Plasma Ramp-up and Sustainment Scenarios for Tokamak Energy’s Fusion Pilot Plant

Tokamak Energy Ltd., Milton Park, Oxfordshire, OX14 4SD United Kingdom

^* Corresponding author: yuichi.takase@tokamakenergy.com

Published online: 7 January 2026

Abstract

Tokamak Energy is designing a Fusion Pilot Plant under the US Department of Energy’s Milestone-Based Fusion Development Program. Tokamak Energy’s Fusion Pilot Plant is based on low aspect ratio tokamak with high-temperature superconducting coils, exploiting the potential to access high confinement, high beta, and high bootstrap current fraction. Representative parameters used in the present modelling are: major radius R0 = 4.25 m, aspect ratio A = 2.15, toroidal field Bt = 4.0 T, and plasma current Ip = 13.6 MA. Since the flux swing capability of the central solenoid (CS) is not sufficient to reach full Ip, a novel Ip ramp-up and sustainment scenario utilising RF power (EC and IC), bootstrap current, and induction by the CS and other poloidal field coils was developed. The plasma is initiated with EC power injected to the “trapped particle configuration”. Following initial ECCD overdrive with CS assist at low density, plasma is densified and ion heating by IC is applied to initiate fusion burn. The increased plasma stored energy drives the bootstrap current, and additional ramp-up to full Ip is achieved with inductive assist from the increasing vertical field. Optimisation of the CS usage during Ip ramp-up is essential to achieve quick Ip ramp-up with minimal use of the CS flux.