langmuir probe peer review josh kallman for the lld team february 13, 2009 nstx supported by college...
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Langmuir Probe Peer ReviewLangmuir Probe Peer Review
Josh Kallmanfor the LLD Team
February 13, 2009
NSTXNSTX Supported by
College W&MColorado Sch MinesColumbia UComp-XGeneral AtomicsINELJohns Hopkins ULANLLLNLLodestarMITNova PhotonicsNew York UOld Dominion UORNLPPPLPSIPrinceton UPurdue USNLThink Tank, Inc.UC DavisUC IrvineUCLAUCSDU ColoradoU MarylandU Illinois UCU RochesterU WashingtonU Wisconsin
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
KBSIKAIST
POSTECHASIPP
ENEA, FrascatiCEA, Cadarache
IPP, JülichIPP, Garching
ASCR, Czech RepU Quebec
NSTXNSTX Langmuir Probe Peer Review (Kallman) 2Feb 13, 2009
Physics requirements for the Langmuir probe array
• Poor coverage of edge diagnostics necessitates a new method for measuring plasma parameters (ne, Te, 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
129019
0.455 0.460 0.465 0.470 0.475
Time (seconds)
ELMs in lower divertor, 129019
0.2 0.4 0.6 0.8 1.0 1.2 1.4
Radius (m)
2
4
6
Q [
MW
/m^2
]
Heat flux, 129019
2
4
6
t = .33st = .36st = .39s
Arb
itrar
y un
its
Strike pointlocation
0.45
NSTXNSTX Langmuir Probe Peer Review (Kallman) 3Feb 13, 2009
• 33 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
NSTXNSTX Langmuir Probe Peer Review (Kallman) 4Feb 13, 2009 4
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
NSTXNSTX Langmuir Probe Peer Review (Kallman) 5Feb 13, 2009 5
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
probemacor spacer
wire
exits
NSTXNSTX Langmuir Probe Peer Review (Kallman) 6Feb 13, 2009
Probe material is vacuum compatible after curing
NSTXNSTX Langmuir Probe Peer Review (Kallman) 7Feb 13, 2009
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
NSTXNSTX Langmuir Probe Peer Review (Kallman) 8Feb 13, 2009
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
NSTXNSTX Langmuir Probe Peer Review (Kallman) 9Feb 13, 2009
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
NSTXNSTX Langmuir Probe Peer Review (Kallman) 10Feb 13, 2009
Backup
NSTXNSTX Langmuir Probe Peer Review (Kallman) 11Feb 13, 2009
Probe material RGA before 2nd cure