TRIUMF

TRIUMF is Canada's National Laboratory for Particle and Nuclear Physics. Located on the UBC campus in Vancouver, British Columbia, it is home to the world's largest cyclotron as well as the ISAC radioactive beam facility.

The Accelerator

The centrepiece of the TRIUMF lab is a 17m diameter, 520 MeV proton cyclotron. Housed in a vault two stories underground, and covered with three interlocking layers of roof beams, it is the largest accelerator of its kind in existence. The tremendous uniform magnetic field required by the cyclotron is provided by a 4.6 T electromagnet shaped in an unusual 'pinwheel' pattern, and the actual acceleration is done by a 93KV, 23KHz alternating electric field. The beam intensity delivered is around 300 microamperes.

The TRIUMF cyclotron uses a clever method to extract multiple beams at varying energies from the accelerator. Although it is nominally a proton accelerator, it actually accelerates H^- ions. To produce the proton beam, thin graphite sheets are placed in the accelerator in the beam path. When the H^- beam collides with the sheet, the two electrons are stripped off, leaving a bare proton. Since the sign of the ion's charge is changed, it changes direction in the magnetic field, arcing out of the chamber rather than spiraling around its centre. Different proton energies, from 60 MeV to the maximum 520 MeV, can be achieved by placing the extraction foil at different radii in the cyclotron chamber. This method also allows up to four beams of different energies to be produced simultaneously by the accelerator.

The accelerator cost 12,000,000 $CDN to build, in 1974 dollars. The first full-energy beam was extracted in December of 1974, under the direction of Dr. Reg Richardson.

Experimental Complex

The original proposal to build the accelerator called for the construction of a 'meson factory', where the primary output of the accelerator would be used to make relatively high-energy, high-intensity beams of pions and muons. Many experiments were done with these beams which would not be possible with a smaller accelerator system. In recent years, fewer meson beam experiments have been proposed, as most of the problems in pion physics have been resolved. Current studies in other labs focus more on heavier mesons such as the kaon that the TRIUMF lab cannot produce. The meson factory is now used mainly for muon scattering resonance experiments in condensed matter physics (solid state physics).

Other early experiments at TRIUMF were carried out using the 500 MeV proton beam directly. These experiments became less common quite a bit earlier than the meson experiments, as much larger and higher energy accelerator facilities for protons were built during the 1980s, based on the synchrotron design. By 1990, most of the proton experiments at TRIUMF had concluded. However, the empty experimental hall was used as a test bed for what has become the largest research area currently at TRIUMF, ISAC.

ISAC (Isotope Separator and ACcellerator)

The ISAC facility is the most recent addition to the TRIUMF lab. Its purpose is to create high-energy beams of short-lived unstable isotope nuclei for experiments. This is achieved with a two-step process. First, the proton beam collides with a target, knocking free target nuclei and also, occasionally, joining with them to form new, less stable nuclei. These nuclei are collected and a mass spectrometer is applied to select only the desired product isotope. The resulting beam of heavy nuclei is then transferred to a linear accelerator referred to as the 'RFQ' (Radio Frequency Quadrupole), and the resulting beam directed to experiments. Some experiments, such as the laser trapping experiment TRINAT, do not require a high-energy beam and so collect the nuclei before they go to the RFQ.

The ISAC facility was constructed from 1996 to 1998, and became operational in 1999, although much of the experiment development wasn't completed until 2001. An addition to the ISAC facility, ISAC-II began construction on January 4, 2002. This extension involves another accelerator for reaching higher beam energies, as well as space for more experiments. The building itself was completed by May 2003, with the offices therein fully operational, but the accelerator and experiments are not expected to be operational until 2005.

Administration

TRIUMF is administered by a consortium of Canadian universities. The name of the lab stands for TRI-University Meson Facility, as the consortium originally had three members: the University of British Columbia, Simon Fraser University, and the University of Victoria. By the time the lab was actually constructed, a fourth university joined, the University of Alberta. Now, there are five primary members and seven associate members. The primary members are the original four plus Carleton University. The associate members are the University of Guelph, the University of Manitoba, McMaster University, the Université de Montréal, Queen's University, the University of Regina, and the University of Toronto. The lab is also funded by the National Research Council of Canada.

Conclusion

Despite the construction of larger and more capable accelerator facilities in the 30 years that TRIUMF has been operational, it still remains one of the larger particle accelerator labs and contributes significantly to science in Canada as well as international collaborations. The TRIUMF website is at http://www.triumf.info/ .