Commentary

Important Progress on a Scientific Grand Challenge

Among the great scientific grand challenges is achieving fusion ignition in the laboratory. Realizing this long-term goal will help us understand the power source of the Sun and stars, enhance our understanding of the physics of nuclear weapons, and allow us to explore the potential of fusion as a source of clean, plentiful energy.

Livermore scientists made substantial progress toward ignition during the three-year-long National Ignition Campaign (NIC), which ended in 2012. NIC experiments were highly successful in establishing the National Ignition Facility (NIF) as an experimental laser system with unprecedented energy, precision, flexibility, and reliability. During NIC, Livermore researchers, working with colleagues from universities, other national laboratories, and our industrial partners, installed diagnostics, established target fabrication capabilities, and developed experimental platforms. The experiments achieved physics regimes of extreme temperature, pressure, and density never before observed in the laboratory and impossible to duplicate elsewhere. In the process, they generated a large set of quality data on high-compression fuel capsule implosions.

NIC experiments gave us an appreciation of the physics that remains to be explored and understood for ignition to be achieved. We also observed, as often occurs when scientists tackle a grand challenge, that nature can surprise us when we reach beyond the known landscape of scientific knowledge.

As the article A Significant Achievement on the Path to Ignition describes, recent efforts at NIF have focused on a new experimental ignition design that lowers the maximum compression of the capsule containing deuterium and tritium fuel. The lower compression is the result of modifying and simplifying NIF’s laser pulse to suppress instabilities that can dampen fusion reactions. These so-called high-foot experiments, named for a characteristic of the new laser pulse, are designed to systematically explore the boundaries of our understanding of fuel compression, with an eye toward establishing clear milestones on the path to ignition.

High-foot experiments have been tremendously successful. Since September 2013, they have increased the yield of fusion neutrons by more than a factor of 10 over previous experiments. In particular, the experiments have demonstrated a significant amount of alpha heating, which is the critical physical process for reaching ignition.

Data from the high-foot experiments are helping us determine the accuracy of supercomputer simulations of inertial confinement fusion implosions. The results have also provided insights into the models we use for stockpile stewardship, leading to new areas of inquiry and improving our confidence in those models.

The high-foot campaign has demonstrated the ability of the Laboratory’s scientific staff to explore new ways of thinking about a problem and to work together to make progress on very difficult challenges. The outstanding experimental results have also engaged and expanded the community of scientists interested in exploring the compelling science of ignition on NIF. I anticipate additional progress in the months and years ahead on our path to ignition, as we probe nature to reveal its deepest secrets.