Bolometry on NSTX-U
Need for Radiated Power Measurements
insert text on motivation (i.e. power balance, confinement and exhaust physics)
Types of Sensors
A variety of sensors are used to make these measurements. Some are commercially available, while others are custom built and maintained by the NSTX-U team.
Resistive bolometers are a conventional tool in high temperature plasma physics to measure the power lost from radiation, typically from short wavelength photons such as soft x-ray (SXR) or vacuum ultraviolet (VUV) radiation.
Radiation imaged onto a thin (few micron Au or Pt) metal foil increases its temperature which is measured by a change in the resistance of meander resister thermally, but not electrically, attached to the absorber.
Systems are under development for FY17 NSTX-U operations to use resisitve bolometers to measure the lower divertor radiation and the bulk plasma.
Infrared video bolometers (IRVB) use a different approach to measure the temperature rise of the foil exposed to plasma radiation. This is done remotely by imaging the IR emission out of the vacuum vessel and detecting it with a high resolution, scientific-grade IR camera.
A system is under development for FY16 NSTX-U operations to use an IRVB to image radiation in the low divertor.
While not bolometers themselves, a special class of photodiode that has enhanced UV and VUV sensitivity is often used to complement resistive bolometer measurements. These Aboslute eXtreme UltraViolet (AXUV) diodes are faster and cheaper to deploy but suffer from sensitivity issues in the VUV that prevent direct, accurate measure of the absolute radiation.
NSTX-U will have several arrays to measure the core radiation (ME-SXR) and divertor (LADA) emission for FY16 operations.
At its heart, the bolometer is precision, remote temperature (or strain gauge) measurement and technology is always evolving. New methods are under investigation, but the requirements for use in a tokamak environment are high.
Radiated Power Diagnostics on NSTX-U
Several systems have been deployed or are currently being developed for the upcoming campaign.
Core Resistive Bolometers (Bay-G Midplane)
Core AXUV Diodes (Bay-G Midplane)
Lower Divertor Resistive Bolometers (Bay-I Lower, Bay-G Upper)
Lower Divertor AXUV Diodes (Bay-G Midplane)
Access to Radiated Power Data for NSTX-U
Link to page which describes the MDS structure of the data
Contact: Matthew L. Reinke (mreinke@pppl.gov) for more information on NSTX-U radiated power measurements.