Cooling System
Why do we cool the accelerator?
Electrical currents flowing in any material generate heat. The currents in the accelerating structure and in the coils of electromagnets are high enough that this heat must be carried off by a cooling system or things start to melt!
For many parts of the accelerator there is an additional problem -- temperature increase causes metal to expand, so changes in temperature changes the size of the cavities, waveguides, etc. Just as a the pitch of flute or trumpet changes a little as the instrument warms up, the frequency at which a cavity resonates changes with temperature. The proper operation of the accelerator requires very careful synchronization of the cavity frequency to the timed passage of the beam bunches, so any frequency change is unacceptable.
How do we cool the accelerator?
The accelerating structure and most conventional magnets (not superconducting magnets) at SLAC are cooled by providing a flow of water in a network of pipes connected to or built into the structures.
Cooling water tubes surround the cooper accelerator structure.
If you drive by SLAC on Highway 280, you may see plumes of steam from the cooling towers in which the hot water from the accelerator system is recooled.
One of the cooling towers that can be seen from Highway 280.
For a superconducting magnet to operate, it must be kept at temperatures well below the freezing point of water. These magnets are cooled by circulating liquid nitrogen and helium.
In addition, the accelerator structure is placed 25 feet underground to minimize the added complication of day-to-night and seasonal changes in air temperature.
