Zhou Wei-Min

Laser-driven proton acceleration using a conical nanobrush target

A conical nanobrush target is proposed to improve the total proton energy-conversion efficiency in proton beam acceleration and investigated by two-dimensional particle-in-cell (2D-PIC) simulations. Results indicate a significant enhancement of the number and energies of hot electrons through the target rear side of the conical nanobrush target. Compared with the plain target, the field increases several times. We observe enhancements of the average proton energy and total laser-proton energy conversion efficiency of 105%. This enhancement is attributed to both nanobrush and conical configurations. The proton beam is well collimated with a divergence angle less than 28{sup Degree-Sign }. The proposed target may serve as a new method for increasing laser to proton energy-conversion efficiency.

Time-Resolved Radiography using Chirp-Pulse Proton Beams

Protons accelerated by the target normal sheath acceleration (TNSA) mechanism have a wide energy spectrum and are called chirp-pulse protons. The numerical simulation of chirp-pulse proton radiography in an implosion process with single shot is carried out using the Monte Carlo method. Two different methods are proposed. The first method, proton framing radiography, uses a stack of radiochromic film layers as the detector. Each layer deposits protons with energy corresponding to the Bragg peak, which can record the transient state of the implosion process. The second method, proton streak radiography, uses an external magnetic field to deflect protons. Different energies correspond to different times. By using a slit before the magnetic field, one-dimensional spatial resolution and temporal resolution can be obtained. This method is more suitable for the diagnosis of the implosion process.

High-energy ion emission from cooled deuterium clusters in 20 TW laser fields

High-energy ion emission from intense-ultrashort (30fs) laser-pulse- cooled deuterium-cluster (80K) interaction is measured. The deuterium ions have an average energy 20keV, which greatly exceeds Zweibacks expectation [Phys. Rev. Lett. 84 (2000) 2634]. These fast deuterium ions can be used to drive fusion and have a broad prospect.

DD proton spectrum for diagnosing the areal density of imploded capsules on Shenguang III prototype laser facility

The primary DD proton spectrum is used for diagnosing the fuel-shell areal density ρR of imploded capsules on Shenguang III (SG-III) prototype laser facility for the first time. A charged particle spectrometer (CPS) with a CR39 nuclear track detector is used to measure the DD proton spectrum. The proton spectrum is determined from both the proton track and its size. A typical proton energy peak shift from 3.02 MeV to 2.6 MeV is observed in our experiment, which yields a maximum ρR larger than 6 mg/cm2.

Characterization of relativistic electrons generated by a cone guiding laser pulse

We demonstrated the interaction of a gold cone target with a femto second (fs) laser pulse above the relativistic intensity of 1.37 × 1018 μm 2W/cm2. Relativistic electrons with energy above 2 MeV were observed. A 25%-40% increase of the electron temperature is achieved compared to the case when a plane gold target is used. The electron temperature increase results from the guiding of the laser beam at the tip and the intense quasistatic magnetic field in the cone geometry. The behavior of the relativistic electrons is verified in our 2D-PIC simulations.

Growth of deuterium clusters in a gas jet and ion energy spectrum of clusters in ultra-short laser field

Large deuterium clusters are generated using a cryogenic pulse valve with a cone nozzle (21 mm long, 4° open angle). Rayleigh scattering experiment is carried out to obtain the scaling relation between scattering signal SR and backing pressure P0. A method using the Coulomb explosion model is proposed to verify that the clusters continue to grow after their leaving the nozzle. Our experiments suggest a tentatively optimized position for laser cluster interaction.

Effects of atomic number Z on the energy distribution of hot electrons generated by femtosecond laser interaction with metallic targets

The effects of atomic number Z on the energy distribution of hot electrons generated by the interaction of 60fs, 130mJ, 800nm, and 7×1017W/cm2 laser pulses with metallic targets have been studied experimentally. The results show that the number and the effective temperature of hot electrons increase with the atomic number Z of metallic targets, and the temperature of hot electrons are in the range of 190–230keV, which is consistent with a scaling law of hot electrons temperature.