Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 53

Performance of a none-isochronous position-sensitive detector for theRare-RI Ring
R. Crane,∗1 S. Naimi,∗1 S. Hosoi,∗2 M. Mukai,∗3 H. F. Li,∗1,∗4 Y. Abe,∗1,∗5 D. Nagae,∗1,∗6 D. Hamakawa,∗2Y. Inada,∗2 D. Kajiki,∗2 M. Sakaue,∗2 W. B. Tou,∗2 and K. Yokota∗2
We have developed a large area position-sensitive detector with a thin foil to be used for mass measurementwith the Rare-RI Ring.1) The principle of the detector operation is shown in the bottom of Fig. 1. Whenhigh energy beam passes through the thin foil, secondary electrons (SEs) are released and reﬂected by
the outer and inner mirror grids potential. The SEs
energy is determined by the acceleration grid placed
after the foil. The beam position is inferred from SEs
position measurement with the delay line MCP placed45◦ from the foil. To minimize the eﬀect of the SEs initial velocity, the detector has an isochronous design,2)which is achieved by careful choice of geometry and potentials: D/(L1 + L2 ) = 0.236Umir /Uacc , where Umirand Uacc are the acceleration and mirror potentials, respectively, D, L1 and L2 are dimensions of detector as
shown in Fig. 1. We have designed the detector to beoperated in the isochronous condition and also in thenone-isochronous condition, simply by modifying thedistance D between the inner and outer mirror grid.
In the isochronous detector operation D = 28 mm,
while for the none-isochronous operation D = 8 mm.
We have tested the detector at HIMAC with
200 MeV/nucleon 84 Kr beam in both isochronous (Iso)and none-isochronous (None-Iso) operation. For theIso detector we tested the performance for a grid pitchof 1 mm, while for the None-Iso detector 1 mm and2 mm pitch were tested. The test results are summarized in Table 1. The detector position accuracy
is determined by the deviation from the foil image reconstructed by two PPACs. The position resolution isdetermined from a 2 mm diameter gate on the reconstructed foil image. For the mass measurement with
the Rare-RI Ring the accuracy and resolution of thehorizontal position are critical. The horizontal resolution of the None-Iso is better than the Iso detector.
The position accuracy of the None-Iso detector with2 mm grid pitch is best, because we introduced a calibration mask in front of the foil to correct for any misalignment between the PPACs and the detector that
could result in a compromised position accuracy.

∗1
∗2
∗3
∗4
∗5
∗6

RIKEN Nishina Center
Department of Physics, Saitama University
Department of Physics, University of Tsukuba
IMP, CAS
National Institute of Radiological Sciences (NIRS), QST
Faculty of Sciences, Kyushu University

Beam 84Kr 200MeV/uTrigger
Plastic

PPAC1DL-E-MCPchamber

PPAC2Correction gridOuter mirror grid

DActive area ofincident heavy ion

Beam

Inner mirror grid

45°SEsConversion foil

L2

L1

Accelerating grid

SEs

Imaging area of SEs

MCP with position sensitive anodeFig. 1. (Top) Experimental setup at HIMAC consisting ofa trigger plastic scintillator, two PPACs and a vacuum chamber containing the DL-E-MCP. (Bottom)
Side view of the DL-E-MCP detector, where the beam
passage through the foil generates secondary electrons
that are reﬂected to the MCP with position-sensitive
delay line anode.
Table 1. The detector position accuracy Ax,y and resolution in sigma (σx,y ) are shown for both horizontal(x) and vertical (y) beam positions for diﬀerent detector operation; Isochronous (Iso.) and none-isochronous(None-Iso.). The performance of the latter is shown for
two diﬀerent grid pitch of 1 mm and 2 mm. The results
are shown for the same acceleration potential and different optimized mirror potential in each conﬁguration.

Ax [mm]Ay [mm]σx [mm]σy [mm]Iso.
1 mm pitch
+4.0
−0.1
3.5
2.2

None-Iso.
1 mm pitch+1.50.02.42.9None-Iso.
2 mm pitch−0.8+0.6
2.9
4.5

References
1) Z. Ge et al., RIKEN Accel. Prog. Rep. 50, (2017).
2) N. Nankov et al., Wiss. Tech. Berichte (Annual Report2004) FZR-423, 25 (2005).

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