Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 47 (2014)

Design work for PALIS system
T. Sonoda,∗1 M. Wada,∗1 I. Katayama,∗1 N. Fukuda,∗1 H. Iimura,∗2 N. Inabe,∗1 T. Kubo,∗1 K. Kusaka,∗1H. Takeda,∗1 H. Suzuki,∗1 M. Wakasugi,∗1 K. Yoshida∗1 and SLOWRI collaboration
In FY2013, the construction budget for a low-energy
RI-beam facility SLOWRI was ﬁnally founded. The
design drawing for the PArasitic slow RI-beam production by Laser Ion Source (PALIS)1) was ﬁnalized.
We will restore unused RI-beams for producing slow
RI-beam by installing a gas catcher in the vicinity ofthe second focal plane (F2) of the fragment separator BigRIPS. This will enable the use of parasitic slow
RI-beams for various precision experiments whenever
BigRIPS experiments are in operation.
In order to realize the reasonable performance undervarious constrained conditions, there are a lot of novel
methods taken into the PALIS design. In particular,
the following three worthwhile items were resolved asto avoid any interference to the BigRIPS main beamexperiments. The ﬁrst item is the position of the gascell, which should be able to move horizontally on thex-axis perpendicular to the BigRIPS beam direction.
At F2, RI-beams with slightly diﬀerent isotones are focused on alongside the x-axis. By applying an overhead
beam extraction, the PALIS gas cell collects such theisotone beams neighboring a BigRIPS main beam at
both the neutron-rich and neutron-deﬁcient sides, respectively. The extracted RI-beams from the gas cell
are transported along the y-axis to the height of 70
cm from the BigRIPS beam, where it bends by 90 degrees in another beam line comprising several bellow
combinations. Using a stepping motor, the PALIS gas
cell can be moved -60 mm away from the central axisof the BigRIPS beam, and is also pulled by +160 mm
toward the evacuation site.
The second item is the diﬀerential pumping system
for realizing the gas cell pressure for Ar/He up to 105
Pa under the totally separated vacuum condition between the PALIS beam line and the BigRIPS F2 chamber. So far, we have developed a novel implementationof diﬀerential pumping, in combination with a sextupole ion beam guide (SPIG), which allows a pressure diﬀerence from 105 to 10−3 Pa within a drastically miniaturized geometry compared to conventionalsystems2) . This system can utilize a large exit holefor fast evacuation times, minimizing the decay loss
for short-lived nuclei during the extraction from a gascell, while a suﬃcient gas cell pressure is maintained
for stopping high-energy RI-beams. By following thismethod, the gas evacuation lines become compact NWbased ﬂanges, resulting in the complete separation ofthe PALIS vacuum from the BigRIPS beam line.
The third issue is the preparation of the high-voltage∗1∗2RIKEN Nishina Center
Japan Atomic Energy Agency- 208 -platform for ion acceleration, which is necessary for theelectrical isolation between the PALIS gas cell, following the beam extraction system including the evacuation lines of diﬀerential pumping, and the grounded
beam lines. The low-energy RI-beam from PALIS
should be transported to the SLOWRI experimentalroom via 50 m long low-energy beam line. Therefore,ion acceleration is indispensable, while any problem induced from high voltage breakdown should be avoided
for the protection of BigRIPS beam proﬁle detectors
placed in the F2 chamber. For the ﬁrst phase, we will
adopt the pulsed cavity method3) located at the outside of the F2 chamber. The extracted low-energy RIbeam transported via SPIG and QMS ﬁrst enters a linear ion cooler-buncher, and then, the produced pulsed
beam is accelerated toward a cavity at the potential of
about 1 kV. When the ion pulse reached the ﬁeld-free
region inside the cavity, the fast switch applies a highvoltage potential about 30 kV, the latter is switchedagain to ground potential for ion acceleration. Thispulsed cavity consists of MRTOF4) in expectation offuture isobar puriﬁcation. By this way, the electricalisolation is no longer necessary.
The PALIS design work has been almost ﬁnalized, as
shown in Fig. 1. The oﬀ-line and on-line commissioning
test for PALIS will be started from June 2014.

Fig. 1. BigRIPS F2 chamber implemented with PALIS.

References
1) T. Sonoda et al.: AIP Conf. Proc. 1104 132 (2009).
2) T. Sonoda et al..: Nucl. Inst. and Meth. B 295 1(2013).
3) F. Herfurth et al..: Nucl. Inst. and Meth. B 469
254(2001).
4) Y. Ishida et al.: Nucl. Inst. and Meth. B 241 983(2005).