Designing tungsten armoured plasma facing components to pulsed heat loads in magnetic fusion machines

TL;DR

This paper proposes a design rule for tungsten plasma facing components in fusion machines to prevent surface damage from thermal transients, based on experiments and engineering principles, aiding in component lifetime management.

Contribution

It introduces a novel, formulation-based design rule for tungsten components that combines loads of different magnitudes and cycles, enhancing durability predictions.

Findings

Allows 2.10^4 transient heat load cycles at a FHF of 10 MJm^{-2}s^{-1/2}

Provides a practical example of load combination and design application

The rule is valid only for surface loading conditions, not volumetric loads.

Abstract

A possible design rule for preventing surface damage from thermal transients to solid tungsten armour is proposed and formulated for the plasma facing components (divertor, first wall) of magnetic fusion machines. The rule is based on combined results from laboratory experiments and operating fusion machines, and fundamental engineering principles such as the heat flux factor (FHF) and fatigue usage fraction (FUF). As an example, the rule would allow 2.10 4 transient heat loads cycles at a FHF of 10 MJm${}^{-2}$s${}^{-\frac{1}{2}}$ before the lifetime is considered exhausted. The formulation of the rule using engineering principles allows combining loads of different magnitudes and various number of cycles. A practical example of the rule usage is provided, illustrating loads combination and how the rule may contribute to the component geometrical design. The proposed rule is only valid for surface loading conditions, hence is not usable for volumetric loading conditions such as runaway electrons. Setting a budget lifetime and a design rule does not preclude actual plasma operation beyond the design lifetime. It is actually normal that experimental devices explore a larger domain than the one defined at the time of the design.