LHC accidental quench of 100 magnets raises questions

By Walter L. Wagner

The accident of September 19, 2008 poses a number of serious questions. It is unheard of to have 100 consecutive magnets quench, totaling some 1.5 kilometers in length.

If the connector between two magnets lost superconductivity, engaged in ohmic resistance heating, and melted, as suggested in initial reports, it raises several questions regarding how that happened.

It occurred while they were testing that sector by raising the current/field-strength from what it takes to curve a 0.45 TeV beam [injection speed/energy] to a field-strength that would curve a 5 TeV beam [stated goal to engage in collisions at 10 TeV in October, 2008]. Each magnet had reportedly been tested independently before installation, but the whole length of magnets had not been tested, thus the testing requirement for each sector as a whole, before beam injection.

So, the question is, at what field strength did the connector fail? At 1 TeV, 2 TeV, 5 TeV?. And the second question, was this the last of the sectors to be tested, or the first?

In any event, it calls into question the engineering design of the connectors. It will likely be determined that they can/will/do fail with their current design. If so, they will all have to be replaced/retrofitted in all magnets along the full 27 kilometer length. That won't happen this Winter, I'm fairly certain.

Another question pertains to potential damage to the magnets during the quench process. It appears the temperature gauges were damaged - they all stopped reporting save one, which stopped reporting five days after the accident. This implies physical damage to the gauges, and ergo, another design defect that would have to be retrofitted/corrected on all magnets.

And then, it still remains to be determined whether heating from 2K to 100K in a fraction of a second caused any damaged. It's not supposed to happen, according to the design. But then, 100 magnets are not supposed to quench simultaneously either, according to the design. So those magnets will need to be tested to see if they suffered any physical damage. If any of them did, that would imply a design defect that would need to be retrofitted on all magnets.

This accident is far more serious than initially being reported - and this is likely known by those engineers in the know, but possibly not yet being reported to management [Engelen/Aymar].

And, they're also having difficulties with maintaining their cool [pun intended]. Both ends of sector 3-4 are slowly warming. And even sector 2-3 is showing some difficulty. Perhaps they need more Helium, and it's not available?

In any event, they also have to worry about keeping everyone busy during the down-time, creating 'make-work' projects. It would be nice if they started working on the ideas we've proposed to look for the proofs of safety, if they exist. That's all good science too.

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