I have written some times about how a synchrotron works (underlining that I am not a physicist and what I write is what I understood from the explanation of other people). Also I have wrote about how can we saw the beam or its effects: visible beam, first xrays or fluorescent screens But there is another way to see the beam: using an scope. Today I have ask to know a little bit more what we can see from an scope that we are reading the signal:
But, 2 questions: who this signal is get and what does this mean? This signal is get from a Fast Current Transformer (FCT) located in sector 02:
Very close to the dcct that is giving us the current of the beam in the machine status. This FCT is an inductor surrounding the vacuum chamber and what we see in the scope is the inducted current by the primary current given by the electron bunches. In the scope picture we can see the bunches in one turn (about 900ns). But a bunch is not one of this eleven groups in the signal. They are composed by bunches. May can help to see that by plots taken with taurus:
With this last picture we can see the bunches themselves. The bunches are separated by 2ns, and the linac is shutting in groups of 32 consecutive bunches and a gap of 24ns. Also I have ask why this groups of bunches have different shapes like:
This 3 examples has been taken over different times during today's start up of the machine. This shapes can be explained because fine configuration or how the equipments works and their efficiency. In the best case, in a world of the theory, this groups would be absolutely squared.
The original title of this post was 'European Strike 14N' because testerday we had a call for strike in many places in Europe. Some of the European countries doesn't have the right for a general strike (like Germany). In fact the bigger calls was in the south of the continent: Portugal, Malta, Cyprus, and Spain have had a journey strike, in Greece they had a 3 hour call for strike (remember that they have had 2 journeys of strike last 10th). In Italy the call has been made for 4 hour. But why the today's news have changed my mind? I thing there is a mismatch in the police actions when the injured people in the demonstrations are more than the arrested (worst when the is not intersection between the arrested joint and the injured joint). Well we have to think that one of the injured is a riot police man that has run over by a police ban:
After watch the video I have hallucinated with the hits on the girl close to where other physically protect the kit. After the girl protest to the riot controller, she have received the shield hit only to be telling something to the police. This girl doesn't look to be a menace to those police men. But after she have received 3 truncheon hits by two different elements of those shielded giants.
News like this ones that gives more injured people than arrested, makes me think that their method is not working because more innocents (because they hasn't been arrested) have been injured, further when they often say that they have identified hundreds of violent persons.
It is also incredible when the police count as injured their riot controllers with wrist pain. Where the origin of this pain is the hit with the truncheon, and they are not counting all the beat by this truncheons. In the case of the people in the protest, you must finish in the hospital with a big damage to be counted in this list.
The afternoon of November 13th, the Albasynchrotron has had an accident. As it has been officially mention by an email to all the staff, during the machine start up after a week shutdown, and accident have vent the vacuum in the storage ring. Having a 3GeV beam with a current of around 100mA some beam studies were on going. It looks that the vertical orbit have suddenly change (+-5mm). The machine protection was off because it was necessary for the works on going and the orbit interlock protection hasn't being triggered to kill the beam. This protection has been design to avoid the beam hits the cavity when the beam goes out of a safe region.
The first indicator of the issue can be saw in the machine status because usually the operation pressure is rounding the 1e-9 mbar (in the Ultra-High Vacuum range) and in the picture taken the evening of that day this pressure is at 6e-2 mbar, where this is medium vacuum. Even that this pressure value is not in one position, is an average. There where out-gassed sectors and sectors where the pressure has been contained:
In the bottom plot is possible to see where this accident have vent the cavity and where the pressure is very far than UHV. Notice that the scale is logarithmic in this plot, and we have already start work to fix that. When the accident has happen, some sectors have raised up to atmospheric pressure...
Now the machine status informs a little bit about this and is not giving a pressure value:
Update: Current user run cancelled. Due to the vacuum accident, the current 3 week run with beam for users has been cancelled. We hope to get it back up and running as soon as possible. Update 20121116: We are recovering the vacuum. Yesterday we where at 0.39mbar on average in the storage ring, and today we are at 0.074mbar (on average).
Update 20121117: Yesterday we've been informed that the breakdown was less than can be thought, if it's possible to say like that. As far as I understood, the electron beam haven't hit the vacuum chamber; the damage has come from synchrotron photons have hit flanges downstream some bending magnets, the feebleest element on the path. The vacuum technicians are working this weekend to speed up as much as possible the recovery of the machine operation. And today, on average we are at 0.0024mbar having only 4 places with pressures in the medium vacuum range (the others are already in UHV). Update 20121119: Back from the weekend It look like the people that work this free days did an incredible work:
Sector 12 have 2 reading of 2.7e-3mbar, but as is show in the plot, the others are below the 1e-8mbar. Sector 7 looks to be in an incredible good 1e-12mbar...
Update 20121119, afternoon: the machine status gui recovers the pressure value
The Vacuum Controls gui (vacca) is also showing much better look:
