Experimental results of the active deflection of a beam from a kicker system Page: 3 of 5
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Experimental results of the active deflection of a beam from a kicker system *
Y. J. (Judy) Chen, G. Caporaso, J. Weir
Lawrence Livermore National Laborator T ;erorc' - aSay T R N
A high current kicker has been designed and tested on the
ETA-II beam line. A bias dipole which surrounds the kicker
acts to deflect the beam in the DC mode. High voltage
pulsers (10kV) with fast rise times ( iOns.) are connected
to the internal strip lines of the kicker. They are used to ma-
nipulate beams dynamically.
Camera photos which show the switching of the beam
from one position to another will be presented. Beam bug
measurements of beam-induced as well as active steering
will be shown. These will be compared with theoretical pre-
Recently there has been considerable interest in providing
advanced flash x-ray radiography capability for stockpile
stewardship[l]. A multi-axis capability is required in
order to produce a tomographic reconstruction of an im-
ploding assembly. It would be very economical to produce
many lines of sight using a single high current electron ac-
celerator if a kicker could be used to axially section a rela-
tively long beam pulse into short pieces which could be di-
rected to different beam lines.
The kicker for this application must be able to handle
continuous kilo-ampere beams with great precision and
high speed. Switching times of order 10 ns are required in
order to make maximum use of the available beam charge.
In addition, beam induced fields arise in the kicker and
cause additional deflections which must be compensated for
by modifying the external pulser voltage waveform.
The idea for this kicker grew out of work done on a "fast
corrector coil" (FCC) that was deployed on the Advanced
Test Accelerator . The FCC consisted of four rods inside
a beam pipe. Each rod was coupled to its own pulser. The
FCC could steer a beam in both the vertical and horizontal
In order to improve field quality the rods were replaced
by curved strip line electrodes approximating a cylindri-
cal boundary as shown in Fig. 1. The resulting structure
strongly resembles a strip line beam position monitor that is
in wide use in the high energy accelerator community .
These kickers are to be used to handle continuous relativis-
tic electron beams of at least several kilo-amperes so that
wake fields in the kicker are significant even for a single
passage of the beam. The wake fields for structures of this
type are strong enough to significantly steer the beam. The
This work was performed under the auspices of the U.S. Department
of Energy by the Lawrence Livermore National Laboratory underContract
Figure 1: Photo of kicker cross-section which shows kicker
input condition on the beam centroid is amplified as a func-
tion of beam current  for both a passive and kicked mode
of operation. The field quality of the shaped electrodes im-
proves field quality but residual higher order moments still
exist. The strongest field after the dipole moment is the sex-
tupole moment. The nonlinearity of a sextupole field can
shape the beam into a triangle and introduce a small amount
of emittance growth .
2 DESCRIPTION OF EXPERIMENT
The kicker experiment, which comprises high voltage
pulsers and the kicker itself with a bias dipole magnet
wound around the outside, sits in the transport section of
a linear induction accelerator (Fig. 2). A complete sys-
tem would also include a septum magnet downstream of the
kicker. It is the only active component in that section. Ex-
periments to test the system have been and are still being
conducted on the Experimental Test Accelerator - II (ETA-
II) at the Lawrence Livermore National Laboratory. Two
existing pulsers can provide 10kV into a 502 load with a
10-90% risetime of 10 nsecs. The pulser is shown in Fig. 3.
Two different beam line configurations were used. The
original layout proved to be inadequate for the set of beam-
induced steering experiments. Two resistive wall monitors
(know locally as beam bugs) upstream of the kicker were
needed to measure input displacement and angle . In
fig. 4a, these were labeled BBT08 and BBTO9. However,
a large focusing magnet, C4A, resided between the two and
was necessary to transport the beam to the output of the
kicker. It was quickly realized that incorporation of the
C4A in the analysis meant the assumption that the magnet
was perfectly aligned. A new beam line was designed such
that two beam bugs can be placed upstream of the kicker
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Yu, J. Experimental results of the active deflection of a beam from a kicker system, article, August 20, 1998; California. (digital.library.unt.edu/ark:/67531/metadc620171/m1/3/: accessed December 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.