At the heart of TRIUMF is the 500 MeV cyclotron that produces the primary proton beams. A large fraction of the TRIUMF program relies on these beams. These include the ISAC, the Centre for Molecular and Materials Science programs in μSR and β-NMR, and the Proton Treatment Facility. The operation of the main cyclotron has enabled TRIUMF to acquire the expertise to operate the three cyclotrons for MDS Nordion and the TR-13 cyclotron used to produce medical isotopes, and assist companies to exploit commercial opportunities for the sale of cyclotron and other accelerator technologies.
The 500 MeV Cyclotron
TRIUMF produces negatively charged hydrogen ions (H⁻: 1 proton, 2 electrons) from an ion source. The ions are transported through an evacuated electrostatic beam line containing elements to focus and steer the beam over its 60 m to the cyclotron. The 500 MeV (million electron volts) variable energy cyclotron accelerates these ions with a high frequency alternating electric field and uses a massive six-sector magnet to confine the beam in an outward spiral trajectory. Inserting a very thin graphite extraction foil strips, or removes, the electrons from the H⁻ ion while allowing the proton to pass through. The proton, because it is a positively charged particle, is deflected in the outward direction due to the magnetic field and is directed to a proton beam line.
The accelerating process takes approximately 0.3 ms before the proton achieves three-quarters the speed of light. The success of TRIUMF’s programs depends on the ability to deliver protons from the cyclotron reliably. Typically, the cyclotron, although over 30 years old, averages an uptime of greater than 90% (2000–2007), with the 15-year average just under 90%. Typically the beam is delivered for about 5,000 hours per year with one major (three month) and one minor (one month) maintenance periods. The cyclotron beam properties and capabilities have improved over the years as a result of systems upgrades. The fundamental infrastructure providing the magnetic and electrical fields and the RF resonators as well as the vacuum vessel remain sound and will serve TRIUMF for many more years. In order to maintain and improve the accelerator facilities, TRIUMF has an ongoing refurbishment program that replaces old and obsolete equipment. This strategy has allowed TRIUMF to maintain the availability of the extracted beam steady at more than 90%.
The Four Proton Beam Lines
TRIUMF has four independent extraction probes with various sizes of foils to provide protons simultaneously to up to four beam lines. Because of the high energy of the proton beam, these beam lines use magnetic rather than electrostatic focusing and steering elements.
Beam line 1A (BL1A) can deliver 180 to 500 MeV protons to two target systems. The beam power ranges from 50 to 75 kW. The first target, T1, services three experimental channels, one of which is used for detector tests for the T2K (Tokai to Kamioka) project. The second target, T2, services two μSR experimental channels. Downstream of T2 is a 500 MeV facility used to produce strontium isotopes for medical-imaging generators as well as the Thermal Neutron Facility (TNF). Beam line 1B separates off BL1 at the edge of the cyclotron vault and provides international users with the Proton Irradiation Facility (PIF) that is used for radiation testing of electronic circuits, for example, mimicking space radiation for testing computer chips. Beam Line 2A (BL2A) is capable of providing 475 to 500 MeV proton beams at up to 50 kW to the ISAC target facility that produces rare-isotope ion beams for a host of Canadian and international experiments. Beam Line 2C (BL2C) is used for the Proton Therapy Program (PT) to treat choroidal melanomas (eye tumours) and proton irradiation to produce strontium isotopes, which are chemically processed and then used for medical imaging generators. This beam line also has the flexibility to provide protons of lower energy for PIF users. The energy range for this line is 70 to 120 MeV. Beam line 4 (BL4) in its present configuration can deliver protons of energy from 180 to 500 MeV, albeit at only 5 kW and was last used as a production facility in 2000 for the parity violation experiment. Other significant experiments on this beam line include charge symmetry breaking and TISOL, the TRIUMF Isotope Separator On-Line, the predecessor to the ISAC facility. An extension of this line, Beam Line 4 North (BL4N), will be used for the proposed expansion of ISAC with a specialized actinide beam line.