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Journal Articles

Odd-parity autoionizing levels of uranium observed by two-color two-step photoionization optogalvanic spectroscopy

Miyabe, Masabumi; Satou, Yukihiko; Wakaida, Ikuo; Terabayashi, Ryohei*; Sonnenschein, V.*; Tomita, Hideki*; Zhao, Y.*; Sakamoto, Tetsuo*

Journal of Physics B; Atomic, Molecular and Optical Physics, 54(14), p.145003_1 - 145003_8, 2021/07

https://doi.org/10.1088/1361-6455/abf89f

Times Cited Count：1 Percentile：8.89(Optics)

Two-color two-step photoionization optogalvanic spectroscopy was performed using high-repetition-rate titanium sapphire lasers and a uranium hollow cathode lamp to find the two-step resonance ionization schemes of uranium. Many ionization transitions were observed by exciting uranium atoms in a ground state into five, even parity, excited levels with the first-step laser and by scanning the second-step laser wavelengths. By blocking the first-step laser, single-color, two-photon ionization transitions were also identified. From these results, we have found more than 50 odd-parity autoionizing levels of uranium in the energy, ranging from the ionization potential (49958.4 cm $^{-1}$ ) to 51150 cm $^{-1}$ . The determined energy levels are within 1 cm $^{-1}$ of previously reported values.

Journal Articles

Tungsten impurity density in fusion plasma

Nakano, Tomohide; Shumack, A.*; Maggi, C. F.*

Journal of Physics B; Atomic, Molecular and Optical Physics, 2 Pages, 2016/01

Collaboration of researchers from Japan Atomic Energy Agency and EUROfusion Consortium (Dutch Institute For Fundamental Energy Research, Max-Planck-Institut fr Plasmaphysik and so on) successfully led to determination of tungsten ion density in high temperature plasmas in Joint European Torus (JET) with an upgraded X-ray spectrometer. The researchers used the FAC code and successfully identified $mbox{W}^{45+}$ , $mbox{W}^{46+}$ and $mbox{Mo}^{32+}$ spectral lines. The $mbox{Mo}^{32+}$ line identification was confirmed experimentally by Mo injection to the plasma. From the measured absolute intensity of these spectral lines, tungsten and molybdenum ion densities in the plasma core were determined.

Journal Articles

Determination of tungsten and molybdenum concentrations from an X-ray range spectrum in JET with the ITER-like wall configuration

Nakano, Tomohide; Shumack, A.*; Maggi, C. F.*; Reinke, M.*; Lawson, K.*; Coffey, I.*; Ptterich, T.*; Brezinsek, S.*; Lipschultz, B.*; Matthews, G. F.*; et al.

Journal of Physics B; Atomic, Molecular and Optical Physics, 48(14), p.144023_1 - 144023_11, 2015/07

https://doi.org/10.1088/0953-4075/48/14/144023

Times Cited Count：33 Percentile：83.11(Optics)

The $mbox{W}^{45+}$ and $mbox{W}^{46+}$ 3p-4d inner shell excitation lines in addition to $mbox{Mo}^{32+}$ 2p-3s lines have been identified from the spectrum taken by an upgraded high-resolution X-ray spectrometer. It is found from analysis of the absolute intensities of the $mbox{W}^{46+}$ and $mbox{Mo}^{32+}$ lines that W and Mo concentrations are in the range of $sim10^{-5}$ and $sim10^{-6}$ , respectively, with a ratio of 5% for ELMy H-mode plasmas with a plasma current of 2.0- 2.5 MA, a toroidal magnetic field of 2.7 T and a neutral beam injection power of 14-18 MW. For the purpose of checking self-consistency, it is confirmed that the W concentration determined from the $mbox{W}^{45+}$ line is in agreement with that from the $mbox{W}^{46+}$ line within 20% and that the plasma effective charge determined from the continuum of the first order reflection spectrum is also in agreement with that from the second order within 50%. Further, the determined plasma effective charge is in agreement with that determined from a visible spectroscopy, confirming that the sensitivity of the X-ray spectrometer is valid and that probably the W and the Mo concentrations are also valid.

Journal Articles

A Streak camera study of superfluorescence at multiple wavelengths from helium atoms excited using free electron laser pulses

Harries, J.; Iwayama, Hiroshi*; Nagasono, Mitsuru*; Togashi, Tadashi*; Yabashi, Makina*; Kuma, Susumu*; Nakajima, Kyo*; Miyamoto, Yuki*; Ohae, Chiaki*; Sasao, Noboru*; et al.

Journal of Physics B; Atomic, Molecular and Optical Physics, 48(10), p.105002_1 - 105002_9, 2015/05

https://doi.org/10.1088/0953-4075/48/10/105002

Times Cited Count：7 Percentile：37.30(Optics)

Journal Articles

Photoelectron-photoion correlation in ultrafast multichannel photoionization of Ar

Itakura, Ryuji; Fushitani, Mizuho*; Hishikawa, Akiyoshi*; Sako, Tokuei*

Journal of Physics B; Atomic, Molecular and Optical Physics, 47(19), p.195602_1 - 195602_9, 2014/10

https://doi.org/10.1088/0953-4075/47/19/195602

Times Cited Count：3 Percentile：18.40(Optics)

Ultrafast multichannel single-photon ionization of Ar is investigated theoretically by a model calculation incorporating correlation between the photoelectron and photoion. It is shown that the coherent hole dynamics in Ar associated with a superposition of the spin-orbit states can be observed by using a Fourier-transform limited laser pulse for ionization, while the coherence is degraded or lost by chirping a laser pulse. We demonstrate that the coherent hole dynamics can be retrieved even in the case of a chirped laser pulse, by labeling the photoion dynamics with the counterpart photoelectron energy.

Journal Articles

Algorithm-based modeling of fractional ion abundance and rates of ionization and recombination for tungsten plasmas

Sasaki, Akira; Murakami, Izumi*

Journal of Physics B; Atomic, Molecular and Optical Physics, 46(17), p.175701_1 - 175701_11, 2013/09

https://doi.org/10.1088/0953-4075/46/17/175701

Times Cited Count：11 Percentile：50.17(Optics)

The fractional ion abundance and rates of ionization and recombination of multiple charged tungsten ions in magnetic fusion plasmas are investigated using a collisional radiative model. Using a computer algorithm to generate a complete set of atomic states to be included into the collisional radiative model, the level population and ion abundance are calculated taking a sufficient number of dieletronic recombination and excitation autoionization channels into account. The atomic data, such as energy levels and rates of radiative decay as well as autoionization are provided from the ab-initio calculation using the HULLAC. The ion abundance is shown to converge with respect to the size of the model in the temperature range of 100 eV to 5 keV, and the ratio between the abundances of W $^{44+}$ and W $^{45+}$ ions agrees well with an experimental result obtained without any artificial adjustment of atomic rates.

Journal Articles

Towards coherent control of SASE pulses using propagation through helium gas at wavelengths corresponding to double excitation

Harries, J.; Nagasono, Mitsuru*; Iwayama, Hiroshi*; Shigemasa, Eiji*

Journal of Physics B; Atomic, Molecular and Optical Physics, 46(16), p.164021_1 - 164021_5, 2013/08

https://doi.org/10.1088/0953-4075/46/16/164021

Times Cited Count：0 Percentile：0.00(Optics)

Journal Articles

Full-coherent free electron laser seeded by 13th- and 15th-order harmonics of near-infrared femtosecond laser pulses

Sato, Takahiro*; Iwasaki, Atsushi*; Owada, Shigeki*; Yamanouchi, Kaoru*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Togashi, Tadashi*; Fukami, Kenji*; et al.

Journal of Physics B; Atomic, Molecular and Optical Physics, 46(16), p.164006_1 - 164006_6, 2013/08

https://doi.org/10.1088/0953-4075/46/16/164006

Times Cited Count：3 Percentile：18.47(Optics)

By introducing 13th- (61.7 nm) and 15th-order harmonics (53.4 nm) of femtosecond laser pulses at 800 nm into an undulator of SCSS (SPring-8 Compact SASE Source) test accelerator at RIKEN, these harmonic pulses were amplified by a factor of more than 10 $^{2}$ with a high contrast ratio through the interaction between accelerated electron bunches and the harmonic pulses. From numerical simulations of the amplification processes of high-order harmonic pulses in the undulator, optimum conditions of the electron bunch duration interacting with the high-order harmonic pulses were investigated for generating full-coherent and intense pulses in the extreme ultraviolet wavelength region.

Journal Articles

Compact XFEL and AMO sciences; SACLA and SCSS

Yabashi, Makina*; Tanaka, Hitoshi*; Tanaka, Takashi*; Tomizawa, Hiromitsu*; Togashi, Tadashi*; Nagasono, Mitsuru*; Ishikawa, Tetsuya*; Harries, J.; Hikosaka, Yasumasa*; Hishikawa, Akiyoshi*; et al.

Journal of Physics B; Atomic, Molecular and Optical Physics, 46(16), p.164001_1 - 164001_19, 2013/08

https://doi.org/10.1088/0953-4075/46/16/164001

Times Cited Count：72 Percentile：94.81(Optics)

Journal Articles

Resonance-enhanced three-photon single ionization of Ne by ultrashort extreme-ultraviolet pulses

Shigemasa, Eiji*; Nagasono, Mitsuru*; Iwayama, Hiroshi*; Harries, J.; Ishikawa, Lisa*

Journal of Physics B; Atomic, Molecular and Optical Physics, 46(16), p.164020_1 - 164020_5, 2013/08

https://doi.org/10.1088/0953-4075/46/16/164020

Times Cited Count：2 Percentile：12.74(Optics)

Journal Articles

Fluorescence decay processes following resonant 2p photoexcitation of Ar atoms and clusters studied using a time-resolved fluorescence and photoion coincidence technique

Gejo, Tatsuo*; Ikegami, Takeshi*; Homma, Kenji*; Harries, J.; Tamenori, Yusuke*

Journal of Physics B; Atomic, Molecular and Optical Physics, 46(7), p.075102_1 - 075102_9, 2013/04

https://doi.org/10.1088/0953-4075/46/7/075102

Times Cited Count：3 Percentile：18.47(Optics)

Journal Articles

Separation of ionization and subsequent electronic excitation for formation of electronically excited ethanol cation in intense laser fields

Ikuta, Tomoya*; Hosaka, Koichi*; Akagi, Hiroshi; Yokoyama, Atsushi; Yamanouchi, Kaoru*; Kannari, Fumihiko*; Itakura, Ryuji

Journal of Physics B; Atomic, Molecular and Optical Physics, 44(19), p.191002_1 - 191002_5, 2011/10

https://doi.org/10.1088/0953-4075/44/19/191002

Times Cited Count：10 Percentile：46.22(Optics)

Ionization and subsequent electronic excitation occurring within the same laser pulse (400 nm, 96 fs, 1.318 TW/cm $^{-2}$ ) are separately investigated by measuring in coincidence an electron and a product ion produced from C $_{2}$ H $_{5}$ OH. We reveal that the nascent population in the electronically excited C $_{2}$ H $_{5}$ OH $^{+}$ prepared by the ionization decreases as the laser intensity increases, while the subsequent electronic excitation is enhanced through the resonant electronic transitions. Ionization and electronic excitation mechanisms are described based on the electronic state distributions of C $_{2}$ H $_{5}$ OH $^{+}$ .

Journal Articles

Determination of the absolute two-photon ionization cross section of He by an XUV free electron laser

Sato, Takahiro*; Iwasaki, Atsushi*; Ishibashi, Kazuki*; Okino, Tomoya*; Yamanouchi, Kaoru*; Adachi, Junichi*; Yagishita, Akira*; Yazawa, Hiroki*; Kannari, Fumihiko*; Aoyama, Makoto; et al.

Journal of Physics B; Atomic, Molecular and Optical Physics, 44(16), p.161001_1 - 161001_5, 2011/08

https://doi.org/10.1088/0953-4075/44/16/161001

Times Cited Count：39 Percentile：83.77(Optics)

The resonant and non-resonant two-photon single ionization processes of He were investigated using intense free electron laser light in the extreme ultraviolet (XUV) region (53.4-61.4 nm) covering the 1s-2p and 1s-3p resonant transitions of He. On the basis of the dependences of the yield of He $^{+}$ on the XUV light-field intensity at 53.4, 58.4, 56.0 and 61.4 nm, the absolute values of the two-photon ionization cross sections of He at the four different wavelengths and their dependence on the light-field intensity were determined for the first time.

Journal Articles

Long-lived, highly excited neutral hydrogen atom production following oxygen 1s photoexcitation of gas-phase water molecules

Harries, J.; Gejo, Tatsuo*; Homma, Kenji*; Kuniwake, Miki*; Sullivan, J. P.*; Lebech, M.*; Azuma, Yoshiro*

Journal of Physics B; Atomic, Molecular and Optical Physics, 44(9), p.095101_1 - 095101_7, 2011/05

https://doi.org/10.1088/0953-4075/44/9/095101

Times Cited Count：9 Percentile：43.17(Optics)

Journal Articles

Spherically symmetric models for X-ray damage and the movement of electrons produced in non-spherically symmetric targets such as bio-molecules

Moribayashi, Kengo

Journal of Physics B; Atomic, Molecular and Optical Physics, 43(16), p.165602_1 - 165602_7, 2010/08

https://doi.org/10.1088/0953-4075/43/16/165602

Times Cited Count：17 Percentile：60.88(Optics)

Journal Articles

Highly charged tungsten spectra observed from JT-60U plasmas at $T_{mbox{e}} approx$ 8 and 14 keV

Yanagibayashi, Jun*; Nakano, Tomohide; Iwamae, Atsushi; Kubo, Hirotaka; Hasuo, Masahiro*; Itami, Kiyoshi

Journal of Physics B; Atomic, Molecular and Optical Physics, 43(14), p.144013_1 - 144013_6, 2010/07

https://doi.org/10.1088/0953-4075/43/14/144013

Times Cited Count：26 Percentile：73.17(Optics)

We observe the vacuum ultraviolet spectra of highly charged tungsten ions in plasmas at electron temperatures of 8 keV and 14 keV. The observed emission lines in a wavelength range of 2.6 3.2 nm for the plasma at 8 keV are identified to be the $3mbox{p}_{3/2}-3mbox{d}_{5/2}$ transitions of $mbox{W}^{47+}-mbox{W}^{54 +}$ . The observed emission lines at 2.0 nm and 2.3 nm at 14 keV are identified to be the $mbox{3p}_{1/2}-mbox{3d}_{3/2}$ transitions of $mbox{W}^{55 +}-mbox{W}^{61+}$ and $mbox{3s}_{1/2}-mbox{3p}_{3/2}$ transitions of $mbox{W}^{60 +}-mbox{W}^{63+}$ , respectively.

Journal Articles

Temporal evolutions of electron temperature and density with edge localized mode in the JT-60U divertor plasma

Nakano, Tomohide; Kubo, Hirotaka; Asakura, Nobuyuki

Journal of Physics B; Atomic, Molecular and Optical Physics, 43(14), p.144014_1 - 144014_7, 2010/00

https://doi.org/10.1088/0953-4075/43/14/144014

Times Cited Count：7 Percentile：35.90(Optics)

The temporal evolutions of the electron temperature and density with ELM, determined from intensity ratios of the three He I lines measured at 20 kHz, start to increase 450 s before the peak of $mbox{D}_alpha$ intensity, which is an ELM indicator. At the peak of $mbox{D}_alpha$ intensity, the electron temperature starts to decrease while the electron density starts to decrease in 300 s. The temporal evolution of the electron temperature is ascribed to heating by the ELM plasma and to energy loss for ionization of recycled neutrals, and that of the electron density is ascribed to electrons supplied in the ionization of the neutrals.