohns Hopkins ULANLLLNLLodestarMITNova PhotonicsNew York UOld Dominion UORNLPPPLPSIPrinceton UPurdue USNLThink Tank, Inc.UC DavisUC IrvineUCLAUCSDU ColoradoU MarylandU RochesterU WashingtonU Wisconsin

Culham Sci CtrU St. Andrews

York UChubu UFukui U

Hiroshima UHyogo UKyoto U

Kyushu UKyushu Tokai U

NIFSNiigata UU Tokyo

JAEAHebrew UIoffe Inst

RRC Kurchatov InstTRINITI

KBSIKAIST

POSTECHASIPP

ENEA, FrascatiCEA, Cadarache

IPP, JülichIPP, Garching

ASCR, Czech RepU Quebec

NSTXNSTX Supported by

NSTXNSTX A. Sontag - 2010 NSTX Research Forum 1-3 Dec. 2009

Proposal: Alter Peeling-Ballooning Stability Boundary by Varying Plasma Triangularity

• NSTX peeling-ballooning stability inconsistent with ELITE calculations– ELMs observed even though

/(*/2) << 1

• PEST indicates ballooning may be important– max. stable N roughly

proportional to avg.

• Reduced can increase ballooning instability drive– high- opens up 2nd stability at

low A

22

•3 4 5 6 7 8•Normalized Pressure Gradient ()

•1.2

•0.8

•0.4

• Ed

ge

cu

rre

nt

• [(j

ma

x+

jse

p)/

2<

j>]

•0.1

NSTX peeling-ballooning stability as calculated by ELITE for a discharge with Type I ELMs

N

0

5

10

upper

0 0.25 0.5

lower = 0.2

lower = 0.3 lower = 0.4

Ballooning stability as calculated by PEST

NSTXNSTX A. Sontag - 2010 NSTX Research Forum 1-3 Dec. 2009

XP 942 Successfully Affected ELM Stability with lower modification

lower decrease coincident with transition to small ELMs– drsep unchanged until well after

small ELM regime (0.46 s)

• Further reduction needed to approach ballooning boundary– PEST indicates n=3 still most

unstable mode– shot development required going

shape with decreased stability

upper scan also needed

– go to higher , Z0 > 0 plasma, or reduce outer gap

33

NSTXNSTX A. Sontag - 2010 NSTX Research Forum 1-3 Dec. 2009

XP Plan: Continue scan from XP 942, independently varying upper & lower

• Decreased possible with increased outer gap– more modeling required for this scenario

• XP 942 target was low- (~1.9) LSN– difficult to affect upper with large separation from

control coils upper always slightly less than lower

• ISOLVER modeling shows more control of upper achievable at increased-– Use PF1AU to push/pull upper

– Fix PF1s & 2s, PCS control of PF3s & PF5– increase request

• Vary upper at fixed lower

– vary upper squareness request4

0.0 0.5 1.0 1.5 2.0R (m)

-2

-1

0

1

2

Z(m)

NSTXNSTX A. Sontag - 2010 NSTX Research Forum 1-3 Dec. 2009

Duration & Required Diagnostics

• XP could be performed in 1 day

• Required diagnostics– CHERS (beam blips in HHFW-only discharges)– USXR arrays– magnetics– Thomson scattering– EFIT (w/MSE)

– D

• Desired diagnostics– edge reflectometer– two color USXR

5