Promising new approach to inertial fusion

14 December 2020

Researchers in the Vulcan control room at the Central Laser Facility, UKRI-STFC Rutherford Appleton Laboratory. Left to right, top: Dr Luke Ceurvorst (CELIA, Univ. Bordeaux), Mr Sam Claxton, Prof Peter Norreys. Left to right, bottom: Dr Ramy Aboushelbaya, Mr Robert Paddock and Mr Benjamin Spiers

Image caption:
Researchers in the Vulcan control room at the Central Laser Facility, UKRI-STFC Rutherford Appleton Laboratory
Left to right, top: Dr Luke Ceurvorst (CELIA, Univ. Bordeaux), Mr Sam Claxton, Professor Peter Norreys
Left to right, bottom: Dr Ramy Aboushelbaya, Mr Robert Paddock and Mr Benjamin Spiers

Robert Paddock, a postgraduate student in Atomic and Laser Physics in Oxford, along with Heath Martin and Rusko Ruskov, both physics undergraduate students in University College Oxford, Stephen Hawkings’ alma mater, have produced a novel target design to realise the possibility of energy breakeven using the National Ignition Facility (NIF). The trio are working as part of an Anglo-American team of researchers from Oxford, the Rutherford Appleton Laboratory (RAL), AWE, the Los Alamos National Laboratory and the Lawrence Livermore National Laboratory. Their results mean that it is now possible to begin discussing what a laser-driven demo reactor might realistically involve and, for that reason, represents a significant step forward in knowledge.

The group used wetted foam capsules instead of an ice layer that is frozen onto the inner wall at cryogenic temperatures, a technique first proposed by Olson and Leeper in 2013 [Physics of Plasmas 20, 092705 (2013)]. The group developed Olson et al’s previous ground-breaking research (R. Olson et al. [Phys. Rev. Lett. Physical Review Letters 117, 245001 (2016)]) where wetted-foam targets were placed inside a hohlraum target and the laser energy was converted to soft X-ray to drive the implosion using the NIF. Paddock et al.’s design was made using over 11,000 different simulations of the laser and target parameters in order to optimise the performance. Although limited to one-dimension at this stage, their simulations were benchmarked against directly driven experiments performed on the OMEGA laser facility in the University of Rochester and at the NIF itself to make sure it was giving realistic results. Their new design promises greatly improved performance and a new path forward for experiments on the NIF, reinforcing conclusions by Gopalaswamy, V., Betti, R., Knauer, J.P. et al., [Nature (London) 565, 581–586 (2019)] published last year.

Paddock et al. are now working closely with colleagues from the Laboratory for Laser Energetics at the University of Rochester, Los Alamos and Lawrence Livermore, UK and European laboratories to extend the modelling this target in two dimensions in preparations for experimental tests on the NIF and Laser Mégajoule (LMJ) facilities in the near future.

Professor Peter Norreys who supervised the research, comments, ‘Robert developed this concept as a major component of his doctoral degree while Heath and Rusko started studying some of these ideas as part of their summer placement with me in 2019. We are very excited to extend their excellent results and insights to two dimensions, so that this new understanding can be tested on the Vulcan laser at the RAL, as well as NIF and LMJ facilities in the next few years. Young researchers still have a big role to play in realising the full potential for inertial fusion.’

The work was published as part of a wide-ranging discussion meeting on future prospects for realising inertial fusion for energy generation that was chaired by Professor Norreys in London earlier this year.

See: Paddock R et al. 2020 One-dimensional hydrodynamic simulations of low convergence ratio direct-drive Inertial Confinement Fusion Capsules Phil. Trans. R. Soc. A 378: 20200224. https://doi.org/10.1098/rsta.2020.0224

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences: Vol 378, No 2184 (royalsociety.org/journals/)

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences: Vol 379, No 2189 (royalsociety.org/journals/)