Conceptual design of the ITER core imaging x-ray spectrometer

Summary form only given. The core ion temperature and bulk ion velocity of ITER plasmas will likely be derived from the thermal Doppler broadening and Doppler shift of X-ray lines emitted by highly charged trace elements and recorded by an array of high-resolution spectrometers. Although several elements could be used to seed the plasma for this purpose, we show that the emission of neonlike tungsten provides important advantages. Tungsten is already a plasma constituent due to its use in the divertor region. Moreover, the relevant tungsten lines have wavelengths that are readily analyzed by X-ray crystals and fall into a region where existing detectors have high quantum efficiency, and the abundance of neonlike W⁶⁴⁺ is thought to peak for the expected core electron temperatures. Experimental studies of the relevant X-ray emission of tungsten ions confined and excited in an electron beam ion trap confirm these predictions. We have made a conceptual design of an imaging spectrometer, which covers the ITER plasma using six viewing angles to produce a time-dependent radial profile of the ion temperature. Our design is based on a recent development of a core imaging X-ray crystal spectrometer implemented on the Alcator tokamak. Each viewing angle will pick up differing amounts of toroidal and poloidal rotation components in order to allow a determination of the radial profile of bulk ion motion. We will present the design and performance characteristics of the imaging crystal spectrometer. In addition, we will discuss the possibility of utilizing a microcalorimeter for measuring the impurity emission over the entire X-ray band with a resolution sufficient to infer the ion temperature from each line.