arXiv subjects

J. G. Zhu

Publications and source records attributed to J. G. Zhu.

5 recordsLinked to original sources

arXiv2022

Transport dynamics study of laser-accelerated proton beams and design of double achromatic beam translation system

Proton beams generated from laser acceleration show merit for their unique spatial (micron-size) and temporal (picosecond) properties, which make them desirable for many potential applications. However, the large energy spread and divergence angle make it difficult to maintain these beam properties after delivery. This hinders the wide application of laser acceleration. In this paper, we design a double achromatic beam translation system (DABTS), based on weak-focusing magnets, to realize achromatic transmission in both the horizontal and vertical directions, and compress the bunch length of the delivered proton beam at the same time. We make use of fringe angles and special steering magnets to effectively reduce the influence of chromatic aberrations and high-order nonlinear terms and realize close to ideal point-to-point optics. We believe this work contributes to the ongoing effort to apply laser accelerators to a variety of fields.

physics.acc-ph↗

arXiv2018

Laser acceleration of highly energetic carbon ions using a double-layer target composed of slightly underdense plasma and ultrathin foil

We report the experimental generation of highly energetic carbon ions up to 48 MeV per nucleon by shooting double-layer targets composed of well-controlled slightly underdense plasma (SUP) and ultrathin foils with ultra-intense femtosecond laser pulses. Particle-in-cell simulations reveal that carbon ions residing in the ultrathin foils undergo radiation pressure acceleration and long-time sheath field acceleration in sequence due to the existence of the SUP in front of the foils. Such an acceleration scheme is especially suited for heavy ion acceleration with femtosecond laser pulses. The breakthrough of heavy ion energy up to multi-tens of MeV/u at high-repetition-rate would be able to trigger significant advances in nuclear physics, high energy density physics, and medical physics.

physics.plasm-ph↗

arXiv2017

Distribution uniformity of laser-accelerated proton beams

Compared with conventional accelerators, laser plasma accelerators can generate high energy ions at a greatly reduced scale, due to their TV/m acceleration gradient. A compact laser plasma accelerator (CLAPA) has been built at the Institute of Heavy Ion Physics at Peking University. It will be used for applied research like biological irradiation, astrophysics simulations, etc. A beamline system with multiple quadrupoles and an analyzing magnet for laser-accelerated ions is proposed here. Since laser-accelerated ion beams have broad energy spectra and large angular divergence, the parameters (beam waist position in the Y direction, beam line layout, drift distance, magnet angles etc.) of the beamline system are carefully designed and optimised to obtain a radially symmetric proton distribution at the irradiation platform. Requirements of energy selection and differences in focusing or defocusing in application systems greatly influence the evolution of proton distributions. With optimal parameters, radially symmetric proton distributions can be achieved and protons with different energy spread within 5% have similar transverse areas at the experiment target.

physics.acc-ph↗

arXiv2013

Preliminary design of laser accelerator beam line

A Compact laser plasma accelerator (CLAPA) is being built in Peking University, which is based on RPA-PSA mechanism or other acceleration mechanisms. According to the beam parameters from preparatory experiments and theoretical simulations, the beam line is preliminarily designed. The beam line is mainly constituted by common transport elements to deliver proton beam with the energy of 1~50MeV, energy spread of 0~1% and current of 0~108 proton per pulse to satisfy the requirement of different experiments. The simulation result of 15MeV proton beam with an energy spread of 1%, current of 1x108 proton per pulse and final spot radius of 9mm is presented in this paper.

physics.acc-ph↗

arXiv2005

Magnetic bistability and controllable reversal of asymmetric ferromagnetic nanorings

Magnetization reversals through the formation of vortex state and the rotation of onion state are two processes with comparable probabilities for symmetric magnetic nanorings with radius of about 50 nanometers. This magnetic bistability is the manifestation of the competition between the exchange energy and the magnetostatic energy in nanomagnets. The relative probability of the two processes in symmetric nanorings is dictated by the ring geometry and can not be altered. In this work, we report the magnetic behavior of a novel type of nanorings -- asymmetric nanorings. By tuning the asymmetry we can control the fraction of the vortex formation process from about 40% to nearly 100% by utilizing the direction of the external magnetic field. The observed results have been accounted for by the dependence of the domain wall energy on the local cross section area of nanoring for which we have provided theoretical calculations.

cond-mat.mtrl-sci↗