long Wen

Study of dielectronic recombination at the CSRm using lithium-like Ar15+ ions

The main cooler storage ring (CSRm) of the HIRFL facility in Lanzhou, China is equipped with an electron-cooler and denotes an ideal platform for dielectronic recombination (DR) experiments. In order to fully understand our DR experimental setup and especially the electron energy detuning system, we have performed a DR calibration experiment using the Li-like argon ions at the CSRm because Ar15+ has a simple electronic structure and the DR spectrum can be calculated with an ultra-high precision and be compared with the existing experimental data. The experiment was carried out over the center-of-mass energy range 0–32 eV that includes all DR resonance associated with 2S1/2 → 2p1/2 and most of the 2S1/2 → 2p3/2 excitations. We present the details of the experimental technique and the DR experimental resonance spectrum of the Ar15+.

Proposal for precision determination of 7.8 eV isomeric state in 229Th at heavy ion storage ring

The ultraviolet optical transition of the isomeric state in 229Th has attracted much attention recently due to its potential application to building an atomic/nuclear clock with ultra-high precision. However, the lowest nuclear excitation energy and the lifetime of the first excited state of 229Th were not measured directly and precisely until now, and how to precisely determine this isomer state of the 229Th is an urgent requirement. Here an experimental approach of using a technique similar to that of dielectronic recombination to measure the transition energy of the isomer state of 229Th at heavy ion storage rings is described. It is expected that the resonant transition can be found and determined with a precision better than several milli-eV.

Studies of laser induced-breakdown spectroscopy of holly leaves

The LIBS spectra of holly leaves produced by Nd:YAG nanosecond laser has been investigated. More than 20 elements and molecules were identified from the spectra. The influence of laser wavelength upon analysis of plant samples via LIBS technique has been investigated. The comparison of LIBS spectra shows that the spectrum for 1064 nm irradiation is more intense than the one for 266 nm irradiation by the same pulse energy in the near-UV region. Investigation of the influence of laser wavelength for LIBS can help to improve the analytical capabilities of LIBS.

RF-bunching of relativistic 12C3+ ion beam for laser cooling experiment at the CSRe

To prepare the upcoming experiment of laser cooling of relativistic 12C3+ ion beams at the experimental cooler storage ring (CSRe), a test experiment was performed with 12C3+ ion beams at an energy of 122 MeV/u on the CSRe, at the Institute of Modern Physics, Lanzhou, China. In this experiment, the main storage ring of CSRm was employed to accumulate and accelerate the ion beam which was injected into the CSRe for the experiments. The number of 12C3+ ions at the CSRe reached 5×108 for every injection, which satisfied the experimental requirement. To fulfil the laser cooling experiment, the 12C3+ ion beams were bunched by sinusoidal waveforms with fixed and sweeping frequencies, respectively. A resonant Schottky pick-up was employed to record the Schottky spectra of these ion beams. The test experimental results demonstrated that the RF-buncher and diagnostic systems at the CSRe worked well and the CSRe was very stable with 12C3+ ion beams, hereby the CSRe is suitable for laser cooling experiment.

New insight into power-law behavior of fragment size distributions in the C60 multifragmentation regime

Previous experimental work has shown that a phase transition in C60 multifragmentation induced by nanosecond laser occurs at almost constant temperature covering a wide range of laser fluency. Here the relative yields of ionic fragments (IFs) C(n)(+) (n = 1-20) resulting from the multifragmentation are measured within the phase transition region. By excluding two small IFs and magic IFs due to their abnormal behavior, the data for residual IFs are used to estimate the size distributions of primary intermediate-mass IFs in the multifragmentation regime. The distributions are found to obey power laws n(-τ). Furthermore, the exponent τ values have sensitive dependence on lower laser fluency and converge to a constant of about 2.4 ± 0.2 for larger fluencies. These observations are in good agreement with an explanation based on the Fisher droplet model, offering the tantalizing possibility of a liquid-to-gas phase transition in C60 systems.

A compact large-format streak tube for imaging lidar

The streak tubes with a large effective photocathode area, large effective phosphor screen area, and high photocathode radiant sensitivity are essential for improving the field of view, depth of field, and detectable range of the multiple-slit streak tube imaging lidar. In this paper, a high spatial resolution, large photocathode area, and compact meshless streak tube with a spherically curved cathode and screen is designed and tested. Its spatial resolution reaches 20 lp/mm over the entire Φ28 mm photocathode working area, and the simulated physical temporal resolution is better than 30 ps. The temporal distortion in our large-format streak tube, which is shown to be a non-negligible factor, has a minimum value as the radius of curvature of the photocathode varies. Furthermore, the photocathode radiant sensitivity and radiant power gain reach 41 mA/W and 18.4 at the wavelength of 550 nm, respectively. Most importantly, the external dimensions of our streak tube are no more than Φ60 mm × 110 mm.

Optimizing codes for compressed ultrafast photography by the genetic algorithm

The compressed ultrafast photography (CUP) technique, providing the fastest receive-only camera so far, has shown to be a well-established tool to capture the ultrafast dynamical scene. This technique is based on random codes to encode and decode the ultrafast dynamical scene by a compressed sensing algorithm. The choice of random codes significantly affects the image reconstruction quality. Therefore, it is important to optimize the encoding codes. Here, we develop a new scheme to obtain the optimized codes by combining a genetic algorithm (GA) into the CUP technique. First, we measure the dynamical scene by the CUP system with random codes and obtain the dynamical scene image at each moment. Second, we use these reconstructed dynamical scene images as the optimization target and optimize the encoding codes based on the GA. Finally, we utilize the optimized codes to recapture the dynamical scene and improve the image reconstruction quality. We validate our optimization scheme by the numerical simulation of a moving double-semielliptical spot and the experimental demonstration of a time- and space-evolving pulsed laser spot.

Electro-optical design of a long slit streak tube

A small size and long slit streak tube with high spatial resolution was designed and optimized. Curved photocathode and screen were adopted to increase the photocathode working area and spatial resolution. High physical temporal resolution obtained by using a slit accelerating electrode. Deflection sensitivity of the streak tube was improved by adopting two-folded deflection plates. The simulations indicate that the photocathode effective working area can reach 30mm × 5mm. The static spatial resolution is higher than 40lp/mm and 12lp/mm along scanning and slit directions respectively while the physical temporal resolution is higher than 60ps. The magnification is 0.75 and 0.77 in scanning and slit directions. And also, the deflection sensitivity is as high as 37mm/kV. The external dimension of the streak tube are only ∅74mm×231mm. Thus, it can be applied to laser imaging radar system for large field of view and high range precision detection.

Dielectronic recombination of Be-like argon at the CSRm

Electron-ion recombination of Be-like 40Ar14+ has been measured for the first time at the main Cooler Storage Ring (CSRm) at Heavy Ion Research Facility in Lanzhou (HIRFL), China. The absolute rate coefficients over 0-60 eV electron-ion energy were obtained and all the resonances associated with the Δn=0 dielectronic recombination channel (2s2→2s2p) were studied. In addition to radiative and dielectronic recombination, the recombination spectrum also shows strong contributions from trielectronic recombination channel (2s2→2p2). The experimental method and preliminary results are presented.

An experimental investigation of the dissociative ionization process of argon cluster ions induced by electron impact

Utilizing the Cold Target Recoil Ions Momentum Spectrometer (COLTRIMS), dissociative ionization of argon cluster was experimentally investigated by electron impact. The recoil ions produced both in the pure ionization process and the dissociative ionization channels are measured with collision energies from 100 and 1000 eV. The ratios of the dimer ions from pure ionization (Ar2P+) and the dimer ions from small cluster dissociation (Ar+2D) to the atomic argon ion (Ar+) in different stagnation pressures were obtained.