Abstract
Indirectly driven Symcap capsules are used at the NIF to obtain information about ignition capsule implosion performance, in particular shape. Symcaps replace the cryogenic fuel layer with an equivalent ablator mass and can be similarly diagnosed. Symcaps are good symmetry surrogates to an ignition capsule after the peak of the drive, radiation-hydrodynamics simulations predict that doping of the symcaps vary the behavior of the implosion. We compare the equatorial shapes of a symcap doped with Si or Ge, as well as examine the reproducibility of the shape measurement using two symcaps with the same hohlraum and laser conditions.
Highlights
Symcaps are good symmetry surrogates to an ignition capsule after the peak of the drive, radiation-hydrodynamics simulations predict that doping of the symcaps vary the behavior of the implosion
To successfully achieve inertial confinement fusion (ICF) in the laboratory with minimal energy, we require maximum compression to sizes a few times an alpha particle range in a central spot heated to an ion temperature close to 10 keV
Alternative capsules, symcaps [2], are ignition capsules where the cryogenic fuel layer in the ignition capsule is replaced by an equivalent mass of ablator material, have the same hydrodynamic behavior as ignition capsules, and have been used to measure the low-order symmetry of the implosion at low nuclear yield
Summary
To successfully achieve inertial confinement fusion (ICF) in the laboratory with minimal energy, we require maximum compression to sizes a few times an alpha particle range in a central spot heated to an ion temperature close to 10 keV These conditions necessitate the use of spherical implosions that have minimal surface losses for a given volume size, and require exquisite spherical symmetry to minimize the energy loss at the surface and to maximize the compression of an initial volume. Considerable amount of studies have been performed to specify tolerable low-order mode perturbation amplitudes that reduce the core-size Measuring such amplitudes in ignition capsules is practically difficult due to the expected large neutron signals that occur while tuning. This is controlled through variation of the laser wavelength difference between the inner and outer beam cones [7] keeping the external energy and external cone fraction fixed
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