NSTX Team Meeting July 21,, 2011 NSTX TF Update NSTX Team Meeting July 21, 2011 NSTX Supported by Culham Sci Ctr U St. Andrews York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu Tokai U NIFS Niigata U U Tokyo JAEA Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI NFRI KAIST POSTECH ASIPP ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep Columbia U CompX General Atomics FIU INL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U ORNL PPPL Princeton U Purdue U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Illinois U Maryland U Rochester U Washington U Wisconsin

NSTX Team Meeting July 21,, 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 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