Cryogenic sensors for monitoring in superconducting RF cavities of linacs

Cryogenic sensors are used worldwide in a number of particle accelerators, including the world’s most powerful one, the Large Hadron Collider (LHC) at CERN, where sensors are used to monitor the temperature of the superconducting magnets used to steer and focus the particle beam. Other applications include linear accelerators commissioned in the U.S., Germany, and Japan. In several of these, Lake Shore supplies thermometry for regulating temperature in superconducting radio-frequency (SRF) cavities, through which charged particles accelerate in vacuum.

Stanford Linear Accelerator

Stanford Linear Accelerator

A specific SRF initiative that we’re following closely is the work that is going into the next version of the Linac Coherent Light Source (LCLS), named LCLS-II, at the SLAC National Accelerator Laboratory in California. For the sourcing of cryogenic systems used in LCLS-II, SLAC is collaborating with Fermilab and the Thomas Jefferson National Accelerator Facility, where scientists are assembling and testing cryomodules that will encase strings of SRF cavities within the accelerator. As Fermilab explains, “Electrons speeding down the accelerator will generate an almost continuous X-ray laser beam with pulses of up to a million times per second — thousands of times faster than the current LCLS puts out.”

To be superconducting, the cryomodule’s cavities must be cooled to 2 K, and any sensor chosen for this application must have reasonably low magnetic field-induced calibration offsets at that operating temperature and be able to withstand radiation exposure. Lake Shore Cernox® sensors offer just such low magnetoresistance and radiation hardness, and a number of these sensors have been used in support of the LCLS-II project, specifically within a prototype of the 1.3 GHz cryomodule. These include sensors used to measure temperature in various areas of the cryomodule, including on the beam tube and magnetic shield as well as inside an LHe vessel. It is yet to be seen whether these same sensors will be included in the cryomodules that end up being used in the LCLS-II accelerator (expected to go into operation in the early 2020s).

For more information about the performance specifications of Cernox® sensors with regard to their suitability for high energy physics accelerator applications, read this paper written by Lake Shore Applications Scientist Scott Courts.

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