Grant: Subatomic Physics Envelope - Research Tools and Instruments

The heart of TRIUMF's Advanced Rare Isotope Laboratory (ARIEL) is a new superconducting 30 MeV electron linear accelerator, the e-linac. As the overall rare isotope production yield is expected to depend strongly on the electron beam energy, maintaining the output above 30 MeV is essential for the ARIEL science program. This requires that the e-linac's performance remains compatible with operation at accelerating gradients over 10 MV/m for extended periods of time. This operational imperative has directed the focus of our research to discovering the root cause of the gradual decline in performance observed in a number of superconducting linear accelerators worldwide. It is established that this degradation is caused by the presence of micrometer-sized field emitters, i.e. dust, in the superconducting cavities. Cavities are installed ultra-clean, but foreign particulates are routinely found inside them post operation. The mechanism that moves these dust particulates from less clean sections of beamline into the ultra-clean niobium cavities, even in the absence of vacuum incidents, remains unknown. Discovering this would constitute a breakthrough, opening a path towards long-term reliable operations of superconducting rf accelerators at their maximum gradient and with maximum power efficiency. We are requesting funds to support the construction of a fully instrumented experimental setup, designed to study the mechanisms leading to the charging, detachment and migration of dust particulates inside ultra-high vacuum accelerator systems. To mitigate the degradation in performance caused by the these dust particulates, we are looking to establish a solid understanding of the dynamics of dust grains in electron linear accelerators. We want to study each step in the dust migration process separately in a controlled environment, where each aspect of the problem can be tested independently from the others. During this study, the vacuum environment will need to be intentionally contaminated with controlled dust samples, requiring these tests to be performed off-line, as we cannot risk contaminating the actual accelerator. To dynamically resolve the migration of dust particulates, we are requesting a key piece of equipment: an in-vacuum particle counter. We must also have the capacity to bias one side of the experimental setup with respect to the other to perform a wide range of measurements and characterize the charge of individual dust grains. Obtaining this award would allow us to purchase key components of this fully instrumented off-line test setup, the likes of which does not yet exist.