| Topic: |
Science > Physics |
| User: |
"John Ng" |
| Date: |
18 Nov 2003 02:51:15 AM |
| Object: |
Quenching of 400 MHz Magnet |
Do any one has the experience on quenching of 400 MHz NMR magnet? In
our laboratory, there is an accident. We don't know the actual reason.
The quenching time is about 5-6 minutes. What kind of collision on the
magnet could induce such quenching? I could find no physical damage on
the magnet. Do any one has the idea about the issuse?
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| User: "The Ghost In The Machine" |
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| Title: Re: Quenching of 400 MHz Magnet |
18 Nov 2003 10:59:30 AM |
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In sci.physics, John Ng
<slng@hkbu.edu.hk>
wrote
on 18 Nov 2003 00:51:15 -0800
<34ab3125.0311180051.5e4d0a8a@posting.google.com>:
Do any one has the experience on quenching of 400 MHz NMR magnet? In
our laboratory, there is an accident. We don't know the actual reason.
The quenching time is about 5-6 minutes. What kind of collision on the
magnet could induce such quenching? I could find no physical damage on
the magnet. Do any one has the idea about the issuse?
Not sure why a magnet would be measured in hertz as opposed
to oersteds or gauss, but IINM a lot of NMRI magnets
are superconducting. A malfunction in the refrigeration
unit could lead to cessation of superconductivity, and
the magnetic field would collapse as the current in the
superconductor dissipates.
I don't believe that will cause physical damage (apart from
the loss of magnetic field) but the refrigeration unit
in my scenario would require replacement and the current
reinstated, presumably by some sort of a charging circuit.
Of course without more details I'm simply guessing. :-)
--
#191,
It's still legal to go .sigless.
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| User: "Rene Tschaggelar" |
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| Title: Re: Quenching of 400 MHz Magnet |
18 Nov 2003 01:15:02 PM |
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The Ghost In The Machine wrote:
In sci.physics, John Ng
<slng@hkbu.edu.hk>
wrote
on 18 Nov 2003 00:51:15 -0800
<34ab3125.0311180051.5e4d0a8a@posting.google.com>:
Do any one has the experience on quenching of 400 MHz NMR magnet? In
our laboratory, there is an accident. We don't know the actual reason.
The quenching time is about 5-6 minutes. What kind of collision on the
magnet could induce such quenching? I could find no physical damage on
the magnet. Do any one has the idea about the issuse?
Not sure why a magnet would be measured in hertz as opposed
to oersteds or gauss, but IINM a lot of NMRI magnets
are superconducting.
Physicists are a bit slack in what measurement units concerns.
Since the precession frequency of hydrogen in this case, is
proportional to the field, the field is measured as MHz.
This not just a joke, as the most precise field measurement
devices are based on NMR, not Hall or such.
For hydrogen, the field proportionality is about 60MHz/Tesla.
Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
.
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| User: "The Ghost In The Machine" |
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| Title: Re: Quenching of 400 MHz Magnet |
19 Nov 2003 02:59:30 AM |
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In sci.physics, Rene Tschaggelar
<none@none.none>
wrote
on Tue, 18 Nov 2003 20:15:02 +0100
<3FBA6FB6.6050003@none.none>:
The Ghost In The Machine wrote:
In sci.physics, John Ng
<slng@hkbu.edu.hk>
wrote
on 18 Nov 2003 00:51:15 -0800
<34ab3125.0311180051.5e4d0a8a@posting.google.com>:
Do any one has the experience on quenching of 400 MHz NMR magnet? In
our laboratory, there is an accident. We don't know the actual reason.
The quenching time is about 5-6 minutes. What kind of collision on the
magnet could induce such quenching? I could find no physical damage on
the magnet. Do any one has the idea about the issuse?
Not sure why a magnet would be measured in hertz as opposed
to oersteds or gauss, but IINM a lot of NMRI magnets
are superconducting.
Physicists are a bit slack in what measurement units concerns.
Since the precession frequency of hydrogen in this case, is
proportional to the field, the field is measured as MHz.
This not just a joke, as the most precise field measurement
devices are based on NMR, not Hall or such.
For hydrogen, the field proportionality is about 60MHz/Tesla.
Rene
Interesting; precession of hydrogen frequency appears valid
(AFAICT, anyway) and not something I would have considered.
As it is, I for one would suspect that the "quenching" in
this case is simply the magnet warming up, though I may
have to do a lot more study on superconductors to be sure.
However, I suspect the warming is not uniform.
--
#191,
It's still legal to go .sigless.
.
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| User: "Uncle Al" |
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| Title: Re: Quenching of 400 MHz Magnet |
18 Nov 2003 12:26:08 PM |
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John Ng wrote:
Do any one has the experience on quenching of 400 MHz NMR magnet? In
our laboratory, there is an accident. We don't know the actual reason.
The quenching time is about 5-6 minutes. What kind of collision on the
magnet could induce such quenching? I could find no physical damage on
the magnet. Do any one has the idea about the issuse?
You didn't do something naughty like pulse a magnetic field inside the
bore or introduce a neutron or gamma radiation source, right?
A local thermal excursion will do the trick. Aside from the obvious
no-no of running low on liquid helium, the magnet may have shifted a
winding under the immense stress of Faraday force trying to explode
them outward. A microscopic winding movement will quench some of its
supercon filaments. If the copper swaging doesn't have enough
specific heat to take up the temperature transient, the disease
exponentially spreads as the whole magnet warms and goes normal.
The vendor is supposed to anneal the magnet by repeatedly energizing
and quenching in a cleverly engineered process, and probably fabricate
the windings severely compressed in a shrunken steel jacket in the
first place. Don't screw around with it trying to be clever - a
typical 300 MHz NMR magnet has the contained energy (field strength
times volume) of a WWII 500 lb bomb.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!
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| User: "Steve Harris" |
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| Title: Re: Quenching of 400 MHz Magnet |
18 Nov 2003 05:23:59 PM |
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Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<3FBA6440.1986B871@hate.spam.net>...
The vendor is supposed to anneal the magnet by repeatedly energizing
and quenching in a cleverly engineered process, and probably fabricate
the windings severely compressed in a shrunken steel jacket in the
first place. Don't screw around with it trying to be clever - a
typical 300 MHz NMR magnet has the contained energy (field strength
times volume) of a WWII 500 lb bomb.
COMMENT:
At 70 H, 35 amps, we're talking 1/2*LI^2 = 42 kJ, not 1 gJ. The
manufacturer here says 85 kJ and probably forgot to divide by 2 (duh),
but given that the below instrument is for 270 MHz, we'll give you
that for 300 MHz, and make it 100 kJ.
Still, that's more like a 0.05 lb = 20 g cherry bomb. Gee, Unc, you're
only off by 4 orders of magnitude, this time.
http://pc16002.pharmazie.uni-marburg.de/www/jeol_magnet/magnet_destruction.html
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| User: "Uncle Al" |
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| Title: Re: Quenching of 400 MHz Magnet |
18 Nov 2003 07:16:17 PM |
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"Steve Harris sbharris@ROMAN9.netcom.com" wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<3FBA6440.1986B871@hate.spam.net>...
The vendor is supposed to anneal the magnet by repeatedly energizing
and quenching in a cleverly engineered process, and probably fabricate
the windings severely compressed in a shrunken steel jacket in the
first place. Don't screw around with it trying to be clever - a
typical 300 MHz NMR magnet has the contained energy (field strength
times volume) of a WWII 500 lb bomb.
COMMENT:
At 70 H, 35 amps, we're talking 1/2*LI^2 = 42 kJ, not 1 gJ. The
manufacturer here says 85 kJ and probably forgot to divide by 2 (duh),
but given that the below instrument is for 270 MHz, we'll give you
that for 300 MHz, and make it 100 kJ.
Still, that's more like a 0.05 lb = 20 g cherry bomb. Gee, Unc, you're
only off by 4 orders of magnitude, this time.
http://pc16002.pharmazie.uni-marburg.de/www/jeol_magnet/magnet_destruction.html
Son of a gun. However, a 900 MHz magnet stores 27-40 megajoules
http://www.pnl.gov/news/back/nmr.htm
http://akahoshi.nims.go.jp/MT-18/prog/abs/2D-p56.html
That is not 3 times 85 kJ. Even small stuff is big stuff,
http://www.cern.ch/accelconf/e98/PAPERS/TUP04F.PDF
The mechanical energy necessary to quench a winding is a few
micro-joules.
http://www.spectroscopyeurope.com/NMR_15_1.pdf
(BTW, a 500 lb bomb only contains about 250 lbs of TNT.)
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!
.
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| User: "Nils Dalen" |
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| Title: Re: Quenching of 400 MHz Magnet |
05 Dec 2003 11:46:21 AM |
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Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<3FBAC461.35D5C414@hate.spam.net>...
"Steve Harris sbharris@ROMAN9.netcom.com" wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<3FBA6440.1986B871@hate.spam.net>...
The vendor is supposed to anneal the magnet by repeatedly energizing
and quenching in a cleverly engineered process, and probably fabricate
the windings severely compressed in a shrunken steel jacket in the
first place. Don't screw around with it trying to be clever - a
typical 300 MHz NMR magnet has the contained energy (field strength
times volume) of a WWII 500 lb bomb.
COMMENT:
At 70 H, 35 amps, we're talking 1/2*LI^2 = 42 kJ, not 1 gJ. The
manufacturer here says 85 kJ and probably forgot to divide by 2 (duh),
but given that the below instrument is for 270 MHz, we'll give you
that for 300 MHz, and make it 100 kJ.
Still, that's more like a 0.05 lb = 20 g cherry bomb. Gee, Unc, you're
only off by 4 orders of magnitude, this time.
http://pc16002.pharmazie.uni-marburg.de/www/jeol_magnet/magnet_destruction.html
Son of a gun. However, a 900 MHz magnet stores 27-40 megajoules
http://www.pnl.gov/news/back/nmr.htm
http://akahoshi.nims.go.jp/MT-18/prog/abs/2D-p56.html
That is not 3 times 85 kJ. Even small stuff is big stuff,
Either physics is different for the two magnets, or there is a
mistake.
First, the correct energy density equation has energy going as B^2,
not B^1.
This will get you another factor of 3.
Second, when using an energy density, you have to integrate over the
volume. In this case, the 900mHz magnet has a *much* larger volume.
The bore size has increased-->probably a factor of 2 more energy.
The height increased a lot (21 foot tall!)-->this probably will get
you at least a factor of 5 more.
So, figure your calculation is off by about a factor of 30.
You can fill in the exact numbers, but this correction bridges the gap
between the two magnets.
a 900mHz magnet<>all 900mHz magnets
Nils
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| User: "Rene Tschaggelar" |
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| Title: Re: Quenching of 400 MHz Magnet |
18 Nov 2003 05:02:41 AM |
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John Ng wrote:
Do any one has the experience on quenching of 400 MHz NMR magnet? In
our laboratory, there is an accident. We don't know the actual reason.
The quenching time is about 5-6 minutes. What kind of collision on the
magnet could induce such quenching? I could find no physical damage on
the magnet. Do any one has the idea about the issuse?
Running low on liquid N, running low on liquid He ?
Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
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