Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 49 (2016)

PPAC high-rate study with Z ∼ 50 beams (MS-EXP15-09)
H. Sato,∗1 K. Kumagai,∗1 D.S. Ahn,∗1 N. Fukuda,∗1 N. Inabe,∗1 T. Komatsubara,∗1 T. Kubo,∗1 K. Kusaka,∗1D. Murai,∗1 M. Ohtake,∗1 Y. Shimizu,∗1 T. Sumikama,∗1 H. Suzuki,∗1 H. Takeda,∗1 Y. Yanagisawa,∗1 andK. Yoshida∗1

ηX = {1 − (1 − ηF 3-1AX )(1 − ηF 3-1BX )}× {1 − (1 − ηF 3-2AX )(1 − ηF 3-2BX )},where ηF 3-1AX is the individual eﬃciency of the X
cathode of the A-side PPAC at F3-1; ηY is similarly
deﬁned.
Under this HV condition, PPACs were irradiatedwith high-rate beams in the range from 1 kHz to1000 kHz, and the occurrence of the discharge and thechange of the total eﬃciency were monitored. Firstly,
there was neither discharge nor trip of the voltage modules even in the case of irradiation with the 600 kHz
and 1000 kHz beams for 70 and 60 minutes, respectively. Secondly, the total eﬃciency decreased as beam
rate increased as shown in Table 1. If the electrodes in
the PPACs sustain damage, this decrease of the total∗1RIKEN Nishina Center- 156 -eﬃciency will happen and will be irreversible. However, ηX and ηY obtained with the 1 kHz beam inruns 612 and 621, which were performed just after irradiation with the 600 kHz and 1000 kHz beam respectively, reproduce the values obtained with the ﬁrst
1 kHz beam in run 602. Thus, we can conclude thatthe electrodes in the PPACs were not damaged by thehigh-rate beams up to 1000 kHz. The reason for thedecrease of ηX and ηY can be explained by the property of the delay line: the total delay time of the signal(118 ns for 150 mm delay line length and 192 ns for240 mm) results in the dead time of the PPAC. As aresult, the eﬃciency decreases for high-rate beams.
100
Individual efficiency [%]Position-sensitive Parallel Plate Avalanche Counter(PPAC) is one of the important focal plane detectors
for the Bρ measurement at RIBF1) . Owing to thefast response of the PPAC with the delay line readout,
the PPAC operated under the counting-rate of several MHz with the 2.5 MeV/u 4 He beam2) . However,sometimes a discharge of the PPAC due to high-rateheavy-ion beams results in damage to the electrodes
and causes the high voltage (HV) modules to trip1) .
Therefore, it is important to investigate the toleranceof the PPAC against intense heavy-ion beams.
An endurance test of the PPAC against high-rateheavy-ion beams was carried out in November 2015.
Two double-PPACs1) were placed in the F3 chamber of the BigRIPS separator. The upstream anddownstream PPAC are named as F3-1 and F3-2, respectively. The size of F3-1 (F3-2) is 150 mm(X) ×150 mm(Y) (240 mm(X) × 150 mm(Y)). Each doublePPAC has two delay-line PPACs in its case, termed
A- and B-side. Each PPAC is equipped with an antidischarge unit, which is currently under development
3). A mixed beam of around 132 Sn was used, whoseenergy at F3 was around 220 MeV/u. The beam sizein σ at F3-1 was 2.1 mm (X) and 3.1 mm (Y), and at
F3-2 the beam size was 7.5 mm (X) and 9.0 mm (Y).
Before irradiating the PPACs with intense beams,
the HV dependence of individual detection eﬃciencies
for each cathode was measured with a 1 kHz beam
(Fig. 1). Subsequently, the HV was adjusted for all
cathodes so as to realize the individual eﬃciency ofaround 95%. At that time, the total eﬃciency for X
and Y plane, ηX and ηY , was 99.86% and 99.92%,
respectively. Here, ηX is deﬁned as

100

9590

90

80

85

F3-180A-side,XA-side,YB-side,XB-side,Y75
7070
60
50
40

F3-2A-side,XA-side,YB-side,XB-side,Y6530690 700 710 720 730 740 750 760 690 700 710 720 730 740 750 760
High voltage [V]Fig. 1. Individual eﬃciency of each cathode. The adjusted
voltage for each PPAC is as follows: F3-1A, 700 V; F31B, 720 V; F3-2A, 720 V; F3-2B, 730 V.
Table 1. Total eﬃciencies of ηX and ηY .
runnumber
602
605
606
608
609
610
612
613
615
616
617
621

beam rate@F3 [kHz]
150
100
200
400
600
1600
600
1000
1000
1irradiation
time [min]51010101010530303030
5ηX[%]
99.8699.70
99.74
99.57
98.89
97.71
99.95
97.65
97.75
90.83
92.94
99.94

ηY[%]
99.92
99.83
99.80
99.72
99.30
98.52
99.96
98.49
98.52
93.30
94.57
99.96

References
1) H. Kumagai et al.: Nucl. Instrum. Meth. B 317, 717(2013).
2) H. Kumagai et al.: Nucl. Instrum. Meth. A 470, 562(2001).
3) Y. Sato et al.: JPS Conf. Proc. 6, 030124 (2015).