E-linac

 

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The flagship of this proposal is the 50 MeV (electron energy), high-average-current (10 mA) continuous-wave (CW) linear accelerator (e-linac) founded on TTF superconducting RF technology at 1.3 GHz and 2 Kelvin. From the outset we have opted to base the e-linac design around Tesla Test Facility (TTF) technology developed for TESLA, XFEL, and ILC. This is for two reasons: to benefit from the extensive development for these accelerators, and to prepare Canada for participation in high-energy physics projects such as CERN-Superconducting Proton Linac and the International Linear Collider (ILC). The SPL is CERN's upgrade path for the LHC.

The e-linac consists of an electron gun, buncher cavity, injector cryomodule, and two main-linac cryomodules. the figure above shows the e-linac baseline layout as it will appear in 2017. The injector module contains a capture section, followed by acceleration in a 9-cell cavity to a few MeV. Each of the main linac cryomodules, accelerating by 20 MeV, contains two 9-cell cavities.

Basing the design on existing High-Power RF (HPRF) technology, the e-linac adopts a HPRF building block of one 130 kW klystron, two 60 kW input couplers and one 9-cell cavity. Five such units operated at 10 MV/m coupled with 10 mA beam current consume 100 kW/cavity and result in a beam energy of 50 MeV. Though the gradient planned for e-linac is a modest 10 MV/m, we intend to leave an upgrade path to a test bed for Fourth Generation Light Source technology operated at up to 20 MV/m; and the cavity fabrication and niobium surface preparation will be consistent with that goal. Light Sources are instruments for sub-microscopic imaging in Life, Chemical and Materials Sciences.

The main linac consists of four 9-cell TTF-style SRF cavities housed in two cryomodules. The cavities operate at 10 MV/m, and each has an active length of 1 m. We confine the gradient options to ≤ 20 MV/m because this is the limit achievable with buffer chemical polishing (BCP) alone of the niobium surfaces. BCP is readily available at TRIUMF, whereas electro-polishing is not. The e-linac cavities will be constructed in collaboration with a BC-based engineering company, PAVAC, with the intention of introducing to Canada the capability to fabricate and process elliptical Nb cavities. The company presently makes bulk-niobium quarter-wave cavities for the ISAC-II project.

In the first stage, to be completed mid-2013, the injector and the first of the main linac modules, and single IOT and klystron drivers are installed providing 25 MeV, 4 mA. In the second stage, to be implemented 2017, the second of the main linac modules is added along with additional high-power RF sources to achieve the final ½-MW goal.

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