STF-2 Beam Operation Demonstrates ILC Specifications


KEK’s Superconducting RF Test Facility (STF) operated the first beams during February and March 2019 and demonstrated results that satisfy the specifications for the International Linear Collider (ILC).

STF was constructed in 2006 aiming to establish the production and operation of high-gradient superconducting accelerating cavities and cold storage devices called cryomodules. At STF, four projects have been undertaken: STF-1 (2008-2009), S1-Global (2009-2011), Quantum Beam (2011-2013), and STF-2 (2014-).The first beams were operated at STF during February and March this year, which showed results that satisfy ILC specifications.

The STF-2 project, began in 2014, produced cryomodules containing 12 superconducting cavities which were installed in a tunnel. By 2016, cooling tests have been performed three times, and the checking of the cavity performance and the simultaneous operation of eight cavities have been successfully performed. Since 2018, preparatory work was performed towards beam testing, the last step of the project, consisting of reservicing the beam line connections and laser electron gun systems, and installing beam monitors and the beam dump (Figure 1). In February and March this year,the beam operation was performed for the first time with a capture cryomodule containing two cavities and a cryomodule containing 7 cavities.

By adjusting the accelerating gradient of the cavities and the radio-frequency control, and by precisely adjusting the beams, the beam energy has reached 271 MeV (Figure 2). The operational accelerating gradient of a single cavity was calculated from this number to be 32 MV/m. This satisfies the specifications for the ILC operation of 31.5 MV/m, and the beam operation satisfying ILC specifications has now been demonstrated at KEK as well. In this fiscal year, work is planned to replace low performance cavities contained in the two cryomodules with cavities processed by a new method. During the beam operation next year, the performance of the newly installed cavities will be tested, and the aim will be to increase the beam energy and the beam current.

Figure 1: Constructing the STF-2 beamline (left); Celebrating the completion of the STF-2 Accelerator (right)

Figure 2: Schematics of the STF-2 Accelerator and images from the beam profile monitors

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