The US DIII-D National Fusion Facility has completed a two-year research campaign, which included a record-breaking 1,600 hours of plasma research as part of 140 ground-breaking studies. The facility, is an Office of Science scientific user facility operated by General Atomics in San Diego for the Department of Energy (DOE). It will now begin a series of major upgrades over the next eight months to prepare for the next phase of research. These scheduled upgrades are intended to keep the facility at the forefront of fusion science as a valuable resource for the entire fusion community.

“The 2023 research campaign was one for the history books. I can’t remember a more productive effort, which is really a testament to the hard work of our wonderful team of scientists and engineers from across the country,” said DIII-D Director Dr Richard Buttery. “But it’s never a quiet time at DIII-D. We’re already getting started on an important set of upgrades as we look ahead to the next campaign.”

The DIII-D tokamak, which has been in operation since the 1980s, is the largest magnetic fusion research facility in the US. It has played an important role in providing data for the engineering design phase of the International Thermonuclear Experimental Reactor (ITER), under construction in France. DIII-D supports more than 650 scientists from 95 institutions across the USA and the international research community.

During the record-breaking campaign, which continued for more than 200 days, the most notable advances included:

  • The demonstration of high performance “diverted negative triangularity” plasma configurations, which alter the shape of the plasma to improve performance and heat dissipation and potentially revolutionise the path to cost-effective fusion energy.
  • The deployment of a new radio-frequency wave injection technology known as “helicon current drive” with an innovative antenna that improves the delivery of energy to the plasma, potentially creating a new method for efficiently sustaining plasmas in a more compact and cost-effective manner.
  • Significant optimisations to DIII-D’s flexible three-dimensional magnetic field configurations, which improved particle confinement and protections for the plasma-facing walls of the machine.

As part of DIII-D’s commitment to developing the next generation of fusion scientists, the programme for the first time reserved two weeks of run time for student researchers. In total, 17 experiments were conducted by students pursuing PhD theses. DIII-D hosts over 200 students, interns, and postdoctoral research fellows annually.

Many additional advances were made in the understanding of fusion plasmas, including improvements to efficiency, performance, and control. Findings from these and other areas of research will be announced in upcoming scientific journals and conferences.

DIII-D has already begun a new upgrade effort which will improve its capabilities for shaping and containing plasma to increase plasma volume and current. These changes will allow DIII-D to reach higher performance levels relevant to fusion power plants and enable new research to improve plasma control and efficiency.

The upgrades will include installation of a new divertor system, which is used to channel excess heat away from the edge of the plasma. The divertor is a permanently installed component in DIII-D that is critical for maintaining efficient plasma operations. Optimising the divertor to efficiently disperse heat without impacting the performance of the plasma is an important research goal for the DIII-D programme.

“DIII-D has utilized different divertor structures in the past to help build the physics basis for handling power in fusion reactors, said Morgan Shafer, Head of DIII-D’s Edge & Boundary Physics Group (Oak Ridge National Laboratory). “The upcoming staged divertor programme accelerates this approach, tackling three separate divertors in the next five years. Each stage of research will answer a key question and take us to the next phase of research. When complete, this upgrade will help influence the design of future power plants.”

Another significant upgrade will be the installation of a new “Lower Hybrid” current drive system as part of a pioneering advancement in fusion power plant technology. As a first-of-a kind technology demonstration co-led by the Massachusetts Institute of Technology’s Plasma Science & Fusion Center (MIT PSFC) and General Atomics (GA), the Lower Hybrid system will give DIII-D additional capabilities to produce reactor-relevant plasma profiles. In theory, this approach should offer the most efficient mechanisms for increasing current drive.

“The new lower hybrid system will improve DIII-D’s current drive capacity and efficiency, which will enable researchers to achieve plasma scenarios that are relevant to steady-state reactor operations, said Dr Theresa Wilks, Lead Scientific Coordinator for DIII-D Collaboration at MIT PSFC. “The Lower Hybrid system will be installed using robotics developed as part of the DIII-D programme. The robot will use advanced This system will be a first-of-a-kind test of novel physics, as well as an important technological advancement demonstrating additive manufacturing of in-vessel components as a new approach for deploying fusion heating and current drive. DIII-D is already a high-performing and versatile machine, and this upgrade is going bring us into a new paradigm of current drive capabilities.”

Image: A worker inside the vessel at the DIII-D National Fusion Facility (courtesy of General Atomics)