The ISAC-I linear accelerators presently deliver beams of radioactive and stable ions to experiment with final energies variables between 150 keV/u and 1.5 MeV/u (corresponding to velocities from 1.8% to 5.6% the speed of light). TRIUMF is now constructing an extension to the ISAC facility, ISAC-II, to further accelerate the ions from 1.5 MeV/u to energies of at least 6.5 MeV/u (v/c=11.7%). At the heart of the installation is a new superconducting linear accelerator. The accelerator is composed of resonant rf structures called cavities and superconducting solenoids that provide periodic focusing for the accelerating beams. The cavities and solenoids are housed in box-like structures called cryomodules that provide a good thermal isolation for the cold elements of the linac. The linac is grouped into medium and high beta (velocity) sections. An initial installation of twenty medium beta cavities corresponding to an accelerating voltage of 20 MV is due for commissioning by the end of 2005. A major milestone, reported here and achieved in July 2005, is the demonstration of the acceleration of an ion beam with a single cryomodule. Thus far a number of cold tests have been completed in the ISAC-II clean room and test facility. The tests establish the vacuum and cryogenic performance, the cold alignment and the rf integrity of the cryomodules.
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In a recent test a cryomodule was moved to the accelerator vault and tested in situ (Fig. 1) with the new refrigerator providing liquid helium. The test allowed us to operate the cavities and solenoid inthe vault environment and with the cabling, control systems and power supplies as for the final linear accelerator. A 26Mg6+ beam at 1.5 MeV/u was delivered from ISAC through a new transport beam-line system and tuned through the cryomodule. |
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A beam profile monitor and Faraday cup in the downstream diagnostic box were used to optimize the beam and a silicon detector was used to measure the final energy. The three operating cavities were turned on and phased sequentially. The final spectra of the unaccelerated beam plus the spectra after each cavity is turned on is shown Fig. 2. The final energy of the 26Mg6+ was 2.3 MeV/u. Each cavity gave a voltage gain of 1.2 MV corresponding to an average gradient of 7.4 MV/m and a peak surface field of 37 MV. These fields are a significant increase above other present day operating heavy ion facilities.The future looks bright for ISAC-II.• |
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| Fig. 2. | Energy spectra of 26Mg6+ beam. Shown are the spectra of the injected beam (a) and the spectra after turning on and phasing three cavities sequentially. | ||||
Robert Laxdal |
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