[3dem] drift

[benoit.zuber at ana.unibe.ch]

Dear colleagues

Our cryo-holder (Gatan 626 70 degrees) has recently started showing an interesting drift behavior under cryo conditions on our Tecnai F20 (imaging with SerialEM). After transfer and the usual temperature stabilization, the holder is quite stable for about one hour. Then the problem starts (see https://dl.dropboxusercontent.com/u/6743833/drift/drift.mp4 ). The sample starts drifting quite fast in one direction, slows down after drifting between roughly 500 and 1000 nm and then drifts in the opposite direction until it returns to its original position and stops. It then remains stable for a variable amount of time (typically 1 minute) and then starts a new cycle of drift. The stage position reading  does not change during this time. The temperature reading of the holder is also stable. Interestingly, the drift direction is perpendicular to the tilt axis.
We suspect a tiny and discontinuous leak in the vacuum chamber of the cryo-holder dewar. Nonetheless, we would have expected the movement to be parallel tilt axis if it was due to thermal changes in the holder rod.
Has anyone faced (and fixed) this problem before? Any tip would be highly appreciated.

Best wishes
Benoît

Benoît Zuber
Institute of Anatomy
University of Bern
Baltzerstrasse 2
CH-3000 Bern 9
Switzerland
Tel. +41 31 631 84 40
benoit.zuber at ana.unibe.ch
http://www.ana.unibe.ch/~exmo/

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