Soft X-ray multi-camera tomography system

A powerful diagnostic for noninvasive measurement of plasma dynamics with high spatial and high temporal resolution is the soft X-ray (SXR) tomography. At W7-X a SXR tomography diagnostic with the name XMCTS (abbreviation for soft X-ray multi-camera tomography system) is installed in one of the five up-down symmetric triangular cross-sections. The XMCTS consists of 20 pinhole cameras, each observing the plasma with 18 lines-of-sight. By tomographic inversion of the 360 measurements along all lines-of-sight the two-dimensional X-ray radiation profile can be obtained by applying  mathematical algorithms similar to medical tomography systems. The spatial resolution is approximately 4cm and the time resolution is approximately 1.0µs.
Fast events in the plasma, for example waves and instabilities can be measured as well as the dynamics of impurity atoms in the magnetized plasma. In addition the increasing horizontal outward shift of the plasma with increasing plasma densities and temperatures, the so-called Shafranov shift, an important quantity for the optimization of the stellarator, can be directly measured by XMCTS.

360 lines-of-sight from 20 poloidally arranged pinhole cameras measure the X-ray radiation from the plasma with 2 MHz sample frequency.
Tomogram of a 1µs time slice measured at 4.018400s after plasma start of W7-X experimental ID 20180904.022. The flux surfaces are calculated by the code VMEC. The resulting X-ray profile fits into the nested flux surface structure of the here shown high iota B-field configuration.
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