Globus-M2

Overview

Globus-M2 is a spherical tokamak (ST) operated by the Ioffe Physical-Technical Institute of the Russian Academy of Sciences. As an upgrade to its predecessor, Globus-M, it is distinguished by its ability to operate at a significantly higher toroidal magnetic field (up to 1.0 T) than other STs of comparable size. This capability allows the exploration of plasma confinement and stability in a regime that bridges the gap between conventional low-field spherical tokamaks and higher-field, larger aspect ratio devices like the tokamak. The primary scientific mission of Globus-M2 is to investigate the physics of high-beta plasmas under reactor-relevant conditions in a compact geometry. Its research program focuses on transport, magnetohydrodynamic (MHD) stability, plasma-wall interactions, and the development of plasma heating and current drive scenarios. The results from Globus-M2 are intended to inform the design of next-generation devices, including compact fusion neutron sources (FNS) and demonstration fusion power plants based on the ST concept.

Physics / Mechanism

The Globus-M2 design is centered on the principle that increasing the toroidal magnetic field in a spherical tokamak can lead to substantially improved plasma performance. The Lawson criterion for fusion, which defines the required product of density, temperature, and confinement time (n·τ·T), scales favorably with the magnetic field. In a tokamak, energy confinement time (τ_E) generally increases with both plasma current (I_p) and toroidal magnetic field (B_t). According to scaling laws for STs, τ_E is proportional to I_p and B_t. The maximum achievable plasma current is itself proportional to the magnetic field. Therefore, doubling the magnetic field, as was done in the transition from Globus-M (0.5 T) to Globus-M2 (1.0 T), is predicted to quadruple the energy confinement time and allow for a significant increase in achievable plasma temperature and density [1].

Globus-M2's low aspect ratio (A = R/a ≈ 1.5) provides intrinsic advantages, such as high plasma beta (the ratio of plasma pressure to magnetic pressure) and a naturally elongated plasma shape, which are beneficial for stability and confinement. The combination of this compact geometry with a high magnetic field allows Globus-M2 to access a unique operational space. The device aims to achieve ion temperatures of several keV and plasma densities in the range of 10^20 m^-3. To reach these parameters, it employs a suite of auxiliary heating systems, including two Neutral Beam Injectors (NBI), Ion Cyclotron Resonance Heating (ICRH), and Electron Cyclotron Resonance Heating (ECRH). This multi-faceted heating approach enables detailed studies of energy transport and the effectiveness of different heating schemes in a high-field ST environment.

Historical Development

The development of Globus-M2 is an evolution of the spherical tokamak program at the Ioffe Institute, which began with the Globus-M device. Globus-M was commissioned in 1999 and operated for over 15 years, establishing itself as a key facility in the international ST research community [2]. It achieved a toroidal field of up to 0.5 T and a plasma current of 0.25 MA, providing valuable data on plasma behavior in low-aspect-ratio configurations.

By the early 2010s, the scientific case for a higher-field ST was well-established. The plan to upgrade Globus-M to Globus-M2 was formulated to push the boundaries of achievable plasma parameters within the existing infrastructure. The primary goal was to double the magnetic field, which required a complete redesign of the central solenoid and the toroidal field coils. This was a significant engineering challenge due to the tight space constraints of the ST's central column. The new central solenoid was designed to handle higher currents and stresses, and the toroidal field coil was manufactured from a tellurium copper alloy to achieve the required strength and conductivity [3].

Decommissioning of Globus-M began in 2016, followed by the assembly of the new Globus-M2 magnetic system. The upgrade also included enhancements to the vacuum vessel, power supplies, and plasma heating and diagnostic systems. The first plasma in Globus-M2 was successfully achieved in the spring of 2018. The initial experimental campaigns focused on commissioning the new systems and demonstrating operation at the increased magnetic field and plasma current. The project was led by a team at the /programs/ioffe-institute, with key contributions from other Russian research institutions.

Current Status

As of 2026, Globus-M2 is fully operational and conducting regular experimental campaigns. It has successfully demonstrated stable operation at its design parameters, including a toroidal magnetic field of 1.0 T and a plasma current of 0.5 MA [4, 5]. The auxiliary heating systems, including the upgraded NBI and RF systems, are routinely used to heat the plasma to high temperatures. Recent experimental results have confirmed the expected improvements in plasma confinement. The device has achieved ion temperatures exceeding 2 keV and central electron densities approaching 1.5 × 10^20 m^-3, representing a significant step towards reactor-relevant conditions for a device of its scale [6].

The research program is focused on several key areas. One major thrust is the study of L-H mode (low- to high-confinement mode) transitions in a high-field ST. Achieving and sustaining H-mode is critical for future fusion reactors, and Globus-M2 provides a unique platform to study the power threshold and physics of this transition at high magnetic fields and densities. Another area of active research is the study of energetic particle physics, driven by the NBI systems, and its interaction with MHD instabilities. The facility's comprehensive set of diagnostics allows for detailed measurements of plasma profiles, fluctuations, and energy transport, providing data for validating theoretical models and simulation codes.

Notable Implementations

Globus-M2's design incorporates several advanced engineering solutions that enable its high-performance capabilities. The most critical component is its magnetic system. The central solenoid, which drives the plasma current, and the single-turn toroidal field coil are tightly integrated into a compact central column. This assembly was engineered to withstand the immense electromagnetic forces generated during 1.0 T operation. The toroidal field coil conductor is made from a high-strength, high-conductivity chrome-tellurium bronze alloy, a key material choice for managing the thermal and mechanical loads [3].

The plasma heating and current drive systems are another core feature. The device is equipped with two neutral beam injectors. The primary NBI operates at 34 keV with 1 MW of power, while a second, more compact injector provides additional heating. The RF heating capabilities are extensive, including a 1 MW ICRH system and a 1 MW ECRH system based on a 2.45 GHz magnetron, which is used for plasma start-up and electron heating [7]. This combination of heating methods provides experimental flexibility to control plasma temperature and current profiles.

The diagnostic suite on Globus-M2 is comprehensive, featuring Thomson scattering for electron temperature and density profiles, charge exchange recombination spectroscopy for ion temperature and rotation, a heavy ion beam probe for plasma potential measurements, and an array of magnetic probes and flux loops. These tools provide the high-resolution data necessary to investigate complex plasma phenomena and validate the performance enhancements predicted for a high-field ST.

Open Challenges

Despite its successes, Globus-M2 faces several scientific and engineering challenges. A primary challenge is managing the high heat and particle fluxes to the plasma-facing components, particularly the divertor. The compact geometry of an ST concentrates power exhaust into a small area. While Globus-M2 operates with relatively short pulse lengths (up to 0.3 s), developing and testing advanced divertor concepts and materials capable of handling reactor-level heat loads remains a critical research area. This work is directly relevant to the design of future devices that will require steady-state or long-pulse operation.

Another significant challenge is achieving and sustaining stable high-beta plasmas for extended periods. While STs are theoretically capable of reaching high beta, plasmas can be susceptible to various MHD instabilities, such as neoclassical tearing modes (NTMs) and resistive wall modes (RWMs), which can degrade confinement or terminate the discharge. The Globus-M2 program is actively investigating methods to control these instabilities, but further research is needed to develop robust control schemes for a reactor scenario.

Finally, non-inductive current drive is a key challenge for the long-term viability of the ST concept. Future ST-based power plants will need to operate in a steady state, which requires driving the majority of the plasma current non-inductively. While Globus-M2 explores some aspects of this with its NBI and RF systems, achieving a high non-inductive current fraction in a high-density, high-temperature plasma is a complex problem that requires further development of efficient current drive methods. The limited pulse length of the device restricts the extent to which steady-state scenarios can be fully investigated.

Outlook

The credible 5-15 year trajectory for Globus-M2 and its research program is focused on solidifying the physics basis for a compact, high-field spherical tokamak as a viable path toward a fusion power plant. In the near term (5 years), the facility will likely focus on maximizing its performance parameters, aiming to push ion and electron temperatures higher and extend pulse duration. A key goal will be the routine achievement and detailed characterization of stable H-mode operation at the highest possible magnetic field and plasma current. This includes systematic studies of the L-H transition power threshold and the behavior of edge localized modes (ELMs) in this unique regime.

Over the medium term (5-10 years), research will likely shift towards more reactor-relevant challenges. This includes the installation and testing of upgraded plasma-facing components and divertor solutions to better manage heat exhaust. Experiments will increasingly focus on integrated scenarios, combining high-beta operation with active instability control and significant non-inductive current fractions. The data gathered will be crucial for benchmarking and validating advanced simulation codes, improving their predictive capability for next-step devices.

In the longer term (10-15 years), the results from Globus-M2 will directly inform the design of a next-generation facility, such as a Fusion Neutron Source (FNS) or a prototype compact power plant. The successful demonstration of stable, high-confinement plasmas in Globus-M2 would significantly de-risk the ST concept and could accelerate the development of compact fusion energy systems. The facility will continue to serve as a valuable platform for training the next generation of fusion scientists and engineers, ensuring the continuity of expertise in this promising area of fusion research.

References

1. First results of the Globus-M2 tokamak operation at increased magnetic field — Nuclear Fusion (2019)
2. The Globus-M spherical tokamak: design, main parameters and results of the first experiments — Nuclear Fusion (2001)
3. Globus-M2 spherical tokamak: design and construction — Fusion Engineering and Design (2018)
4. Overview of the first experimental results on the Globus-M2 tokamak — Plasma Physics and Controlled Fusion (2021)
5. Globus-M2 Spherical Tokamak: From Ohmic to High-Performance Discharges — Journal of Fusion Energy (2023)
6. Recent results from the Globus-M2 spherical tokamak — IAEA Fusion Energy Conference (2021)
7. First experiments on plasma start-up by a 2.45 GHz magnetron at the Globus-M2 spherical tokamak — Nuclear Fusion (2021)