[3dem] 626 holder temperature

[Wim Hagen]

Dear Reinhard,

We have an older 626, things might be different depending on how old the holder is. To my knowledge the temperature is measured near the tip. We do a zeolite bake-out regularly (although we have carbon packs instead of zeolite now) and monitor the heating current. The bake-out will heat the tip to 100 degrees but will use a maximum current of 750 mA. As the vacuum gets better, thermal isolation gets better and less current is needed to maintain 100 degrees at the tip. We aim for less than 450 mA, then the holder is ok to use. This is especially important when the holder is not used for a while and not pumped.I found this out at FEI, new holders could have been in the warehouse for months, we had trouble getting them to work, this current monitoring procedure tackled the problem. If current needed does not drop during bake-out, things are bad. Lower current is better vacuum.

Clip ring is also crucial. The images Gary sent show the same thing I see when people here clip the Polara cartridges wrongly. Overnight the grid gets too warm. Here are images of a badly clipped Polara cartridge and the effect it had after one night in an otherwise properly working Polara: https://oc.embl.de/index.php/s/1wW380d1vasQHvj <https://oc.embl.de/index.php/s/1wW380d1vasQHvj> 

One crude way of measuring temperature in the scope is to put a beam on the cryo sample and look at the diffraction pattern of just vitreous ice. Vitreous ice should disappear from radiation damage only. If it does not disappear but goes cubic and crystalline, temperature is suspect.

Best,

Wim Hagen
EMBL Heidelberg

> On 8. Mar 2018, at 16:42, Reinhard Rachel <Reinhard.Rachel at biologie.uni-regensburg.de> wrote:
> 
> dear cryo-holder 626 experts, 
> 
> another question to this holder. 
> We have a 626/70 Jeol version (vintage 2012) and were happy, so far. 
> a closer look (yesterday, after a rest for 3 months) made us at least curious
> to look into details and have a careful check (hopefully, not repair?): 
> a) heating the holder is done with the smart controller set for 36 to 48 hrs,
> to 80°C (whether good or not? remarks are welcome). How to check whether this
> temperature is really set? a digital thermometer - inserted into the dewar and
> touching the metal part, the bottom of the dewar - reads something like 41 C
> (set at 70 C : about 36-38 or so) ... hmm. This means either, the temperature
> meter of Gatan is "somewhere else" (likely the case; everything ok??), or the
> temperature is not reached, at all. Or anything else?
> b) the clipring - when inserted - is rather loose, and not as tight as I
> thought it was; or, it should be. "It does not fit any more" - but is this the
> only explanation? are the metal parts holding the clipring 'bent'? we will try
> the other cliprings (we have 4 more, to try), but I also would appreciate any
> comments from other users, regarding this point. 
> 
> thank you in advance! 
> Kind regards, 
> Reinhard
> 
> 
> -- 
> Prof. Dr. Reinhard Rachel
> University of Regensburg
> Centre for EM / Anatomy
> Faculty of Biology & Preclin. Med.
> Universitaetsstrasse 31
> D-93053 Regensburg - Germany
> tel +49 941 943 -2837, -1720
> mail reinhard.rachel at biologie.uni-regensburg.de
> office: VKL 3.1.29 
> 
> Next microscopy conferences:
> - 19th International Microscopy Congress, Sydney; 9-14 Sept 2018
> http://imc19.com/
> - Microscopy Conference MC2019: 1.-5. Sept 2019 in Berlin 
> - next Microbiol. conferences: 
> VAAM - Annual Conf.: 15-18 April 2018 Wolfsburg
> 
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