CERN webcam

That's an improvement. On the news last night, they were claiming that
it was 7 trillion electron volts.

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An improvement on here at any rate. A discussion on economics involving
lawyers, actors and radio 'personalities' in a round table situation
invoked the word 'billion' and none of them were too sure what it really
meant until the actor chappie piped up it was a hundred million and
that's the end of it.

****'s sake, I mean, ****'s ****'s sake.

 

Bloody Americans devaluing our billions with pesky milliards.

 

Bloody hell.

There really is no excuse.

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I'm sure there's a Pratchett reference to be made here, but I'm not
going to make it, oh no.

 

That's right, 20 kA at the time IIRC, so quite a bit of energy
stored in the coils (E = 0.5 * L * I*I). Super joint -> normal -> melt -> arc
-> melting of LHe containment -> BOOM!

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Ivan Reid, School of Engineering & Design, _____________ CMS Collaboration,
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I'm intrigued with the amount of energy after having quite an
energetic (sic) discussion about energy with a couple of workmates on
after work drinks tonight. I don't think they quite got my point and
were talking about Kirlian photography of mobile phones at which point
I stated cringing a lot.

But back to your project, I assume you build up a potential then fire
it off in a very short but very violent burst?

Kev

 

" "

 

The Durex leak thread is down there vvv

 

Actually, no. If you look at the pages
http://op-webtools.web.cern.ch/op-webtools/vistar/vistars.php?usr=LHC1 or
http://op-webtools.web.cern.ch/op-webtools/vistar/vistars.php?usr=LHC3

you'll see graphs with three quantities varying over time: the blue and the
red are the number of protons in each beam (currently they are using just
one "bunch" per beam; this will change), while the black is the current in
the dipoles ("bending" magnets) which is also proportional to the energy
in the beams when they are following a perfect circuit.

The black does a bit of overshooting when they adjust it because
of hysteresis in the magnets. To get a repeatable fiels in an electromagnet
for a given current you always have to approach it from "far enough away"
in a given direction.

So they set the field to correspond to the injection energy (450 GeV)
and fire pulses into both beams until they have the desired pattern of
bunches. The fields and energies match so the pulses keep circulating
around the ring. Then, as each bunch approaches a certain point in the
ring, it is given a "kick" by an RF pulse, which increases its energy --
simultaneously the magnet current is increased so that the higher-energy
beams still circulate perfectly. They continue doing this, boosting the
beam energy and "ramping" the magnet current, until the desired energy
is reached. Then they "flat-top" the magnet currents and stop applying
RF boosts.

The final step is to ramp down small magnets near each collision
point which had been deflecting the beams around each other; the
bunches now pass through each other in the centre of the experiments.
A small fraction collide, providing the "events" of particles you may have
seen in the papers. Since only a small proportion are lost, this is
essentially a steady-state and each "fill" can last for hours before some
condition requires that the beam be "dumped" -- they seem to have run for
about 8 hours on one fill last night. After the beam is spilt, the magnets
are ramped down to the injection energy again, and the process repeated.

It's the thousands and millions of RF kicks that boost the beams
up to their fantastic energies. In theory you could reverse the process and
bring the beams back down in energy but in practice (and in an emergency!)
it's better to fire one mofo septum magnet which deflects both beams into
massive concrete and metal structures to absorb their energy. Ah, we've
just flat-topped -- this may be the third physics run ever at 3.5+3.5 GeV.

--
Ivan Reid, School of Engineering & Design, _____________ CMS Collaboration,
Brunel University. Ivan.Reid@[brunel.ac.uk|cern.ch] Room 40-1-B12, CERN
GSX600F, RG250WD "You Porsche. Me pass!" DoD #484 JKLO#003, 005
WP7# 3000 LC Unit #2368 (tinlc) UKMC#00009 BOTAFOT#16 UKRMMA#7 (Hon)
KotPT -- "for stupidity above and beyond the call of duty".

 

****
This used to be a nice clean monitor.

Kev

 

Thanks for that, interesting stuff. I envy you.

Cheers
Kev