Yongtao Zhao

Trends in heavy ion interaction with plasma

In this work, we review current trends in China to investigate beam plasma interaction phenomena. Recent progresses in China on low energy heavy ions and plasma interaction, ion beam-plasma interactions under the influences of magnetic fields, high energy heavy ion radiography through marginal range method, energy deposition of highly charged ions on surfaces and Raman spectroscopy of surfaces after irradiation of highly charged ions are presented.

X-ray emission of Xe 30+ ion beam impacting on Au target

X-ray emission from Xe 30+ ions at 350–600 keV impacting on an Au target was investigated at the Heavy Ion Research Facility at Lanzhou. Characteristic X-rays of Xe ions at energy of about 1.65 keV were observed. This X-ray emission is induced by the decay of very high Rydberg states of Xe ions. It was also found that the yield of such characteristic X-rays is decreasing with increasing the projectile kinetic energy. Simultaneously, the yield of the characteristic Au X-rays from the M shell increases also. These phenomena are qualitatively analyzed with the classical Coulomb over the Barrier Mode (COBM) for highly charged ions interacting with solid state surfaces.

Radiative transitions of excited ions moving slowly in plasmas

The electric dipole transitions of excited ions moving slowly in plasmas are studied. The results show that some transitions forbidden for excited ions at rest become allowed for moving excited ions. The transition rates change with varying speed of the ions. Forbidden transitions are strongly influenced by the speed, non-forbidden transitions are weakly influenced.

Heavy-ion radiography facility at the Institute of Modern Physics

In order to identify the density and material type, high energy protons, electrons, and heavy ions are used to radiograph dense objects. The particles pass through the object, undergo multiple coulomb scattering, and are focused onto an image plane by a magnetic lens system. A modified beam line at the Institute of Modern Physics of the Chinese Academy of Sciences has been developed for heavy-ion radiography. It can radiograph a static object with a spatial resolution of about 65 mu m (1 sigma). This paper presents the heavy-ion radiography facility at the Institute of Modern Physics, including the beam optics, the simulation of radiography by Monte Carlo code and the experimental result with 600 MeV/u carbon ions. In addition, dedicated beam lines for proton radiography which are planned are also introduced.

Modulation of continuous ion beams with low drift velocity by induced wakefield in background plasmas

Two-dimensional particle-in-cell simulations are performed to investigate the propagation of low energy continuous ion beams through background plasmas. It is shown that the continuous ion beam can be modulated into periodic short beam pulses by the induced wakefield, which can be adopted as a method to produce ultrashort ion beam pulses. Furthermore, the transport of the continuous ion beam in plasma with density gradient in the beam propagation direction is proposed and an enhanced longitudinal compression by density gradient is found due to the phase lock of ion pulses in the focusing regions of wakefield and reduced heating of plasma electrons.

X-ray emission induced by 1.2-3.6 MeV Kr13+ ions

X-ray emission from Kr13+ ions in the energy range 1.2-3.6 MeV in steps of 0.6 MeV impacting on an Au target was investigated on electron cyclotron resonance ion source at the Heavy Ion Research Facility in Lanzhou. It was found that a shift of the X-ray lines to the higher energy side occurred. We measured the relationship between the characteristic of X-ray yield of Au M X-rays and Kr L X-rays as a function of incident energy. Furthermore, M-shell X-ray production cross-section of Au induced by Kr13+ was measured. The measured cross-section of target is compared to the classical binary-encounter approximation and plane-wave-born approximation theoretical model, which is a significant different between experimental and theoretical model.

High energy electron radiography scheme with high spatial and temporal resolution in three dimension based on a e-LINAC

We present a scheme of electron beam radiography to dynamically diagnose the high energy density (HED) matter in three orthogonal directions simultaneously based on electron Linear Accelerator. The dynamic target information such as, its profile and density could be obtained through imaging the scattered electron beam passing through the target. Using an electron bunch train with flexible time structure, a very high temporal evolution could be achieved. In this proposed scheme, it is possible to obtain 10 10 frames/second in one experimental event, and the temporal resolution can go up to 1 ps, spatial resolution to 1 µm. Successful demonstration of this concept will have a major impact for both future inertial confinement fusion science and HED physics research.

Energy levels of a heavy ion moving in dense plasmas

In this paper, the potential of a slowly moving test particle moving in collisional dense plasmas is studied. It is composed of the Debye-shielding potential, wake potential, and collision term. The Ritz variational-perturbational method is developed for calculating relativistic binding energy levels of a heavy ion moving in dense plasmas. Binding energy levels of a heavy ion moving in plasmas are calculated. The results show that both non-relativistic energy levels and relativistic energy levels become more negative as the temperature becomes high. They also become more negative as the number density decreasing. Relativistic correction is important for calculating binding energy levels. Both relativistic energy levels and non-relativistic energy levels vary minutely as the speed of heavy ion varies.

A study of highly charged ions transmission through polycarbonate nanocapillaries with multi-holes

The transmission of highly charged Xe and Ne ions through polycarbonate (PC) nanocapillaries with multiple holes (m-PC) was investigated at the Institute of Modern Physics (IMP) in Lanzhou. In particular, Au films were evaporated on both the front side and the back to prevent the surface from charging up. The time effect was observed and the charging up model in an insulating nanocapillary was employed to explain the phenomenon. It was found that more than 98% of the transmitted ions remained in their initial charge state. The guiding effect and the relationship between the charge state and the critical angle were also studied.

K-shell ionization of Al induced by ions near the threshold energy

The K-shell ionization cross sections of Al induced by H+ and Ne7+ were studied. The ionization cross sections obtained are compared with the predictions of ECPSSR theory (based on the perturbed-stationary-state approach including Coulomb deflection, energy loss and relativistic corrections), BEA (binary encounter approximation) and 1sσ molecular-orbital ionization. It is found that the ECPSSR theoretical results agree with the experimental data very well for proton impact, while the BEA model with correction of Coulomb deflection shows good agreement with experimental results.