II-9. Instrumentation

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Safety interlock system for LINAC building
A. Akasiho,∗1 H. Sakamoto,∗1 and K. Tanaka∗1
An interlock system of the LINAC building toward
human safety (LHIS) works for human radiation safety
and compliance with radiation lows. Because the previous interlock system was operated for 30 years, it was
too complicated to operate and maintain through longterm repeated system improvements and generationalchanges of developers. Further, a machine protection
system (MPS), that is applied to accelerator machinesafety, was part of the previous interlock system. This
was an operational risk wherein both machine protection
and human safety systems were in the same system as
it was possible to cause operational conﬂict. Therefore,
the new LHIS was completely separated from MPS.
Figure 1 shows the chart for a new LHIS. In this system, a programmable logic controller (PLC) controls
each safety device in the LINAC building directory. The
indicator light shows “beam on” or “beam oﬀ” at the entrance doors of the irradiation room and the accelerator room, as shown in Fig. 2. The status of the doors
are monitored, and then the LHIS determines whether
beam irradiation is possible. When the radiation workers enter the irradiation rooms, all take safety keys torecognize the LHIS where the workers are in the roomand to inhibit beam irradiation. A radiation monitor
generates a signal to the LHIS if it detects an abnormal
dose level. Radiation dose level are recorded to radiation
monitoring system. An access control PC independent
from LHIS and operated by an access management system generate a signal to the LHIS if a worker handles
its entry operation during beam irradiation.
Figure 2 shows an operational screen for the LHIS
operational PC (LHIS PC) that sends operational commands to PLC as shown in Fig. 1. The schematic di-Fig. 2. Part of screen of LHIS PC. Positions of BSs are indicated.

agram of the LINAC building is displayed. The LHIS
covers three areas which are accelerator room, irradiation room of the Linac building, and the Connecting
building. Each area has its own beam shutter (BS) tostop the beam discretely if an interlock incident occur.
Each BS on the accelerator is set on its upstream partto stop a beam before entering the room, as shown inFig. 2. In the previous systems, a faraday cup, which
is applied for accelerator operation, is also commonly
applied as BS. The BSs are independent of the faraday
cups at LHIS.
Instructions are issued from the LHIS PC to PLC remotely. The LHIS PCs are set at a radiation control
room in the Nishina building and an accelerator operation room in the LINAC building. The position of each
operated device such as doors for the accelerator roomand the irradiation room is shown in Fig. 2. Green color
for the devices shows an acceptable status of a beamirradiation, corresponds to “close” for the door case. Ayellow color door shows abnormal status of door “open.”
All operations for the devices are recorded in the LHIS
PCs.
LHIS is handled by the accelerator operators for RILAC. The operators choose a button on the screen forthe beam irradiation area. Then LHIS analyzes conditions of the safety devices for accelerator operation andbeam irradiation. A BS opens if all statuses are good.
If any status is not suﬃcient, an “abnormal” indication
is displayed and the BS does not open. While the BS
open, if a door for accelerator or irradiation rooms open,
the LHIS status changes to “abnormal” and BS closes.
The LHIS operation was successfully started at October 2019. At 2020, a rotating red light was installed at
the entrance of the irradiation room to show the X-ray
risk by the RILAC RF cavity.

Fig. 1. Conceptual diagram for new LHIS.
∗1

RIKEN Nishina Center- 119 -1