Comments on HC Measurements for NSTX-Upgrade

SPG

CS Upgrade Meeting11/2/11

NSTX Supported by

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

NFRIKAIST

POSTECHASIPP

ENEA, FrascatiCEA, Cadarache

IPP, JülichIPP, Garching

ASCR, Czech Rep

Columbia UCompXGeneral AtomicsFIUINLJohns Hopkins ULANLLLNLLodestarMITNova PhotonicsNew York UORNLPPPLPrinceton UPurdue USNLThink Tank, Inc.UC DavisUC IrvineUCLAUCSDU ColoradoU IllinoisU MarylandU RochesterU WashingtonU Wisconsin

NSTX Meeting name – abbreviated presentation title, abbreviated author name (??/??/20??)

SPG Understanding of the Present State.

• Halo currents in the outer divertor of NSTX have been measured reasonably well.– This was a low priority “hobby” of mine.

• Halo currents on the CS midplane have not been measured.• I wasn’t involved with discussions at the review, but…

– Small crisis regarding CS midplane HCs in weeks before review.• Because we didn’t have the measurements to conclusively answer this.

– Issues were:• What is total halo current fraction.• What is the toroidal peaking of the currents flowing up the CSC• How is this related to the peaking of the halo currents where they enter

the CS? – Design changes implemented.– I infer that this is the driver of the discussion?

NSTX Meeting name – abbreviated presentation title, abbreviated author name (??/??/20??)

NSTX Halo Current Diagnostics (I)

NSTX Meeting name – abbreviated presentation title, abbreviated author name (??/??/20??)

NSTX Halo Current Diagnostics (II)

NSTX Meeting name – abbreviated presentation title, abbreviated author name (??/??/20??)

Detector Layout That Would Resolve The Present Issue

NSTX Meeting name – abbreviated presentation title, abbreviated author name (??/??/20??)

Detector Layout That Would Resolve The Present Issue

Discrete BT Sensor Imbedded in Tile(measures total halo current fraction, and estimates peaking)

Shunt Tile(peaking at the entrance points)

NSTX Meeting name – abbreviated presentation title, abbreviated author name (??/??/20??)

Final Comments

• We may need to modify the shunt tile design to account for the curved CS surface.

• Main benefit to NSTX-U project:– Validate assumptions about CS HCs during lower-field, lower-current first

year of the project, in preparation of the higher current and field discharges.• These would be useful for physics analysis and design of the next

device.• About DCPS…

– This measurement do not provide any utility for realtime interlocks.• The HC blip is only a few ms long…too fast for any interdiction effort.• Significant processing can be required to find the useful signal.

– It is possible that one could have a post-processing algorithm waving a flag if anomalously large HCs were observed.

– Topic requires significantly more engineering and physicist support if it is part of machine protection…I don’t recommend this.