NSTX Team Meeting July 21,, 2011

NSTX TF UpdateNSTX TF Update

NSTX Team MeetingJuly 21, 2011

NSTXNSTX 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 Team Meeting July 21,, 2011 2

A TF failure occurred during ISTP on July 20, 2011

Initial Observation:- TF power tripped due to hitting the current limit. - The audio showed some unusual arcing like sound.- Turn-to-turn short developed at low current from the beginning of the

shot (see traces from Stefan next slides).- The short is likely to be due to an insulation failure (perhaps caused by a

water leak) and not because of JxB force or high current level.

Test Cell Observation:- Some faint odor of something burning?- Water dripping from one of the inner TF cooling tube #13.- Looking up to TF bundle, some discoloration, a sign of arcing.- A piece of solder-like material found on the floor below.

Further examination:- Water drained from inner TF but three lines (out of 36) were clogged.- Borescope inspection showed that the line clogging was due to solder in

the line (two near the end and one several inches from the end).

NSTX Team Meeting July 21,, 2011

Comparison of failed shot (blue) vs. good shot (red) taken on July 19

NSTX Team Meeting July 21,, 2011

Comparison of failed shot (blue) vs. good shot (red) taken on July 19 - II

NSTX Team Meeting July 21,, 2011

TF bundle cross section

Observation:• Water dripping from one of the inner TF cooling tube and some solder-like material found. • Three TF cooling paths clogged with solder material.A possible explanation:

• A short occurred among those three TF conductors (or cooling tubes) at a location some distance (several inches?) up from the bottom• The heat due to the short caused melting of the cooling tube wall and the surrounding solder material entered the tube.

Looking up from the bottom of the machine with borescope

?

Cooling tube for outer layer TF runs parallel between the inner layer TF conductor

Initial Inspection Result

NSTX Team Meeting July 21,, 2011

• Plan A: Repair the TF as soon as possible– We need to find out first where and why the failure has occurred. – Our engineering team will be disassembling the lower TF hub to

expose as much affected area as possible for further inspection and possible repair (this week)

– If needed, the TF bundle could be lifted out of the machine without breaking the high vacuum for further inspection and possible repair

• Plan B: If the TF repair is determined to take too long, we need to consider starting the upgrade outage early. – The upgraded TF design is much more robust.– By starting the outage early, we maybe able to start up the

upgraded machine that much sooner in FY 2014.

• Toward end of next week, we should be able to report to you what we find and what will be our path forward.

Present Plan

NSTX Team Meeting July 21,, 2011

Present TF bundle(Diameter is ~ ½ of the Upgrade TF) Upgraded TF bundle

Upgraded TF Have Much Improved Design

• Complicated two layer design• Complicated cooling water path• 3/16” refrigeration cooling tube • B-stage insulation

• Identical simple conductors • Simple straight cooling water path• 3/8” K-type straight copper tube• More robust VPI insulation