Multiphysics Simulations of Thermal Shock Testing of Nanofibrous High Power Targets

TL;DR

This paper uses multiphysics simulations to investigate thermal shock failure in nanofiber targets, revealing that reduced permeability in high-density samples causes pressure buildup and damage.

Contribution

It introduces a multiphysics simulation approach to identify the cause of failure in nanofiber targets under thermal shock conditions.

Findings

High-density samples exhibit major damage due to pressure buildup.

Lower density samples show no apparent damage.

Failure is linked to reduced permeability and air flow restriction.

Abstract

Increase of primary beam power for neutrino beam-lines leads to a reduced lifespan for production targets. New concepts for robust targets are emerging from the field of High Power Targetry (HPT); one idea being investigated by the HPT R&D Group at Fermilab is an electrospun nanofiber target. As part of their evaluation, samples with different densities were sent to the HiRadMat facility at CERN for thermal shock tests. The samples with the higher density, irradiated under a high intensity beam pulse, exhibit major damage at the impact site whereas those with the lower density show no apparent damage. The exact cause of this failure was unclear at the time. In this paper, we present the results of multiphysics simulations of the thermal shock experienced by the nanofiber targets that suggest the failure originates from the reduced permeability of the high density sample to air flow. The air present in the porous target expands due to heating from the beam, but is unable to flow freely in the high density sample, resulting in a larger back pressure that blows apart the nanofiber mat. We close with a discussion on how to further validate this hypothesis.