Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 50 (2017)

Design work of rf ion guide system at the SLOWRI facility
A. Takamine,∗1 M. Rosenbusch,∗1 P. Schury,∗2 J. Y. Moon,∗3 M. Wada,∗1,∗2 H. Miyatake,∗2 Y. Ito,∗1
T. Sonoda,∗1 Y. X. Watanabe,∗2 Y. Hirayama,∗2 T. Sato,∗1 T. M. Kojima,∗1 I. Katayama,∗1 H. Wollnik,∗1,∗4and H. Ueno∗1
We are developing an rf ion guide1) gas catcher cellat the SLOWRI facility towards online commissioning in FY2017. We initially designed a large travelingwave rf carpet for the ion transport in the gas cell.
The carpet had such a large capacitance due to its
large area of 600 cm2 with 0.28 mm pitch and 0.14 mm
separation for stripe electrodes that the resonance frequency was less than 1 MHz to obtain a voltage greater
than100 Vp.p. .
We designed a new conﬁguration that consists ofthree-stage rf transport electrodes as shown in Fig. 1
so as to reduce the areas of the rf carpets. The ﬁrst
electrode is composed of DC, RF+DC, gap, RF+DC,and DC parts with long strip electrodes. It producesa hemisphere’s electrostatic potential to collect thermalized ions onto the central RF+DC parts. Whenthe ions reach close to the electrode surface, they are
guided to the gap by the rf ion guide method,1) extracted from the gap, and pulled onto the second electrode by electrostatic ﬁelds between the ﬁrst and thesecond electrodes. We utilize the ion surﬁng method2)
to transport the ions downstream with a traveling wave
produced with superimposed RF and AF ﬁelds. Whenthe ions arrive at the downstream edge, they are again
pulled onto the third electrode, transported to an exit
hole, and extracted to the outside of the gas cell. We
plan to place a block in front of the third electrode to
avoid the direct impinging of ion beams on the electrode. This scheme has an advantage in that He ions,which create space charge, produced by beam thermalization can be killed on the ﬁrst electrode because of
the small mobility of He ions. Although the ion surﬁng
method provides faster transport compared with theconventional rf ion guide method, it is more susceptible to a space charge eﬀect. This is why we selectively
use the two methods.

s-eye viewFig. 1. New design of the rf ion guide system in the gas cell.
The size of the cuboid frame is 160×260×1470 mm.
∗1∗2∗3∗4RIKEN Nishina Center
Wako Nuclear Science Center (WNSC), IPNS, KEK
Institute for Basic Science
Department of Chemistry & BioChemistry, New Mexico
State University- 193 -021126

Fig. 2. Enlarged drawing of a part of the ﬁrst-stage electrode.

The DC potential conﬁguration on the ﬁrst electrodedetermines the amount of ions collected in a narrow region, which is important to reduce the area of an RFpart. Because the ion’s motion simply follows the linesof the electric ﬁeld, a ∝ 1/x potential produced by apoint charge would be the best solution to focus ions.
In order to emulate such a ﬁeld, we designed a DC partas shown in the Fig. 2 by changing the width of eachelectrode. The blue line in Fig. 2 shows the potential with a constant voltage step between the adjacentelectrodes and the red line shows a ∝ 1/x potential on
the DC part and a ∝ x potential on the RF+DC part.
We also conﬁrmed that the ∝ 1/x potential produces
the best focusing ion collection among three types ofpotentials (∝ 1/x, ∝ x, and ∝ log(x)) in SIMION simulations. From the simulation result, we set the area of
each RF+DC part as 121 cm2 (25 mm×485 mm) with
0.32 mm pitch and 0.16 mm separation. We expectthat the capacitance will be reasonably small and wecan apply an rf voltage at several MHz with suﬃcient
voltages for the rf ion guide. We will start an rf testwith an actual electrode soon.
Simulations for space charge in this conﬁguration are
also in progress. The simulation is based on a stateof-art simulation code “3DCylPIC”3) in coorperation
with Dr. Ringle from NSCL. In the simulation forthe case of the incoming beams in the mid-heavy mass
region, preliminary results show that this system will
be tolerable to an incoming beam intensity of 106 pps.
We ﬁnalized the design of the ﬁrst-stage rf carpet.
The designs of the second- and the third-stage electrode will also be ﬁnalized soon. We plan to start ofﬂine tests of the rf transport system using ion sourcesfrom Mar. 2017 and conduct online commissioning in
the later half of FY2017.
References
1) M. Wada et al., Nucl. Instr. Meth. B 204, 570 (2003).
2) G. Bollen: Int. J. Mass Spectrom. 299, 131 (2011).
3) R. Ringle: Int. J. Mass. Spectrom. 303 42 (2011).