100 years of chasing the fusion dream.

The potential promise of fusion energy has inspired scientists and engineers since the 1920s, when Arthur Eddington first suggested hydrogen/helium fusion as the source of our own sun’s energy. But 100 years on and the dream of replicating a solar burn to produce almost limitless clean energy is still only theoretical.

Nuclear fusion reactors generate power by joining, or fusing, two atomic nuclei to produce one or more heavier nuclei – a process that releases vast amounts of energy. However, achieving fusion in a sustained and controlled fashion is yet to be realised and remains one of the most important unsolved problems of nuclear science. A major sticking point is the behaviour of the extremely hot gas – referred to as plasma – which, unsurprisingly, is difficult to deal with.

Generations of researchers have dedicated their careers to understanding how to control this extremely hot hydrogen plasma.

The plasma problem: taming fusion plasmas

UQ’s Associate Professor Vincent Wheatley has made it his business to understand the behaviour of plamsa in fusion experiments and control any instabilities before the fusion reaction begins.

[insert first video showing uncontrolled plamsa implosion, file name: implosion_high-res.mp4]

Caption: Uncontrolled plasma implosion: two fluid plasma simulation of a low density plasma implosion showing electron density on the left and ion density on the right

His research focuses on Inertial Confinement Fusion (ICF), a type of fusion energy technology that has the potential to generate abundant energy safely and with little waste and no CO2 emissions.

In inertial confinement fusion, lasers implode a tiny spherical capsule containing fusion fuel, creating plasma and initiating a fusion reaction at the centre of the capsule. Ideally, the implosion would remain perfectly spherical and a contained fusion burn would consume the fuel. Unfortunately, the imploding capsule is highly unstable. Imagine trying to crush a ping-pong ball while maintaining its even spherical form.  The unwanted mixing between the fuel and capsule material (a result of the instabilities) deactivates the fusion burn as the capsule material acts like a fire retardant.

So, despite billions of dollars of investment, a fusion burn has yet to be achieved.

During his time at the prestigious California Institute for Technology (Caltech), Dr Wheatley developed a model, which indicated that a magnetic field might actually work at supressing plasma instability.

Back at UQ, Dr Wheatley, together with his Postdoctoral Fellow Dr Daryl Bond, an international research team and multimillion-dollar grants, has used computer simulations (known as Computational Fluid Dynamics (CFD)),  to test his model and determine that these instabilities - known as Richtmyer-Meshkov instability (RMI) and Rayleigh-Taylor instability - in plasma implosions can be diminished via a seed magnetic field. The team then designed realisable magnetic field geometries that control the instabilities, and don’t heavily distort or weaken the implosion, thus maintaining maximum energy output.

[insert second video showing effect of magnetic field, file name: ion_dS1_compare.mp4]

Caption: The effect of a magnetic field on one wavelength of the instability. The simulation on the top has no magnetic field and in the bottom one we apply a seed magnetic field and see less instability growth.

Satisfied that the team had cracked the first plasma problem, they moved on to explore two-fluid plasma simulations, again with CFD, and in a world first, discovered that the situation changes yet again.  

“Our world first two-fluid plasma RMI simulations revealed a wealth of new physical phenomena. These imply that the RMI may be more detrimental to ICF than predicted by single-fluid models”, Dr Wheatley said

Never giving up, Dr Wheatley’s latest work identifies a new suppression mechanism that simpler plasma models cannot capture.

[insert here image/simulation video with caption]

But will it work: validation experiments

Experimentally validating theoretical and CFD findings – i.e. that you can control shock driven plasma instabilities by applying a magnetic field - is the next step in the research program. Which begs the question – how can you mimic the plasma dynamics in Inertial Confinement Fusion?

Fortunately, the answer lies very close to home at the School’s Centre for Hypersonics. Working together with Dr David Gildfind and Daniel Smith, the team discovered it was possible to conduct plasma RMI experiments in UQ’s expansion tubes. This combination of expertise and world class infrastructure provides a unique capability to conduct never before seen experiments.

“Successfully validating the computational and theoretical findings will give our approach the traction to be applied in international, multibillion-dollar inertial confinement facilities”, Dr Wheatley said. [potential break out quote]

Global impact

Dr Wheatley’s continued major contributions to this field have earned him international recognition and have impact both within the field and beyond. Validating these computational findings will greatly reduce the uncertainty delaying the application of magnetic instability suppression on international, multi-billion-dollar ICF facilities. The UQ experimental validation experiments will be a world first and closely observed by the global research community. The results will inform the next generation of experiments by fusion energy researchers worldwide.

“Controlling instability is regarded as the ‘missing link’ in fulfilling ICF. Once the physics of applying magnetic fields to suppress instability is understood, we will be great deal closer to realising the fusion energy dream.”

Key international collaborators on this project are Professor Ravi Samtaney (KAUST, Saudi Arabia), Professor Dale Pullin (Caltech, USA) and Dr Wouter Mostert (Princeton, USA, UQ graduate).

About Associate Professor Wheatley

Dr Wheatley is a mechanical engineering researcher whose career has taken him full circle, with noteworthy highlights along the way.

Starting out at UQ as an undergraduate Mech Eng student, he progressed through to his masters before heading to the US to complete a PhD at the California Institute of Technology (Caltech), recognised as one of the world’s leading and influential institutes for engineering research.

Dr Wheatley then went to another world leading institute for his postdoctoral studies – the Swiss Federal Institute of Technology in Zürich (ETH- Zürich).

Following a time at the University of Adelaide, Dr Wheatley returned home and has led hypersonic and fusion instability research at the School.

Dr Wheatley has maintained close links to these high-level institutes and his collaborations place UQ at the forefront of this field globally.

He is currently Chair of Teaching and Learning for the School of Mechanical and Mining Engineering and a member of the Centre for Hypersonics.

 

Professor Vincent Wheatley

Professor
School of Mechanical and Mining Engineering
Chair, Teaching & Learning Committee
School of Mechanical and Mining Engineering
Summary: 
Generations of researchers have dedicated their careers to understanding how to control this extremely hot hydrogen plasma