Can't hold my helium. [Archive]

Gregory L. Hansen

Jun4-04, 02:49 PM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>I can\'t keep helium in my cryostat, it boils away in about an hour. I\ncan\'t find a leak, I can\'t find a touch, the heat shields are intact, the\nvacuum looks good, the liquid nitrogen hold time is typical. I can\'t\nthink of any changes I\'ve made that could account for that. It\'s worked\nbefore, I\'ve warmed up and opened up and buttoned up and cooled down many\ntimes.\n\nDoes that sound familiar to anyone? What can I check?\n\n\n--\n"There\'s nary an animal alive that can outrun a greased Scottsman!" --\nGroundskeeper Willy\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>I can't keep helium in my cryostat, it boils away in about an hour. I
can't find a leak, I can't find a touch, the heat shields are intact, the
vacuum looks good, the liquid nitrogen hold time is typical. I can't
think of any changes I've made that could account for that. It's worked
before, I've warmed up and opened up and buttoned up and cooled down many
times.

Does that sound familiar to anyone? What can I check?

--
"There's nary an animal alive that can outrun a greased Scottsman!" --
Groundskeeper Willy

Gregory L. Hansen

Jun6-04, 04:25 PM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>In article <c9lfs4\\$1s2\\$3@hood.uits.indiana.edu>,\nGrego ry L. Hansen <glhansen@steel.ucs.indiana.edu> wrote:\n>I can\'t keep helium in my cryostat, it boils away in about an hour. I\n>can\'t find a leak, I can\'t find a touch, the heat shields are intact, the\n>vacuum looks good, the liquid nitrogen hold time is typical. I can\'t\n>think of any changes I\'ve made that could account for that. It\'s worked\n>before, I\'ve warmed up and opened up and buttoned up and cooled down many\n>times.\n>\n>Does that sound familiar to anyone? What can I check?\n\nEh. I was just a little over-zealous in filling the helium. I hadn\'t\nsufficiently pre-cooled, the boil-off was just from the heat of the\napparatus. I tried another fill and it held and is operating normally.\n\nBut thanks to the moderators for passing along my request.\n\n\n--\n"I\'m giving you the chance to look fate in those pretty eyes of hers\nand say, \'Step off, *****. This is my party and you\'re not invited.\'"\n-- Chris Shugart, _Testosterone Magazine_\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>In article <c9lfs4$1s2$3@hood.uits.indiana.edu>,
Gregory L. Hansen <glhansen@steel.ucs.indiana.edu> wrote:
>I can't keep helium in my cryostat, it boils away in about an hour. I
>can't find a leak, I can't find a touch, the heat shields are intact, the
>vacuum looks good, the liquid nitrogen hold time is typical. I can't
>think of any changes I've made that could account for that. It's worked
>before, I've warmed up and opened up and buttoned up and cooled down many
>times.
>
>Does that sound familiar to anyone? What can I check?

Eh. I was just a little over-zealous in filling the helium. I hadn't
sufficiently pre-cooled, the boil-off was just from the heat of the
apparatus. I tried another fill and it held and is operating normally.

But thanks to the moderators for passing along my request.

--
"I'm giving you the chance to look fate in those pretty eyes of hers
and say, 'Step off, *****. This is my party and you're not invited.'"
-- Chris Shugart, _Testosterone Magazine_

Murray Arnow

Jun6-04, 04:26 PM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) wrote:\n> I can\'t keep helium in my cryostat, it boils away in about an hour. I\n> can\'t find a leak, I can\'t find a touch, the heat shields are intact, the\n> vacuum looks good, the liquid nitrogen hold time is typical. I can\'t\n> think of any changes I\'ve made that could account for that. It\'s worked\n> before, I\'ve warmed up and opened up and buttoned up and cooled down many\n> times.\n>\n> Does that sound familiar to anyone? What can I check?\n>\n\nIt doesn\'t sound familiar, but liquid helium always does the unexpected.\nIf your thermal jacket is working, as it appears to be, you are probably\nnot losing the helium through a heat leak.\n\nLiquid helium sees any crack, even microscopic, as an open road to new\nadventure. Thermal recycling of your system has likely produced some\nmicro-fissures in the seams. It is almost impossible to find these leaks\nwithout a helium detector, and if your leak is into the jacket, then it\nis impossible to find.\n\nSorry, it looks like you\'ll need to do a tear down and rebuild. Maybe\nsomeone else has better advice to offer.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) wrote:
> I can't keep helium in my cryostat, it boils away in about an hour. I
> can't find a leak, I can't find a touch, the heat shields are intact, the
> vacuum looks good, the liquid nitrogen hold time is typical. I can't
> think of any changes I've made that could account for that. It's worked
> before, I've warmed up and opened up and buttoned up and cooled down many
> times.
>
> Does that sound familiar to anyone? What can I check?
>

It doesn't sound familiar, but liquid helium always does the unexpected.
If your thermal jacket is working, as it appears to be, you are probably
not losing the helium through a heat leak.

Liquid helium sees any crack, even microscopic, as an open road to new
adventure. Thermal recycling of your system has likely produced some
micro-fissures in the seams. It is almost impossible to find these leaks
without a helium detector, and if your leak is into the jacket, then it
is impossible to find.

Sorry, it looks like you'll need to do a tear down and rebuild. Maybe
someone else has better advice to offer.

OC

Jun7-04, 04:54 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nglhansen@steel.ucs.indiana.edu (Gregory L. Hansen) wrote in message news:<c9lfs4\\$1s2\\$3@hood.uits.indiana.edu>...\n > I can\'t keep helium in my cryostat, it boils away in about an hour. I\n> can\'t find a leak, I can\'t find a touch, the heat shields are intact, the\n> vacuum looks good, the liquid nitrogen hold time is typical. I can\'t\n> think of any changes I\'ve made that could account for that. It\'s worked\n> before, I\'ve warmed up and opened up and buttoned up and cooled down many\n> times.\n>\n> Does that sound familiar to anyone? What can I check?\n\nHave you already checked for cold leaks?\nHave you checked O-rings and other seals?\n\nWhat about heat load?\nDo you boil off He while the cryostat is just sitting there, or while\nyou are running an experiment (like sweeping a magnetic field)?\n\nThe worst leak I remember was due to strain on a (bent) tube that\nshowed up ONLY at low temperatures (the strain was due to thermal\ngradient). But it did not affect that much the boil-off rate of LHe.\n\nWithout a more detailed description, the only thing I can suggest is\nto check the vacuum at LN2 temperatures and LHe temperatures.\n\nIf it is a leak in the vacuum chamber that shows up at LN2\ntemperature, the way to check it, is to fill slowly the main bath with\nLN2 and monitor the pressure of the vacuum chamber while the level of\nLN2 increases.\n\nOC\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) wrote in message news:<c9lfs4$1s2$3@hood.uits.indiana.edu>...
> I can't keep helium in my cryostat, it boils away in about an hour. I
> can't find a leak, I can't find a touch, the heat shields are intact, the
> vacuum looks good, the liquid nitrogen hold time is typical. I can't
> think of any changes I've made that could account for that. It's worked
> before, I've warmed up and opened up and buttoned up and cooled down many
> times.
>
> Does that sound familiar to anyone? What can I check?

Have you already checked for cold leaks?
Have you checked O-rings and other seals?

What about heat load?
Do you boil off He while the cryostat is just sitting there, or while
you are running an experiment (like sweeping a magnetic field)?

The worst leak I remember was due to strain on a (bent) tube that
showed up ONLY at low temperatures (the strain was due to thermal
gradient). But it did not affect that much the boil-off rate of LHe.

Without a more detailed description, the only thing I can suggest is
to check the vacuum at LN2 temperatures and LHe temperatures.

If it is a leak in the vacuum chamber that shows up at LN2
temperature, the way to check it, is to fill slowly the main bath with
LN2 and monitor the pressure of the vacuum chamber while the level of
LN2 increases.

OC

Charles DH Williams

Jun7-04, 04:54 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nIn article <c9lfs4\\$1s2\\$3@hood.uits.indiana.edu>,\nglhanse n@steel.ucs.indiana.edu (Gregory L. Hansen) wrote:\n\n> I can\'t keep helium in my cryostat, it boils away in about an hour. I\n> can\'t find a leak, I can\'t find a touch, the heat shields are intact, the\n> vacuum looks good, the liquid nitrogen hold time is typical. I can\'t\n> think of any changes I\'ve made that could account for that. It\'s worked\n> before, I\'ve warmed up and opened up and buttoned up and cooled down many\n> times.\n>\n> Does that sound familiar to anyone? What can I check?\n\nIt\'s probably trace amounts of helium in the vacuum space between the\nnitrogen shields and the helium bath. You\'ll need a mass-spectrometer leak\ndetector to see this.\n\nOtherwise unplug all electrical connections to the cryostat. And I said\nUNPLUG.\n\nOtherwise tell us more about the type of cryostat and insert.\n\nCharles.\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>In article <c9lfs4$1s2$3@hood.uits.indiana.edu>,
glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) wrote:

> I can't keep helium in my cryostat, it boils away in about an hour. I
> can't find a leak, I can't find a touch, the heat shields are intact, the
> vacuum looks good, the liquid nitrogen hold time is typical. I can't
> think of any changes I've made that could account for that. It's worked
> before, I've warmed up and opened up and buttoned up and cooled down many
> times.
>
> Does that sound familiar to anyone? What can I check?

It's probably trace amounts of helium in the vacuum space between the
nitrogen shields and the helium bath. You'll need a mass-spectrometer leak
detector to see this.

Otherwise unplug all electrical connections to the cryostat. And I said
UNPLUG.

Otherwise tell us more about the type of cryostat and insert.

Charles.

Gregory L. Hansen

Jun7-04, 08:57 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nIn article <C.D.H.Williams-0D53D4.22122204062004@news.ex.ac.uk>,\nCharles DH Williams <C.D.H.Williams@exeter.ac.uk> wrote:\n>\n>In article <c9lfs4\\$1s2\\$3@hood.uits.indiana.edu>,\n> glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) wrote:\n>\n>> I can\'t keep helium in my cryostat, it boils away in about an hour. I\n>> can\'t find a leak, I can\'t find a touch, the heat shields are intact, the\n>> vacuum looks good, the liquid nitrogen hold time is typical. I can\'t\n>> think of any changes I\'ve made that could account for that. It\'s worked\n>> before, I\'ve warmed up and opened up and buttoned up and cooled down many\n>> times.\n>>\n>> Does that sound familiar to anyone? What can I check?\n>\n>It\'s probably trace amounts of helium in the vacuum space between the\n>nitrogen shields and the helium bath. You\'ll need a mass-spectrometer leak\n>detector to see this.\n>\n>Otherwise unplug all electrical connections to the cryostat. And I said\n>UNPLUG.\n>\n>Otherwise tell us more about the type of cryostat and insert.\n>\n>Charles.\n\nLooks like, due to moderation lag, I\'m getting some suggestions after I\'ve\ngiven the resolution.\n\n[Moderator\'s note: Yes. On moderated newsgroups such as s.p.r. posts don\'t necessarily\nappear in the order in which they were posted. -usc]\n\nAs I said, the problem was nothing more than\nimproper pre-cooling, due to a little bit of carelessness on my part, and\na little bit of ignorance because I didn\'t realize pre-cooling was so\nimportant. When I put a stick in the empty helium bath and it came out\nfrosty, I thought that must be cooled enough. The usual routine would\nhave been to put some LN2 in the He bath and wait until the thermometers\nat the bottom are as cold as they\'ll be, then empty the LN2 and flow\nhelium gas until the thermometers start to warm a little, to be sure the\nliquid is gone. I just filled the LN2 jacket and let it sit for a day.\nLive and learn.\n\nBut thanks to all respondents for thinking about it.\n\n--\n"For every problem there is a solution which is simple, clean and wrong."\n-- Henry Louis Mencken\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>In article <C.D.H.Williams-0D53D4.22122204062004@news.ex.ac.uk>,
Charles DH Williams <C.D.H.Williams@exeter.ac.uk> wrote:
>
>In article <c9lfs4$1s2$3@hood.uits.indiana.edu>,
> glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) wrote:
>
>> I can't keep helium in my cryostat, it boils away in about an hour. I
>> can't find a leak, I can't find a touch, the heat shields are intact, the
>> vacuum looks good, the liquid nitrogen hold time is typical. I can't
>> think of any changes I've made that could account for that. It's worked
>> before, I've warmed up and opened up and buttoned up and cooled down many
>> times.
>>
>> Does that sound familiar to anyone? What can I check?
>
>It's probably trace amounts of helium in the vacuum space between the
>nitrogen shields and the helium bath. You'll need a mass-spectrometer leak
>detector to see this.
>
>Otherwise unplug all electrical connections to the cryostat. And I said
>UNPLUG.
>
>Otherwise tell us more about the type of cryostat and insert.
>
>Charles.

Looks like, due to moderation lag, I'm getting some suggestions after I've
given the resolution.

[Moderator's note: Yes. On moderated newsgroups such as s.p.r. posts don't necessarily
appear in the order in which they were posted. -usc]

As I said, the problem was nothing more than
improper pre-cooling, due to a little bit of carelessness on my part, and
a little bit of ignorance because I didn't realize pre-cooling was so
important. When I put a stick in the empty helium bath and it came out
frosty, I thought that must be cooled enough. The usual routine would
have been to put some LN2 in the He bath and wait until the thermometers
at the bottom are as cold as they'll be, then empty the LN2 and flow
helium gas until the thermometers start to warm a little, to be sure the
liquid is gone. I just filled the LN2 jacket and let it sit for a day.
Live and learn.

But thanks to all respondents for thinking about it.

--
"For every problem there is a solution which is simple, clean and wrong."
-- Henry Louis Mencken

Charles DH Williams

Jun7-04, 12:37 PM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>In article <ca1rho\\$121\\$2@hood.uits.indiana.edu>,\nglhanse n@steel.ucs.indiana.edu (Gregory L. Hansen) wrote:\n\n> As I said, the problem was nothing more than\n> improper pre-cooling, due to a little bit of carelessness on my part, and\n> a little bit of ignorance because I didn\'t realize pre-cooling was so\n> important.\n\nIf you take 100g of copper at 300K, to cool it to 77K requires\nextracting heat equivalent to the latent heat of vaporisation\nof either 0.05 litre of LN2 or about 3 litres of liquid helium.\n\nThe difference is less extreme if you can exploit the enthalpy of\nthe boil-off gas but the basic message is correct...\n\nCharles\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>In article <ca1rho$121$2@hood.uits.indiana.edu>,
glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) wrote:

> As I said, the problem was nothing more than
> improper pre-cooling, due to a little bit of carelessness on my part, and
> a little bit of ignorance because I didn't realize pre-cooling was so
> important.

If you take 100g of copper at 300K, to cool it to 77K requires
extracting heat equivalent to the latent heat of vaporisation
of either .05 litre of LN2 or about 3 litres of liquid helium.

The difference is less extreme if you can exploit the enthalpy of
the boil-off gas but the basic message is correct...

Charles