Design study of a DPIS injector for a heavy ion FFAG Page: 3 of 5
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DESIGN STUDY OF A DPIS INJECTOR FOR A HEAVY ION FFAG *
M. Okamura#, D. Raparia, BNL, Upton, NY 11973, U.S.A.
K. Ishibashi, Y. Yonemura, T. Kanesue, Kyushu University, Ito, Fukuoka 819-0395, JapanAbstract
A new heavy ion injector linac is proposed for
providing heavy ion beams to a fixed field alternating
gradient (FFAG) accelerator, in Kyushu University. A
combination of the new intense laser source based injector
and the FFAG will be able to accelerate high current ion
beams with 100 Hz of a repetition rate. The planned
average current reaches 7 A with carbon 6+ beam.
A NEW INTENSE PULSED
ACCELERATOR
To obtain large beam power within a limited space,
cyclotrons have been chosen since they provide CW
beams even with relatively small peak beam current. In
this report, we propose a new approach to utilize
comparatively large beam power using a laser ion source
and a FFAG synchrotron accelerator.
Generally a synchrotron can have larger peak current
than cyclotron has, however most of the time is occupied
for ramping up and down the bending magnets in the
operation and the beam pulse width is very limited. To
increase the total beam power, it is effective to have high
repetition rate. The maximum repetition rate is about 1 to
25 Hz for normal conducting synchrotrons [1]. Recently
FFAG accelerators are being focused as high repetition
synchrotrons and some FFAGs have already been built by
KEK and Kyoto University groups both lead by Y. Mori
[2]. It has been proved to operate it at 100 Hz in KEK and
possibly it will run at 1 KHz. Also FFAG has large
transverse acceptance and is expected to deliver large
current.
A laser ion source (LIS) has an advantage to induce a
powerful pulsed beam and can operate at high repetition
rate which is restricted by a driver laser system. A typical
flash lamp pumped solid laser can reach 100 Hz and a
LED pumped laser easily achieves above 1 kHz operation
with good stability. Hence both a laser source and a FFAG
are operational at same high frequency range. Since a LIS
can provide large current, beam losses in a transport line
which connects from the ion source to a first stage
accelerator, typically RFQ, was always tough issue. To
overcome this difficulty caused by space charge effect,
direct plasma injection scheme (DPIS) has been studied.
Using the DPIS, several tens of mA heavy ion beams have
been accelerated effortlessly in an RFQ [3]. A rapid cycle
LIS with DPIS and a high current heavy ion RFQ suit a
FFAG well to boost the beam power.
In Kyushu University, a new facility called "Center for
accelerator and beam applied science" is established [4].
A new building was already constructed to accommodate
*Work supported by U. S. DOE
"okamura@bnl.gova FFAG accelerator which was originally designed and
constructed in KEK as a prototype 150 MeV FFAG. The
installation of the FFAG to the new building is in
progress. A small proton cyclotron will be used as an
injector in the first stage and in the next stage we plan to
install a new injector system to provide heavy ions for
various application including medical, engineering studies
and educational activities. A photo of the FFAG and its
design parameters are shown in Fig. 1 and Table 1.Table 1: Design Parameters of 150 MeV FFAG
Energy 10 - 125 MeV (proton)
2.5 - 31 MeV/u (C6-)
Type of magnet Triplet radial (DFD)
Number of cell 12
Average radius 4.47 - 5.20 m
Magnetic field Focus: 1.63 T
Defocus: 0.78 T
Revolution Frequency 1.5 - 4.2 MHz (proton)
0.78 -2.3 MHz (C6+)
Repetition rate 100 Hz (2 RF cavities)
The proposed heavy ion injector will accelerate fully
stripped ion beams up to 2.5 MeV/u with the highest
available current which will be induced by a conventional
table top laser system with the DPIS.
LASER ION SOURCE
Beam Pulse Width
The harmonic number of the FFAG ring is one and
revolution period at the injection energy is 1.28 s. With
single turn injection scenario, the required beam pulse
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Okamura,M.; Raparia, D.; Ishibashi, K.; Yonemura, Y. & Kanesue, T. Design study of a DPIS injector for a heavy ion FFAG, article, September 29, 2008; United States. (https://digital.library.unt.edu/ark:/67531/metadc901046/m1/3/: accessed April 26, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.