Max-Planck-Institut fur Plasmaphysik, EURATOM Association, Greifswald, Germany†Associacao Euratom/IST Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico1049-001 Lisboa, PortugalIntroductionThe Wendelstein 7-X (W7-X) device, presently under construction in Greifswald, will allowhigh power quasi-steady state discharges with durations of up to 30 min. Diagnostics shouldtherefore be able to cope with large heat loads (requirement of active cooling) and drift com-pensation for a good signal measurement stability. Moreover, the recorded data might be usedfor controlling the discharge flow. For more advanced scenarios, a conditional branching intodifferent discharge segments will be possible within the framework being developed by the W7-X software group [1]. For these scenarios online data analysis capabilities for the diagnosticsare very favourable. On the other hand, the data rates of diagnostics with a high temporal andspatial resolution will make very fast data analysis methods necessary, either for identifyingthe interesting bits inside a huge amount of raw data, or – if fast data acquisition for the wholedischarge is not feasible – online triggering capabilities for setting fast time windows for thedata acquisition. One diagnostic with very high spatial and temporal resolution is the soft-XrayMulti Camera Tomography System (XMCTS) with 400 lines of sight (crossing through theplasma from 20 cameras located around the minor circumference) and 500 kHz bandwidth. Thesignals from the photo diode arrays will be digitized with 14 Bit at 1 MSample per second.The total data of this diagnostic alone are a huge 1400 GBytes per 30 min discharge. The sys-tem will allow a tomographic inversion of the radiation distribution in a poloidal plane of theplasma, giving information on plasma position and -shape as well as MHD-stability (consider-ing pressure constancy on magnetic flux surfaces). Since the plasma shape has a specific formfor different values of the plasma-beta, it is possible to derive this important quantity from theinversion. We note here that an obvious application of this technique for the case of tokamaks,namely the plasma position control, is not an issue for stellarators, due to their inherent stabilityof the magnetic configuration.The method of choice for offline tomographic reconstruction will be based on regularizedmatrix inversion methods. Due to the iterative minimization involved, these methods will pre-sumably be too slow (although there are interesting attempts in the community to speed up these