Ⅱ-8. Accelerator

RIKEN Accel. Prog. Rep. 52 (2019)

Radiation monitoring for cycrotrons in RIBF
M. Nakamura,∗1 K. Yamada,∗1 A. Uchiyama,∗1 H. Okuno,∗1 and M. Kase∗1
Recently, we attempted to monitor the radiation due
to beam loss in the RIBF using ionization chambers(ICs).1) Usually, we investigate the radiation from theelectrostatic deﬂection channels (EDC) at RRC andSRC. We input the alarm signal from these ICs to thebeam interlock system (BIS).2,3) However, four ring cyclotrons RRC, fRC, IRC, and SRC are used in the caseof 238 U86+ beam acceleration. Hence, we installed theICs near the EDC of fRC and IRC. Last year, we conducted tests by inputting the alarm signal from the IC
signal near the EDC of the IRC. In this report, we attempted to input the alarm signal from the IC near theEDC of fRC to BIS.
We considered the alarm levels of the ICs by comparing the signals from the ICs with those from the thermocouples (TCs) set at the septum of RRC, IRC, andSRC.2,3) Suppose that a beam deposits a 600 W heatat the septum electrode of the EDC. The temperaturerise at the beam loss point is estimated to be 800◦ C
based on a thermal analysis using the ﬁnite element
method. At this moment, the temperature diﬀerence
between the TC set at the nearest part where the beam
was irradiated and the cooling water of the septum becomes 10◦ C. In contrast, the septum is made of Cu andits melting point is 1080◦ C. Therefore, the septum cannot be melted at these conditions. However, to protect
against the risks of damage caused to the septum, thealarm level of the temperature diﬀerence of TCs was
set to 10◦ C. Hence, we compared the temperature difference on the septum with the IC signal near the EDCof fRC in the user time (UT) of the 238 U86+ beam. Theresult is shown in Fig. 1. The data demonstrated little
dispersion and we can obtain a calibration curve (redline), as shown in Fig. 1. From this curve, we can recognize that the voltage of the IC became approximately
0.55 V when the temperature diﬀerence became 10◦ C.
From October 16 to December 16, the 238 U86+ ion
beam was accelerated to 345 MeV/nucleon. Usually,
we collected the data of TCs and IC within 7–10 days
from the beginning of the UT of RIBF. Based on thisobservation, we determined the alarm level of IC andset it to BIS, which is the time available between thisexperiment and the next. However, in this term, wecould not ﬁnd any vacant time to input the alarm signal
to BIS. Thus, we compared the data when the BIS acted
on the signal from the TCs set at EDC of fRC withthe data of IC set near the EDC of fRC. We can thenconsider the propriety of the alarm level of the IC signal.
The IC signal from 0:00 to 5:00 on 12/3/2018 isshown in Fig. 2 as typical example data. From 2:08
to 2:50, BIS acted 20 times by the sudden temperaturerising of EDC for the instability of electric ﬁeld of fRC.
∗1Fig. 1. Correlation of IC voltage and the temperature difference on the septum.

Fig. 2. Signals from the IC installed near the EDC of fRC.

During this term, the value of IC set near the EDC
distributed from 0.56 to 1.05 V. Such phenomena werefrequently observed on other days of this UT. On observing the IC signals when the BIS from TCs signals
acted in this UT, the alarm level of IC described above
is found to be reasonable.
We performed investigations by inputting the alarm
signal to the BIS during the machine time of the238 86+Uion beam. However, we could not input thesignal from the IC set near the EDC of fRC. Hence, wewill investigate the alarm signal from fRC to BIS nexttime.
References
1) M. Nakamura et al., RIKEN Accel. Prog. Rep. 50, 152(2017).
2) M. Nakamura et al., RIKEN Accel. Prog. Rep. 49, 146(2016).
3) M. Nakamura et al., RIKEN Accel. Prog. Rep. 48, 237(2015).

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