Beam dynamics studies on the ISAC-II post-accelerator at TRIUMF. Page: 1 of 3
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BEAM DYNAMICS STUDIES ON THE ISAC-II POST-ACCELERATOR AT
TRIUMFM. Pasini, R.E. Laxdal, TRIUMF, Vancouver, Canada
P.N. Ostroumov, Argonne National Lab, USAAbstract
The TRIUMF/ISAC facility, now a world leader in rare
isotope production and acceleration, is constructing ISAC-
II [1, 2], that will allow the acceleration of ion beams with
3 < A/q < 7 to an energy of at least 6.5 MeV/u for masses
up to 150. The upgrade will include the addition of a su-
perconducting heavy-ion linac delivering an effective volt-
age of 43 MV. The first order design of the new transfer
lines and post-accelerator have been optimized to provide
simultaneous acceleration of several charge states (multi-
charge). The quarter wave resonators providing the accel-
eration have inherent rf electric and magnetic asymmetric
components that complicate multi-charge acceleration and
can lead to transverse emittance growth. In particular we
report the realistic field simulations of the medium beta
section of the SC-DTL for multi-charge acceleration.
1 INTRODUCTION
A first stage of ISAC-II installation will see a trans-
fer line constructed from the ISAC-I DTL exit to join the
medium-beta section of the ISAC-II SC linac for accelera-
tion of lighter ions, A < 60, to energies above the Coulomb
barrier. A schematic of the ISAC-JI linear accelerator com-
plex is shown in Fig. 1. The building for ISAC-II is now
under construction with beam delivery from the first stage
due in 2005.
A comprehensive first order design study[3], now com-
plete, set the parameters of the floor layout prior to building
construction. The solution includes all transport beamlines,
including the first stage transfer line and second stage 90
isopath bend section[4] as well as the first order dynam-
ics of the super-conducting linac. Designs are compatible
with multi-charge acceleration to preserve beam intensity
and/or allow the possibility of a second optional stripping
stage to boost the final ion energy. A two-gap quarter waveStage 2
34A/qs10 E=6.5MeV/u (A/q=7)
MEBT2 HEBT2-Exp.
Low f S2 Medium P High P
S1 E=0.4MeV/u
E=1.5MeV/u
IH-DTL2
11Stage 1
7 A/q'6
.E=0.15-15SMeV/u --'
HEBT1-Exp.
IH-DTL1
Figure 1: A schematic for the ISAC-II linac with Stage 1
and Stage 2 installations complete.bulk niobium structure[5] is chosen for ISAC-JI with three
cavity geometries corresponding to low, medium and high
)o (4.2%, 7.2%, 10.5%) values and rf frequencies of 70.7,
106.08 and 141.4 MHz respectively. Design gradients are
set at 5 MV/m for the low beta cavities and 6 MV/m for the
medium and high beta sections. The large gradients pro-
duce proportionally larger defocussing and steering fields
and together with multicharge acceleration pose new chal-
lenges for heavy ion linac design.
2 BEAM SIMULATION CODES
The envelope codes TRACE-3D and COSY-oc have been
used to design transfer lines and optimize linac lattice pa-
rameters. The Monte-Carlo code LANA has been used to
set the first order specifications of linac parameters assum-
ing standard cavity field approximations. Electromagnetic
fields created with HFSS and CST-MWS are then installed in
LANA and TRACK to study 'realistic' acceleration dynamics.
TRACK is also used to study the effect of misalignments of
linac components.
3 STAGE 1 BEAM DYNAMICS
Detailed beam dynamics simulations have concentrated
on Stage 1 with five, four cavity medium beta cryomodules
and two six cavity high beta cryomodules. A single su-
perconducting solenoid is positioned at the center of each
cryomodule for transverse focussing with diagnostic boxes
positioned between cryomodules at waists in the transverse
envelopes (Fig. 1). Solenoids provide a larger transverse
acceptance than quadrupoles for transporting beams with
multiple charge states[6].
3.1 First Order Simulations
The simulations include all transport from the output of
the ISAC DTL to the end of the 7-module ISAC-JI SC linac
for two single charge cases corresponding to ions with A/q
of 3 and 6 and for a multicharge case with reference ion
132Sn31+ with five charge states, Q 29, ...33, accelerated
through the SC linac simultaneously. The lattice easily ac-
commodates the rf defocussing from the high gradient cav-
ities (Fig. 2(a)). The longitudinal emittance is broadened as
each charge revolves around a different synchronous phase.
The transverse emittance increase is < 5%.
3.2 Realistic Field Dynamics
Realistic field studies are complete for the 10.5 m long
medium beta section consisting of five cryomodules with
four cavities and one 35 cm long superconducting solenoid
in each. Two main asymmetries in the medium beta cavity
fields are responsible for differences between the 'simple
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Pasini, M.; Laxdal, R. E. & Ostroumov, P. N. Beam dynamics studies on the ISAC-II post-accelerator at TRIUMF., article, June 26, 2002; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc742995/m1/1/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.