Status of the intense pulsed neutron source Page: 3 of 28
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The plans are to accelerate on the second harmonic two bunches from the
injection energy to 1250 MeV. At this energy a stack of altogether 12 bunches
is built up and finally accelerated as a single bunch to 1500 MeV. Extraction
is accomplished with a one-turn fast kicker magnet. The pulse length of the
single extracted bunch which is transported to the target is about 325 ns.
There are two possible approaches for the FFAG to get the transverse
focusing (see Figures 3 and 4). Up.^to now, mainly the spiral focusing with
normal conducting magnets was studied'^. Recently, a study based on radial
focusing with reversed field magnets^ ' showed several important advantages
compared to the earlier studies. By using superconducting coils with a peak
field of about 4 T, the radial FFAG can be built with the same radius as the
spiral machine but with much longer effective straight sections between the
magnets. Therefore, the rf cavity gap can be placed perpendicular to the beam
orbit. Additionally, the stability region in the phase space will be larger and
therefore the machine will be less sensitive to field arid alignment errors.
Nearly all the machine parameters from Table I will be unchanged. The magnetic
field distribution along the azimuthal direction is given in Figure 5. The
maximum positive field on the extraction orbit will be 4 T and the minimum
negative field along the same orbit will be -1.3 T. The spiral angle will be
Further topics which are under study and basically identical for both types
of machines are beam loading and collective phenomena. First calculations show
that beam loading can be controlled by a cathode follower; alternatively a
feedback amplifier operating on the second harmonic could correct the waveform
distortion. The transverse coherent instability is a critical issue and needs
to be studied in much more detail. The outcome of this study might increase the
Target Station Developments
It is a pleasure to report that che target and its cooling, monitoring and
other associated systems have continued to operate with no significant problems.
Two of the most significant accomplishments of the past year which relate to the
neutron source itself, are the installation of a new solid methane moderator,
and the characterization of the pulse shapes of the room temperature
Continuing what is now a long sequence of moderator developments at IPNS,
we have installed a grooved, solid methane moderator which operatoes at a
physical temperature of 12 K, and produces a spectrum with a temperature of 20
K. The system has operated quite well since its installation in January, 1985,
and the increased intensity of long wavelength neutrons has brought our cold
neutron instruments up to a high level of performance. Figure 6 shows the
spectrum of neutrons from the new moderator. Another paper provides more details
on the new system'3 .
Vith Susurnu Ikeda, who visited us from KEK, we have performed careful
measurements of the pulse shapes as a function of energy for the two ambient-
temperature polyethylene moderators. The outcome has been to produce a new set
of functions which fit the pulse shapes in a simple and intuitively-appealing
way. Ikeda's pulse shape function is of the form
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Carpenter, J.M.; Brown, B.S.; Kustom, R.L.; Lander, G.H.; Potts, C.W.; Schulke, A.W. et al. Status of the intense pulsed neutron source, article, January 1, 1985; United States. (digital.library.unt.edu/ark:/67531/metadc1064256/m1/3/: accessed January 22, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.