Around the Lab
Laser-Driven Magnetized Liner Inertial Fusion
Until recently, most of the research into nuclear fusion (which holds the promise of creating unlimited, clean power production) focused on either magnetic confinement (low plasma density) or inertial confinement (high plasma density). However, hybrid techniques, such as magneto-inertial fusion, are gaining increased attention since their smaller size, energy, and power-density requirements are proving to be cost effective.
In 2010, Sandia National Laboratories (SNL) began conducting experiments with the Z Pulsed-Power Facility (Z machine), which led to the development of magnetized liner inertial fusion (MagLIF), an inertial confinement fusion (ICF) scheme using magnetized preheated fuel to enable cylindrical implosions with lower velocities and lower convergence ratios than conventional ICF. MagLIF is now a key component in the U.S. ICF Program. As such, SNL and the University of Rochester’s Laboratory for Laser Energetics (LLE) have entered into a collaboration to test the scaling of MagLIF over a range of absorbed energy of the order of 1 kJ on OMEGA to 500 kJ on Z. This work is being funded with a two-year, 3.8-million-dollar award from the Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) to study the potential of combining these two different technologies to produce controlled fusion reactions. LLE recently received the news that the ARPA-E project will provide a no-cost extension through 24 November 2018.
The advantages of scaling MagLIF from a pulsed-power–driven device down to a laser-driven device were outlined by Daniel Barnak:1 “Pulsed-power devices, like the Z machine in Sandia National Labs, are very violent environments in terms of debris and electromagnetic noise, making it very difficult to field diagnostics and maintain a high shot rate. Furthermore, diagnostic access around the target chamber in Z is limited by the installation of the axial magnetic field coils and the geometry of the current delivery system.” OMEGA, on the other hand, has the ability to:
- perform approximately 10× more shots than Z,
- offer more-precise statistics, and
- present wider scans of MagLIF parameter space.
Graduate student, Daniel Barnak, at the MIFEDS development unit with cover removed
Nose cone attached to MIFEDS development unit with coil
In addition, OMEGA has a wide range of experimental diagnostics and can capture data not currently possible on the Z machine. Examples of such diagnostics include: proton radiography of the compressed axial magnetic field, low-yield neutron measurements, and time-resolved x-ray measurements of the liner trajectory. These capabilities offer a solid, scientific foundation to investigate the physics of MagLIF on OMEGA.
A laser-driven equivalent of MagLIF experiments on Z is being developed on the OMEGA Laser System using a target that is roughly 10× smaller in size. To date, OMEGA experiments have focused on preheating to determine the temperature achieved, compress unmagnetized targets without preheat to optimize beam pointing, and measure implosion velocities.2 Future shots on OMEGA will use two magneto-inertial fusion electrical discharge systems (MIFEDS) and new coil designs to achieve magnetic fields twice as high as before, and proton radiography to measure the compression of the magnetic field.
Laser-driven MagLIF experiments could eventually be carried out at the National Ignition Facility (NIF), but the drive energy would still be 10× lower than MagLIF experiments on Z. However, one-dimensional modeling has indicated that the NIF experiments could achieve at least 500× the neutron yield of OMEGA. Additionally, the simulations predict that by using a 30-T initial axial magnetic field, it would be possible to achieve measurable magnetic confinement of charged fusion products.
1D. H. Barnak et al., Phys. Plasmas 24, 056310 (2017).
2J. R. Davies et al., Phys. Plasmas 24, 062701 (2017).