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Fusion Energy:
High-power Lasers for Clean Energy

PS&A's fusion energy systems and science (FESS) program element develops the high-energy, high-average-power laser technologies that will be required to generate electric power from laser-based inertial fusion.

Fusion is the process by which our sun and other stars convert or "burn" hydrogen (the lightest element) and produce helium (the next lightest element). The fusion of hydrogen releases immense amounts of energy. Conditions needed to burn fusion fuel include extremely high temperatures and pressures. The controlled release of fusion, or thermonuclear energy, in the laboratory remains an alluring goal due to its potential as a source of unlimited, environmentally friendly energy for humankind.

The Mercury LaserThe Mercury laser is the world's highest-energy and power, nanosecond-pulse, diode-pumped laser.

The two main approaches to achieving controlled release of thermonuclear energy in the laboratory are magnetic fusion and inertial confinement fusion. The National Ignition Facility (NIF) is designed to demonstrate fusion by inertial confinement. Inertial confinement fusion involves the rapid compression of small fuel capsules (containing isotopes of hydrogen) to reach densities and temperatures greater than those in the core of the sun. When the correct temperature and density are reached (100 million kelvins and a density 100 times that of lead) the fuel capsule ignites and then burns while confined by its own inertia.

NIF is expected to demonstrate fusion ignition – the release of more energy via fusion burn than the laser energy used to initiate ignition. NIF is able to fire its laser at a rate of a shot every few hours. For laser inertial fusion energy (see LIFE) to become practical, targets will have to be ignited at a rate of several shots per second.

PS&A's efforts to develop the necessary laser technology for LIFE include the development of low-cost, high-energy, high-efficiency laser drivers with repetition rates of several times a second. The Mercury laser project has been an important part of this PS&A mission. The Mercury laser was constructed as scalable diode-pumped laser test bed and has demonstrated the viability of diode-pumped laser technology to produce energetic laser pulses at repetition rates of ten shots per second with the electrically efficiency required for commercial laser fusion power.

While the Mercury laser has generated only a small fraction (1/30,000) of the peak power of NIF, because of its high repetition rate it has operated at a higher average power. Mercury currently holds the world record for nanosecond pulse energy from a diode-pumped laser system. The design of Mercury takes advantage of the optical technology advances developed for NIF and of LLNL's expertise in high-power diode-laser arrays. Since the mid-1980s, LLNL has been the world leader in the development of high-power semiconductor diode-laser arrays, including advances in diode-laser packaging, radiance conditioning and efficient pump light delivery.

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HEC-DPSSL Workshop 2012

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