ALICE FoCal pixel layer update

• Max Philip Rauch (University of Bergen (NO))

ALICE FoCal (Forward Calorimeter) is planned to be installed at ALICE for data taking starting from 2029. The detector, featuring an electromagnetic Si-W sampling calorimeter and a hadronic Cu-scintillating fiber spaghetti calorimeter, is designed and optimized for the measurement of forward isolated photons at pseudo-rapidities between 3.0 and ~5.8, in order to measure the parton distribution functions at low-x (x < 1e-4). The University of Bergen group develops two pixel layers with ALPIDE monolithic active pixel sensors for the electromagnetic calorimeter. These pixel layers will be used for discrimination against the background from two-gamma events from pi0 decays by providing the two-shower separation information. This talk gives an update on recent activities and beam test results.

Modelling of fast beam-ion instability in future accelerators

• Fredrik Sommerfelt Groenvold (Norwegian University of Science and Technology (NTNU) (NO))

Future accelerators such as the compact linear collider is expected to be vulnerable to fast beam-ion instability (FBII) due to their high beam intensity and small transverse beam size. Unlike classical ion instability, FBII manifests along the length of the bunch train which means that it can arise in linear accelerators (LINAC) as well as circular accelerators. Ions are generated through the beam's interaction with the gases present in the beam duct and induce a coherent motion of the bunches which causes the beam to become unstable. The numerical macroparticle modelling tools PyECLOUD and PyHEADTAIL have previously been used to study fast beam-ion instability in the CLIC damping ring. In this project the numerical modelling tools have been applied for studying the effects of residual gas pressure in the CLIC main LINAC. Simulations setups with multiple species gas composition have been tested and the ion generation process has been updated to handle electric field ionisation.