Update [2008-9-10 3:2:3 by someone]:Now we have a count down timer saying 1 minute 30s? Are they turning it on at 9?? Hmm. Also, network is sloooowwww.
Update [2008-9-10 3:2:3 by someone]:Ah, that was the countdown to show us a propaganda video. Quite nice. Shiny graphics.
Update [2008-9-10 4:33:1 by someone]:After having fixed problems all night long they seem to in fact be ready to start it. The control room is filled with people mingle. And it seems that finally they have decided to start the clockwise beam first. Oh, and soon we will be addressed. I think right now we are listening to the BBC or something?
Update [2008-9-10 4:33:1 by someone]:Yes, it is the project leader. This will take a while as he has to repeat everything in French and English. It seems they will start it up two sectors at a time, before going the whole way around.
Update [2008-9-10 4:33:1 by someone]:And now the director general is speaking. He is the big cheese of CERN, the supreme leader, the unchallengeable autocrat. I think he is concluding that CERN is great.
Update [2008-9-10 4:33:1 by someone]:How long will the start-up take? well, LEP (the previous machine) took 12 hours. They hope for less today. Injection in LHC in 5 minutes. The Big Button is ready!
Update [2008-9-10 4:33:1 by someone]:But I see no button? They didn't actually get a button? Hmmm, we've been betting on how the button would look, and now we find there might not be one? Disaster!
Update [2008-9-10 4:33:1 by someone]:Ahhh! Now we get the human interest part! "How do you think the people in the control room feel?" The BBC reporting...
Update [2008-9-10 4:33:1 by someone]:Hmm, de dum. So, of course we are just waiting here. Nothing is actually happening, but the broadcast we are hearing makes a good job of keeping talking. So I will keep posting. And there will be briefings every hour, so I suppose they will have something to report?
Update [2008-9-10 4:33:1 by someone]:Ready? Ready? Go!
Update [2008-9-10 4:33:1 by someone]:"The tension is so high one could cut it with a knife". Ok, BBC. I'm taking away your cliché rights.
Update [2008-9-10 4:33:1 by someone]:APPLAUSE! The beam just made the first 8th of a turn. Now for the next eights.
Update [2008-9-10 4:33:1 by someone]:All around next? No, just to point three.
Update [2008-9-10 4:33:1 by someone]:3..2..1..BING!
Update [2008-9-10 4:33:1 by someone]:Now we wait again, and then another quarter of the way.
Update [2008-9-10 4:33:1 by someone]:48seconds. I love how they do the suspense over and over again. Smart move.
Update [2008-9-10 4:33:1 by someone]:No beam!??!! Next cycle. 48 seconds...
Update [2008-9-10 4:33:1 by someone]:BING! Half way around now. The crowd goes wild! Go Protons! Now, it should be said that the visual evidence of a passing beam is a round white and grey spot on a black background. And an oscilloscope pulse on another monitor. They should add some better graphics.
Update [2008-9-10 4:33:1 by someone]:Reload suspense. Watch the second screen on the bottom. Ready! In 48 seconds. (The length of a cycle for the ring prior to LHC injection.) Now we will test the beam dump. As in, can we safely kick the beam out of the machine if needed.
Update [2008-9-10 4:33:1 by someone]:READY! BING! Beam was dumped as planned. They will now make some corrections before continuing.
Update [2008-9-10 4:33:1 by someone]:No, the beam did not make it to the dump yet. That would be the next step. Now this beam is low energy and low charge, which is why dumping is not really an issue yet. One can just slam it in to a graphite/concrete block without problem. When the full beam at full energy is in the machine this will no longer be possible. Instead, the beam will be dumped in a special way, where it is 'painted' onto the target. A magnet will spiral it so that it spreads over a large area rather than striking all in one point. This process is very important, since hitting in one spot would simply blow the dump block to pieces, and we would have to do a lengthy and costly access to the tunnel and replacement of the block.
Update [2008-9-10 4:33:1 by someone]:Maybe a full turn next? Time to get ready to drum up that suspense again. All eyes on the monitors.
Update [2008-9-10 4:33:1 by someone]:No, one more eight covered. The oscillations of the beam are too large, so they will try to correct before continuing.
Update [2008-9-10 4:33:1 by someone]:Something just happened. Maybe we made another 8th? That would bring us to 7/8 of a turn, I think.
Update [2008-9-10 4:33:1 by someone]:
This is the beam from synchronization tests a few weeks ago. So, coloured spot on coloured background.
Update [2008-9-10 4:33:1 by someone]:So, we have made 3/4 of the ring. I think they will try to complete it next shot. Next cycle, 48 seconds...
Update [2008-9-10 4:33:1 by someone]:Bang! Smash! 7/8th. The beam just crossed one of the large detectors and are trying to look at the data they get just from the passing beam with no collisions. Oh so very close to have a circulating beam in the whole machine.
Update [2008-9-10 4:33:1 by someone]:Now we are ready, they say. Full lap next. Look at the screen and don't blink. You might miss it! The last block is being lifted, and the whole circle is free. So, soon, circulating beam, and then some surprises according to the LHC boss. Surprises? Sounds ominous...
Update [2008-9-10 4:33:1 by someone]:OKAY! DONE AND FINISHED. THE MACHINE HAS BEEN OFFICIALLY STARTED. Now we do two turns!
Update [2008-9-10 4:33:1 by someone]:So a very fast start-up compared to the LEP. Probably because they learned their lesson. Before beam was ever attempted the checked that the passage trough the beam pipe was in fact unobstructed, by, ..., beer bottles. Which is what they discovered in the LEP pipe when trying to start it up.
Update [2008-9-10 4:33:1 by someone]:Now I go for a coffee. I'll be back to try posting some pictures a bit later.
Update [2008-9-10 9:31:33 by someone]:
As the machine is running and all went well, I am sure everyone is asking, what exactly is down there, under ground. And how does it work. So here, a very brief overview of what make up a particle accelerator.
First, we know that an object in motion tends to continue in a straight line unless acted upon by some force. In this case, since we wish to have our particle go around a ring, we need to somehow bend their trajectories. The force delivered to the particles to accomplish this is from a magnet known as a dipole magnet. It creates a vertical, constant magnetic field, and a charged particle moving trough this field will experience a horizontal force. This force is such that the direction of the field, the direction of motion of the particle, and the force are all perpendicular to each other. That is, the field is vertical (up or down), the particle moves forward, but under the influence of a force bending it left or right.
The last magnet being lower into the tunnel. Photo ©CERN
Magnets in the tunnel. (A nice picture where you can see the tunnel bend in the distance) Photo ©CERN
This is a particle accelerator, so we need some way to accelerate those things. This is accomplished by creating a beam consisting of bunches of particles, i.e. packets of tightly packed protons, with space in between. The beam at one point in the ring passes through a Radio Frequency cavity. This is a volume that can be filled with RF, that is an electromagnetic wave such as used for radio and other wireless transmissions. Here, however, the RF is packed in tight, with lots of energy, that is absorbed by the passing beam. Since the RF is an oscillating field, we need to also make sure that the wave moves with the particles, so that at all times in the cavity the electric field point in the direction of motion. Half a period later in the wave, the force from the field would be retarding rather than accelerating.
A cavity with RF and beam. See how the beam bunches travel along with the wave.
An LHC cavity under construction ©CERN
A cavity in the tunnel ©CERN
An ideal particle bunch would have all the particles at exactly the same spot, travelling down the centre of the beam pipe, and with no transverse velocity at all. We are however not so lucky as to be able to create such a bunch. Instead we make something having a Gaussian distribution around the mean, and a slice of a bunch looks a bit like this:
We can imagine that this would be a slice right through the beam as it travels down the tube. It could also be a representation of a bunch where the horizontal axis is the location is the horizontal, transverse plane of the particles, and the vertical axis is a measure of the speed of the particles in this same transverse plane. We have thus a bunch of particles with a transverse speed, and if left to themselves they would just smash into the walls of the beam-pipe after a very short while. Somehow they must be contained.
For this we use a second type of magnet. A so called quadrupole. We arrange four magnets such that right in the centre there is no field at all, and the further out you go, the large is the field. Now, such a magnet will have an inward force in one direction, and an outward in the other. So we arrange these magnets, alternating the direction in which the beam is focused and defocused from one to the next.
Quadropole field, blue lines. Focusing in the horizontal plane, and defocusing in the vertical one. The particle in the centre feels no force.
The particles thus bounce back and forward, oscillating about the centre as the hurl down the tube:
Trajectories of particles in one plane as they travel down a quadrupole lattice. The blue lines mark focusing quads, and the red lines defocusing ones. Initially some particles are rejected as they entered the arrangement with too large vertical offset or speed. I.e. they crossed the black lines I put in to mark the beam pipe. The others can continue within this containment indefinitely, though.
Slice of a quadrupole. Two, actually, one for each beam line in the LHC. The four metallic segments around each pipe give rise to the four magnetic poles. Photo ©CERN
Quads being assembled at CERN. Photo ©CERN
To be continued...