Research on high density tomography Page: 4 of 20
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Research on High Density Tomography
Principal Investigator: G. J. Caporaso
Coinvestigator: H. Kirbie
The project goal is to define the beam transport system and pulsed power architecture for
an advanced radiography machine that would permit obtaining a temporal sequence of multiple-
line-of-sight views of a given dynamic event. A long (200ns-1000ns) beam pulse would be split
temporally by fast kicker "coils" and made to travel down separate beamlines to illuminate a target
from two to four different angles. The beam pulse could be repeated at intervals down to 1
microsecond. The beam transport system and pulsed power architecture for this machine have
been scoped out.
Radiography is a powerful tool for studying dynamic events, such as
explosively driven implosions, explosively formed projectiles, or dynamic systems
such as an operating diesel engine. One of the key radiographic devices now in
use is FXR - a flash x-ray machine that was designed for imaging rapidly
imploding objects at a critical moment in time . The x-ray flash is generated by
focusing a high energy electron beam from an induction accelerator onto a target
made from high-Z material. The best radiographic image is obtained by a high
quality electron beam that has high current, low emittance, and low transverse
motion on the target. Further radiographic information can be obtained from
multiple x-ray views of the object (tomography) and from multiple observations of
the same hydrodynamic event in time. The result is a tomographic "movie" of the
event, rather than a one-view snapshot.
Efforts are underway at LLNL and LANL to improve each laboratory's
radiographic capability by the methods mentioned above. At LLNL, the FXR
accelerator is being refurbished with new solenoid magnets that will focus they
beam with less corkscrew motion . Modifications to FXR are also proposed
that will enable the accelerator to generate two beam pulses with a variable pulse
spacing . At LANL, construction is underway on the Dual-Axis Radiographic
HydroTest Facility (DARHT) that will house two 16-MeV induction accelerators
that face the object at a 90-degree included angle . The DARHT Facility will
obtain two radiographic snapshots of the same hydrodynamic event at different
times or a single tomographic image of the object at a fixed time.
During the past year, a feasibility study was funded to examine a new
accelerator and beam transport system that goes well beyond the capabilities of
DARHT and FXR . The study concluded that the technology is at hand to
construct a high current accelerator (-3-kA at 20-MeV) that can generate multiple
pulses into multiple beamlines. The design adopted for technology evaluation
will generate up to five, 200 ns beam pulses in rapid succession. Each beam
pulse will then be cleaved by fast kickers into four, 50-ns beamlets that
simultaneously illuminate the object from four view points. The study went on to
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Caporaso, G. J. & Kirbie, H. C. Research on high density tomography, report, June 26, 1995; California. (digital.library.unt.edu/ark:/67531/metadc792337/m1/4/: accessed January 21, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.