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