Abstract
A method based on the laser differential confocal principle is proposed for measurement of the uniformity of the inner and outer radius and shell thickness for an inertial confinement fusion (ICF) capsule. Firstly, this method uses the laser differential confocal measurement system (LDCS) driven by a precision air-bearing slide to scan and measure radially the outer radius, R, inner radius, r, and shell thickness, T, accurately. Secondly, a precision air-bearing rotation system is used to drive the capsule to rotate an angle, θ, in sequence, and the LDCS is used to measure R, r and T at the corresponding angle. Finally, the uniformity of the ICF capsule’s R, r and T can be calculated by the values of R, r and T measured at the position of each rotation angle. This method provides an approach for achieving high-precision, non-destructive, comprehensive, and rapid measurement of the uniformity of the inner and outer radius and shell thickness of an ICF capsule. Preliminary experiments indicate that measurement precision, using the proposed method for the uniformity of the outer radius, shell thickness and inner radius of the capsule, can reach 7.02 × 10−5, 5.87 × 10−4 and 6.52 × 10−5, respectively.
Highlights
The first achievement of fusion fuel gains exceeding unity by the US National Ignition Facility (NIF) is a significant milestone in the field of laser inertial confinement fusion (ICF) ignition
Geometrical parameters, such as uniformity of the inner and outer radius and shell thickness of the ICF capsule, are the key factors leading to the Rayleigh-Taylor instability
The optical coordinates ZA, ZB and ZO precisely corresponding to points A, B and O, respectively, are calculated by the normalized differential confocal intensity curves IA, IB and IO, and the outer radius, R, inner radius, r and shell thickness, T, of the ICF capsule can be calculated by a ray tracing algorithm
Summary
The first achievement of fusion fuel gains exceeding unity by the US National Ignition Facility (NIF) is a significant milestone in the field of laser inertial confinement fusion (ICF) ignition. High-precision measurement of the uniformity of the inner and outer radius and shell thickness of an ICF capsule is important for successful ignition. An unmagnified image of an ICF capsule, obtained by placing the capsule directly in contact with a photographic plate and passing through X-rays, nearly parallel to the capsule, is processed digitally to achieve measurement of the ICF capsule’s geometrical parameters. This method has the disadvantages of a long exposure time and complex processing. The proposed method provides an approach to the high-precision measurement of the uniformity of the ICF capsule’s inner and outer radius and shell thickness
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