High Power Laser Science and Engineering, (2017), Vol. 5, e21, 7 pages.
© The Author(s) 2017. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/
licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
doi:10.1017/hpl.2017.20
Surface characterization of ICF capsule by
AFM-based profilometer
Jie Meng
1
, Xuesen Zhao
2
, Xing Tang
1
, Yihao Xia
1
, Xiaojun Ma
1
, and Dangzhong Gao
1
1
Research Center of Laser Fusion, CAEP, Mianyang 621000, PR China
2
P.O.Box 413, Harbin Institute of Technology, Harbin 150001, PR China
(Received 8 October 2016; revised 23 January 2017; accepted 5 May 2017)
Abstract
Outside surface fluctuations of inertial confinement fusion (ICF) capsule greatly affect the implosion performance. An
atomic force microscope (AFM)-based profilometer is developed to precisely characterize the capsule surface with
nanometer resolution. With the standard nine surface profiles and the complete coverage data, 1D and 2D power spectra
are obtained to quantitatively qualify the capsule. Capsule center fast aligning, orbit traces automatic recording, 3D
capsule orientation have been studied to improve the accuracy and efficiency of the profilometer.
Keywords: inertial confinement fusion; target design and fabrication
1. Introduction
Due to Rayleigh–Taylor instability during inertial confine-
ment fusion (ICF) experiment, the imperfection of capsule
surface degrades the final symmetry of the implosion and
creates mix at the pusher–fuel interface, potentially quench
the ignition
[1, 2]
. Obviously, our goal is to fabricate capsules
with perfect surface through optimization of the process of
fabrication. However the optimization is based on precise
measurement of capsules. Therefore, the ability to precisely
characterize the capsule surface is extremely important.
In the 1990s, Lawrence Livermore National Laboratory
(LLNL) and General Atomics (GA) developed an atomic
force microscope (AFM)-based spheremapper, for mapping
the outer surface profiles of ICF capsule
[3]
. An average
fluctuation power spectrum for capsule surface was estab-
lished as the National Ignition Facility (NIF) standard for
acceptance of capsule surface quality
[4]
. Power spectrum
became a significant parameter for capsule characterization.
With the progress in capsule fabrication techniques and the
increasing requirements for capsule precise characterization
in ICF experiments, several surface analysis methods have
been developed since 1999
[5–7]
. Some of them are not
adequate. Optical inspection and white-light interferometer
cannot detect localized defects or surface roughness less
Correspondence to: D. Gao, Research Center of Laser Fusion,
CAEP, No. 64 Mianshan Road, Mianyang 621000, China. Email:
dgaocn@163.com
than 1/10 wavelength in height. It is also difficult for these
methods to detect micron-sized fluctuations if they do not
have abrupt edges on a curved surface. Therefore, an AFM-
based profilometer is established to measure surface ge-
ometry parameters with nanometer resolution, including an
overview of capsule surface mode-power spectrum, surface
roughness, roundness and sphericity parameters
[8–10]
. The
capsule, supported on a vacuum chuck, is rotated while an
AFM records the circumferential surface profile. A high-
precision rotary air bearing with low speed and small diame-
ter is developed to rotate the capsule. Several key techniques,
including capsule fast aligning to rotation axis, automatic
recording of surface traces in one orbit, and 3D capsule
orientation, have been developed to improve the functions
of profilometer.
2. Profilometer
The AFM is an effective tool for characterizing the topogra-
phy of ICF capsules, due to its nanometer resolution and tiny
acting force. However, the limited scanning range restricts
its application for capsule surface profile measurement. A
motion system with nanometer precision is indispensable to
cooperate with AFM.
The capsule profilometer setup is shown in Figure 1. The
capsule is held with a vacuum chuck while rotating in front
of the horizontal AFM tip. The vacuum chuck is mounted on
1