I'm afraid all the concerns are very well justified:
We're all doomed :duck:
Regards,
Tempest
Gordan Freeman shouldn't concern us... we should be thankful for his presence
...because, guess who else is there.
Large Hadron Collider goes online tonite!
- Thread starter Chuck289
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Gordan Freeman shouldn't concern us... we should be thankful for his presence
...because, guess who else is there.
Flashanator
Flashlight Enthusiast
hmmm, 
shomie911
Enlightened
- Joined
- Jul 26, 2008
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Let's hope not.
MikeSalt
Flashlight Enthusiast
Ahh yes, the LHC has broken. Let that be a lesson to all those multi-mode flashlight manufacturers out there that simplicity is best.
From what they know so far, one of the bus-bars that connects the dipole magnets was faulty, causing a small resistance in the superconductor, which is supposed to have zero resistance. This tiny resistance was enough to generate the heat required to change the the temperature from the superconducting temperature region (1.9K, -271.25C) to normal conducting, thus generating more resistance, more heat, more resistance etc... etc... until it spiralled out of control, heating 100 magnets by 100 degrees in next to no time. The rapid thermal expansion caused the cryogenic seals to fail and thus 1 tonne of helium was dumped into the tunnel.
Now if this were a normal-conducting accelerator, this would be a two-week job. But, being that it is superconducting, it must be warmed, fixed and then cooled again - minimum of two months!
Needless to say, the proposed Compact Linear Collider (CLIC) is due to be normal conducting.
From what they know so far, one of the bus-bars that connects the dipole magnets was faulty, causing a small resistance in the superconductor, which is supposed to have zero resistance. This tiny resistance was enough to generate the heat required to change the the temperature from the superconducting temperature region (1.9K, -271.25C) to normal conducting, thus generating more resistance, more heat, more resistance etc... etc... until it spiralled out of control, heating 100 magnets by 100 degrees in next to no time. The rapid thermal expansion caused the cryogenic seals to fail and thus 1 tonne of helium was dumped into the tunnel.
Now if this were a normal-conducting accelerator, this would be a two-week job. But, being that it is superconducting, it must be warmed, fixed and then cooled again - minimum of two months!
Needless to say, the proposed Compact Linear Collider (CLIC) is due to be normal conducting.
js
Flashlight Enthusiast
Superconducting magnets are an order of magnitude more complicated than normal conducting ones, it is true. It's hard to image a tiny 24 gauge wire conducting 100 or 150 amps! But it does. But if that niobium wire goes normal conducting with all that current in it, POOF!, it will melt in next to no time. Very bad. Which is why super conducting magnets are supposed to be designed to quench (which removes heat from the coils) and have some method for quickly removing the stored energy via large resistive banks.
Yes, they are a PITA, but in order to get the same field strength out of a normal conducting magnet, you are talking many times the size, bulk, weight, heat, and so on. In many places, optically, you simply have to use super conducting magnets. CESR had a set of superconducting magnets near the IR, as well as a superconducting solenoid around the detector, and a set of superconducting anti-solenoids on either side of it. And also, two sets of two super conducting RF cavities, one set in the west, one set in the east. Oh, and also, about a dozen super conducting wigglers for running at low energy. Our small accelerator (compared to the LHC) had that much superconducting stuff. And it wasn't 'cause we wanted to make our lives complicated. On the contrary. Normal conducting RF cavities and magnets can be very painful to run, too.
I havent gone and asked for a report on what happened at the LHC, or seen anything in the elevator yet, but I'm pretty sure that a safety system / interlock (or two) must have failed. This sort of thing is specifically considered and interlocks are designed to prevent it from happening. Because when it does happen it's bad. Very bad.
Yes, they are a PITA, but in order to get the same field strength out of a normal conducting magnet, you are talking many times the size, bulk, weight, heat, and so on. In many places, optically, you simply have to use super conducting magnets. CESR had a set of superconducting magnets near the IR, as well as a superconducting solenoid around the detector, and a set of superconducting anti-solenoids on either side of it. And also, two sets of two super conducting RF cavities, one set in the west, one set in the east. Oh, and also, about a dozen super conducting wigglers for running at low energy. Our small accelerator (compared to the LHC) had that much superconducting stuff. And it wasn't 'cause we wanted to make our lives complicated. On the contrary. Normal conducting RF cavities and magnets can be very painful to run, too.
I havent gone and asked for a report on what happened at the LHC, or seen anything in the elevator yet, but I'm pretty sure that a safety system / interlock (or two) must have failed. This sort of thing is specifically considered and interlocks are designed to prevent it from happening. Because when it does happen it's bad. Very bad.
PhotonWrangler
Flashaholic
What is a superconducting wiggler? It sounds like a Fisher-Price toy on steroids.
js
Flashlight Enthusiast
wiggler = horizontal undulator = take the beam and make it go left and right and left and right and left and right and etc. which makes it give off x-rays like crazy. Increases damping, which is needed for optical reasons, but it also increases the power needed to keep the beam in the machine.
PhotonWrangler
Flashaholic
Thanks, js. The description (and the name) reminds me of a term from old time radio & tv - the wobbulator circuit. It's a sweep generator that moves an oscillator from "left" to "right." :huh:
TedTheLed
Flashlight Enthusiast
"150 amps" yes, but at what voltage? or how many watts?
and why 24 gauge? I mean would 16 gauge be so much more difficult to cool? at least they'd be a little more robust. or do the wires need to be that small physically? or perhaps niobium is very expensive?
and why 24 gauge? I mean would 16 gauge be so much more difficult to cool? at least they'd be a little more robust. or do the wires need to be that small physically? or perhaps niobium is very expensive?
HarryN
Flashlight Enthusiast
I read the link - interesting project. Super conductors at a bit of a challenge, but I am not so sure that it will be so easy to achieve 100 MV / meter and 10s of GHz switching to drive that system either.
I suppose if the CERN system were built today, perhaps they would be able to use some of the LN2 temperature superconductors ?
jtr1962
Flashaholic
Electromagnet field strength is based on ampere-turns. You get a lot more turns with 24 gauge wire as opposed to 16 gauge. As for what voltage, ideally zero since it the resistance of a superconductor approaches zero. In the real world probably greater than zero. Perhaps 24 gauge optimized the number of ampere-turns.
asdalton
Flashlight Enthusiast
TedTheLed
Flashlight Enthusiast
JTR -- windings! oh of course. and zero voltage --- of course again! duh.
thanks. :duncehat:
thanks. :duncehat:
js
Flashlight Enthusiast
Yup. What jtr said.
Practically there is usually some lead voltage at the connections to the superconducting magnet. As long as the connection is cool and low resistance, this resistance is small. On our SC magnets the leads were cooled by the gaseous Nitrogen coming out of the cryostat, and the lead voltages were on the order of a tenth of a volt. If any of these crept up above .2 volts, interlocks would trip off and/or warnings would go off, depending. There were also precision resistance shunts between the power supplies and the SC coils to allow for a measure of the current in the coils.
But the coils themselves, having exactly zero ohms resistance, had no voltage differential across their inputs, and the wire was small to allow for more turns, but large enough to allow for some amount of stored energy to be safely transfered out as heat, into the liquid helium. Too small a wire and any quench would destroy your magnets. And quenches WILL happen at one point or another.
So . . . on another note, the problem at the LHC was at a bus bar connection between super conducting magnets, in a whole series of cryogenically connected SC magnets. There was quench protection on the magnets themselves, but not on the bus bar. This is where the failure happened, and the bus bar went normal conducting, got hot, developed high resistance, and boiled off the cryogenic cooling for that section of magnets. This caused a quench and an interlock trip, of course, but about half of the stored energy in the magnets (which is enormous) went into the resistive load presented by the bus bar. And freaking EXPLODED IT. VAPORIZED IT. Which destroyed the containment of the cryogenics, which flooded the tunnel with non-oxygen type gases like helium and nitrogen. Not very conducive to, you know, BREATHING. So they couldn't even enter the tunnel for days, I think.
So, now they have to warm up that whole section of magnets in a controlled way--which takes a long time--fix the problem, and fix the potential for this to ever happen again on all of the other SC sections, then cool back down. And at that point they are at a scheduled down anyway, so they won't be back up intil late winter, early spring.
That's the report I got from one of the higher-ups here at my lab.
Practically there is usually some lead voltage at the connections to the superconducting magnet. As long as the connection is cool and low resistance, this resistance is small. On our SC magnets the leads were cooled by the gaseous Nitrogen coming out of the cryostat, and the lead voltages were on the order of a tenth of a volt. If any of these crept up above .2 volts, interlocks would trip off and/or warnings would go off, depending. There were also precision resistance shunts between the power supplies and the SC coils to allow for a measure of the current in the coils.
But the coils themselves, having exactly zero ohms resistance, had no voltage differential across their inputs, and the wire was small to allow for more turns, but large enough to allow for some amount of stored energy to be safely transfered out as heat, into the liquid helium. Too small a wire and any quench would destroy your magnets. And quenches WILL happen at one point or another.
So . . . on another note, the problem at the LHC was at a bus bar connection between super conducting magnets, in a whole series of cryogenically connected SC magnets. There was quench protection on the magnets themselves, but not on the bus bar. This is where the failure happened, and the bus bar went normal conducting, got hot, developed high resistance, and boiled off the cryogenic cooling for that section of magnets. This caused a quench and an interlock trip, of course, but about half of the stored energy in the magnets (which is enormous) went into the resistive load presented by the bus bar. And freaking EXPLODED IT. VAPORIZED IT. Which destroyed the containment of the cryogenics, which flooded the tunnel with non-oxygen type gases like helium and nitrogen. Not very conducive to, you know, BREATHING. So they couldn't even enter the tunnel for days, I think.
So, now they have to warm up that whole section of magnets in a controlled way--which takes a long time--fix the problem, and fix the potential for this to ever happen again on all of the other SC sections, then cool back down. And at that point they are at a scheduled down anyway, so they won't be back up intil late winter, early spring.
That's the report I got from one of the higher-ups here at my lab.
Darkpower
Newly Enlightened
- Joined
- Dec 11, 2007
- Messages
- 185
Oh darn it Kids! The end of the world has been delayed, this means we really gotta get Congress to hurry up on that Banking Bailout thing with Hank Paulson then!! :nana:
Sorry to correct you, but a wiggler is not just a "horizontal undulator".
If you really felt like it you could make a helical wiggler, too.
The main difference is the deflection coefficient: A undulator deflects the beam so little that there is spatial coherence preserved between the individul bends. Thus emitted power scales with the square of the periods
A wiggler, otoh, is on the far end of the coherent-incoherent scale: Each bend adds incoherently (linear scaling), with a bending magnet profile (thus superconducting wigglers: The stonger field allows to extract more and higher energy bending radiation at each period).
While the undulator has moderatly sharp peaks that depend on magnetic field and spacing (the energy is proportional to the square of gamma divided by the magnet period).
Wigglers put out a lot more power than undulators, but A LOT less brilliance in the peak. T
Darkpower
Newly Enlightened
- Joined
- Dec 11, 2007
- Messages
- 185
Superconductivity is an amazing thing with real world applications. Years ago, there were many discussions about building high-tension power transmission lines with pipes, cooled with liquid nitrogen to achieve zero resistance over long runs or at least as close to zero resistence. The whole project was interesting because pipes were also an ideal geometry for conduction of electrons because of the skin effect. Particles with like charges repel each other and it is believed that in a solid copper wire the majority of the current is carried on the skin of the wire as the internal electrons repel away from each other. Anyhow, I never heard again of the cryogenic transmission power lines other then the Soviets had actually been able to build a stretch of it somewhere in Siberia.
js
Flashlight Enthusiast
Don't be sorry to correct me. No problem. I was painting in very broad brush strokes, and I was wrong. Sorry!
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TedTheLed
Flashlight Enthusiast
..I read the busbar failed because of a "bad solder joint" (made by a human)
Could this be true? Is the busbar really soldered? Or is this just a metalurgical analogy?
If so how exactly did the connection fail?
Could this be true? Is the busbar really soldered? Or is this just a metalurgical analogy?
If so how exactly did the connection fail?
PhotonWrangler
Flashaholic
Is this normally soldered or spot welded?
