Abstract
In recent years, our understanding of high energy density plasmas has played an important role in improving inertial fusion confinement and in emerging new fields of physics, such as laboratory astrophysics. Every new idea required developing innovative experimental platforms at high power laser facilities, such as OMEGA or NIF. These facilities, designed to focus all their beams onto spherical targets or hohlraum windows, are now required to shine them on more complex targets. While the pointing on planar geometries is relatively straightforward, it becomes problematic for cylindrical targets or target with more complex geometries. This publication describes how the distribution of laser beams on a cylindrical target can be done simply by using a set of physical laws as a pointing procedure. The advantage of the method is threefold. First, it is straightforward, requiring no mathematical enterprise besides solving ordinary differential equations. Second, it will converge if a local optimum exists. Finally, it is computationally inexpensive. Experimental results show that this approach produces a geometrical beam distribution that yields cylindrically symmetric implosions.
Highlights
In recent years, a large fraction of high power laser shots was focused on research not directly related to inertial confinement fusion
When a cylindrical target is used like a hohlraum, the beam distribution becomes more problematic, especially when a 3-D thermal radiation code like VISRAD5 has to be used to compute the absorption of light throughout a complex system of surfaces
We present the configuration that was used for an experimental campaign at the OMEGA laser facility. 36 laser beams were used to implode a cylinder filled with argon gas
Summary
A large fraction of high power laser shots was focused on research not directly related to inertial confinement fusion. Laser facilities like OMEGA1 or NIF2 have been used successfully to produce and study plasma jets or hydrodynamic shocks.. Laser facilities like OMEGA1 or NIF2 have been used successfully to produce and study plasma jets or hydrodynamic shocks.4 In these experiments, the target geometry was not spherical and beam positioning was nontrivial. In the case of a sphere, maximizing the laser intensity on target, distributing homogeneously the beams on target, and minimizing incidence angles come down to pointing all beams at the center of the sphere. When a cylindrical target is used like a hohlraum, the beam distribution becomes more problematic, especially when a 3-D thermal radiation code like VISRAD5 has to be used to compute the absorption of light throughout a complex system of surfaces. The locations on the target are not defined in advance since they are a part of the problem we are trying to solve (unlike the traveling salesman problem where locations are given beforehand)
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