Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 51 (2018)

Timing performance of a mirror-type MCP detector use for massmeasurements at the Rare RI Ring
Z. Ge,∗1,∗2,∗5 S. Naimi,∗1 D. Nagae,∗1 Y. Abe,∗1 S. Omika,∗1,∗2 F. Suzaki,∗1 H. F. Li,∗1,∗5 T. Uesaka,∗1Y. Yamaguchi,∗1 M. Wakasugi,∗1 T. Yamaguchi,∗1,∗2,∗3 N. Tadano,∗2 K. Wakayama,∗2 A. Ozawa,∗1,∗3S. Suzuki,∗3 T. Moriguchi,∗1,∗3 H. Arakawa,∗2 K. Inomata,∗2 T. Kobayashi,∗2 G. Lorusso,∗4 and Y. Yano∗1High resolution time-of-ﬂight (TOF) measurements
are crucial for mass measurements via TOF methods
such as in-ring isochronous TOF or beam-line BϱTOF. To characterize and optimize the timing resolution of a mirror-type micro-channel plate (MCP)
detector1) with a timing anode, an experiment aimed
at studying the performance of the detector was conducted at HIMAC (Heavy Ion Medical Accelerator inChiba). We demonstrate preliminary online results ofthe timing detector which can be used for the revolution time measurement inside the Rare RI Ring2)(R3), start TOF of the total TOF for in-ring circulation, beam-line TOF measurement for beam-line mass
determination and velocity reconstruction for in-ringmass correction.
To investigate the properties of the detector,a primary beam of 84 Kr36+ at the energy of
200 MeV/nucleon is used. The experimental setup is
shown in Fig. 1(a). The setup consisted of two parallel plate avalanche chambers (PPACs) for beam tracking, one electrostatic MCP detector, two plastic scintillators for intrinsic timing resolution deduction of themirror detector. The MCP with a diameter of 40 mm ismounted on a triangular detector structure as shown inFig. 1(b). The conversion foil is made of mylar (2 µm)
coated with aluminium. The accelerating grid consisting of gold-plated tungsten (W+Au) wires (40 µm indiameter) possesses a distance of 8 mm from the conversion foil with a 1 mm pitch, and wires (W+Au) for
the inner and outer mirror grids are arranged with a3 mm pitch. During the experiment, the high voltage (HV) potential of the MCP, accelerating grid andinner mirror were set at 2.5 kV and the accelerating
HV of the foil and outer mirror grid were varied. The
timing resolution for isochronous and non-isochronouscondition3) has both been studied by the experimentand simulation performed via SIMION4) as shown inFigs. 1(c) and (d). The distance between the outermirror and inner mirror is 20 mm for isochronous condition, while it is 8 mm for the non-isochronous condition. As demonstrated from Figs. 1(c) and (d), when
the accelerating HV is increased, the timing resolution
improves for both conﬁgurations with the corresponding settings.
∗1
∗2
∗3
∗4
∗5

As can be seen from Figs. 1(c) and (d), the trendsof timing resolution (only statistical errors included)
as a function of the accelerating HV for the simulation and experimental results are consistent with eachother. Simulation results show that a timing resolutionof less than 20 ps could be achieved. However, the experimental results could not be achieved and seem tobe saturated around 40 ps for both conditions. One
possibility could be systematic error from the data acquisition electronics. The detection eﬃciency reaches∼ 96% by suitable arrangement of the MCP positionon the support plate of the triangular structure fromthe theoretical calculation of the electromagnetic motion of the secondary electrons inside the detector.

Fig. 1. (a) Schematic diagram of the setup for HIMAC
experiment. (b) The side view of the MCP detector
structure. (c) and (d) depict the timing resolution (inσ) as function of the accelerating HV potential (the HV
diﬀerence between the accelerating grid and conversionfoil) for isochronous and non-isochronous condition, respectively. The red points are simulation results andthe blue points display the experimental results. The
HV values described in this report are all negative andin the unit of kV, and values in brackets correspond to(accelerating HV, outer mirror HV).

References
1) Y. Abe et al., RIKEN Accel. Prog. Rep. 47, 200 (2014).
2) A. Ozawa et al., Prog. Theor. Exp. Phys. 2012, 03C009(2012).
3) Z. Ge et al., RIKEN Accel. Prog. Rep. 50, 187 (2017).
4) http://www.simion.com.

RIKEN Nishina Center
Department of Physics, Saitama University
Institute of Physics, University of Tsukuba
Department of Physics, University of Surrey
Institute of Modern Physics, Chinese Academy of Sciences- 152 -