Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 50 (2017)

Properties of ion trapping measured by the SCRIT LMon
A. Enokizono,∗1,∗2 T. Fujita,∗1 K. Adachi,∗1 M. Hori,∗1 K. Kasama,∗3 K. Kurita,∗1 K. Namba,∗3 T. Ohnishi,∗2
S. Sasamura,∗1 T. Suda,∗2,∗3 T. Tamae,∗3 N. Uchida,∗1 K. Tsukada,∗2,∗3 M. Togasaki,∗1,∗2 M. Wakasugi,∗2M. Watanabe,∗2 and K. Yamada∗1150mA

190mA

230mA

Ion IN
Ion OUTIon IN-OUT

3000

OUT decreases as a function of the trapping-time, implying that trapped target 132 Xe ions are depleted withtime. On the other hand, the number of trapped residual gas ions, which is shown by Ion OUT, can be increased as a function of the trapping-time since there
are virtually inﬁnite neutral residual gas atoms inside the chamber, which are continuously ionized by
the electron beam and trapped by the SCRIT device. Figure 2 shows the Nbr /t of Ion IN-OUT as afunction of the trapping-time for several currents andbeam energies. Nbr /t increases as the electron beam
current/energy increases, which can be naturally explained by the fact that the beam density increases
with increasing beam current/energy. It is interesting
to note that there are fast and slow components in thetrapping-time dependence, and the slow component
becomes prominent as the beam energy and/or current increases. A feasible explanation is that the slow
component originates from high-charged-state nuclei,
which increase at time scales on the order of hundredsof milliseconds.
In summary, the properties of ion trapping at theSCRIT experiment have been measured by LMon.
This information is useful for tuning the electron beamand SCRIT device parameters to optimize the ion trapping and maximize the luminosity, even though moredetailed studies using simulations and calculations arerequired to reproduce the observation.
10090190mA (300MeV)

230mA (300MeV)

50
40
30

10
100

200

300

400

500

600

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800

900

Trapping time (msec)

200

400

600

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Trapping time (msec)

200

400

600

800

Trapping time (msec)

200

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Fig. 2. Trapping-time dependence of Nbr /t measured for
diﬀerent beam currents and energy regions.

800

Trapping time (msec)

Fig. 1. Trapping-time dependence of Nbr measured for different beam currents for 132 Xe at Ee = 150 MeV.

∗3230mA (200MeV)

150mA (300MeV)

60

1000

∗2230mA (150MeV)

190mA (200MeV)

70

0∗1190mA (150MeV)

150mA (200MeV)

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2000

0150mA (150MeV)

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Count rate (kHz)The SCRIT detector is composed of a Windowframe Spectrometer for Electron Scattering (WiSES)
to measure the angular distribution of scattered electrons1) and a Luminosity Monitor (LMon) to measure
the absolute luminosity of electron-RI scatterings.2)
LMon is measuring the bremsstrahlung photons anddetermine the luminosity as L = Nbr /tσbr  (cm−2 s−1 ),where Nbr /t is the number of bremsstrahlung photons
per second, σbr is the bremsstrahlung cross-section,and  is the detector acceptance. σbr can be calculated using a theoretical model3) , and LMon consists of two main components to measure the remaining factors: a CsI calorimeter to measure Nbr /t anda two-dimensional ﬁber scintillator detector to measure the spatial distribution of bremsstrahlung photons
which have to be compared with GEANT4 to determine . The ﬁrst physics experiment using 132 Xe and208
Pb targets was performed in 2015-2016. Results ofthe experiment using WiSES are reported elsewhere,4)
and progress on LMon with respect to the determination of  and its uncertainty is described in a separate
report.5) In this article, detailed measurements of ion
trapping by LMon using 132 Xe data are reported.
With a recent upgrade of LMon, it has acquired
the ability to measure Nbr as a function of trappingtime, which revealed detailed properties of the ion
trapping. Figure 1 shows Nbr as a function of thetrapping-time measured at an electron beam energy(Ee ) of 150 MeV for diﬀerent beam currents. HereIon IN and Ion OUT denote measurements with andwithout trapped 132 Xe ions, respectively. That is,Ion OUT is the background contribution from residual
gases (e.g H2 , O2 ), and the net amount of Nbr from132
Xe ions is estimated as Ion IN-OUT. The Ion IN-Department of Physics, Rikkyo University
RIKEN Nishina Center
Research Center for Electron-Photon Science, Tohoku University- 189 -References
1) T. Suda et al., Accel. Prog. Rep. 47, 195 (2014).
2) S. Yoneyama et al., Accel. Prog. Rep. 48, 227 (2015).
3) Y. S. Tsai, Rev. Mod. Phys. 46, 815 (1974).
4) K. Tsukada et al., in this report.
5) T. Fujita et al., in this report.