Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 49 (2016)

Current status of a gas-cell system for precision experiments withGARIS-II
Y. Ito,∗1 P. Schury,∗1,∗2 M. Wada,∗1,∗2 F. Arai,∗1,∗3 I. Katayama,∗1 I. Murray,∗1 K. Okada,∗4 M. Reponen,∗1T. Sonoda,∗1 A. Takamine,∗1 H. Wollnik,∗1,∗5 H. Haba,∗1 D. Kaji,∗1 K. Morimoto,∗1 K. Morita,∗1,∗6
S. Kimura,∗2,∗3 and H. Koura∗7
We constructed a gas cell for precision experiments
on fusion-evaporation residues coupled with GARIS-II.
In the last report1) , we presented the commissioningresults. In this report, we present the current statusof the whole system, from the gas cell to the multireﬂection time-of-ﬂight mass spectrograph (MRTOF)(Fig. 1).
For precision mass measurement with MRTOF2) , weinstalled an upstairs radio-frequency ion trap systemafter extraction from the gas cell. The ion trap system comprises a ﬂat trap3) (FT) and a pair of resistive ion traps (RT). The RT stores and pre-cools
ions before transferring them to the FT. For this function, we adopted four silicon electrodes with electricalcontacts at both edges and 30 mm from the FT side.
The electrodes have 6 mm width and 145 mm length
which corresponds to the resistance of 330(10) Ω andan inter-strip gap of 8.4 mm. Ions extracted from thegas cell were ﬁrst stored in the RT for several millisecGas cellERs fromGARIS-II

Resistive
Sitraptrap

upstairs trap
up-OrthosystemFlat trap

SPIG
up-PDT
RF carpet

Alkali ISSSD
CEM

LTOF1

up-Thru

DegraderMultipole lensBN gateLTOF2dn-PDTMCP

MRTOF

downstairs trapsystemdn-Ortho

Reference IS
dn-Thru

Fig. 1. Schematic view of the gas cell setup with MRTOF.
∗1∗2∗3∗4∗5∗6∗7

RIKEN Nishina Center
Institute of Particle and Nuclear Studies (IPNS), High Energy Accelerator Research Organization (KEK)
Department of Physics, University of Tsukuba
Department of Physics, Sophia University
Department of Chemistry and Biochemistry, New Mexico
State University
Department of Physics, Kyushu University
Advanced Science Research Center, Japan Atomic Energy
Research Institute (JAEA)- 183 -onds, and then, they were transfered to the FT andbunched in the FT (3 ms). The ion bunch was ejectedto the experimental room located downstairs througha 3-m beam transport line (BTL). To accelerate the ionbunch, we used pulsed drift tubes (PDT) that hace a
15 mm inner diameter and 150 mm length. The PDT
was switched from -1.5 kV to a GND potential of theBTL with 200 ns rise time when the ions are traveling in the tube. As a result, the ions gain 1.5 keVand are transported in the grounded BTL. In the middle of the BTL, we installed a Bradbury-Nielsen (BN)gate that has a 50 µm gold-coated tungsten wire witha 0.5 mm pitch and is capable of eliminating unwanted
ions by fast voltage switching. After the BN gate, weplaced another PDT that is switched oppositely to theone upstairs. The ions are decelerated to be ∼50 eVfrom the PDT by focusing lenses toward a downstairs
trap system identical to the one upstairs. The decelerated ions were re-bunched in the same manner as thoseupstairs and ejected toward the MRTOF at the TDC
start time to measure time-of-ﬂight.
Using several diagnostics, SSD and channeltron(CEM) detectors, we evaluated eﬃciencies. First, wecounted the 205 Fr rate by SSD in front of the gas cell;then we counted the 205 Fr+ rate by SSD at LTOF2
located after the BN gate. The eﬃciency to LTOF2
compared to the incoming 205 Fr was given as 19%.
Second, we measured the BTL transmission eﬃciency
using SSDs at LTOF1 and LTOF2, and obtained theeﬃciency of 70%. By using the pre-measured gas-cell
eﬃciency of 29%1) , we could obtain the eﬃciency of94% for the upstairs trap system. Finally, the retrapping eﬃciency for the downstairs trap system wasmeasured to be 1.6% using the 205 Fr+ rate at MCP after the MRTOF and 205 Fr+ rate at LTOF2. In total,
the overall eﬃciency of 0.3% was obtained.
The bottleneck was after re-trapping eﬃciency thatwas expected to be more than 20%. We recently foundmis-wiring to apply DC voltages for the downstairs
trap system. The potential created with this wiring
resulted in an unreasonable potential conﬁguration fortransferring ions to the FT. We ﬁxed the problem andwill check the eﬃciencies in next beam time.
References1) P. Schury et al.: RIKEN Accel. Prog. Rep. 48, 22(2015).
2) P. Schury et al.: arXiv:1512.00141.
3) Y. Ito et al.: Nucl. Instrum. Meth. B 317, 544 (2013).