Fast heating of ultrahigh-density plasma as a step towards laser fusion ignition

Modern high-power lasers can generate extreme states of matter that are rel evant to astrophysics(1), equation-of-state studies(2) and fusion energy re search(3,4). Laser-driven implosions of spherical polymer shells have, for example, achieved an increase in density of 1,000 times relative to the sol id state(5). These densities are large enough to enable controlled fusion, but to achieve energy gain a small volume of compressed fuel (known as the 'spark') must be heated to temperatures of about 10(8) K (corresponding to thermal energies in excess of 10 keV). In the conventional approach to cont rolled fusion, the spark is both produced and heated by accurately timed sh ock waves(4), but this process requires both precise implosion symmetry and a very large drive energy. In principle, these requirements can be signifi cantly relaxed by performing the compression and fast heating separately(6- 10); however, this 'fast ignitor' approach(7) also suffers drawbacks, such as propagation losses and deflection of the ultra-intense laser pulse by th e plasma surrounding the compressed fuel. Here we employ a new compression geometry that eliminates these problems; we combine production of compresse d matter in a laser-driven implosion with picosecond-fast heating by a lase r pulse timed to coincide with the peak compression. Our approach therefore permits efficient compression and heating to be carried out simultaneously , providing a route to efficient fusion energy production.