Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physreva.102.023119

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevA.102.023119/fulltext

Publishing type：Research paper (international conference proceedings)  

Synopsis We studied radiative cooling dynamics of the triatomic molecular ion N2O+ stored in RICE. We observed the evolution of the populations at vibrational and rotational levels up to several 100 s by measuring neutral fragments from the laser-induced predissociation process. We found clear evidence of radiative cooling of the vibrational level populations with a time constant of several seconds. In contrast, absence of significant changes in the rotational levels revealed that the time scale of the rotational cooling is far longer, which is consistent to our simulation.

DOI： 10.1088/1742-6596/1412/23/232002

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Publishing type：Research paper (international conference proceedings)  

Synopsis A new cryogenic linear ion trap beamline has been commissioned for use with the RIKEN Cryogenic Electrostatic (RICE) storage ring. Testing of the beamline at room-temperature and cryogenic conditions was conducted using methylene blue cations MB+ and carbon cluster anions Cn-. Action spectroscopy measurements of pre-cooled Cn- A nions injected into RICE will help determine the effectiveness of the so-called Pre-Trap Beamline, as well as provide structural and dynamical information on these cluster anions at cryogenic temperatures.

DOI： 10.1088/1742-6596/1412/23/232003

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Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

DOI： 10.1088/1742-6596/1412/12/122006

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Other Link： https://iopscience.iop.org/article/10.1088/1742-6596/1412/12/122006

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.5051044

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing LLC  

A new electrostatic ion storage ring, the RIKEN cryogenic electrostatic ring, has been commissioned with a 15-keV ion beam under cryogenic conditions. The ring was designed with a closed ion beam orbit of about 2.9 m, where the ion beam is guided entirely by electrostatic components. The vacuum chamber of the ring is cooled using a liquid-He-free cooling system to 4.2 K with a temperature difference of 0.4 K at most within all the positions measured by calibrated silicon diode sensors. The first cryogenic operation with a 15-keV Ne+ beam was successfully performed in August 2014. During the measurement, the Ne+ beam was stored under a ring temperature of 4.2 K with a residual-gas lifetime of more than 10 min. This permits an estimation of the residual gas density at a few 104 cm−3, which corresponds to a room-temperature-equivalent pressure of around 1×10−10 Pa. An effect of longitudinal pulse compression at the bunching cavity in the ring was clearly identified by monitoring the pick-up beam detector. Th...

DOI： 10.1063/1.4978454

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Physics Publishing  

We report on the resonant coherent excitation (RCE) of the 2s-2p3/2 transition in Li-like U89+ with an enhanced energy resolution, which was achieved by reducing the projectiles momentum spread. The kinetic temperature of the beam was decreased by electron cooling in the ESR, and the collisional momentum broadening in the target was suppressed by the use of thin crystal (1.0 and 2.5 μm-thick). The resonance width was observed to be ∼1.4 eV in FWHM, which is three-times narrower than that from the previous work.

DOI： 10.1088/1742-6596/635/3/032016

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Language：English   Publishing type：Research paper (international conference proceedings)  

© Published under licence by IOP Publishing Ltd. We have been developing a cryogenic electrostatic ion storage ring to explore especially the cooling process and collision dynamics of the cold molecular ions in the specific vibrational and rotational state. Recently, we succeeded in storing of 15 keV Ne+ ions in the ring stably.

DOI： 10.1088/1742-6596/635/2/022028

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report on the selective production of the 2s metastable state of 390-MeV u(-1) H-like Ar17+ ions by the resonant coherent excitation (RCE). The RCE to the 2s state was achieved by using Stark mixing of n = 2 states under planar channeling conditions in a 1-mu m thick Si crystal. The population of the 2s state was quantitatively estimated from the ionization probability in a stripper foil installed 50 mm downstream of the crystal. The 2s population was found to be 0.05 of the total number of Ar17+ ions at the stripper. The result is in good agreement with a theoretical calculation performed with the density matrix approach.

DOI： 10.1088/0953-4075/48/14/144026

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We measured resonant coherent excitation of a 2s electron of 83.3 MeV/u Fe23+ ions planar-channeling in the ((2) over bar 20) plane of the silicon crystal. A silicon surface barrier detector (SSD) was used as a crystal target in order to obtain information on the ion trajectory in the channel since the energy deposit (Delta E) to the SSD gives information on the ion trajectories where the resonant transitions occur. For the low Delta E, i.e., near the channel center, optically allowed 2s-3p transitions were much stronger compared with other transitions. Increasing Delta E, i.e., increasing the amplitude of ion trajectory, the optically forbidden 2s-3s transition rapidly became strong. On the other hand, the optically forbidden 2s-3d transitions did not become strong as rapidly as 2s-3s transition. Furthermore, it was found that the transition energies to the n = 3 states changed with Delta E. The shifts of the transition energies were consistent with the estimation for the energy levels of the Stark-mixed n = 3 states depending on the distance from the channel center. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2013.05.072

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We studied the anisotropy of Ly-alpha x-rays from H-like Ar17+ ions excited by polarization-controlled resonant coherent excitation. The effects of fine-structure depolarization on the 2p(1/2) and 2p(3/2) states were experimentally demonstrated as a reduction in anisotropy of decay radiation.

DOI： 10.1088/0031-8949/2013/T156/014061

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Language：English   Publishing type：Research paper (scientific journal)  

We report our observation of the resonant fluorescence from highly charged uranium ions. Using the resonant coherent excitation (RCE) technique, the 2s-2p3/2 transition in 191.68 MeV/u Li-like U89+ ions was excited at 4.5 keV with a resonance width of 4.4 eV. The result demonstrated that the RCE can be applied to resonant fluorescence spectroscopy of high-Z ions up to uranium with high efficiency and resolution. © 2013 American Physical Society.

DOI： 10.1103/PhysRevA.87.060501

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report our observation of the resonant fluorescence from highly charged uranium ions. Using the resonant coherent excitation (RCE) technique, the 2s-2p(3/2) transition in 191.68 MeV/u Li-like U89+ ions was excited at 4.5 keV with a resonance width of 4.4 eV. The result demonstrated that the RCE can be applied to resonant fluorescence spectroscopy of high-Z ions up to uranium with high efficiency and resolution.

DOI： 10.1103/PhysRevA.87.060501

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Selective production of the doubly excited state in 464 MeV/u He-like Ar16+ ions was accomplished using three-dimensional resonant coherent excitation in a thin foil of silicon crystal. Through a coherent interaction with the periodic crystal field, the Ar16+ ions were resonantly excited sequentially from the ground state to the 1s2p (P-1) state and then 2p2 (D-1) state in a way analogous to two-color x-ray laser excitation. The periodic crystal fields of 10(11) V/m in the projectile's frame are equivalent to the fields generated by x-ray lasers with photon energies of 3139.55 and 3286.95 eV and an energy flux of 10(16) W/cm(2). We confirmed the doubly excited state formation through observation of the subsequent collisional ionization, Auger ionization, and radiative deexcitation.

DOI： 10.1103/PhysRevA.85.020701

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Physics Publishing  

In an experiment with relativistic highly charged ions (β=v/c=0.56) channeled through a silicon crystal the resonant coherent excitation of the 2s1/2-2p3/2 transition in 191 MeV/u Li-like uranium ions was observed. The resonant condition was identified by measuring the x-ray emission as a function of the ion incidence angle with respect to the [110] crystal axis in the (220) plane. The position and the width of the resonance where determined from the dependence of the x-ray yield from the 2p 3/2-2s1/2 decay on the angular orientation of the crystal.

DOI： 10.1088/1742-6596/388/8/082036

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Physics Publishing  

Projectile ionization of highly-charged Ar and Fe ions in the excited states passing relativistically fast through a thin crystalline foil was experimentally studied. We selectively controlled the population of the excited states of the projectiles, and their alignment by choosing a specific m-state through three-dimensional resonant coherent excitation technique by periodical electric fields in a crystalline. We measured energy-differential spectra of electron emission released from projectiles at zero degree. Under the resonance condition, we found an evident enhancement of the convoy electron yield, which reflects the electron momentum distribution of the initial bound state of the excited ions. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/388/13/132013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We observed the x-ray emission of 191.7MeVu(-1) Li-like uranium associated with resonant coherent excitation from 1s(2)2s to 1s(2)2p(3/2) (4459 eV) in a thin silicon crystal target. De-excitation x-rays were observed by using large-area silicon drift detectors installed inside the target vacuum chamber together with their preamplifiers. We found that the x-ray yield under the resonance condition was clearly enhanced by a factor of three compared to that under the random incidence condition.

DOI： 10.1088/0031-8949/2011/T144/014010

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We observed convoy electrons emitted from 416 MeV/u He-like Ar(16+) passing through a thin Si crystal under the condition of three-dimensional resonant coherent excitation (3D-RCE). The convoy electrons, which originate from electrons released from ions into the continuum by collisions with target atoms, emerged in the forward direction and formed a cusp-shaped peak in the energy distribution. We selectively controlled the population of the ground and excited states of ions traveling through the crystal by using 3D-RCE, where the 1s electron was excited to the 2p state by a periodic crystal field. Under the resonance condition, we found an enhancement of the convoy electrons with a narrowing in the energy distribution, which reflects the electron momentum distribution of the initial bound state of the excited ions.

DOI： 10.1088/0031-8949/2011/T144/014044

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Language：English   Publishing type：Research paper (international conference proceedings)  

We observed the x-ray emission of 191.7 MeV u-1 Li-like uranium associated with resonant coherent excitation from 1s22s to 1s 22p3/2 (4459 eV) in a thin silicon crystal target. De-excitation x-rays were observed by using large-area silicon drift detectors installed inside the target vacuum chamber together with their preamplifiers. We found that the x-ray yield under the resonance condition was clearly enhanced by a factor of three compared to that under the random incidence condition. © 2011 The Royal Swedish Academy of Sciences.

DOI： 10.1088/0031-8949/2011/T144/014010

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Physics Publishing  

We demonstrate the alignment of H-like and He-like heavy ions by three-dimensional resonant coherent excitation in a thin crystalline target. The projectile ions experienced a linearly polarized oscillating field in a crystal and were excited to a specific magnetic substate, forming the aligned 2P state. We prepared the different directions of the aligned states and observed the anisotropy of deexcitation x-ray emission, which was in good agreement with theoretical estimates.

DOI： 10.1088/1742-6596/194/13/132036

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Language：English   Publishing type：Doctoral thesis  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We present an experimental demonstration of an ingenious technique to control the alignment of the atomic internal state in the x-ray region using a periodic crystal field. The alignment directions of Ar(16+) and Fe(24+) ions were readily controlled by selecting the array of atomic planes using three-dimensional resonant coherent excitation, and were probed via the anisotropy of the deexcitation x-ray emission. We applied this method to a double resonance experiment, and succeeded in controlling the population of the specific magnetic substate in a Lambda-type three-level configuration.

DOI： 10.1103/PhysRevLett.102.085502

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

We investigated resonant coherent excitation (RCE) of 445 MeV/u Li-like Ar15+ under the planar channeling and non-channeling conditions. The K-shell and L-shell excitations are observed as decreases in the survival fraction of the Ar15+ ions after passing through a thin Si crystal. RCE under the planar channeling condition provides the opportunity to study a strong static Stark effect on the Li-like system with K-shell or L-shell vacancy. Under the non-channeling conditions, the observed excitation energies and the reported theoretical calculations were in reasonable agreement. © 2009 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/163/1/012094

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevLett.101.113201

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Language：English  

DOI： 10.1088/1742-6596/58/1/081

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We observed resonant coherent excitation (RCE) of Is electron to the n = 2 states in 390 MeV/u Ar17+ ions passing through thin Si crystals of about I mu m in the {220} planar-channeling condition by measuring both the exit charge state and the exit angle of the emerged ions simultaneously in a list mode. The yield of the de-excitation X-rays from the Ar17+ ions was also measured. The thin crystal is suitable to study trajectory dependent RCE dynamics, because the exit angle of the high energy planar-channeling ion is uniquely related to the ion trajectory. From the de-excitation X-ray yield on resonance, we learned that RCE occurs with a fairly large probability within the traveling length of about I mu m, and a majority of the excited ions survive from ionization by the collisions with target electrons or nuclei. and de-excite into the ground state by emitting the X-rays. On the other hand, the observed resonance profile of the exit charge state is shallow and broadened by the Stark effect. We found that the ionization of the excited ions takes place when the ions travel close to the atomic plane from the observed relation between the charge state and the exit angle of the emerged ions. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2006.11.115

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

We have observed resonant coherent excitation (RCE) of H-like Ar17+ ions traveling through a 1 mu m-thick Si crystal at an energy of 391 MeV/u in the nonchanneling condition. A three-dimensional periodic array of atomic planes induces RCE of the nonchanneling ions. The high energy heavy ions together with the thin crystal allow us to observe this new RCE through the measurements of the charge-state distribution of the emerging ions. The observed resonances are much narrower than those of planar-channeling ions due to the absence of the large Stark shift caused by the planar potential.

DOI： 10.1103/PhysRevLett.97.135503

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：English   Publisher：IOP PUBLISHING LTD  

An extremely-thin Germanium crystal (0.8 mu m-thick) has been firstly exploited in the resonant coherent excitation (RCE) experiment. The 460 MeV/u H-like Fe2+ ions were incident on the Ge crystal under the (220) planar channeling as well as non-channeling conditions, The RCE from 1s to 2p(1/2) and 2p(3/2) states were successfully observed as an enhancement of the x-ray fluorescence.

DOI： 10.1088/1742-6596/488/13/132040

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

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Language：English   Publisher：Institute of Physics Publishing  

We exploited the double resonance technique in three-dimensional resonant coherent excitation to the production of hollow He-like and Li-like heavy ions. The two K-shell electron were sequentially excited to the L-shell using two frequency components of the oscillating fields arising from the different arrays of atomic planes in a Si crystal.

DOI： 10.1088/1742-6596/194/13/132042

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Language：English   Publisher：Institute of Physics Publishing  

Convoy electrons emitted from 416 MeV/u heliumlike Ar16+ ions excited by three-dimensional resonant coherent excitation (3D-RCE) have been explored. The 1s electron in the ground state was excited to the 2p state by a periodic crystal field during the passage through a Si crystal and released into the continuum by collisions with target atoms to form a cusp-shaped peak in the energy distribution, referred to as convoy electron. Under the resonance condition, we found not only enhancement of the convoy electron yield but also significant narrowing in the energy distribution, reflecting the initial bound state momentum distribution of the excited ions. This suggests that RCE is well-suited to study fast ion collisions involving the specific excited state.

DOI： 10.1088/1742-6596/194/13/132034

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