Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Improvements in cooling operations of the SAMURAI magnet
H. Sato,∗1 H. Otsu,∗1 M. Kurata-Nishimura,∗1 M. Ohtake,∗1 and K. Kusaka∗1
The operational policy for the SAMURAI superconducting dipole magnet is that the magnet is cooled foreach SAMURAI campaign experiment and warmed after the experiments in order to save operating time andthus extend the cryocooler maintenance cycle. In linewith this policy, the magnet has been at room temperature since 2020. Cooling operation of the magnet
was performed from 2022/5/9 to 2022/6/2 for the upcoming experiments. Previously, we reported on theﬁrst magnet cooling conducted in 2014.1) This report
describes the improvements made to the work environment and operating procedures since then.
The procedure for cooling is as follows:



(1) evacuation of the vacuum layers of the coil vessels,(2) pre-cooling of the coils with liquid nitrogen,(3) removal of liquid nitrogen,(4) replacement of the inside of the coil vessels withgaseous helium,(5) transfer of liquid helium into the coil vessels.
This series of operations are performed in parallel,
shifting by one week for the upper and lower coils.
For (2), we have extended the liquid nitrogen inlet
to be closer to the magnet (Fig. 1). As a result, thehandling of liquid nitrogen ﬁlling was improved, theﬁlling operation was reduced from three days to twodays for a coil, and total liquid nitrogen was reduced
from 7125 L (2014) to 5700 L (2022).
For (5), a new gaseous helium recovery port wasinstalled near the magnet to facilitate recovery line
preparation and eﬀective collection of gaseous helium(Fig. 1(b)). We also introduced a 1000 L liquid helium
container and a long transfer tube. Previously, morethan ﬁve 250 L containers were needed to cool a coil. In
practice, two containers were used one after the other,making it laborious to reﬁll liquid helium and transport
the containers from the RIBF building to the heliumliquefaction building in the south area of the Wako
campus. After introducing the 1000 L container, it
was only necessary to transport one 1000 L and one
250 L container at a time. Furthermore, because of
the long transfer tube, liquid helium could be poured
from the containers placed on the ﬂoor (Fig. 2). Inaddition, as the container only needs to be exchanged
once, the loss of liquid helium was reduced, resulting ina reduction in total liquid helium from 3145 L (2014)
to 2237 L (2022). The ﬁlling process was also reduced
for a coil from two days to one day.
One of the remaining issues to be improved would beto place the exhaust port near the magnet for gaseous∗1Fig. 1. The tube for liquid nitrogen and the recovery port
for gaseous helium. (a) photo in 2014. There was norecovery port near the magnet. (b) photo in 2022.

Fig. 2. Liquid helium transfer to the lower coil using the1000 L container with the long transfer tube.

nitrogen generated during pre-cooling. Currently, weuse the port located in the ceiling of the elevator hall.
Reference1) H. Sato et al., RIKEN Accel. Prog. Rep. 48, 201 (2015).

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