Numerical study of the cryogenic cooling of amplifiers for high power lasers

TL;DR

This study uses Large Eddy Simulations to analyze cryogenic helium cooling of high-power laser amplifiers, focusing on heat exchange and turbulent flow to improve beam quality.

Contribution

It provides detailed numerical modeling of cryogenic helium cooling in laser amplifiers, including validation against existing data and simulation of turbulent flow.

Findings

Validated LES approach for cryogenic helium flow

Characterized turbulent heat transfer in amplifier cooling

Insights into thermal boundary layer development

Abstract

The French collaborative Trio4CLF project aims to understand and control the cryogenic cooling of amplifiers for high power (~1 PetaWatt) and high repetition rate (1-10 Hertz) lasers. In such amplifiers, the fluid (low temperature gaseous helium) evacuates the thermal power absorbed by the solid amplifying plates. A precise knowledge of the heat exchange and of the turbulent fluid flow in the amplifier is requested to evaluate its impact on the laser beam quality. Large Eddy Simulations representative of the amplifier cooling are performed using TrioCFD, a code developed by the CEA. First, validation simulations are carried out for heated periodic channel flows, allowing comparisons with Direct Numerical Simulation results from the literature. They are conducted using conjugate heat transfer calculation between the fluid and the solid. The channel flow is turbulent, with a bulk Reynolds number (based and the bulk velocity and the total height of the channel) of about 14000. Large Eddy Simulation of a heated open turbulent cryogenic helium flow with developing thermal boundary layers is then presented.