1. Some Halo Current Measurements in 2009 S.P. Gerhardt Thanks to: E. Fredrickson, H. Takahashi, L. Guttadora NSTX Results Review, 2009 NSTX Supported by College W&M Colorado Sch Mines Columbia U CompX General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI 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 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 KBSI KAIST POSTECH ASIPP ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec

2. NSTX 2009 NSTX Results Review, Halo Currents (Gerhardt)9/16/2009 2 Halo Current Detection in NSTX 3 Rogowskis on the Center Column (pre-2008) One rogowski (CSCL1) broken into three segments. The other two (CSCL2 and CSCU1) continuous Arrays of Toroidal Field Sensors (2008) Poloidal current flowing in vessel wall One array of 6 sensors near CHI gap (Inner Ring) One array of 6 sensors between OBD and SPP (Outer Ring) Arrays of Instrumented Tiles (2009) 4 Tiles in row 3 of the outboard divertor (OBDLR3) 90º Toroidal Separation Highly localized measurements of the current

3. NSTX 2009 NSTX Results Review, Halo Currents (Gerhardt)9/16/2009 3 Novel Instrumented Tile Design Implemented For Four Tile #3s in the Lower Outboard Divertor Design by S. Gerhardt, L. Guttadora, E. Fredrickson, and H. Takahashi Mica Insulator Folded Stainless Resistor Resistor and Insulator “Sandwich” Tile: Thinned, with a small pocket Bolts and Washers with Insulating Ceramic Coating Insulating Mica Washers T-Bar: Thinned with small pocket Stainless leads spot-welded to resistor, then spliced to shielded twisted Cu pair.

4. NSTX 2009 NSTX Results Review, Halo Currents (Gerhardt)9/16/2009 4 Example #1: Currents Flowing Out of OBD Row #3 (132186) t=0.36t=0.376 t=0.379 t=0.381 Currents flow into the OBD near the CHI gap, and out of the OBD near tile #3 Row-3 currents peak before the Inner-Ring currents Essentially no currents on the center-stack.

5. NSTX 2009 NSTX Results Review, Halo Currents (Gerhardt)9/16/2009 5 Example #2 Upward VDE (132422) No conducting path between machine top and bottom. Current flows down the outer vessel, along the machine bottom, and up the center-stack No current flow through row #3 tiles t=0.438 t=0.436 t=0.425 Halo currents local to the vessel top are undiagnosed in NSTX

6. NSTX 2009 NSTX Results Review, Halo Currents (Gerhardt)9/16/2009 6 Have Reasonable Measurements of HCF vs. TPF at Three Different Locations Row 3 of Outboard Divertor New for 2009 For Positive I HC, HCF Vacuum Vessel Near CHI Gap 2008 & 2009 Data Lower Center Stack Casing Correction to account for poor TPF sensitivity of segmented CSC rogowski. Upward Going VDEs show small peaking on the lower CSC Downward VDEs show more peaking ?

7. NSTX 2009 NSTX Results Review, Halo Currents (Gerhardt)9/16/2009 7 Axisymmetric Halo Current Directions Changed After B T was Flipped (~135702) On Vessel Wall Near CHI GapShunt Tiles in Row #3 of Outboard Divertor I p Direction Force -free HCs induced during I P quench to replace this current. DivertorFloor B T (forward) I HC B T (reversed) I HC Out of Floor I HC Into of Floor Downward Going VDEs Landing Near CHI Gap Upward Going VDEs Downward Going VDEs Landing Near CHI Gap Downward Going VDEs Landing Near SPP

8. NSTX 2009 NSTX Results Review, Halo Currents (Gerhardt)9/16/2009 8 Preliminary Analysis Shows that Currents of 20-30 kA per LLD Segment Should Be Anticipated For Rare Events Current density measured from tiles in outboard divertor. LLD Area is ~1m 2, divided into four quadrants. –A=2  R  R=2  0.78  0.2=1m 2 Maximum halo current density in row 3 observed for the low- , dr sep <0 cases. –These are exactly the conditions of the LLD baseline scenario. Halo currents of 20-30 kA/segment should be assumed for the rare worst case. –Caveat, need to carefully look at the data for these worst cases. Halo current measurements will be an important part of the LLD operational experience. Likely LLD Operating Space

9. NSTX 2009 NSTX Results Review, Halo Currents (Gerhardt)9/16/2009 9 Substantial Upgrade to Capability For 2010 Shunt Tiles In Red Rogooskis in Blue Keep the Old Diagnostics Center stack casing rogowskis Lower vacuum vessel current measurements Add Some New Ones Each LLD Segment has a Small Rogowski on its single point ground 6 shunt tiles in row 3 of the lower outboard divertor 6 shunt tiles in row 4 of the lower outboard divertor