Twenty years of research on the SUNIST spherical tokamak

TAN, Yi; GAO, Zhe; ZENG, Long; the SUNIST Group

Tsinghua University
Beijing, China
Email: tanyi@tsinghua.edu.cn

Web edition · October 2026 · adapted from the review manuscript by TAN Yi, GAO Zhe, ZENG Long and the SUNIST Group.

Abstract

The spherical tokamak SUNIST developed by Tsinghua University and Institute of Physics, Chinese Academy of Sciences has achieved remarkable progress over the past 20 years. With its compact design and advantageous confinement scaling, the spherical tokamak continues to hold promise as an attractive candidate for future fusion reactors. This review summarises key findings and technological innovations from two decades of research on SUNIST. The improved plasma performance through upgrades, unique physics phenomena observed, and advanced diagnostic systems developed are highlighted.

Editor's note (2026). This review reflects the status at the time of writing (2022). SUNIST-2 has since achieved first plasma on 12 March 2023 and is now in operation; see the SUNIST-2 page for current results.

Introduction

The spherical tokamak (ST) represents a pivotal diversion from conventional tokamak designs, characterized by a significantly reduced aspect ratio and a compact, spherical vacuum vessel. With the promise of superior confinement and stability properties, the concept has drawn significant attention from the magnetic confinement fusion community. Capitalizing on these advances, Tsinghua University and Institute of Physics, Chinese Academy of Sciences decided to construct China's first spherical tokamak. Named the Sino UNited Spherical Tokamak (SUNIST), the ambitious project was launched in 1999. After three years of intense engineering and construction, SUNIST successfully achieved first plasma on November 4, 2002[1]. Over the past 20 years, SUNIST has made important contributions to the understanding of ST physics and technology. Key findings include the observation of good confinement at low aspect ratio and mechanisms for density limit disruptions unique to the ST geometry. With a thriving diagnostic development program, SUNIST has also served as an invaluable hands-on education platform for training fusion researchers. This series reviews the scientific journey of SUNIST over two decades of operation.

In this series

Eight chapters on two decades of SUNIST

The review is published here as a linked series of pages, each focused on one part of the SUNIST story. Figures and equations are taken from the manuscript.