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Faraday shield (active cooling)

So called HF-Ionsources are being used for plasmageneration in the Max-Planck-Institure for plasmaphysics in Garching. Those are three-walled containers with an integrated quartzshell, that are obvolved by a coil to create high-frequenzy.

Because the quartz-shell is meachnically not solid enough to sustain the vacuum within, this vacuum is adapted to the external pressure step by step with aid of the partitions.

Apart from there mustn’t be a “line of sight” between plasma and quartz because else the plasma would dissolve SiO2 partickles out of the quartz. This would have great effects on other pieces as well and – in the end – distract the source’s operation.

To prevent such things a Faraday cage is fitted between quartz and plasma. This is a rather complicated construction, though, because the coil that runs in vacuum is difficult to access.

It was aimed at an alternative to this construction described above that would avoid such problems. A solution was found during one of GT’s experiments in which Al2O3 ceramic was joint with copper in a gas-tight manner. This enables a better design with thinner walls (10mm) and the combination of Faraday cage and quartzcontainer (that are now Al2O3 ceramic stripes). The Al2O3 isn’t visible for the plasma anymore through an offset of crosspieces and ceramic stripes which makes a dissolving of SiO2 impossible. Apart fromt that the whole corpus as well as the ceramic can be cooled with a slight overhead because of the intregral structure to dissipate the that comes from plasma and HF-eddy-currents.

With one of the already manifactured prototypes that was a smaller sized model of the planned ion-source it was already possible to generate plasma. It’s the object of the experiments to test the ion-source under conditions of practice to make a soon start of construction of the 1:1 ion-source possible.