Laser Blow-Off System

The laser blow-off (LBO) system will be used to insert impurities from the edge into the W7-X vessel. Therefore, a pulsed laser beam (20 Hz, 1 J, 1064 nm) is guided through two mirrors and two lenses to the glass target and blows-off the thin metal coating. The glass targets are coated with different materials with different thicknesses, see table I. The holder for the glass target is mounted on the head of the multi-purpose manipulator. Therewith, 4 glass targets can be inserted and positioned in the W7-X vessel (port AEK40). However, there is an opportunity to cut the glasses (depending on the coating material) and mount maximum 8 targets. The spot size and position of the laser beam on the glass target can be varied by moving the lenses and mirrors. Furthermore, the energy density can be changed leading to different ablation amounts and the ablation of single atoms, clusters and macrsocopic particles. The coating material can be ablated in the repetition mode with 20 Hz and in the single shot mode every multiples of 250 ms. It is possible to inject two different materials in one experimental program with some uncertainties within every multiples of 250 ms. The timing of the laser pulse can be set with an accuracy of 150 ms. The emission of the impurity in the plasma will be recorded by a monochromator in combination with an EMCCD camera with a temporal resolution of about 0.02 ms. The ablation process can be observed by the visible video camera (EDICAM, AEQ31) which is nearly perpendicular directed to the AEK40 port.

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