Beam screen issues

TL;DR

This paper discusses the challenges related to beam screen issues in the High Energy LHC, focusing on the effects of using 20 T dipole magnets and their impact on material resistivity and surface resistance at high energies.

Contribution

It analyzes the magneto-resistance and anomalous skin effect mechanisms affecting beam screen performance with high-field dipoles in the HE-LHC.

Findings

Magneto-resistance increases material resistivity at high magnetic fields.

Anomalous skin effect causes increased surface resistance at low temperatures.

These effects impact the design and operation of beam screens in high-energy accelerators.

Abstract

In the High Energy LHC (HE-LHC), a beam energy of about 16.5 TeV is currently contemplated. The beam screen issues linked to the use of 20 T dipole magnets instead of 8.33 T are discussed, with a particular emphasis on two mechanisms, the magneto-resistance and the anomalous skin effect, assuming the nominal machine and beam parameters. The magneto-resistance effect always leads to an increase of the material resistivity (as the mean free path in the presence of a transverse magnetic field becomes smaller). As concerns the anomalous skin effect, the anomalous increase of surface resistance of metals at low temperatures and high frequencies is attributed to the long mean free path of the conduction electrons: when the skin depth becomes much smaller than the mean free path, only a fraction of the conduction electrons moving almost parallel to the metal surface is effective in carrying the current and the classical theory breaks down.