II-9. Instrumentation

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Ion-beam-profile monitor using MCP at the SCRIT electron scattering
facility
T. Ohnishi,∗1 S. Ichikawa,∗1 and M. Wakasugi∗1,∗2
At the SCRIT electron scattering facility,1) ion-beamproﬁle monitors2) are installed in the ion-beam transport line for injecting low-energy (∼10 keV) ions into theSCRIT device.1) They are composed of a meshed Faraday cup, a CsI(Tl) scintillator, an optical prism, and anetwork-based CCD camera. Using these monitors, ionbeam tuning is performed in real time. However, it isdiﬃcult to apply them to a low-rate ion beam, such as acontinuous beam with 107 ions/s or a pulsed beam with
106 ions/pulse, because the number of produced photons
is considerably less than the expected value calculatedusing the conversion factor, 2 × 104 photons/MeV. Oneof the reasons for this suppression is that the low-energy
ions stop near the surface of a CsI(Tl) scintillator and thenumber of involved CsI molecules is insuﬃcient. Thus,
a new ion-beam-proﬁle monitor is required for real-time
beam tuning with low-energy RI beams. This year, wetested a new monitor using a micro channel plate (MCP)
and report out ﬁrst results in this paper.
Figure 1 presents a schematic view and photograph ofan ion-beam-proﬁle monitor using an MCP. This monitor
consists of two MCPs equipped with a phosphor screen(HAMAMATSU F2806 with P46), an optical prism,
and a network-based CCD camera (Basler scA640-70gc).
The horizontal and vertical dimensions of the eﬀective
area of the MCP are 45 mm and 35 mm, respectively. A
collimator, which has a 28-mm diameter hole, is installedin front of the optical prism to deﬁne the eﬀective detection area because the eﬀective area of the MCP is larger
than the entrance size of the optical prism, 30 mm2 . In
the present setting, ion beams are directly observed withMCPs. The applied voltages of MCP-in, MCP-out, andPhos-in, which are electrodes shown in Fig. 1, are 0, 2,CCD
Viewport
Phos-in
MCP-out
MCP-inPhotons
Ion beam

Optical prism
Collimator

MCP×2

Phosphor screenFig. 1. Schematic view and photograph of the ion-beamprofile monitor. MCP-IN, MCP-OUT, and Phos-in represent electrodes of the monitor.
∗1∗2RIKEN Nishina Center
ICR, Kyoto UniversityFig. 2. Beam profile of 1 pulse with a 104 ions/pulse beam.
Left figure is the image of the beam profile and right figure
is its digital number distribution.

and 6 kV, respectively. The extracted electron cloud resulting from the beam encountering the MCP surface isconverted to photons in the phosphor screen, which aretransported to the CCD camera through the collimatorand the optical prism. The exposure time of the CCD
camera is set to 500 µs. Data from the CCD camera
are monitored through a network in real time. With apulsed beam, the trigger of the CCD camera is synchronized with the injection timing.
The commissioning of the new ion-beam-proﬁle monitor was performed using a 138 Ba-ion beam of 6 keV. Figure 2 shows the measured beam proﬁle of only 1 pulse
using a 1-Hz pulsed beam with 104 ions/pulse. The number of ions with a low-intensity pulsed beam was estimated with the current of a continuous beam, 13 pA,
measured at the Faraday cup installed in front of theion-beam-proﬁle monitor. Calibration was performed using a 0.3-nA continuous beam and a pulsed beam with
5×105 ions/pulse. Figure 2 shows an image of the beam
proﬁle (left) and its digital number distribution (right).
More detailed analysis is being performed to estimate
the number of injected ions using only the digital number distribution.
We tested the new ion-beam-proﬁle monitor using anMCP with a low-intensity pulsed ion beam. The beam
proﬁle of a low-intensity pulsed ion beam was successfully measured in real time. In the case of RI beams using the present monitor, electrons corresponding to thedecay of the RIs can cause background events. To avoid
this problem, a thin foil is installed in front of the MCPs
to stop RI beams, and electrons produced during the decay of RIs are used as an MCP signal. Next year, wewill test a new setup using RI beams and evaluate its
applicability considering the eﬃciency and position resolution.
References

1) M. Wakasugi et al., Nucl. Instrum. Methods Phys. Res. B
317, 668 (2013).
2) M. Togasakai et al., RIKEN Accel. Prog. Rep. 44, 173 (2011).

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