Italian Divertor Test Tokamak (DTT)

Overview

The Italian Divertor Test Tokamak (DTT) is a major European fusion research facility designed to address one of the most critical challenges for a future fusion power plant: the management of extreme heat and particle fluxes exhausted from the core plasma. As a dedicated satellite facility within the EUROfusion roadmap, DTT's primary objective is to develop and test divertor solutions capable of withstanding the heat loads anticipated in a Demonstration Power Plant (DEMO). These loads are projected to reach steady-state values of 10–20 MW/m², a significant step beyond the conditions expected in ITER. By operating in a plasma environment with reactor-relevant power densities and plasma parameters, DTT will provide an integrated test bed for qualifying divertor technologies, materials, and operational scenarios, thereby bridging a critical gap between ITER and the first generation of fusion power plants.

Physics / Mechanism

DTT is a high-field (6 T), high-current (5.5 MA) superconducting tokamak designed for operational flexibility. Its core mission revolves around the physics of the plasma edge and the scrape-off layer (SOL), the region where plasma particles are channeled out of the confined core and onto the divertor targets. The machine is designed to achieve a high power-to-major-radius ratio (P/R ≈ 22 MW/m), a key figure of merit for replicating the SOL and divertor conditions of a larger reactor like DEMO.

The DTT heating system will deliver up to 45 MW of auxiliary power through a combination of Electron Cyclotron Resonance Heating (ECRH), Ion Cyclotron Resonance Heating (ICRH), and Neutral Beam Injection (NBI). This substantial power input is essential for generating the high parallel heat flux (q∥) in the SOL that is characteristic of a reactor. The device's magnetic configuration is highly flexible, allowing for the exploration of various divertor geometries, including conventional single-null (SN) and advanced configurations like the double-null (DN) and snowflake divertors.

The central challenge is to dissipate the exhaust power before it reaches the solid target plates. DTT will investigate techniques for achieving a detached divertor regime, where a significant fraction of the power is radiated away through impurity seeding (e.g., with nitrogen or neon) in the divertor volume. This process creates a cold, dense plasma cushion in front of the targets, reducing the incident heat flux and mitigating erosion. The DTT design allows for the replacement of the entire divertor cassette, enabling the testing of different target materials (primarily tungsten) and cooling technologies, such as high-pressure water cooling and advanced concepts like helium cooling. The machine's long-pulse capability (up to 1000 s) is crucial for studying long-timescale phenomena like material migration, erosion, and tritium retention, which are critical for the lifetime and safety of reactor components.

Historical development

The concept for a dedicated divertor test facility emerged from the European fusion community's long-term planning for DEMO. The EUROfusion roadmap, established in the mid-2010s, identified power exhaust as a critical mission that required a dedicated experimental device beyond ITER. While ITER will test a tungsten divertor, its operational parameters and pulse length are not sufficient to fully qualify a component for the sustained, high-performance conditions of a commercial power plant.

In 2015, Italy, through its national agency for new technologies, energy, and sustainable economic development (ENEA), formally proposed to host and construct such a facility. The proposal leveraged Italy's extensive experience in fusion technology, particularly in superconductivity and plasma-facing components, developed through its contributions to projects like JET, ITER, and the Frascati Tokamak Upgrade (FTU). The DTT project was officially launched following a competitive site selection process within Italy, with the ENEA Frascati Research Center chosen in 2018.

The project is structured as a public-private partnership. The implementing body, DTT Scarl, is a consortium led by ENEA with participation from Italian universities and industrial partners. Initial funding was secured from the Italian government, with subsequent significant financial support from the European Investment Bank (EIB) and EUROfusion. The conceptual design was completed in 2019, followed by the finalization of the engineering design. Ground was broken for the main tokamak building in 2023, marking the formal start of the construction phase.

Current status

As of early 2026, the DTT project is in the advanced construction and procurement phase. Civil engineering works for the main tokamak hall and auxiliary buildings at the Frascati site are well underway. The procurement of major components is proceeding in parallel, representing a significant industrial effort across Europe.

Key procurements include the superconducting magnets, which are a central technology of the device. The 18 Toroidal Field (TF) coils, using Nb3Sn conductors, and the 6 Poloidal Field (PF) coils, using NbTi, are under fabrication by industry. The vacuum vessel, a double-walled stainless steel structure, is also in production. Contracts have been awarded for the powerful heating systems, cryoplant, and power supplies. The first full-scale prototype of the tungsten monoblock divertor target, the component at the heart of the DTT mission, has undergone high-heat-flux testing to validate its manufacturing and performance. The project remains on schedule for the start of integrated commissioning in the late 2020s, with the first plasma operation anticipated around 2029–2030.

Notable implementations

The DTT project is executed by DTT Scarl, a purpose-built consortium company. The primary stakeholders and implementers are:

ENEA: Italy's National Agency for New Technologies, Energy and Sustainable Economic Development is the host institution and main shareholder, providing the site, scientific leadership, and significant technical expertise.
EUROfusion: The European Consortium for the Development of Fusion Energy provides scientific and technical oversight as part of the European Roadmap to Fusion Energy. It also co-funds the scientific exploitation phase.
Industry: A broad consortium of industrial partners, primarily from Italy and Europe, is responsible for the manufacturing of all major DTT components. Key players include ASG Superconductors for the magnets and Walter Tosto for the vacuum vessel. This industrial involvement is crucial for developing the supply chain necessary for future fusion power plants.
European Investment Bank (EIB): The EIB has provided substantial loan financing, underscoring the project's strategic importance for European energy and technology policy.

Open challenges

Despite significant progress, DTT faces several scientific and engineering challenges that its experimental program is designed to address:

Integrated Divertor Scenarios: Achieving and maintaining a stable, fully detached divertor regime at DEMO-relevant heat fluxes is the primary scientific challenge. This requires precise control of impurity seeding, plasma density, and magnetic geometry in an integrated system.
Material Performance and Lifetime: The divertor targets must withstand not only high steady-state heat loads but also transient events like edge-localized modes (ELMs), which can deposit immense energy in milliseconds. Understanding and predicting the long-term evolution of tungsten surfaces under these conditions, including erosion, re-deposition, and neutron-induced damage (though DTT is not a nuclear facility, it will inform material choices for nuclear environments), is critical.
Tritium Retention: As DTT will have the capability to operate with Deuterium-Tritium (D-T) plasmas in its later research phases, minimizing tritium retention in the plasma-facing components is a key safety and fuel-cycle challenge. The machine will test techniques for tritium removal and inventory control.
Superconducting Magnet Technology: DTT employs advanced Nb3Sn superconducting magnets to achieve its high toroidal field. The construction, assembly, and reliable operation of this large-scale, high-field magnet system represent a significant engineering undertaking.
Diagnostics and Control: Developing robust diagnostic systems that can survive the harsh environment of the divertor region and provide real-time measurements for feedback control is essential for the successful execution of the DTT research plan.

Outlook

The credible 5-15 year trajectory for DTT is focused on construction, commissioning, and the initial phases of scientific operation. Over the next 5 years (to ~2031), the project will complete construction and assembly, followed by integrated commissioning of all plant systems. The first plasma is expected at the end of this period, marking the start of the operational phase.

The subsequent 10 years will be dedicated to a staged experimental program. The initial deuterium plasma campaigns will focus on qualifying the first divertor configuration and establishing the operational space of the machine. This will involve systematically exploring the parameter range for achieving divertor detachment and characterizing plasma-material interactions. Following this, the machine will be prepared for more advanced operations, including the testing of alternative divertor concepts by replacing the divertor cassettes. A later phase of operation with tritium is planned to directly address D-T specific physics, such as isotope effects on the plasma edge and tritium retention. The results from DTT are expected to provide the definitive basis for the design and licensing of the DEMO divertor, directly enabling the next major step in the quest for commercial fusion energy.

References

DTT: The Divertor Tokamak Test facility — DTT Scarl (2024)
Divertor Tokamak Test facility: a key step in the European roadmap to fusion energy — Nuclear Fusion (2020)
The DTT project: a facility for the test of DEMO divertor concepts — Fusion Engineering and Design (2021)
The DTT Divertor: A Test Bed for DEMO Power Exhaust — IEEE Transactions on Plasma Science (2021)
Italy: EIB supports new ENEA and DTT project with €250 million for research and development in fusion energy — European Investment Bank (2019)
The DTT Toroidal Field coils: Design, qualification tests and procurement strategy — Fusion Engineering and Design (2021)
European Research Roadmap to the Realisation of Fusion Energy — EUROfusion (2018)