gas flow cryostats

[dq]

So if you are doing microscopy though a gas flow-cryostat and it looks
like your subject is below the surface of a pond, it likely means you
have liquid helium flowing over your sample when you should really only
be getting cold gas helium.

I think the best way to avoid this is to choke off the helium flow a
little and turn up the resistive heat slightly, to make sure you boil
off the incoming helium before it gets into your optical path. I tried
this today and built up enough pressure to blow out the sample insert
out of its position (luckily, nothing was damaged).

How do I avoid this? My guess is that I need to make sure to get the
helium flow down to a minimum before I go heating up the element.

Does anyone have any other cryo tips? There's precious little
literature on this subject, so I'm making an appeal to the great usenet.