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Journal Articles

Study of X-ray emission enhancement via a high-contrast femtosecond laser interacting with a solid foil

Chen, L.-M.; Kando, Masaki; Xu, M. H.*; Li, Y.-T.*; Koga, J. K.; Chen, M.*; Xu, H.*; Yuan, X.-H.*; Dong, Q. L.*; Sheng, Z. M.*; et al.

Physical Review Letters, 100(4), p.045004_1 - 045004_4, 2008/02

 Times Cited Count:90 Percentile:92.62(Physics, Multidisciplinary)

We observed the increase of the K-$$alpha$$ X-ray conversion efficiency (hK) produced by a 60 fs frequency doubled high contrast laser pulse focused on Cu foil, compared to the case of the fundamental laser pulse. hK shows a strong dependence on the nonlinearly skewed shape of the laser pulse. It reaches a maximum for a 100 fs negatively skewed pulse. The electron spectrum shaping contributes to the enhancement of hK. Simulations demonstrate that high contrast lasers are an effective tool for optimizing the X-ray emission, via the enhanced Vacuum Heating mechanism.

Journal Articles

Experimental progress on zonal flow physics in toroidal plasmas

Fujisawa, Akihide*; Ido, Takeshi*; Shimizu, Akihiro*; Okamura, Shoichi*; Matsuoka, Keisuke*; Iguchi, Harukazu*; Hamada, Yasuji*; Nakano, Haruhisa*; Oshima, Shinsuke*; Ito, Kimitaka*; et al.

Nuclear Fusion, 47(10), p.S718 - S726, 2007/10

 Times Cited Count:100 Percentile:95.33(Physics, Fluids & Plasmas)

Present status of experiments on zonal flows is overviewed. Innovative use of modern diagnostics has revealed the existence of zonal flows, their spatio-temporal characteristics, their relationship with turbulence, and their effects on confinement. Particularly a number of observations have been accumulated on the oscillatory branch of the zonal flow, dubbed as geodesic acoustic modes suggesting necessity of theories to give their proper description. Several new methods have elucidated the zonal flow generation processes from the turbulence. Further investigation of relationship between the zonal flows and confinement is strongly encouraged as cross-device activity.

Journal Articles

Heat suppresses activation of an auxin-responsive promoter in cultured guard cell protoplasts of tree tobacco

Dong, M. A.*; Bufford, J. L.*; Ono, Yutaka; Church, K.*; Dau, M. Q.*; Michels, K.*; Haughton, M.*; Tallman, G.*

Plant Physiology, 145(2), p.367 - 377, 2007/10

 Times Cited Count:3 Percentile:9.41(Plant Sciences)

Cultured guard cell protoplasts (GCP) of Nicotiana glauca, tree tobacco, comprise a novel system for investigating the cell signaling mechanisms that lead to acquired thermotolerance and thermoinhibition. At 32 $$^{circ}$$C in a medium containing an auxin and a cytokinin, GCP expand, regenerate cell walls, dedifferentiate, and divide. At 38 $$^{circ}$$C, GCP acquire thermotolerance, but their expansion is limited and they neither regenerate walls nor re-enter the cell cycle. Protoplasts were transformed with the fusion gene of BA auxin-responsive promoter and green fluorescent protein (GFP) gene. Heat suppressed auxin-mediated activation of BA. Heat-stressed cells accumulate reactive oxygen species, and H$$_{2}$$O$$_{2}$$ suppresses auxin-responsive promoter activation. H$$_{2}$$O$$_{2}$$ did not suppress BA activation at 32 $$^{circ}$$C, nor did superoxide and H$$_{2}$$O$$_{2}$$ scavengers prevent BA suppression at 38 $$^{circ}$$C.

Journal Articles

Experimental progress on zonal flow physics in toroidal plasmas

Fujisawa, Akihide*; Ido, Takeshi*; Shimizu, Akihiro*; Okamura, Shoichi*; Matsuoka, Keisuke*; Hamada, Yasuji*; Hoshino, Katsumichi; Nagashima, Yoshihiko*; Shinohara, Koji; Nakano, Haruhisa*; et al.

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 12 Pages, 2007/03

Present status of experiments on zonal flows is overviewed. Innovative use of traditional and modern diagnostics has revealed unambiguously the existense of the zonal flows, their spatio-temporal caracteristics, their relationship with turbulence, and their effects on confinement. Particularly, a number of observations have been accumulated on the oscillatory branch of zonal flows, dubbed geodesic acoustic modes, suggesting necessity of theories to give their proper description. Furthur investigation of relationship between zonal flows and confinement is strongly encouraged as cross-device activity.

Oral presentation

Spatial and pulse shape dependence of K$$_alpha$$ source from high contrast fs laser plasmas in regime of Relativistic Engineering

Chen, L.-M.; Koga, J. K.; Kando, Masaki; Kotaki, Hideyuki; Nakajima, Kazuhisa; Bulanov, S. V.; Tajima, Toshiki; Xu, M. H.*; Li, Y.-T.*; Dong, Q. L.*; et al.

no journal, , 

Interaction of intense Ti: Sapphire laser with Cu foil targets has been studied by measuring hard X-ray generation. Hard X-ray spectroscopy and K$$_alpha$$ X-ray conversion efficiency ($$eta_K$$) from Cu plasma have been studied as a function of laser intensity via pulse duration scan (60 fs $$sim$$ 600 fs), laser pulse energy scan (60 mJ $$sim$$ 600 mJ) and target displacement scan from best focus. For intensity I $$>1times 10^{17}$$ W/cm$$^2$$, the Cu $$eta_K$$ keep on increasing to reach a maximum value of $$1times 10^{-4}$$ at an intensity $$I = 1times 10^{18}$$ W/cm$$^2$$. The focusing is varied widely to give a range of intensities from 10$$^{15}$$ W/cm$$^2 sim 10^{18}$$ W/cm$$^2$$. Comparing to a recent publication, two individual emission peaks are obtained, one is at best focal spot and the other is at larger target offset corresponding to $$sim 10^{15}$$ W/cm$$^2$$. Each peak is corresponding to different energy absorption mechanism. In addition, when we introduce slightly detuning of compressor gratings at the best focal condition, it shows $$eta_K$$ generated by negatively skewed 100 fs pulse width laser irradiation reach $$5times10^{-4}$$ and almost 7 times greater than the case of positively skewed pulse. Vacuum Heating is greatly stimulated in this case and preciously control of pre-plasma is the key factor in tuning control of X-ray emission in relativistic fs regime.

Oral presentation

Sustained heat suppresses activation of the BA auxin-responsive promoter in cultured guard cell protoplasts of tree tobacco

Dong, M.*; Bufford, J. L.*; Ono, Yutaka; Church, K.*; Dau, M. Q.*; Michels, K.*; Haughton, M.*; Tallman, G.*

no journal, , 

At 32$$^{circ}$$C in media containing an auxin and a cytokinin, cultured guard cell protoplasts (GCP) of Nicotiana glauca (Graham), expand, regenerate cell walls, dedifferentiate, and divide. At 38$$^{circ}$$C, GCP acquire thermotolerance within 24 h but their expansion is limited and they neither regenerate walls nor re-enter the cell cycle. Protoplasts were transformed with BA-mgfp5-ER. After 21 h in media with NAA, 49.0% and 7.9% of GCP transformed with BA-mgfp5-ER expressed GFP at 32$$^{circ}$$C and 38$$^{circ}$$C, respectively. Expression at 38$$^{circ}$$C was not increased by incubating GCP for 48 h or by increasing NAA concentrations 20X. Tiron and N-acetylcysteine, superoxide and H$$_{2}$$O$$_{2}$$ scavengers, respectively, did not prevent BA suppression at 38$$^{circ}$$C nor did H$$_{2}$$ O$$_{2}$$ suppress BA activation at 32$$^{circ}$$C.

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