Accelerator Science

A computer simulation using the GEANT4 nuclear transport toolkit was developed to model the production of isotopes from rare isotope beam targets used at ISAC. In combination with in-depth isotope beam characterization (via nuclear spectroscopy) at the ISAC yield station, the simulation data is a pivotal foundation for the development of better targets and the production of new and more intense isotope beams. Using simulation and yield results, the average release time of francium from uranium carbide targets was determined, providing a better understanding of the dynamics that govern the extraction of isotopes from the target. Yield and simulation results are accessible in a database, helping researchers to devise and plan experiments.

Around the experimental regions of the Large Hadron Collider (LHC), beams travel in a common vacuum chamber and therefore experience the fields of the opposing beams - so-called ‘long-range interactions’. These are unavoidable and, being nonlinear, limit the LHC's luminosity. Studies of this effect are essential for designs crucial for the ongoing high-luminosity upgrade (or HL-LHC; a program to bring a factor-of-10 performance improvement to the LHC), due to begin operating in 2025. The usual method of investigating the effect is by multiparticle simulations, and TRIUMF is part of the international collaboration charged with these calculations. These are compute-power limited, so it is highly desirable that an alternative analytic model be found. Recently, we have discovered such a model. This has the potential of making beam-beam calculations more tractable.

Superconducting radiofrequency (SRF) technology is the enabling advances in a new generation of proton linacs for discovery science or industrial application. Strong electromagnetic fields created in specially designed resonators are used to accelerate the protons. A class of resonators, termed spoke cavities, is efficient in acceleration but suffers from a phenomenon called ‘multipacting’ wherein a cascade of electrons is released from the surface by the high fields, which can limit the cavity performance. The TRIUMF SRF team has invented a new type of spoke resonator called the `balloon cavity’ with a special shape that virtually eliminates multipacting as an issue for single spoke resonators. A prototype cavity was fabricated and tested at TRIUMF and recent tests confirm the unique capabilities of the new variant.

An efficient but accurate beam dynamics model for linear accelerators has been developed and is being used in our control rooms, and in particular to commission the electron linear accelerator (e-linac). Other labs use simulations of up to ond million particles and then distill these down to only the 3 size parameters of the beam bunches. These multi-particle simulations are too slow to be used in online tuning of an accelerator. We have developed a technique that tracks bunch sizes, including space charge, instead of individual particles. Such applications have existed for many years but only for beam transport, not for linear accelerators. Our application allows operators to calculate new linac tunes online. It has generated international interest and an invited talk at the 2016 Linac Conference.

Virtually contamination-free radioactive ion beams can now be provided at ISAC from a new ion-guide laser ion source (IG-LIS) [1]. This IG-LIS allows for experiments on isotopes that for decades have been overwhelmed by contamination from surface-ionized isobars. TRILIS now routinely provides isotopes from 37 different elements. Laser ionization schemes for an additional 24 elements are ready for off-line testing. TRILIS also supports an in-source laser spectroscopy program that investigates fundamental properties of the rarest isotopes such as atomic energy levels and elemental ionization potentials have been determined for the first time [2] or improved significantly [3].

On May 26th, 2018, the AWAKE collaboration (to which TRIUMF has been an active contributor of beam instrumentation since 2014) successfully accelerated witness-electrons for the first time. AWAKE has demonstrated that these low energy electrons can gain energy while “riding” waves generated in plasma (ionized gas) by a proton beam, at a rate of around 200 MV/m (million volts per meter) over a distance of just 10 m. This represents current-day state-of-the-art technology in particle accelerators, for the overall distance over which acceleration can be sustained and ensuring intensity and quality of accelerated beams. These results are an important step towards the future development of smaller high-energy particle accelerators.

Via nuclear reactions induced by a high-energy primary beam of particles, porous uranium carbide with excess graphite is the international benchmark material for the production of exotic isotopes via the isotope on-line (ISOL) method. This process enables a broad range of science programs with increasing interest in the development of cancer imaging and treatment agents [1]. While the production rate for a specific isotope is determined by the primary beam and the target nucleus, the amount of available isotopes can fall a million times below the production yield, caused by losses inside the target material. De-novo engineered material nanostructures show significantly enhanced performance [2]. Combined with new production methodologies, TRIUMF is aiming to meet the future demand in terms of material availability and isotope yields [3].

Superconducting radio-frequency acceleration involves creating strong electromagnetic fields inside a cryogenically cooled superconducting vessel that can be used to accelerate charged particles. The superconducting state is limited by the ability of the material to repel magnetic flux penetration from the strong surface fields. New materials or new material treatments are being developed to allow higher fields and more efficient acceleration before flux penetrates the material. Recent experiments at the TRIUMF muSR facility have shown that coating niobium with a high Tc material (like Nb³Sn or MgB²) of variable coating thickness can increase the field of first flux penetration by 40% with respect to a non-coated sample. The measurements suggest a path forward to increase the performance of niobium SRF resonators through modification to the surface.

The ARIEL front-end is a complex switchyard consisting of more than 200 m of electrostatic beam lines designed to transport two rare isotope beams simultaneously from the new target stations to the ISAC experimental facilities in a vacuum of eleven orders of magnitude smaller than atmospheric pressure (10^-8 Torr). The switchyard includes a new generation high resolution separator (HRS) system engineered to differentiate between two beams with a mass difference of only one part in twenty thousand. The HRS system, which is part of the CANREB project, includes two state-of-the art, 16-tonne magnetic dipoles manufactured with a field flatness of the order of one part in one hundred thousand and a unique multipole corrector that will remove any imperfection stemming from aberrations from a beam thinner than a sheet of paper (or 100 mm).