Exciting tasks in the underground CMS cavern February 28, 2008Posted by dorigo in personal, physics, science.
I am currently at CERN, where I am on shift for the CMS tracker (right). The CMS detector is in its final assembly phase, and the tracker – a cylindrical volume made by a dozen layers of silicon microstrip sensors- is being wired to its power, cooling, and readout systems. While this is being done, an important feedback can be given to the technicians by powering up the parts already wired and checking that everything is in good shape.
The microchips installed on silicon detectors in operation produce heat which, if not removed promptly and efficiently, causes overheating and eventually damage to the device. Because of that, one cannot power up the system without proper cooling in place. While the final cooling circuit is not operational yet, a temporary circuit of coolant has been installed on a part of a layer inside the tracker, such that we have a chance to spot problems connected to the assembling procedures early on.
Any temporary system requires a close babysitting. That is presently my job: as a SLIMOS (Shift Leader In Matters Of Safety) I am sitting in front of a desk in a control room inside the P5 cavern, 100 meters underground. I have to watch the temperature of the coolant, its pressure, and take a walk to the detector hall to check periodically the dry air flowing in the system, the cooling pump and the flow circuits, plus the power supplies that run the modules we are testing.
The walk is the fun part of my job: even though I have not contributed in any way to the mechanical construction of the titanic project, I feel it as my own as I walk with steel-tip shoes through the maze of stairs and passages surrounding the detector, a hard hat on my head, a notebook and pen in my hands, and a professional look printed on my face.
Above you can see a part of the temporary cooling circuit that has been assembled to allow the powering up of layer 4 of the TIB (the tracker inner barrel). Pressure gauges, valves, and tubing – cool stuff! Every couple of hours they get checked up by the SLIMOS on duty.
Below instead you can see the graphs I have to keep an eye on during most of my shift. The temperature oscillates between 10 and 12 degrees during cooling cycles. Of course, an automated system is capable of alerting and shutting down the power to the sensors by itself, but in a temporary setup one has to be careful and oversee things: we do not want to burn our detector before it has a chance of seeing proton collisions!
So, if you watch closely, you can see that indeed, human intervention is required now and then. The jump up of the curves in the top graphs signals abnormal growths of temperature in the detectors being powered at about 12:17 hours today. Following the event, sensors were powered down with no trouble, but I then had to run and enable the power interlock and check the status of the cooling pump: the latter was showing an overpressure situation. I restarted it by following a 13-step idiot-proof procedure (in course of being updated!), and the system is now up and running smoothly again (as shown by the normal cycles on the right of the spike).