Secondary emission monitor grids for a muon collider proton linear accelerator : a feasibility study

Abstract

A muon collider, capable of reaching centre-of-mass energies beyond 10 TeV, positions itself as a leading candidate for the next generation of particle colliders. Beam instrumentation is essential to ensure reliable monitoring and control of the beam throughout the entire facility. However, the collider’s proton driver subsystem is foreseen to operate at a final energy of 5/10 GeV, delivering 5 × 1014 protons in short bursts at a repetition rate of 5 Hz. This creates an environment that risks damaging traditional interceptive diagnostics, particularly secondary emission monitor (SEM) grids. In light of this challenge, this work assesses thermomechanical feasibility of SEM grids for reliable use in the proposed muon collider proton driver. A staged methodology is adopted, beginning with analytical and Monte Carlo simulations of energy deposition in candidate grid materials (tungsten, tantalum, molybdenum, titanium, silicon carbide, and carbon) across a range of wire diameters. These results establish baseline heat loads for subsequent analyses. A three-dimensional finite element thermoelastic model is developed to simulate coupled thermal and mechanical responses under pulsed energy deposition, and predict various mechanisms of damage. Model validation is carried out through comparison with experimental observations, including a documented thin-foil damage event at CERN’s HiRadMat facility and thermionic emission measurements at CERN LINAC4. Ultimately the validated framework is applied to evaluate the operational performance of SEM grids across beam conditions representative of the proton driver. Results indicate that while metallic wires exhibit narrow operational windows and are prone to melting, yielding, or fracture, fibre-based materials, particularly carbon fibre, offer significantly enhanced resilience, maintaining safe operation across a broader parameter space. This study therefore provides the first systematic mapping of SEM grid feasibility under projected muon collider conditions, offering insights on material and design choices and advancing the understanding of thermomechanical modelling in interceptive instrumentation for high-intensity proton beams.