Ⅱ-8. Accelerator

RIKEN Accel. Prog. Rep. 50 (2017)

Sensitivity improvement and miniaturization ofHTc-SQUID beam current monitor
T. Watanabe,∗1 N. Fukunishi,∗1 S. Inamori,∗2 and K. Kon∗2To measure the DC current of heavy-ion beams nondestructively at high resolution, we have developed
a high- critical- temperature (HTc) superconducting
quantum interference device (SQUID) beam current
monitor (SQUID monitor) for use in the RIBF. We
have completed the development of a prototype of theSQUID monitor and installed it in one of the beamtransport lines in the RIBF.1) Presently, we have beenusing the SQUID monitor for current measurement ofheavy-ion beams. Furthermore, with the aim of higher
sensitivity and miniaturization of the SQUID monitor,
we have started the investigation for developing a newmethod.2)
We investigated a low- critical- temperature (LTc)
SQUID monitor, which was expected to be use formonitoring the beam of the Antiproton Accumulator
in the Fermi National Accelerator Laboratory.3) Furthermore, we considered why an LTc SQUID monitor
has a high sensitivity, which was developed for atomicphysics experiments on the electron-ion collision processes in the cooler synchrotron TARN II ring.4) As
a result of consideration, we concluded that it is essentially important to improve the coupling eﬃciency
between the SQUID and the magnetic ﬂux produced
by a beam current. To achieve strong coupling, ahighly permeable magnetic core with large inductanceis necessary. Fig. 1 shows a new scheme of an HTc
SQUID monitor. Both an HTc shielding ring andan HTc induction ring are fabricated by dip coatinga thin Bi2 -Sr2 -Ca1 -Cu2 -Ox (Bi-2212) layer on a Ag
substrate. The Bi-2212 layer is approximately 100μm thick. When a charged-particle beam passes along
the axis of the HTc induction ring, a shielding current
produced by the Meissner eﬀect ﬂows in the opposite
direction along the wall of the HTc induction ring.
The shielding current acts to eliminate the magnetic
Toroidal Magnetic Core

Induction
Ring

Shielding
Ring

BeamBeam(a)

∗1(a)

(c)
Permalloy Shield(b)Induction Ring
Signal 20Hz 0.5 mA(d)Fig. 2. Several parts for testing (a)-(c) and measured result(d).

ﬁeld produced by the beam. The shielding current also
ﬂows on the shielding ring in the same manner. Since apermeable core with a magnetic gap is installed in theinduction ring, the magnetic ﬂux produced by the current ﬂow is strongly coupled with the magnetic core.
An HTc SQUID installed in the magnetic gap of theinduction ring can detect the magnetic ﬂux. We theoretically estimated the expected signal voltage2) andmade several parts (Fig. 2 (a)-(c)) to verify whether
the theory is correct. After all parts were cooled by liquid nitrogen, the test was performed using a simulated
beam current of 0.5 mA at 20 Hz. Fig. 2 (d) shows
the output voltage from the HTc SQUID controller,
which was analyzed in the frequency domain. Since
the theoretically expected voltage was 2.6 Vpp and themeasured voltage was 2.2 Vpp , it was conﬁrmed thatthe theoretical estimation was correct.
The authors are grateful to Prof. S. Tanaka of Toyohashi university of technology for cooperation regarding the above mentioned test. This work was supported by JSPS KAKENHI Grant Number 15K04749.

1) T. Watanabe et al., Proc. 4th Int. Beam Instr. Conf.
IBIC2015 (2014), p. 590.
2) T. Watanabe et al., Proc. 13th Ann. Meet. of Particle
Accel. Society of Japan, (2016), p. 1127.
3) M. Kuchnir et al., IEEE Trans. Mag. MAG 21, No.2,997 (1985).
4) T. Tanabe et al., NIM A 427, 445 (1999).

Shielding Current

Fig. 1. New scheme of a HTc SQUID monitor.
∗2

HTc SQUID

References(b)HTc SQUID
HTc Pick Up Loop

ToroidalMagnetic Core

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