RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-9. Instrumentation

Concept design for cold highly charged ion generation
toward time variation detection of ﬁne structure constant αN. Kimura,∗1,∗2 K. Okada,∗1 N. Nakamura,∗3 N. Ohmae,∗4,∗5,∗6 H. Katori,∗4,∗5,∗6 and M. Wada∗7,∗2
A ground uniﬁcation theory approves that funda1)
mental physicalphysical constants
constants have
have aatime
timedependence.
dependence.
1)
Over
recentdecades,decades,time-variation
time-variation detections
detections ofOver
recentfundamental physical constants have been attempted
through several approaches. In astrophysical research,J. K. Webb et al. reported that a variation ofﬁne-structure constant α was observed as δ α/α =0.72(±0.18) × 10−5 by comparison with quasar spectra.2) Recently, V. V. Flambaum et al. have focusedon achieving a high enhancement factor K of highly
charged ion(HCI) atomic transitions and suggested
high-sensitivity measurements for the detection of αtime variation by Ho14+ precision spectroscopy.3) Additionally, they proposed special enhanced measurements using highly charged Actinide ions Cf15+ andEs16+ .4)
As mentioned above, HCI precision spectroscopy is
expected to be a candidate for the next-generation
atomic clock for conducting the constancy test of fundamental physical constants. We plan to measure
the frequency diﬀerence between a Sr optical latticeclock and a clock transition of HCI using an opticalfrequency comb3,5) in the detection of α-time variation
during a realistic experimental period. In this experiment, we have to prepare an HCI Coulomb crystal
for Doppler-shift reduction. However, there are few
studies on HCI Coulomb crystals awing to experimental diﬃculties. In 2015, Ar13+ Coulomb crystallization in laser-cooled Be+ ions was demonstrated by anexternal HCI injection system from an electron beam
ion trap via a deceleration tube.6) For the demonstration of HCI Coulomb crystallization and clock transition detection, we also set a plan to generate an HCI
Coulomb crystal using a sympathetic cooling method
via laser cooled Be+ in a compact instrument as explained below.
Figure 1 shows a temporary assembled ion trap without a solenoid coil and a ﬂexible printed circuit. It will
be mounted on the 4K cryogenic chamber as shown inFigure 2,under an ultra-high-vacuum condition withsuperconductive driving. This ion trap based on thelinear Paul trap is divided into three areas and is com∗1
∗2
∗3
∗4
∗5
∗6
∗7

Department of Physics, Sophia University
RIKEN Nishina Center
Institute for Laser Science, The University of ElectroCommunications
Quantum Metrology Laboratory, RIKEN
Innovative Space-Time Project, ERATO
Department of Applied Physics, Graduate School of Engineering, The University of Tokyo
Wako Nuclear Science Center (WNSC), Institute of Particle and Nuclear Studies (IPNS), High Energy Accelerator
Research Organization (KEK)- 202 -

bined with the Penning ion trap. In the 1st area,
HCI and Be+ are generated by laser ablation andan electron beam. The oﬀ-axis cold cathode injects
an electron beam into a trap region while maintaining the cryogenic thermal condition and cooling laser
path. A superconductive Nb:Ti wire will be loopedon quadrupole rods directly. This wire will become asolenoid coil and generate a strong magnetic ﬁeld forPenning trap driving and the concentration of the electron beam. Generated HCI ions are transported to the
3rd area by electrical manipulation and cooled by theprepared Be+ Coulomb crystal.
A function test of this instrument will be performedby observations of Be+ trapping and cooling. After
this test, we will try to perform HCI generation andsympathetic crystallization.

Fig. 1. HCI trap (without coils and print circuits).

Fig. 2. Cryogenic chamber system.

References
1) J. -P. Uzan, Rev. Mod. Phys. 75, 403(2003).
2) J. K. Webb, et al., Phys. Rev. Lett. 87, 091301(2001).
3) V. A. Dzuba, et al., Phys. Rev. A 91, 022119 (2015).
4) V. A. Dzuba, et al., Phys. Rev. A 92, 060502(R) (2015).
5) N. Nemitz, et al., Nature Photonics 10, 258261 (2016).
6) L. Schmoger, et al., Science 347, 12331236 (2015).