Heat balance in the capillary as critical component of laser–plasma electron accelerator

Laser wakefield accelerators (LWFAs) provide a transformative approach to compact, high-energy particle acceleration by harnessing the intense electric fields generated in plasma wakefields driven by high-intensity laser pulses. In the laser-based electron accelerators utilizing a preformed plasma channel, an electrical discharge within a capillary generates a stable and uniform plasma prior to the arrival of the laser pulse, facilitating efficient laser propagation and wakefield formation. Operating at high repetition rates, such as 100 Hz, is crucial for practical applications. Achieving stable plasma formation at such high repetition rates presents significant thermal challenges due to the intense heat loading on the capillary. The repeated energy deposition from electrical discharges and/or laser–plasma interactions causes potentially rapid temperature rises, material stress, and potential degradation of the capillary structure. Understanding and mitigating heat loading effects are vital for optimal capillary design, ensuring long-term operational stability and advancing the scalability of LWFAs. This article examines the mechanisms of heat loading in discharge capillaries, the related thermal management challenges. There are two types of heat balance. The first one corresponds to the mean heat balance averaged over the many repetition periods. The second type corresponds to the damages caused by single-shot pulsed energy deposition in the capillary. For both cases, we consider energy (or heat) income caused by the driving laser pulse. The extra heat caused by the electrical discharge, if it occurs, gives relatively lower energy output.