THE DIVERTOR TOKAMAK TEST FACILITY RESEARCH PLAN

Summary

This document summarises the content and scientific objectives of the Divertor Tokamak Test facility (DTT) Research Plan, currently under construction at the ENEA site in Frascati, Italy. Designed with breakeven-class performance and dimensionless parameters close to ITER and DEMO, DTT addresses the heat exhaust challenge in fusion reactors across three operational phases. Key research areas include the exploration of advanced divertor configurations, detached regime control, power decay length scaling, ELM mitigation, wall erosion, and energetic particle physics.

Page 1 - Introduction and Machine Parameters

Topic: OV

P. MARTIN0,1, C. ANGIONI2, S. BREZINSEK3, F. CRISANTI4, C. DAY5, G. DOSE6, M.V. FALESSI7,10, G. GIRUZZI8, P. INNOCENTE11, P. MANTICA9, E. NARDON8, C. SOZZI9, D. TERRANOVA0,11, E. TSITRONE8, D. VAN EESTER3, P. VINCENZI0,11, G. VLAD7, M. WISCHMEIER2 AND THE DTT CONTRIBUTORS12

0Consorzio RFX, corso Stati Uniti 4, 35127 Padova, Italy 1University of Padova, Dipartimento di Fisica e Astronomia, Padova, Italy 2Max-Planck-Institut für Plasmaphysik, D-85748 Garching, Germany 3Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung—Plasmaphysik, 52425, Jülich, Germany 4University of Tuscia, Via del Paradiso 47, 01100 Viterbo Italy 5Kyoto Fusioneering, Tokyo, Japan 6General Atomics, PO Box 85608, San Diego, CA 92186-5608, United States of America 7ENEA via E. Fermi 45, 00044 Frascati, Italy 8CEA, IRFM, F-13108 Saint Paul Lez Durance, France 9ISTP-CNR, via R. Cozzi 53, 20125 Milano, Italy 10Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Roma, Piazzale Aldo Moro 2, Roma, Italy 11ISTP-CNR, Corso Stati Uniti 4, Padova, Italy 12DTT S.c.a r.l., Via E. Fermi 45, Frascati, Italy

Email: [email protected]

This paper summarises the content of the Divertor Tokamak Test facility (DTT) Research Plan [1]. DTT, presently under construction in the Frascati (Italy) ENEA site, will be a device with breakeven class performance, which is designed to address one of the main challenges towards the construction of a fusion power plant, i.e., the development of credible solutions for the heat exhaust.

The Research Plan describes the objectives and research strategy of the DTT experiment [2,3], and proposes a set of programmatic headlines of its scientific programme. The activity for the preparation of the DTT Research Plan (DTT-RP) has been performed during the past three years by an international team comprising approximately 100 European fusion scientists belonging to 20 research institutes from 10 different countries. The RP will be regularly updated and will catalyse and guide the research activities in preparation of the experimental phase.

The Research Plan is based on the expected performance of DTT, which will be one of the world most advanced tokamaks in the next decade. The main parameters of DTT are shown in Fig. 1. DTT is equipped with full W actively cooled plasma facing components and has the capability of investigating various divertor configurations. Its compact size and large auxiliary heating power allow to simulate DEMO divertor heat loads and to produce ITER/DEMO relevant plasmas. Moreover, as shown in Fig. 2, DTT has relevant dimensionless parameters as close as possible to those typical of ITER & DEMO-class reactors. For instance, it has a key wall load parameter PSOL/R ~ 15 (ratio of power flowing out the SOL to major radius); simultaneous high edge density and low collisionality; scrape-off layer width of the same order as for ITER and DEMO; ITER/DEMO relevant core confinement properties. In 2024, the EUROfusion Facilities Review report stressed the potential of DTT “for major impact on the design of DEMO”, as a device “ideal for testing ITER and DEMO scenarios in relevant conditions”. Based on these considerations, DTT was classified by the Facilities Review international panel as one of the few “indispensable” tokamak facilities of the future European fusion programme, without which “the programme goals cannot be realized on the required timescale”.

The DTT-RP is an extensive document (~200 pages) organized in nine chapters and nine technical appendices, which provide a synthetic description of the device main characteristics. The DTT programme which emerges from the RP will follow the evolution of the machine along three distinct phases, as illustrated in Fig. 3, taken from [4].

[Fig. 1: DTT main design parameters: R (m) = 2.19 a (m) = 0.7 Volume (m³) = 35 Ip (MA) = 5.5 BT (T) = 5.85 ne (10²⁰ m⁻³) = 1.5 PTOT (MW) = 45 PECRH (MW) = 29 PICRH (MW) = 6 PNNBI (MW) = 10]

[Fig. 2: DTT dimensionless parameters, taken from [4]]

Page 2 - Scientific Contribution Headlines and References

Topic: OV

The paper will discuss in particular the development of half current/half field scenarios, which will allow a full exploitation of the device since its very beginning, in particular for the exploration of high βN regimes.

[Fig. 3: DTT exploitation phases: Phase 1 (5 years, High level commissioning and testing divertor modules, 14.5 MW ECRH, 3.0 MW ICRH), Phase 2 (5 years, Exploit the divertor configurations at relevant power flux, 14.5 MW ECRH, 3.0 MW ICRH, 9.5 MW NNBI), Phase 3 (Full scale test of DEMO-like divertors, 29.0 MW ECRH, 6.0 MW ICRH, 9.5 MW NNBI)]

The main top-level headlines of the DTT scientific contribution to the European fusion programme, in support to ITER and in preparation of DEMO are:

(A) Development and assessment of baseline and advanced scenarios for various divertor configurations, at nominal field and current, for performance comparison. The available divertor magnetic configurations, even within the same discharge, are in priority order: Single Null, X divertor and Negative Triangularity. They are all presently analysed based on the Wide Flat Divertor presently selected for DTT.

(B) Development of scenarios at half field and current, with 2nd harmonic ECRH heating, to study high βN regimes. These studies, carried out in a full tungsten device, will complement those performed by JT-60SA with carbon plasma facing components.

(D) Detached regimes optimization and control by impurity seeding in various scenarios. DTT will be equipped with a divertor gas injection system, which is traditionally used in tokamaks. As a risk mitigation strategy, DTT shall investigate alternative actuators and qualify for their requirements during detachment control and during ramp-up. Candidate technologies are supersonic molecular beam injection and micro shattered pellet injection, a novel first-of-a-kind approach.

(E) Evaluation of λq at high toroidal field; DTT will be instrumental to pin down the crucial scaling of the power decay length at the plasma edge, λq, as DTT can reach a fully integrated scenario where high core performance with low pedestal collisionality and high density goes together with edge parameters relevant for the next generations of fusion devices.

(F) Development of small/no ELMs scenarios and their control with non-axisymmetric coils and pellets. Like ITER, DTT will be equipped with a set of 27 internal active coils – each independently driven and arranged in three toroidal rows – which together with other actuators allow active control of stability and ELMs. The paper will explain also how DTT will address the development of the science and technology for off-normal events control. In particular, DTT will be equipped with a SPI Disruption Mitigation System similar to the ITER one, which will be discussed together with the simulations result in this field.

(G) Wall erosion, W migration, D retention and removal studies and assessment in view of application to DEMO. The actively cooled tungsten first wall and divertor, associated with the long discharge duration will allow understanding the impact of tungsten impurities and wall erosion/redeposition on plasma performance. Extensive testing with the Divertor Test Modules for new first wall and divertor materials will be done.

(I) Transport, MHD, Energetic Particle physics studies with reactor relevant dimensionless parameters. The simultaneous use of ICRH and High-energy NNBI will generate an energetic particle population with an energy density comparable with that of the core plasma, and characteristic energy more than the critical energy. These are distinctive features of reactor relevant burning plasmas and will be accessible in DTT.

References: [1] F. CRISANTI, G. GIRUZZI, P. MARTIN et al., Divertor Tokamak Test Facility Research Plan, Version 1.0, May 2024, https://www.dtt-project.it/index.php/about/dtt-research-plan.html [2] F. ROMANELLI et al., Nucl. Fusion 64 (2024) 112015. [3] F. ROMANELLI et al, “The Divertor Tokamak Test project: strengths and critical issues”, this conference [4] F. CRISANTI et al 2024 Nucl. Fusion 64 106040