Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 51 (2018)

Present status of the beam transport line from SRC to BigRIPS
K. Kusaka,∗1 K. Yoshida,∗1 M. Ohtake,∗1 and Y. Yanagisawa∗1
The beam transport line that delivers a primary beam
extracted from SRC to the BigRIPS target has been
operated since 2007 and is called the “T-course” beamline. The T-course beam line consists of three bending
magnets and 17 quadrupoles.1,2) All of them are of theresistive type, and the maximum magnetic rigidity of thebeam line is 8.0 Tm. Two identical 50◦ bending magnets
DMT2 and DMT3 in the T-course are “2-Tesla” roomtemperature dipoles, the maximum current of which is650 A. Here we report the incident we faced in 2017 atthe DMT3 magnet.
Since the DMT2 and DMT3 magnets are designed as
high-ﬁeld resistive-type magnets with suﬃciently uniform ﬁeld distribution, saddle-shaped correction coils
are installed in the gap of the magnet in addition to themain coils. The main and correction coils are excited inseries with one power supply. As shown in Fig. 1, the12-layer main coil consists of 6 double pancakes in which
a 13.5 × 13.5 mm hollow conductor is wound 6 times ineach layer. For the correction coils, a 14 × 10 mm rectangular hollow conductor of is wound 6 times in eachlayer, forming a 2-layer double pancake. The correction
coil end is located between the main coil and the poleend.
At the beginning of the uranium beam time in October 2017, we found that one of the correction coils in theDMT3 magnet was damaged. Figure 2 shows the excitation voltage at each pancake of the DMT3 coils loggedon October 14. The voltage of the lower correction coil
was unstable and much lower than that of upper correction coil. We concluded that the layer isolation of
the lower correction coil was damaged. We then investigated the lower correction coil by inserting a ﬁberscope
CCD camera into the space between the main coils of
the DMT3 magnet. Damage to the epoxy isolation between the coil layers was found at many places on theouter circumference of the lower correction coil (Fig. 3).
In order to proceed with the scheduled beam time, wehave isolated the lower correction coil from the excitation circuit, and the DMT3 magnet was re-excited after
increasing the ﬂow rate of the cooling water for the coils.
After beam-time suspension for 5 days, a uranium beam
was transported from SRC to the BigRIPS target andscheduled experiments were performed. The excitation
current of the DMT3 magnet during the beam time wasapproximately 647 A, which is close to the maximum
current of 650 A. The temperature and excitation voltage of the DMT3 coils were carefully monitored during
the beam time.
A new correction coil is being fabricated at Toshiba,
and the disassembly of the DMT3 magnet and installation of the new coil is scheduled for March 2018. The
origin of the incident is under investigation.
∗1

RIKEN Nishina Center

Fig. 1. Schematic of the upper-half cross section of theDMT3 magnet.

Fig. 2. Excitation voltage at each pancake of the DMT3 coils.

Fig. 3. Damaged correction coil of the DMT3 magnet.

References
1) K. Kusaka et al., RIKEN Accel. Prog. Rep. 39, 259(2006).
2) K. Kusaka et al., IEEE Trans. Appl. Supercond. 18, 318(2008), and references therein.

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