P. Krkotić | Searcharxiv

arXiv2025

Characterising the Surface Resistance of Laser-Treated LHC Beam Screens with the Shielded Pair Method

The presence of strong electron clouds in the quadrupole magnetic field regions of the Large Hadron Collider (LHC) leads to considerable heating that poses challenges for the cryogenic cooling system, and under certain conditions to proton beam quality deterioration. Research is being conducted on laser-treated inner beam screen surfaces for the upgraded High-Luminosity LHC to mitigate this issue. Laser-induced surface structuring, a technique that effectively roughens surfaces, has been shown to reduce secondary electron emission; an essential factor in controlling electron cloud formation. Conversely, the resulting surface roughening also alters the material's surface impedance, potentially impacting beam stability and increasing beam-induced resistive wall heating. Different laser treatment patterns have been applied to LHC beam screens to estimate this potential impact and assessed for their microwave responses.

physics.acc-ph↗

arXiv2025

Influence of nanoparticulates and microgrooves on the secondary electron yield and electrical resistance of laser-treated copper surfaces

Laser surface structuring has proven to be an effective technique for achieving a copper surface with secondary electron yield (SEY) values close to or below unity. However, the attributes that minimize SEY, such as moderately deep grooves and redeposited nanoparticles, may lead to undesirable consequences, including increased radio frequency surface resistance. This investigation systematically examined data about different cleaning procedures designed to eliminate redeposited adsorbed particulates. Various analysis techniques were used iteratively after each consecutive cleaning step, providing insights into the evolving surface characteristics. The collected experimental results identified distinct impacts of microgrooves, groove orientation, and associated particulates on secondary electron yield and surface resistance. Exposing the crests while retaining high particulate coverage in the grooves leads to reduced SEY values and surface resistance, suggesting that the tips of the grooves exert a more significant influence on surface current density than the groove depth. At the same time, nanoparticles in the grooves have a more significant impact on SEY values than the exposed tips at the surface.

physics.acc-ph↗