Speaker
Description
Beam losses caused by interactions between the circulating beam and dust grains have been observed at many particle accelerators, leading to premature beam dumps, quenches of superconducting magnets, and pressure bursts. At some facilities, these events have a significant impact on overall accelerator performance.
The mechanisms by which dust grains detach from vacuum-chamber surfaces and enter the beam are still not well understood; one possible process is charge build-up on the grain followed by lofting due to the beam potential.
We present an experimental study of the charging and mobilisation of silica dust on accelerator-relevant surfaces: copper, NEG-coated substrates and samples treated with VacSeal, a silicone-based resin widely used to seal vacuum leaks. Dust is deposited on a grounded surface in a vacuum chamber and exposed to a homogeneous transverse electric field comparable to that in existing colliders.
Grains were charged using UV light and their motion is recorded with a high-speed camera. The trajectories are reconstructed to extract charge-to-mass ratios and launch velocities. First results indicate distinct behaviour for dust grains deposited on VacSeal-treated surfaces compared to untreated ones.
The observations provide input parameters for dust-dynamics simulations, which in turn allow detailed studies of dust-grain ionisation, grain penetration into the beam, the consequent perturbation of beam quality, and the mechanisms leading to beam losses.
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