Ⅱ-8. Accelerator

RIKEN Accel. Prog. Rep. 49 (2016)

HTc-SQUID beam current monitor at the RIBF†
T. Watanabe,∗1 N. Fukunishi,∗1 M. Kase,∗1 S. Inamori,∗2 and K. Kon∗2For measuring the DC current of heavy-ion beams
non-destructively at high resolution, we developed
a high critical temperature (HTc) superconducting
quantum interference device (SQUID) beam current
monitor for use in the radioactive isotope beam factory(RIBF) at RIKEN1) . Because of its low vibration, apulse tube refrigerator cools the HTc fabrications thatinclude the SQUID such that the size and operationalcosts of the system are reduced. Two years ago, wesigniﬁcantly reinforced the magnetic shielding system.
The new strong magnetic shielding system can attenuate the external AC magnetic noise by 10−10 . With theaim of practical use in acceleration operation, we disassembled the prototype high-Tc SQUID current monitor (SQUID monitor), installed improved parts, andre-assembled it. Last year, we installed the SQUID
monitor in the beam transport line in the RIBF. We
are presently using the SQUID monitor for measuringof the current of beams of heavy-ions such as uranium.
To increase the beam current resolution of theSQUID monitor, we investigated the improvement of
the coupling eﬃciency between the magnetic ﬁeld thatis generated at the bridge circuit and the input coil ofthe HTc SQUID. We developed a new HTc SQUID2)
with a high-permeability core that was installed in thetwo input coils of the HTc SQUID. Furthermore, toincrease the magnetic ﬁeld produced by the bridge circuit, we successfully fabricated an HTc current sensor
with two coils using a newly developed spraying machine3) . In general, the performance of monitors suchas the SQUID monitor is determined by the signal tonoise ratio. To improve the measurement resolution,Helmholtz Coils
for Noise Canceller

Beam Line䣄䣇䣃䣏Pulse Tube Refrigerator

HTc SQUIDCurrentMonitor

Magne�c Sensor
for Noise Canceller

11.0

100(a) 1minute100(b) 1hour

100(c) 1dayFig. 2. The 11 µA 78 Kr36+ intensity of the beam (50MeV/u) was successfully measured with a 500 nA resolution.

it is important to attenuate external magnetic noise.
Therefore, we developed a hybrid magnetic shielding
method based on the properties of perfect diamagnetic
materials (superconductors) and ferromagnetic materials4) .
Figure 1 shows the SQUID monitor equipped with
the noise cancellation system, which was installed in
the transport line between the fRC and the IRC.
We successfully measured the intensity of an 11 µA
beam of 78 Kr36+ (50 MeV/u) with a 500 nA resolution (Fig. 2). We calibrated the SQUID output voltage
with a simulated beam current beforehand. Prolonged
1 min, 1 h, and 1 day recordings of the Kr beam current extracted from the fRC were achieved. In theserecordings, several dips in beam intensity due to theECR ion source discharge can be observed. The amplitude of the ripples in the modulated beam current
increased with the beam current. Although we canmeasure the intensity of a sub-µA beam, a two ordersof magnitude lower current resolution is required at theRIBF. Therefore, we are now investigating the possibility of coating a thin layer (70 µm) of Bi2 -Sr2 -Ca1 Cu2 -Ox (Bi-2212) on a silver (Ag) substrate capable ofcorresponding to the complex shape.
This work was supported by JSPS KAKENHI Grant
Number 15K04749.
ReferencesFig. 1. SQUID monitor equipped with the noise canceller
system, which was installed in the transport line between the fRC and the IRC .
†∗1∗2

Condensed from the the proceedings in 2015 International
Beam Instrumentation Conference (IBIC 2015)
RIKEN Nishina Center
TEP Corporation- 145 -1) T. Watanabe et al., Proc. 2010 Beam Instrumentation
Workshop (BIW10), 523-532 (2010).
2) M. I. Faley, Applications of High-Tc Superconductivity,
148-176 (2011).
3) T. Watanabe et al., J. Supercond. Nov. Magn., 26 (4),1297-1300 (2013).
4) T. Watanabe et al., IOP Publishing Journal of Physics:
Conference Series, 507, 042047 (2014).