X-ray imaging detectors advance plasma research

Reading Sol Gruner’s article on the advancement of x-ray imaging detectors (Physics Today, December 2012, page 29 ) was a pleasure, and I share his excitement for how the new technology is motivating research in multiple fields. A few years ago, I was part of a team of MIT and Princeton Plasma Physics Laboratory scientists and graduate students who used pixel-array detectors when we deployed a new x-ray imaging crystal spectrometer ¹ on the Alcator C-Mod tokamak. When doped with small (less than 0.1%) amounts of high-Z atoms like argon, high-temperature plasmas can emit a wealth of information, in the form of x-ray line radiation, that includes flow and temperature data gathered via the Doppler shift and Doppler broadening mechanisms. Since that information is emitted from the plasma volume, tomographic techniques are required to unfold what is happening locally. ²

The high-resolution images provided by the new detector technology have enabled us to better understand the plasma state and use C-Mod experimental resources more efficiently. What could have taken dozens of repeated discharges when scanning with older instruments can now be done dynamically during a single plasma shot.