Improved Ion Heating in Fast Ignition by Pulse Shaping

TL;DR

This paper introduces a novel pulse shaping technique for fast ignition in inertial fusion, significantly improving ion heating efficiency and reducing ignition energy by over 20%.

Contribution

It presents an analytical model and a new pulse shape that optimizes ion heating, surpassing traditional constant-power pulses in fast ignition.

Findings

Optimized pulse shape enhances ion heating efficiency.

Reduced ignition energy by over 20%.

Allows for smaller hotspots, improving fusion gain.

Abstract

The fast ignition paradigm for inertial fusion offers increased gain and tolerance of asymmetry by compressing fuel at low entropy and then quickly igniting a small region. Because this hotspot rapidly disassembles, the ions must be heated to ignition temperature as quickly as possible, but most ignitor designs directly heat electrons. A constant-power ignitor pulse, which is generally assumed, is suboptimal for coupling energy from electrons to ions. Using a simple model of a hotspot in isochoric plasma, a novel pulse shape to maximize ion heating is presented in analytical form. Bounds are derived on the maximum ion temperature attainable by electron heating only. Moreover, arranging for faster ion heating allows a smaller hotspot, improving fusion gain. Under representative conditions, the optimized pulse can reduce ignition energy by over 20%.