Saturday we were Peters guests at Diamond Light Source. It was a fascinating tour with plenty of information about what we were seeing. It is a new particle accelerator they have recently built in the contryside south of Oxford, with the main holding ring running at 3GeV – enough to be twice as bright as the sun.
(ETA: BC “…said the beam was twice as bright as the sun but realized later that was a _logarithmic_ scale. The sun is 10^10 photons per square mm, that baby is 10^20. About a trillion times brighter than the sun!”)
The accelerator consists of three main parts, the accelerator, the holding ring and the beamlines. It is housed in a large donut shaped building in Harwell. The accelerator, or synchrotron, is fed low powered electrons by something a bit like a CRT television, it accelerates them to 3GeV for storage in the holding ring.
The most interesting part is the beamlines, because thats where all of the experiments happen, there are places for 48 beamlines although I suspect infrastructure limits will mean that not all of those can be used. There are three or four currently functional with about the same in various stages of construction. These are arranged as a fan around the holding ring such that there are 48 junction points and exits. When the beam exits the holding ring it travels in a straight line through the beamline lead experiment hutch where the experimental equipment is housed.
This is all very boring so far. Either you’re a physicist and you know all this already or you were never a physicist and don’t care. More interesting is the atmosphere of the place.
The engineering involved in creating and running such a machine is incredible, there are cranes everywhere, there has to be because there is lead everwhere and it needs moving around from time to time. All of the yellow things you see in the pictures (see link above) are made of lead, those are the experimental hutches. They look a bit like this on the inside…well, before they’ve got an experiment in them. The beam entrance is behind Eugenes head, with the optics and experiment equipment being placed where we are standing. Each of these hutches has a controlled atmosphere, with any vents being chicanes such that any radiation cannot escape in a straight line. There are also a number of nitrogen vents around steaming coldness into the atmosphere.
Infrastructure was the focus for the day, with that being the bulk of Peters interest there, there is an incredible amount of sensors in each experiment, with each sensor being a source for various amounts of data which all has to be collected, processed and stored. So there is considerable computing power in each of the experimental hutches, and significant network infrastructure pulling the data off to storage systems elsewhere in the building. And of course a lot of power is needed to get electrons up to their holding speed, the hum of stepdown transformers inside the space in the middle of the donut, theres a bank of ten or so (not that I actually counted them) transformers the size of those that power a small village.
Another thing that struck me was the sheer amount of equipment lying around, there is a lot of work in progress with parts being put aside for later assembly, diagnosis or disposal. A lot of this is precision engineering to a degree you wouldn’t find in many places, an electron beam straying a couple of millimetres off course would unsettle the whole thing and cause no end of damage.
The holding ring looks impressive, in its own tunnel bathed in spooky blue light which says that the area is dangerous to enter.
There were no experiments actually in progress while we were there, they were doing some calibration of the holding ring or something, so we could take a closer look at a number of the experiments. None of which really made much sense but they were built in a style that would feel at home to the steam pioneers, but with small D9 serial sockets all over, feeding sensor information to control and monitor systems.
Our planned one hour ‘quick scoot around’ turned into a rather epic four hour grand tour. Quite enjoyable but lunch beforehand would have been a good idea.
I would recommend a visit if you get a chance – they have open days on a reasonably regular basis, or, if we are lucky, Peter might be able to arrange another days tour if we can gather an appropriate set of interested sorts.
