Plasma Science and Fusion Center
Massachusetts Institute of Technology
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yhAlcator C-Mod
Diagnostic Needs
Profiles
Electron density profiles:
We desire a density profile diagnostic with much finer time resolution than Thomson scattering. The measurement should be such that there is minimal ambiguity of interpretation. It should not require spatial inversion. Target capabilities would be 100 microsecond time resolution and 1 cm spatial resolution. Measurements with ~1 mm resolution in the edge plasma would aid studies of the H-mode pedestal.
Contact: M. Greenwald
Transport
Multiple measurements of plasma profiles during disruptions:
We desire to follow the evolutions of the electron temperature and density profiles during the thermal quench of a disruption. Such a diagnostic would measure profiles during both disruptions mitigated by a massive gas puff and "unmitigated" disruptions. The disruption time scale is a few msec, so measurements on a ~100 microsec time scale are desired.
Contact: R. Granetz
MHD
Ion temperature profiles:
Ion temperature profiles across the entire cross section are desired. Ideally these would have time resolution of 5-10 msec and spatial resolution of 1 cm.
Contact: M. Greenwald
Transport
Velocity profiles:
Toroidal and poloidal velocity profiles across the entire cross section are desired. Ideally these would have time resolution of 5-10 msec and spatial resolution of 1 cm.
Contact: M. Greenwald
Transport
q or magnetic shear profile:
The ability to measure these profiles across the entire cross section with good spatial resolution (~ 2cm) and good time resolution 20-50 msec are essential to computing micro (and macro) stability. High resolution measurements in the plasma edge (~1 mm) would aid studies of pedestal stability.
Contact: M. Greenwald
Transport
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Fluctuations
Localized density fluctuations:
We desire a measurement of density fluctuations localized to 1-2 cm with a kperp range from kperp rhoi ~ 0.1 to kperp rhoe ~ 0.5
Contact: M. Greenwald
Transport
Core fluctuations in other quantities:
We desire measurement of core fluctuations in any of the quantities Te, Ti, phi, V, or B in wavenumber and frequency ranges relevant to turbulent transport.
Contact: M. Greenwald
Transport
Turbulence imaging:
High resolution imaging of any fluctuating field would aid in the study of turbulent transport. Time dependent measurements are of even greater value. Spatial and temporal resolution must be sufficient to resolve some part of the transport-relevant turbulence fields.
Contact: M. Greenwald
Transport
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Power Balance
RF power deposition:
A "first principles" measurement of ICRF or LH power deposition would aid all confinement studies.
Contact: M. Greenwald
Transport
Transmission grating monochromator for 10-20 nm radiation:
We desire a simple (no moving parts), compact transmission grating monochromator to be used for detection of mid- to high-Z impurity line emission in the 10-20 nm spectral range. The instrument should have at least moderate spectral resolution, delta_lambda/lambda ~1%. The instrument must be vacuum compatible with the C-Mod vacuum (all metal seals, low outgassing components). Ideally, the design is such that imaging in the non-dispersion dimension is possible. The instrument would be used as a dedicated monitor of Mo or W line radiation and concentration. As such, it should be absolutely calibrated.
Contact: M. Reinke
Transport
Extensive Coverage of Divertor Surface Temperatures:
We desire a routine measurement of the surface temperature of a large fraction of the divertor surfaces. This would be accomplished using IR cameras/imaging. Spatial resolutions at the few mm level are desired. Ideally, some IR fast imaging (i.e. ~50 microsec time resolution) could be obtained over a small subset of the imaged regions.
Contact: J. Terry
Plasma Boundary
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Plasma-Material Interactions
Boron coatings
We desire a diagnostic that would measure the thickness of the poloidal pattern of B films on the C-Mod molybdenum tile surfaces. The diagnostic should have shot-to-shot time resolution to inform plasma operations. In particular, we want to monitor the longevity of boron coating on the shelf of the outer divertor target. These surfaces are field-line connected to the ICRH antennae, and have been indirectly identified as the area of critical importance for molybdenum core contamination which can limit C-Mod H-mode performance.;
Contact: B. Lipschultz
Plasma Boundary
Hydrogen and deuterium fuel retention in the wall
We desire a diagnostic that would measure the absolute and relative hydrogen and deuterium fuel content in the wall. The H/D ratio is critical for efficient ICRH heating and must be reduced after a vent to ~2%, typically requiring significant run-time. Therefore a desired time resolution is shot-to-shot to inform conditioning operations. Additionally the quantification of the D content in the wall is desired for extrapolating C-Mod experience with Mo tiles to tritium retention in D-T burning plasmas.
Contact: B. Lipschultz
Plasma Boundary
Tungsten and/or Molybdenum Monitor
We desire a routine monitor of Tungsten and/or Molybdenum concentration in the core plasma. Beginning with the 2007 run campaign, a full toroidal ring of 120 Tungsten lamella tile modules is present near the outer strike-point location on the lower divertor cassettes. The rest of the divertor surfaces are covered with Mo tiles, as are the outboard poloidal limiters and inner wall. Because of C-Mod's high power density, it is desirable to monitor, on a routine basis, the core concentrations of Mo and W. Ideally such a monitor would take up little or none of the scarce port space. (See also the "Transmission grating monochromator for 10-20 nm radiation" above.)
Contact: J.Terry
Plasma Boundary
Diagnostics for Dust
We desire diagnostics that provide measurements of composition, spatial-distribution, size-distribution, and/or dynamics of intrinsic dust particles existing in C-Mod. In particular, the accounting of dust in shadowed or poorly-accessed regions is desired.
Contact: R. Granetz
MHD
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General
Poloidal/radial distribution of the Edge Ionization Source:
We desire a measurement of the ionization source (ionization of deuterium atoms) over the entire poloidal cross-section of C-Mod's "main-chamber" plasma. Probably this would be accomplished optically, using either Balmer alpha or Lyman alpha line emission. Resolution in the radial (poloidal) dimension of a few mm (cm) is desired.
Contact: J. Terry
Plasma Boundary
In-vessel illumination:
We desire a simple in-vessel illumination system that would light up the inside of C-Mod on a between-shot basis. The safest system would bring the light into the vessel via fibers, but in principle light-producing filaments inside the vessel are not ruled out, as long as they are non-contaminating and robust.
Contact: J. Terry
Plasma Boundary
Long Optical Periscopes:
We desire a number of optical periscopes that would be used bring views of the plasma and various in-vessel components to regions outside C-Mod superstructure. Once outside of the superstructure the periscopes would couple the views to CCD cameras. The periscopes must be less than 1 cm in the transverse dimension, but must transfer the image over a length of ~ 1m. They must be mechanically robust and stable.
Contact: J. Terry
Plasma Boundary
Additional "Sensor" for Disruptions and Disruption Mitigation:
We desire a non-magnetics-based diagnostic that senses a future major disruption in time to activate the existing disruption-mitigation-by-massive-gas-injection system. Typically at least 3 ms is needed after receipt of a sensor's "fire" signal for the injected gas to reach and affect the about-to-disrupt plasma. Thus detection must take place at least 3 ms before the disruption. There are a number of different kinds of disruptions (e.g. Vertical Displacement Events, High-Beta, Locked-Mode, Density-Limit, Impurity-Radiation-Induced). To date we have used magnetics-based plasma-position sensors to successfully sense VDE disruptions. We desire a non-magnetics-based sensor for redundancy and for possible relevance to disruption mitigation on ITER. Ideally this sensor should sense reliably any of these types of disruptions. (For more details see http://www.psfc.mit.edu/research/alcator/pubs/APS/APS2006/Granetz-poster.pdf)
Contact: R. Granetz
MHD
Fast Ion Diagnostic Upgrade:
The fast ion tail distribution in C-Mod is presently diagnosed using a multi-channel Compact Neutral Particle Analyzer (CNPA) system. The CNPA system uses Si-diode detectors to measure energetic (>50 keV) neutral particles that have charge exchanged with fast ions. Since new codes such as AORSA and CQL3D, as well as ORBIT RF, are producing more detailed predictions, e.g., off-axis power deposition, we want to increase the spatial coverage of the current system from 4 channels (3 vertical and 1 horizontal) to nearly full coverage of the poloidal cross-section using two spatially imaging arrays of detectors. Chordal separation of ~1 cm is desired.
Contact: R. Parker
Lower Hybrid Systems
