Production of a short hydrogen pulse by laser induced desorption from titanium hydride for the investigation of transport processes in fusion plasmas
The investigation of particle transport in fusion plasmas requires short intense gas pulses to produce spatially and temporally localised density perturbations. Such gas pulses can be produced by laser induced desorption of hydrogen from titanium hydride. To study the properties of this method, samples of TiH(1.5) were heated by 1ms ruby laser with an energy content up to 10J. With target spot diameters of 4.5mm, desorption rates of 2 x 1.0 E18 hydrogen atoms were achieved. When heating the same target spot repeatedly, the release of hydrogen is reduced drastically. This is due to the depletion of the 100 micron thick heated region at the target surface which cannot be refilled by hydrogen from the bulk because of the low diffusion coefficient of hydrogen in titanium at temperatures below 200 C. With respect to radiation cooling of the plasma, the titanium content of the hydrogen pulses is important. The experiments show a 1% contamination with titanium atoms, mainly produced by evaporation from edges of cracks in the target surface. By proper conditioning of the target surface with short giant laser pulses, the titanium contamination could be reduced by a factor of two without reduction of the hydrogen release. The results of the measurements show that with a 40J laser system, gas pulses suitable for transport studies can be produced.
Bibliographic Reference: Report: IPP III/155 DE (1990) 81 pp.
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
Record Number: 199011465 / Last updated on: 1994-12-02
Original language: de
Available languages: de