4,947 research outputs found

    US LHC Accelerator Research Program High-Field Magnet R&D

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    Picosecond photoinduced transmission associated with deep traps in phosphorous doped őĪ-Si:H

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    Journal ArticlePhotoinduced transmission was observed in the picosecond time domain in phosphorusdoped a-Si:H and connected with deep hole traps produced by doping. The hole transport was found to be dispersive starting before 5 ps and temperature dependent. This shows that the energy distribution of shallow traps is exponential beginning below 10-2 eV from the valence-band top. The deep traps are negatively charged defects, the trapped holes are removed from the recombination process, and their distribution peaks at 0.45 eV above the valence-band top

    Picosecond photoinduced optical anisotropy in trans-(CH)x : direct measurement of soliton diffusion

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    Journal ArticlePhotoinduced dichroism caused by bleaching of the interband transition in trans - (CH)X was observed in the picosecond time domain. The bleaching is induced instantaneously and decays with time as t - 1 / 2 , changing to a lower power after ~ 50 ps. Although the photoinduced bleaching persists to long times, polarization memory is lost after ~ 10-9s. The results provide a measurement of the diffusion constant of the charged excitations; D ‚Čą 2 x 10-2 cm2 s - 1 at 300K and 80K

    Picosecond trapping of photocarriers in amorphous silicon

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    Journal ArticleTrapping of photoexcited carriers in the picosecond and subnanosecond time domains was studied by measuring the decay of photoinduced absorption (PA) in a-Si, a-Si:F, a-Si:H, and a-Si:H:F. We found that when the midgap density of states decreases, both the trapping time and its temperature dependence increase. The observed PA decays are compared to the picosecond photoconductivity decays, and the differences in the response curves are explained. The possibility that geminate recombination might explain our results is ruled out

    Picosecond photoinduced dichroism in trans-(CH)x: direct measurement of soliton diffusion

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    Journal ArticlePhotoinduced dichroism caused by bleaching of the interband transition in tran s-(CH)x was observed in the picosecond time domain,, The bleaching is induced instantaneously and decays with time as £~1 / / 2 , changing to a lower power after ~50 psec. Although the photoinduced bleaching persists to long times, polarization memory is lost after ~10"9 sec. The results provide a measurement of the diffusion constant of the charged excitations; D^ 2x 10"2 cm2 sec"1 at 300 and 80 K

    Dual equilibrium in a finite aspect ratio tokamak

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    A new approach to high pressure magnetically-confined plasmas is necessary to design efficient fusion devices. This paper presents an equilibrium combining two solutions of the Grad-Shafranov equation, which describes the magnetohydrodynamic equilibrium in toroidal geometry. The outer equilibrium is paramagnetic and confines the inner equilibrium, whose strong diamagnetism permits to balance large pressure gradients. The existence of both equilibria in the same volume yields a dual equilibrium structure. Their combination also improves free-boundary mode stability
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