Laser Inertial Fusion Energy

LIFE, short for Laser Inertial Fusion Energy, was a fusion energy effort run at Lawrence Livermore National Laboratory between 2008 and 2013. LIFE aimed to develop the technologies necessary to convert the laser-driven inertial confinement fusion concept being developed in the National Ignition Facility (NIF) into a practical commercial power plant, a concept known generally as inertial fusion energy (IFE). LIFE used the same basic concepts as NIF, but aimed to lower costs using mass-produced fuel elements, simplified maintenance, and diode lasers with higher electrical efficiency. Two designs were considered, operated as either a pure fusion or hybrid fusion-fission system. In the former, the energy generated by the fusion reactions is used directly. In the later, the neutrons given off by the fusion reactions are used to cause fission reactions in a surrounding blanket of uranium or other nuclear fuel, and those fission events are responsible for most of the energy release. In both cases, conventional steam turbine systems are used to extract the heat and produce electricity. Construction on NIF completed in 2009 and it began a lengthy series of run-up tests to bring it to full power. Through 2011 and into 2012, NIF ran the 'national ignition campaign' to reach the point at which the fusion reaction becomes self-sustaining, a key goal that is a basic requirement of any practical IFE system. NIF failed in this goal, with fusion performance that was well below ignition levels and differing considerably from predictions. With the problem of ignition unsolved, the LIFE project was canceled in 2013. The LIFE program was criticized through its development for being based on physics that had not yet been demonstrated. In one pointed assessment, Robert McCrory, director of the Laboratory for Laser Energetics, stated: 'In my opinion, the overpromising and overselling of LIFE did a disservice to Lawrence Livermore Laboratory.' Lawrence Livermore National Laboratory (LLNL) has been a leader in laser-driven inertial confinement fusion (ICF) since the initial concept was developed by LLNL employee John Nuckols in the late 1950s. The basic idea was to use a driver to compress a small pellet known as the target that contains the fusion fuel, a mix of deuterium (D) and tritium (T). If the compression reaches high enough values, fusion reactions begin to take place, releasing alpha particles and neutrons. The alphas may impact atoms in the surrounding fuel, heating them to the point where they undergo fusion as well. If the rate of alpha heating is higher than heat losses to the environment, the result is a self-sustaining chain reaction known as ignition. Comparing the driver energy input to the fusion energy output produces a number known as fusion energy gain factor, labelled Q. A Q value of at least 1 is required for the system to produce net energy. Since some energy is needed to run the reactor, in order for there to be net electrical output, Q has to be at least 3. For commercial operation, Q values much higher than this are needed. For ICF, Qs on the order of 25 to 50 are needed to recoup both the electrical generation losses and the large amount of power used to power the driver. In the fall of 1960, theoretical work carried out at LLNL suggested that gains of the required order would be possible with drivers on the order of 1 MJ. At the time, a number of different drivers were considered, but the introduction of the laser later that year provided the first obvious solution with the right combination of features. The desired energies were well beyond the state of the art in laser design, so LLNL began a development program in the mid-1960s to reach these levels. Each increase in energy led to new and unexpected optical phenomena that had to be overcome, but these were largely solved by the mid-1970s. Working in parallel with the laser teams, physicists studying the expected reaction using computer simulations adapted from thermonuclear bomb work developed a program known as LASNEX that suggested Q of 1 could be produced at much lower energy levels, in the kilojoule range, levels that the laser team were now able to deliver. From the late-1970s, LLNL developed a series of machines to reach the conditions being predicted by LASNEX and other simulations. With each iteration, the experimental results demonstrated that the simulations were incorrect. The first machine, the Shiva laser of the late 1970s, produced compression on the order of 50 to 100 times, but did not produce fusion reactions anywhere near the expected levels. The problem was traced to the issue of the infrared laser light heating electrons and mixing them in the fuel, and it was suggested that using ultraviolet light would solve the problem. This was addressed on the Nova laser of the 1980s, which was designed with the specific intent of producing ignition. Nova did produce large quantities of fusion, with shots producing as much as 107 neutrons, but failed to reach ignition. This was traced to the growth of Rayleigh–Taylor instabilities, which greatly increased the required driver power.