Ⅱ-8. Accelerator

RIKEN Accel. Prog. Rep. 47 (2014)

RIKEN Accel. Prog. Rep. 47 (2014)

Online monitoring of beam phase and intensity
using lock-in ampliﬁers†
R. Koyama,∗1,∗2 N. Sakamoto,∗1 M. Fujimaki,∗1 N. Fukunishi,∗1 A. Goto,∗3 M. Hemmi,∗1
M. Kase,∗1 K. Suda,∗1 T. Watanabe,∗1 K. Yamada,∗1 and O. Kamigaito∗1methods. The phase diﬀerence was improved to a discrepancy of less than 0.4 ns (≅4 rf degree) when we
corrected for the radial variation of the observed bunch
width, as shown in Fig. 2(b).
RRC isochronism [ns] SRC isochronism [ns]We developed a monitoring system dedicated for
RIBF that incorporates lock-in ampliﬁers (LIAs) thatcan measure the beam phase and intensity of signals
from the phase probe (PP) with an amplitude of a few
hundred nanovolts. The conﬁguration of the LIA system is schematically shown in Fig. 1. The rf is also
monitored using the LIA system. We compared theperformance of the LIA system with that of a conventional system that incorporates oscilloscopes (OSCs).
It was conﬁrmed that LIA has much higher precisionand smaller deviation than the OSC; LIA has a resolution of 0.02◦ for a 1.0 V standard signal and can measure a signal as small as 200 nV, which corresponds to10 electric nA of beam current.

1.0

OSC (Zero cross)

0.8

OSC (FFT)

LIAa) SRC

0.6
0.4
0.2
0.0

-0.2/
1.0 b) RRC
0.6
0.4
0.2
0.0-0.2051015
Phase probe number

20Fig. 2. Comparison of isochronism in a) the SRC and b)
the RRC on the basis of three measurement methods.

Since the PPs are placed at relevant positions along
the beam lines of the RIBF, we can easily ﬁnd the instability or decrease of beam intensity caused by thevariation of rf or magnetic ﬁeld by using the LIA system. The correlations between rf, beam phase, beam
intensity, and environmental factors such as the ambient temperature and cooling water temperature havealso been revealed.1,2) In addition, we can clearly observe the deterioration of a solid-state charge stripper
and the pressure variation of a gas charge stripper.3)
The isochronism measurement results for the SRC,
which has a low velocity gain of 1.5, showed excellent agreement between the three measurement methods (OSC zero-corss, OSC FFT, and LIA) with a discrepancy less than 0.2 ns (≅2 rf degree), as shown in
Fig. 2(a). The isochronism measured for 10 frequency
components (1f –10f ) was also in good agreement withan accuracy discrepancy less than 0.5 ns (≅5 rf degree). However, in the RRC, which has a high velocity
gain of 4.0, a phase diﬀerence of up to 0.7 ns (≅7 rfdegree) was observed between the three measurement
†∗1
∗2
∗3

Condensed from the article in Nucl. Instr. & Meth. A 729,(2013) 788–799
RIKEN Nishina Center
SHI Accelerator Service Ltd.
Planning Department, Yamagata University

Amplitude [mV]Fig. 1. Conﬁguration of the LIA system.

The remaining phase diﬀerence between LIA andOSC is considered to be the eﬀect of the cable dispersion. In fact, it was observed that the cable dispersion
via 80 m increases asymmetric distortion of the bunchshape, and it produces a timing advance of 0.14 ns
relative to the actual timing, as shown in Fig. 3. Because we measure the single-frequency component ofthe beam-bunch signal in the LIA system, such cabledispersion does not disturb the beam-phase measurement, and it is concluded that the LIA system gives amore accurate beam phase if the measurement is performed at the control room.
2015 a) Observed at console
1050-5-10PP-RRC#20
PP-RRC#1-15404b) Closeup of a)

2PP-RRC#10-0.34ns-2
PP-RRC#20-4c) Observed at entrance of RRC vault4d) Closeup of c)

220PP-RRC#100-20PP-RRC#1

PP-RRC#20-40
02468-2-0.47ns

PP-RRC#20-410 4.8
Time [ns]

55.2

5.4

5.65.8Fig. 3. Bunch shapes observed at the console 90 m downstream of PP-RRC (a) and at the entrance of the RRC
vault 10 m downstream of PP-RRC (c).

References
1) R. Koyama et al.: RIKEN Accel. Prog. Rep. 42, pp.
xviii–xix (2009).
2) K. Suda et al.: Proc. of CYCLOTRONS 2010, Lanzhou,China, MOPCP068, pp.186–188.
3) R. Koyama et al.: Proc. of PASJ10, Nagoya, Aichi, August 2013, SAP013, in press.

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