Langmuir Probe Peer Review Josh Kallman for the LLD Team February 13, 2009 NSTX Supported by College W&M Colorado Sch Mines Columbia U Comp-X 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 Maryland U Illinois UC 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

NSTX Langmuir Probe Peer Review (Kallman)Feb 13, Physics requirements for the Langmuir probe array Poor coverage of edge diagnostics necessitates a new method for measuring plasma parameters (n e, T e, Γ) in the divertor region, especially with the LLD installation Heat flux profile at outer strike point has FWHM of 10 cm –current IR camera resolution is 16 data points over this region –higher spatial resolution could allow more accurate particle flux measurements ELMs occur on a time scale of several ms –temporal resolution should be sufficient to operate during transient events (single tip probes would be limited by voltage sweep rate) –triple probes would provide instantaneous data Time (seconds) ELMs in lower divertor, Radius (m) Q [MW/m^2] Heat flux, t =.33s t =.36s t =.39s Arbitrary units Strike point location 0.45

NSTX Langmuir Probe Peer Review (Kallman)Feb 13, radially arrayed triple-probes will provide edge temperature and density characterization on a continuous basis Probes based on MAST design involving a macor cassette of closely spaced probes embedded in a carbon tile –tile mount with radial coverage of divertor (Bay B) –electronics to be provided by UIUC Close spacing of probes will provide better resolution in high-gradient (strike point) regions –each probe covers 3.5 mm radially, including spacing –probe heads are 2.5mm radial x 7mm toroidal rectangles Triple Langmuir probe array will address edge diagnostic needs carbon tile and endcap

NSTX Langmuir Probe Peer Review (Kallman)Feb 13, Cassette design will allow for ease of probe mounting and will include channels for wire transport Macor cassette features grooves that will allow probes to slide in easily without necessitating screws to secure probes vertically –screwless design reduces mechanical stresses on the probes Wiring channels allow for the wires from each group of probes to exit independently –wires will exit on sides of edge probes and through base of central probes macor cassette wire channels

NSTX Langmuir Probe Peer Review (Kallman)Feb 13, Probe design includes features to protect underlying surfaces and uses novel materials to facilitate assembly Probes will be shaped so as to minimize direct exposure of macor to plasma or lithium –probe bend prevents direct line of sight for lithium or plasma down to cassette –probe widening at top allows for smaller gaps and greater shielding of surfaces below Macor spacers between probes will provide insulation and structure to probe assembly –widened probe and spacer bases couple to cassette grooves Probe fabrication concept has been developed –material is molded graphite cement to allow precise shaping –wires can also be attached with graphite cement, obviating need for mixed materials or additional screws graphite probe macor spacer wire exits

NSTX Langmuir Probe Peer Review (Kallman)Feb 13, Probe material is vacuum compatible after curing

NSTX Langmuir Probe Peer Review (Kallman)Feb 13, In-vessel wiring Maximum current through probes is estimated at ~1 A (transient) –based on Isat of existing probes and comparison of probe area 24-gauge wires will be used, unshielded within probe tile –capacitive coupling test on representative twisted pair shows minimal cross-talk Wire bundles for each radial row of triple probes will be run out through channels in cassette to channels in outboard tiles and eventually under passive plate to feedthrus

NSTX Langmuir Probe Peer Review (Kallman)Feb 13, New probe electronics will permit continuous triple-probe operation a M. Jaworski, UIUC Triple probe interpretation will be supplemented by single-tip tile probe sweep characteristics –single tip probes can provide ion saturation current data –existing probe hardware can be migrated to new rack to be used with single tip probes Initial implementation provides for 10 triple-probe sets –future upgrades will expand probe electronics –wiring scheme will allow external (to vessel) selection of which probes to operate

NSTX Langmuir Probe Peer Review (Kallman)Feb 13, Ex-vessel wiring Langmuir probes will be cabled through 4 Bay J feedthrus Instrumentation will be located in the LLD diagnostic rack –rack will be placed next to LLD control rack on east mezzanine F. Jones

NSTX Langmuir Probe Peer Review (Kallman)Feb 13, Backup

NSTX Langmuir Probe Peer Review (Kallman)Feb 13, Probe material RGA before 2 nd cure