Those expecting the end of the world etc. can now rest easy for about 2-3 months.
£3.6billion toy halted due to an electrical 'short'...ah the irony
Not quite that simple. This is what I've heard:Originally Posted by bsodmike
£3.6billion toy halted due to an electrical 'short'...ah the irony
Basically a whole bunch of superconducting magnets quenched (reasons yet unknown - but suspected not because of beam), and one of the bus bars that runs between two of the big superconducting magnets was not welded/bolted to proper specification. What then happened is that the bus-bar went from superconducting to conducting, and because it was connected poorly it melted because its resistance was too high (the current passing through the bus bar was about 8500 Amps at this point). This then spewed molten metal everywhere, damaging the cryogenic containment (hence loss of 1 ton of helium - about 30 million quids worth, apparently!). It also contaminated the vacuum in the beam pipe, so there must be a hole in that too.
bsodmike (22-09-2008),j.o.s.h.1408 (22-09-2008),Lanky123 (22-09-2008)
Fraz, thanks for a a much more detailed update. Could the heating of the bus-bar be a result of the quench, and therefore due to heating up it went from superconducting to conducting? (At which point the 8.5 kA simply melted it)...Not quite that simple. This is what I've heard:
Basically a whole bunch of superconducting magnets quenched (reasons yet unknown - but suspected not because of beam), and one of the bus bars that runs between two of the big superconducting magnets was not welded/bolted to proper specification. What then happened is that the bus-bar went from superconducting to conducting, and because it was connected poorly it melted because its resistance was too high (the current passing through the bus bar was about 8500 Amps at this point). This then spewed molten metal everywhere, damaging the cryogenic containment (hence loss of 1 ton of helium - about 30 million quids worth, apparently!). It also contaminated the vacuum in the beam pipe, so there must be a hole in that too.
That doesn't sound like it's something a bit of gaffer tape is going to fix, then....
neither does it sound like it will take a 'mere' 2-3 months. They would also need to investigate as to the cause of the quench and fully inspect rest of the LHC, not to mention a group of 'undesirables' even managed to deface one of their systems.
http://www.theregister.co.uk/2008/09...e_while_u_can/
Obviously the story is already broken but those Register news-monkeys have probably (and hilariously) been on the quadruple espressos this morning.
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In case anyone was wondering what was going on over at the LHC here is a link to the webcams
http://www.cyriak.co.uk/lhc/lhc-webcams.html
(apologies if this has been posted already)
What you are saying is a bit of a circular argument (I think). A quench is when a superconductor goes from a superconducting state to a conducting state... so something quenched, and then things definitely got hot. However, all the magnets are designed to withstand quenches, because they just happen from time to time - e.g. a beam "incident" can cause a quench. I guess this poorly connected bus-bar meant that the quench protection didn't work properly, and something just got vaporised.
Is it worth that much? This article reckons the whole 120 tonnes is worth about $4m...it is a year out of date though. If 1 ton costs £30m then the 120 ton stock would have cost £3.6bn initially, that cant be right.I can see the damage as a whole costing £30m though...sorry if that's what you meant anyway.
lol...Yes - the number I was told is almost certainly complete crap at these volumes (well, masses). Someone in my dept did the calculation based on some random number he looked up on the web for liquid helium costs. I imagine CERN gets a nice bulk discount...Is it worth that much? This article reckons the whole 120 tonnes is worth about $4m...it is a year out of date though. If 1 ton costs £30m then the 120 ton stock would have cost £3.6bn initially, that cant be right.
Please tell me they didn't just look up figures on the web for the welding specs as well...
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Fraz, what I was actually trying to say was that the heat generated from the quench would have caused the bus-bar to heat up over its critical temperature. Therefore it's electrical resistance is no longer approximately zero (i.e. no longer exhibiting superconductivity) and as you initially stated, thus became conductive.
Due to the presence of a relatively high resistance (LOL, what isn't in the presence of 8.5 kA!) a real power is developed, hence the melting of the bus-bar.
Thanks again for your input
Last edited by bsodmike; 22-09-2008 at 06:58 PM.
I think you are really referring to the feedback caused by a quench. Sure, the quench spreads rapidly due to the resistive heating. But by definition, a quench is when some part of the superconductor has already fallen into the normally conductive state.
No problem.Thanks again for your input
<dodgyMechanic>"Fffhhhhhhhhhh.... it's gonna cost ya."</dodgyMechanic>Please tell me they didn't just look up figures on the web for the welding specs as well...
In summary: Black hole doom to continue from spring 09.Press-release
LHC re-start scheduled for 2009
Geneva, 23 September 2008. Investigations at CERN following a large helium leak into sector 3-4 of the Large Hadron Collider (LHC) tunnel have indicated that the most likely cause of the incident was a faulty electrical connection between two of the accelerator’s magnets. Before a full understanding of the incident can be established, however, the sector has to be brought to room temperature and the magnets involved opened up for inspection. This will take three to four weeks. Full details of this investigation will be made available once it is complete.
“Coming immediately after the very successful start of LHC operation on 10 September, this is undoubtedly a psychological blow,” said CERN Director General Robert Aymar. “Nevertheless, the success of the LHC’s first operation with beam is testimony to years of painstaking preparation and the skill of the teams involved in building and running CERN’s accelerator complex. I have no doubt that we will overcome this setback with same degree of rigour and application.”
The time necessary for the investigation and repairs precludes a restart before CERN’s obligatory winter maintenance period, bringing the date for restart of the accelerator complex to early spring 2009. LHC beams will then follow.
Particle accelerators such as the LHC are unique machines, built at the cutting edge of technology. Each is its own prototype, and teething troubles at the start-up phase are therefore always possible.
“The LHC is a very complex instrument, huge in scale and pushing technological limits in many areas,” said Peter Limon, who was responsible for commissioning the world’s first large-scale superconducting accelerator, the Tevatron at Fermilab in the USA. “Events occur from time to time that temporarily stop operations, for shorter or longer periods, especially during the early phases.”
CERN has received similar words of support from several laboratories, including Germany’s DESY, home of the HERA superconducting particle accelerator, which ran from 1992 to 2007.
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