Lifetime requirements for semiconductor lasers in inertial fusion energy systems

Successful demonstration of fusion ignition at the National Ignition Facility (NIF) has prompted renewed interest in the use of laser-driven inertial fusion energy (IFE) power plants for electricity generation to deliver baseload power to the electrical grid. Baseload power plants must operate at a high plant availability with a reliability aim of over 90%, excluding plant downtime for maintenance events. Additionally, IFE power plants must be capable of decades-long facility operational lifetimes for economic viability to offset the high, upfront capital investment. A promising design for IFE plants employs diode-pumped solid-state lasers (DPSSLs) to drive ignition. The stringent operating requirements for an IFE power plant impose the corresponding requirements on the beamlines and their semiconductor laser pumps. A simplistic flow down might assume that the diode pumps must last the duration of an IFE power plant’s life, necessitating pump lifetimes on the order of 10 to 20 Gshots at continuous, 10 Hz operation for a 30 to 60-year plant life. However, this approach may lead to overly conservative estimates. Plant operating strategies such as line replaceable units (LRUs) successfully deployed on the NIF, and short-duration beamline overdrive can significantly reduce pump lifetime requirements. Moreover, these simplistic approaches do not inform the definition of pump diode lifetime, and do not account for economic impacts of pump diode replacement costs. This paper discusses how pump diode requirements are informed by IFE plant operating requirements, and economic considerations such as plant operating costs. Since pump diode lifetime validation at the 10s of Gshots level can be time-consuming and expensive, this information may be used by laser diode manufacturers planning to support the pathway to commercialization of IFE power plants.