Plasma Physics for Fusion (PP4F)

Research axis 1 – Fusion plasma for production of nuclear fusion energy

The project is dedicated to nuclear fusion physics research in close collaboration with existing experimental fusion devices and the ITER organization which is a huge international nuclear fusion R&D project. The goal of the ITER project is to demonstrate an energy production by nuclear fusion which is the reaction that powers the sun. The nuclear fusion on the earth requires very high temperature ionized particles of ~3x10⁸ C which can be confined by strong magnetic fields. This is essential because no material can be sustained against such high temperatures reached in a fusion reactor. The magnetic field structure is a torus, a donut-shaped structure to close the magnetic field. This is called ‘Tokamak’ which is the currently furthest developed magnetic confinement device. However, it is a demanding task to achieve sufficiently good confinement for a ‘burning plasma’ due to various kinds of plasma instabilities.

The project towards the objectives of the European Fusion Roadmap of EUROfusion, the European fusion research program for Horizon 2020. Fusion energy is the most promising technology to offer a long-term supply of energy while satisfying the global agreement on the reduction of CO2 on the atmosphere.

Our research covers wide range of plasma dynamics studies from turbulence which is micro-scale non-linear plasma dynamics up to MHD (MagnetoHydroDynamics) which is macro-scale plasma dynamics. My research on the plasma turbulence study contributes the understanding of fundamental plasma physics by use of simplified models which aim to address the global control of plasma turbulence as the final achievement. On the other front, my research on the MHD study contributes the study of practical application in existing fusion reactors. Both of research subjects are necessary to improve the plasma confinement for fusion energy production.

Selected topics:

- Non-linear MHD simulations of ELM control by pellet injection: One of the critical undissolved problems is MHD (MagnetoHydroDynamics) instabilities at the plasma boundary, called Edge Localized Modes (ELMs). Fusion reactors can be damaged by ELMs as they release large energy from plasmas to the reactor wall in a few hundred microseconds. Due to their fast time scale, ELMs will cause very large transient heat fluxes to the plasma facing components. Naturally occurring ELMs could lead to an enhanced erosion of the divertor. One of the methods of ELM mitigation is injection of small pellet (small deuterium ice cube) to induce small ELMs before large ELM occurs. The pellet ELM triggering technique is experimentally proven and the theoretical understanding has been advanced considerably. However, for both ELM control schemes, predictive simulations are needed to reliably assess the efficiency in future machines. This work aims to improve the understanding of the physics processes involved in plasma control by pellet injection, using the three-dimensional non-linear MHD simulation code JOREK which solves pellet ablation physics self-consistently with the MHD activity for the application of the plasma control method to ITER plasmas. MHD simulations also provide valuable contributions to improved physics understanding, particularly of the strongly non-linear processes.

  - Study of the MHD instabilities in stellarators: Stellarator is another type of fusion device which exploits strangely-shaped magnets that is hard to build but potentially easier to operate. The MHD behavior is strongly affected by the magnetic field configuration. It is not easy to do a simulation of the complex magnetic fields, especially of stellarator. MEGA is capable to solve non-linear MHD in both, tokamaks and stellarators. The MHD stability/instabilities is being studied and compared with those existing fusion stellarator machines.

-Study of the interaction between energetic particles and non-linear MHD instabilities: Energetic particles can be generated externally via Neutral Beam Injection (NBI) or Ion Cyclotron Heating (ICRH) or, internally, via fusion reactions, e.g. alpha particles in DT reactions. Those energetic particles are an essential source of energy and momentum in a fusion reactor that can drive or stabilize a broad spectrum of MHD fluctuations. The work is to study the fast-ion role in ELM stability and associated losses using the non-linear 3D hybrid kinetic-MHD MEGA code.

Research axis 2 – Non-linear plasma physics for application of plasma propulsion

The so-called dynamo action is considered a key phenomenon to understand the origin of magnetic fields in different electrically conductive fluids (plasma and/or liquid metal) and presents a rich complexity of spatial and temporal multi-scales. The modeling of high-performance computational MHD and the dynamo which is driven by MHD instability has important industrial applications and impact, for example, in electrical engineering for plasma arc simulations of Voltage Circuit Breakers and DC relays for High-Voltage batteries in electric cars. My special interest is in the application in aerospace; Plasma thrusters, also known as magneto-plasma-dynamic thrusters or Lorentz force accelerators, are plasma jet engines for satellites, manned or unmanned aerial vehicles for space exploration that make use of the interplay between a plasma jet and an externally superimposed or self-generated magnetic field for propulsion. For instance, the Hayabusa unmanned spacecraft (developed by the Japan Aerospace Exploration Agency) has demonstrated the world's first implementation of microwave discharge ion engines. The dynamo effect, in particular, which is caused by the MHD instability of the magnetic pressure can be applied for plasma acceleration purposes. The self-organized process of the dynamo instability affects the plasma shape according to the magnetic configuration in which the plasma is immersed, with consequences on the concentrated plasma density and the magnetic pressure which might be exploited for intensive propulsion.

The research project addresses this fundamental question with a state-of-the-art numerical modeling approach. It sets up a new numerical suite of codes based on OpenFOAM. OpenFOAM is a free and open-source CFD (Computational Fluid Dynamics) software released and developed under the GPL license. OpenFOAM provides the user with a wide range of physics solvers for different fluid dynamics situations making it a very versatile software tool. The usage of this software tool in the academic environment is strongly encouraged by its open-source nature, allowing researchers to monitor and modify the code to provide new applications and numerical schemes. Thus, together with an apparently user-friendly program based on C++ and a tight collaborative environment with a highly experienced wide-research community, OpenFOAM has a potential capability for high-performance solver of plasma simulations and easy to attract new researchers to start fusion research as well as other plasma-related research such as astrophysics and solar physics.

Contact person: Shimpei Futatani