Technology development of the soft X-ray tomography system in Wendelstein 7-X stellarator

Abstract

The engineering and design of the soft X-ray Multi Camera Tomography System (XMCTS) in Wendelstein 7-X stellarator (W7-X) must fulfill several additional requirements compared to short pulse machines. The XMCTS has to withstand irradiation and electron cyclotron microwave loads in addition to being ultra high vacuum compatible, having low magnetic permeability and using low neutron activation materials (e.g. Co ≤ 2000 ppm). A further difficulty is the limited space inside the plasma vessel, which requires special engineering solutions.After detailed design development, supported by finite element analyses, prototypes have been manufactured and tested. At the end all test results have successfully proven that the components fulfill the requirements and that reliable and stable measurements will be possible with the XMCTS diagnostics during W7-X operation.The paper describes the design and the technological development, in particular on the electric multipin feedthrough (UHV barrier between in vessel detectors and the preamplifiers), the active cooling of the electronic components (reducing dark current/ noise increase), the pneumatic shutter (protection of the detectors from sputtering and during baking) and the fiber optics illumination system (calibration of the detectors).

Deep learning for plasma tomography using the bolometer system at JET

“…Besides the diagnostics available at JET, a similar approach could be used in other fusion devices. For example, the tomography diagnostic in Wendelstein 7-X has as many as 20 X-ray cameras with a total of 360 lines of sight [52]. A deep learning approach such as the one proposed here could bring significant savings in the time required to compute the reconstruction of the plasma profile from that amount of data.…”

Soft x-ray tomograms are consistent with the magneto-hydrodynamic equilibrium in the Wendelstein 7-X stellarator

“…Inside its opening, the aperture of the pinhole-type camera is visible. In the background, the Bourdon spring operating the shutter can be spotted (details in [20]).…”

Soft x-ray tomography measurements in the Wendelstein 7-X stellarator

“…For the conditions in Wendelstein 7-X, especially the long pulse plasma operation of 30 min, a set of additional requirements had to be met [12]. In particular necessary water cooling of the cameras is required [13,14]. After the installation in the vacuum vessel, the frame segments (five cameras are grouped in one frame segment) were measured to an accuracy of ∼1.5 mm by metrology (see section 2).…”

“…For the mechanical installation of the XMCTS cameras at the W7-X stellarator and for safe operation during high power programs a number of mechanical solutions have been developed and implemented [11,14]. According to the required number of x-ray cameras at preferably one single toroidal position, but due to the limited number and limited access of ports in the design phase of W7-X, the whole camera system has been placed inside the vacuum vessel.…”

“…Cables for signals, control and electric power, and pipes for cooling water, compressed air and signals are guided to the camera system inside the vacuum vessel via four plugins each connected with an interface at one port. More details about the assembly and mechanical setup can be found in [11,14].…”