Illustrating Progress Towards Fusion Energy Breakeven and Gain

Achieving sufficiently high energy gain is a requirement for the realization of fusion energy. The figures below illustrate progress towards energy gain and are the main results of a peer-reviewed publication [Physics of Plasmas 29, 062103 (2022); free download at] by ARPA-E Technology-to-Market (T2M) Advisor Sam Wurzel and ARPA-E Program Director Scott Hsu.

ARPA-E Fusion Publication - Figure 1

Caption: Maximum achieved fusion “triple product” for each concept over time.  

ARPA-E Fusion Publication - Figure 2

Caption: Animation of achieved Lawson parameter versus temperature over time. 

In support of T2M for ARPA-E’s fusion programs, the paper seeks to explain to a wide audience, especially potential fusion investors, the key physics requirements for achieving energy breakeven and gain for high-temperature fusion fuel (plasma), as embodied by the fuel density (n), energy confinement time (τE) or confinement time (τ), and temperature (T). Upon publication, the paper held the #1 spot on the journal’s “most read” list (with more than 4,000 views in the first three weeks) and generated much interest among fusion investors, students, and researchers in the field.

The main figures, as well as the introduction and conclusions, are accessible to a non-expert audience, while the bulk of the paper provides a detailed technical review of J. D. Lawson’s original 1955 paper, which first stated the key physics requirements of a “useful” fusion energy system. A video tutorial that summarizes the paper is also available below.