next generation scanning probes in c-mod · next generation scanning probes in c-mod test...
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Next Generation Scanning Probes in C-Mod
MotivationScanning Langmuir-Mach probes have proven essential for undercovering SOL physicsCross-field profiles, bursty transport in far SOL, density limit physics, transport-driven parallel flows, influence of topologies, connection to L-H threshold...
Inner Scanning Probe has provided important insightsNear-sonic flows, topology-dependent effects
Still, key information is lacking
Inner SOL:profiles and flows just inside separatrixn,F fluctuations, correlations, fluxes
Inner & Outer SOL:cross-field flow information,Te fluctuationsreliable operation during ICRF
B. LaBombardN. Smick
C-Mod Ideas Forum, December 2004
OuterScanningProbeInner
ScanningProbe
VerticalScanningProbe
B
The WASPWall Actuated Scanning Probe
N. Smick, B. LaBombardOverall Plan
Build an advanced scanning probe for inner midplane location ==> WASP Actuated by embedded coil Four electrodes Langmuir/Mach probe Same geometry as outer probe "Linear" plunge motion (+R direction)
Installation target: summer of 2005
Investigate use of "Bohm-Chodura Mach Probe" geometries
May allow measurement of both parallel and cross-field flow velocities (M//, M^)
Build fast I-V sweep probe drive circuitry sweep rate > ~1 MHz record Te, n, F fluctuations
Design work 95% done. Prototype late 2005?
Next Generation Scanning Probes in C-Mod
C-Mod Ideas Forum, December 2004
B
B
Standard Mach & Fluctuation probe
"Bohm-Chodura"Mach probe
Plan for Spring 2005 Run Campaign
Next Generation Scanning Probes in C-Mod
Test "Bohm-Chodura Mach Probe" geometry on A-port drive (ASP)
A new prototype B-C head is presently installed on ASP
Additional sweep-bias power supplies (2kHz) need to be assembled
Request dedicated run time (1day):- Ohmic discharges in LSN, DN and USN topologies (0.8 MA, 5.4 Tesla)- Density scan- Make contact with previous measurements of parallel flows and cross-field flows as inferred from ExB & fluctuation phase velocities
Radial-spaced probe head geometry on ASP
Fall back: Standard geometry probe on ASP (flux-surface aligned)
New and improved standard-geometry probe heads have been fabricated and are ready to install
C-Mod Ideas Forum, December 2004
A new radial-spaced probe head has been fabricated and is ready to install
Request dedicated run time (1day, coordinated with QCM enthusiasts):- "dial-up" some Ohmic EDA discharges with strong QCM- Poke deep across QCM layer- Look for probes passing through layer; record attenuation effects, if any
Possible additional run day to look at radial correlations of turbulence