Yubin Zou

Efficient proton beam generation from a foam-carbon foil target using an intense circularly polarized laser

Energetic proton acceleration from interaction of intense circularly polarized laser pulse with a foam-carbon foil target is investigated using two-dimensional particle-in-cell simulation. It is found that protons from this target are accelerated to much higher energy in comparison with double-layer targets and simple flat targets. This result can be attributed to an enhancement of energy conversion efficiency from laser to electrons inside foam region. When a large number of energetic electrons are generated from the nearcritical plasma, they transport through the foil and form a strong backside sheath field which accelerates protons more efficiently.

Study on scattering correction in fast neutron tomography at NECTAR facility

Fast neutron tomography has been established as an inspection and detection tool at the NECTAR facility at the FRM-II reactor. Scattered neutrons from the object become a major disturbance and bring in artifacts and deviations in reconstruction results, especially for hydrogenous material object. In this article, an iterative scattering correction method for fast neutron tomography was proposed. In each loop of iteration the scattering component of the projections will be simulated by Monte-Carlo program MCNPX based on the previous reconstruction result and then it will be subtracted from original projections. The differences between scattering components at different perspectives were quantitatively evaluated and an average scattering component image was used for all projections finally. Smooth and uniform slices with more clear edges were obtained and the new reconstructed attenuation coefficients are quite close to the real one compared to the results without scattering correction, in which case the relative error of the reconstructed attenuation coefficients is about 10%–30%.

Four-Rod RFQ Beam Dynamics Design of PKUNIFTY Upgrade*

The Peking University neutron imaging facility (PKUNIFTY), an RFQ-based neutron source, aims at developing industrial applications. During the past 3 y operation, some problems have appeared, such as RF sparking for the RFQ high power operation, full power level instability of RF transmitter, and the misalignment of RFQ electrodes assembling and deformation. The PKUNIFTY upgrade endeavors to adopt a modest inter-voltage beam dynamics design. The new beam dynamics design of 201.5 MHz RFQ of PKUNIFTY, which accelerates 35 mA of from 50 keV to 2.0 MeV at 10% duty factor, is performed. The averaged beam will be about 3 mA. The source will deliver a fast neutron yield of 2.5×1012 n/s via the deuteron–beryllium reaction, which is about 10 times higher than the current status.

Ultrafast Optical Response of Phthalocyanine Langmuir-Blodegett Film

The mechanism of 2, 9, 16, 23- tetra-heptadecylamido substituted vanadyl phthalocyanine Langmuir-Blodegett film was studied with femtosecond laser pulses. An ultrafast decay due to phonon-exciton coupling greatly affected by temperature, and exciton-exciton annihilation leading to the recovery of the ground state (T similar 10 ps) and an even slower relaxation were observed.

Optical field induced refractive index change due to collision-enhanced zeeman coherence

The collision-enhanced Zeeman coherence ?(w1-w2)(2) has been demonstrated by the effect of optical field induced index of refraction change, which is described by the real part of the nonlinear susceptibility ?(-w1,w1,-w2,w2)(3). The experiments are performed in sodium vapor by a Mach-Zehnder interferometer. The dependences of the effect on the magnetic field, pump beam intensity, and Ar pressure are consistent with the theory.