KSTAR

Overview

The Korea Superconducting Tokamak Advanced Research (KSTAR) device is a pivotal experimental facility in the global effort to develop fusion energy. Located in Daejeon, South Korea, and operated by the Korea Institute of Fusion Energy (KFE), KSTAR is a medium-sized tokamak distinguished by its use of fully superconducting magnets. It was the first tokamak to employ Niobium-tin (Nb3Sn) for its toroidal field (TF) coils, the same conductor technology used in the much larger ITER project. This design choice enables KSTAR to investigate the physics of long-pulse, high-performance plasmas, which are essential for the operation of a future fusion power plant.

The primary mission of KSTAR is to establish the scientific and technological basis for an attractive steady-state fusion reactor. Its research focuses on developing "advanced tokamak" (AT) operating modes. These modes aim to achieve high plasma pressure (high beta) and a high fraction of self-generated bootstrap current, reducing the need for external power to sustain the plasma current. By exploring these AT scenarios in long-pulse discharges, KSTAR directly addresses key challenges for ITER and provides critical data for the design of demonstration power plants (DEMOs).

Physics / Mechanism

KSTAR's design incorporates several advanced features that enable its research mission. The device has a major radius (R) of 1.8 m and a minor radius (a) of 0.5 m, with a plasma elongation (κ) up to 2.0 and triangularity (δ) up to 0.8, allowing for a highly shaped plasma cross-section. This shaping is crucial for achieving high plasma stability and confinement.

Superconducting Magnet System: The core of KSTAR is its magnet system. The 16 TF coils generate a magnetic field of up to 3.5 T on the plasma axis. They are made from Nb3Sn, a superconductor capable of handling high magnetic fields but which is notoriously brittle and complex to manufacture. The poloidal field (PF) coil system, which shapes and controls the plasma, uses Niobium-titanium (NbTi). The entire magnet system is cooled by supercritical helium to 4.5 K. This superconducting nature eliminates resistive power losses in the magnets, allowing for pulse lengths of up to 300 seconds at full field and current, a capability far beyond that of comparable copper-magnet machines.

Heating and Current Drive: To heat the plasma to fusion-relevant temperatures (over 100 million K), KSTAR employs a suite of auxiliary heating systems. As of the mid-2020s, these include:

Neutral Beam Injection (NBI): Two NBI systems inject high-energy neutral deuterium atoms into the plasma, providing a total power of up to 13 MW. NBI is a primary source of both heating and non-inductive current drive.
Electron Cyclotron Heating (ECH): A high-frequency microwave system operating at 105 and 140 GHz delivers power directly to the electrons. ECH is used for core electron heating, current drive, and for suppressing magnetohydrodynamic (MHD) instabilities like neoclassical tearing modes (NTMs).
Ion Cyclotron Heating (ICH): This system uses radio-frequency waves to heat plasma ions. It provides an additional source of bulk ion heating.

The combination of these systems allows for flexible control over the plasma temperature and current profiles, which is essential for exploring and optimizing advanced tokamak scenarios.

Plasma Facing Components: The initial configuration of KSTAR used carbon tiles for its plasma-facing components (PFCs). While robust, carbon has issues with tritium retention. In the early 2020s, KSTAR underwent a major upgrade to install a tungsten divertor, similar to the one planned for ITER. Tungsten has a higher melting point and lower fuel retention than carbon, but it is a high-Z material, meaning impurities in the core plasma can lead to significant radiation losses. Managing plasma-wall interactions with the new tungsten divertor is a key research area.

Historical Development

The KSTAR project was officially initiated in 1995 as a flagship of the Korean National Fusion Program. The primary goal was to secure core technologies for fusion energy and to contribute to the international ITER project. The design phase leveraged international collaboration, but the construction and fabrication were largely a domestic effort, developing South Korea's industrial capacity in advanced manufacturing.

Key milestones include:

1995: KSTAR project officially launched.
2001-2007: Construction of the device and its subsystems. This period saw significant R&D in Nb3Sn cable-in-conduit conductor technology.
2008: First plasma was achieved on July 15, marking the successful commissioning of the world's first fully superconducting tokamak with Nb3Sn TF coils.
2010: Achieved H-mode (high-confinement mode), a critical operating regime for high fusion performance.
2016: KSTAR achieved a 70-second-long H-mode discharge, a world record at the time for this type of plasma.
2018: Reached an ion temperature of 100 million K for the first time.
2021: Sustained a plasma at an ion temperature exceeding 100 million K for 30 seconds, demonstrating significant progress in integrating high temperature with long-pulse operation.
2023-2024: Major shutdown for the installation of a full tungsten divertor and upgrades to the NBI heating system.

These achievements have progressively pushed the boundaries of long-pulse plasma operation, providing invaluable data on the stability and control of steady-state plasmas.

Current Status

As of early 2026, KSTAR is operating with its newly installed tungsten divertor and enhanced heating capabilities. The primary research campaigns are focused on demonstrating the KSTAR research goal of 300-second H-mode operation with an ion temperature greater than 100 million K. This objective requires the simultaneous optimization of plasma heating, current drive, stability control, and plasma-wall interaction management.

Experiments are heavily focused on mitigating the challenges associated with the tungsten PFCs. This includes developing techniques for divertor heat flux control, such as detached divertor operation, and preventing tungsten impurity accumulation in the plasma core. The upgraded NBI system and refined ECH control are being used to develop robust, fully non-inductive current drive scenarios that meet the criteria for the Lawson criterion in a steady state.

KSTAR also serves as a critical testbed for ITER-relevant technologies and operating scenarios. Joint experiments are frequently conducted with international partners to validate plasma control strategies and physics models that will be deployed on ITER. The operational experience with the superconducting magnet system continues to be a unique and vital source of data for the fusion community.

Notable Implementations

KSTAR is the central facility of the [/programs/korean-national-fusion-program](Korean National Fusion Program), which is managed by the Korea Institute of Fusion Energy (KFE). KFE is the sole operator of the device and leads the domestic research program, which involves extensive collaboration with South Korean universities and industries.

Internationally, KSTAR is a key partner in the global fusion research network. It has formal collaboration agreements with major fusion laboratories, including:

ITER Organization: KSTAR provides direct experimental data to validate ITER's design and operational plans, particularly concerning long-pulse operation, disruption mitigation, and NTM control.
Princeton Plasma Physics Laboratory (PPPL), USA: A long-standing collaboration focuses on areas like MHD stability, plasma control, and diagnostics.
National Institutes for Quantum Science and Technology (QST), Japan: Collaboration with the JT-60SA project allows for comparative studies between two large superconducting tokamaks.
EUROfusion Consortium, EU: Researchers from European labs frequently participate in KSTAR experiments, contributing to a shared knowledge base for DEMO design.

This collaborative structure ensures that the results from KSTAR have a broad impact, accelerating the overall pace of fusion energy development.

Open Challenges

Despite its successes, KSTAR faces several significant scientific and engineering challenges in its quest for 300-second, high-performance operation.

Integrated Scenario Development: Achieving high temperature, high density, and high confinement simultaneously for long durations remains a formidable challenge. These parameters are often in tension; for example, high-density regimes required for heat flux mitigation can sometimes lead to degraded confinement. Integrating all required conditions into a stable, steady-state scenario is the primary physics challenge.
Plasma-Wall Interactions: The new tungsten divertor presents a major challenge. While it solves the fuel retention problem of carbon, it introduces the risk of core plasma contamination. A small amount of tungsten in the plasma core can radiate away a large fraction of the heating power, quenching the discharge. Developing reliable methods to control tungsten sputtering and transport is critical.
MHD Stability in Steady State: Over long pulses, subtle instabilities that are benign in short-pulse machines can grow to become disruptive. Neoclassical tearing modes (NTMs) are a particular concern in high-beta, steady-state scenarios. While KSTAR has demonstrated successful NTM suppression with ECH, optimizing these techniques for 300-second discharges is an ongoing effort.
Heating and Current Drive Efficiency: Achieving 100% non-inductive current drive requires a precise combination of bootstrap current and externally driven current from NBI and ECH systems. Maximizing the efficiency and synergy of these systems to drive current in the desired plasma locations is a complex control problem.

Outlook

The credible 5-15 year trajectory for KSTAR is centered on fully realizing its design potential and solidifying its role as a leading research facility for ITER and DEMO. In the near term (next 5 years), the primary goal is to achieve the 300-second, 100-million-K operational target. Success in this endeavor would represent a landmark achievement in fusion research, demonstrating a level of plasma control and sustainment approaching that required for a power plant.

Looking further ahead (5-15 years), KSTAR is expected to transition its focus towards more DEMO-relevant research. This will likely include testing advanced divertor concepts beyond the current tungsten design, exploring novel plasma control algorithms using AI and machine learning, and investigating the physics of burning plasmas by studying the behavior of high-energy alpha particles using surrogate ion populations. KSTAR will also play a crucial role in developing and testing components for the Korean DEMO design, which aims for construction in the 2040s. The facility's unique long-pulse capabilities ensure that it will remain at the forefront of steady-state tokamak research for the foreseeable future, providing essential data to bridge the gap between ITER and commercial fusion energy.

References

Overview of KSTAR research progress and future plans — Nuclear Fusion (2021)
KSTAR: The instrument for advanced fusion plasma research — Fusion Engineering and Design (2007)
First plasma in the KSTAR superconducting tokamak — Nuclear Fusion (2009)
A new world record for KSTAR — ITER Organization Newsline (2021)
KSTAR reports new plasma record: 20 seconds at 100 million °C — Phys.org (2020)
Upgrade of KSTAR for long-pulse high-performance plasma operation — Fusion Engineering and Design (2023)
Development of steady-state operation scenarios in KSTAR — Plasma Physics and Controlled Fusion (2022)