Search

Four kinds of coordination structures formed by lanthanide--picolinamide complexes, including [La(C6H6N2O)2(H2O)5]Cl3 (La-pa, Pr-pa, Nd-pa, Sm-pa and Gd-pa), [Er(C6H6N2O)2 (H2O)4]Cl3(H2O) (Er-pa), [Pr(C6H6N2O)2(H2O)5]Br3 (PrBr-pa) and [Nd(C6H6N2O)3(NO3)2] (C6H6N2O)(NO3) (NdN-pa) are reported. The crystal structures in the solid state vary with the change of anions and lanthanide ions as revealed by X-ray single crystal diffraction, FTIR, Raman, FIR and THz spectroscopy. In these crystal structures, the pyridyl nitrogen and carbonyl oxygen of picolinamide are coordinated to metal ions to form a five-membered ring structure or are hydrogen-bonded. The results indicate the differences in the coordination of different lanthanide ions (the Er ion is special for its small atomic radius), the changes of hydrogen bonds and the conformation of the ligands induced by complexation, and the influence of different anions. When nitrate ions are involved in the coordination structure, the coordination number of lanthanide ions is higher. Chloride and bromine ions do not coordinate to metal ions, so lanthanide bromine and lanthanide chloride-pa complexes have similar structures. The results provide models for the coordination structures of lanthanide ions with ligands that have amide groups. [ABSTRACT FROM AUTHOR]

A practical 2.45-GHz microwave-driven Cs-free H− source was improved based on the experimental H− source at Peking University (PKU). Several structural improvements were implemented to meet the practical requirements of Xi’an Proton Application Facility (XiPaf). Firstly, the plasma chamber size was optimized to enhance the plasma intensity and stability. Secondly, the filter magnetic field and electron deflecting magnetic field were enhanced to reduce co-extracted electrons. Thirdly, a new two-electrode extraction system with farther electrode gap and enhanced water cooling ability to diminish spark and sputter during beam extraction was applied. At last, the direct H− current measuring method was adopted by the arrangement of a new pair of bending magnets before Faraday cup (FC) to remove residual electrons. With these improvements, electron cyclotron resonance (ECR) magnetic field optimization experiments and operation parameter variation experiments were carried out on the H− ion source and a maximum 8.5-mA pure H− beam was extracted at 50 kV with the time structure of 100 Hz/0.3 ms. The root-mean-square (RMS) emittance of the beam is 0.25π⋅mm⋅mrad. This improved H− source and extraction system were maintenance-free for more than 200 hours in operation. [ABSTRACT FROM AUTHOR]

A miniaturized 2.45 GHz permanent magnet electron cyclotron resonance (PMECR) ion source, which has the ability of producing a tens-mA H+ beam, has been built and tested at Peking University (PKU). Its plasma chamber dimension is Φ30 mm × 40 mm and the whole size of the ion source is Φ180 mm × 130 mm. This source has a unique structure with the whole source body embedded into the extraction system. It can be operated in both continuous wave (CW) mode and pulse mode. In the CW mode, more than 20 mA hydrogen ion beam at 40 kV can be obtained with the microwave power of 180 W and about 1 mA hydrogen ion beam is produced with a microwave power of 10 W. In the pulse mode, more than 50 mA hydrogen ion beam with a duty factor of 10% can be extracted when the peak microwave power is 1800 W. [ABSTRACT FROM AUTHOR]

Optical emission spectroscopy (OES), as a simple in situ method without disturbing the plasma, has been performed for the plasma diagnosis of a 2.45 GHz permanent magnet electron cyclotron resonance (PMECR) ion source at Peking University (PKU). A spectrum measurement platform has been set up with the quartz-chamber electron cyclotron resonance (ECR) ion source [Patent Number: ZL 201110026605.4] and experiments were carried out recently. The electron temperature and electron density inside the ECR plasma chamber have been measured with the method of line intensity ratio of noble gas. Hydrogen plasma processes inside the discharge chamber are discussed based on the diagnostic results. What is more, the superiority of the method of line intensity ratio of noble gas is indicated with a comparison to line intensity ratio of hydrogen. Details will be presented in this paper. [ABSTRACT FROM AUTHOR]

High current hydrogen molecular ion beam is obtained with a specially designed stainless steel liner permanent magnet 2.45-GHz electron–cyclotron resonance (ECR) ion source (PMECR II) at Peking University (PKU). To further understand the physics of the hydrogen generation process inside a plasma chamber, theoretical and experimental investigations on the liner material of the plasma chamber in different running conditions are carried out. Several kinds of materials, stainless steel (SS), tantalum (Ta), quartz, and aluminum (Al) are selected in our study. Experimental results show that stainless steel and tantalum are much better than others in generation. During the experiment, an increasing trend in fraction is observed with stainless steel liner after O2 discharge inside the ion source. Surface analyses show that the roughness change on the surface after O2 discharge may be responsible for this phenomenon. After these studies, the pure current of ions can reach 42.3 mA with a fraction of 52.9%. More details are presented in this paper. [ABSTRACT FROM AUTHOR]

With the development of laser technology, laser-driven proton acceleration provides a new method for proton tumor therapy. However, it has not been applied in practice because of the wide and decreasing energy spectrum of laser-accelerated proton beams. In this paper, we propose an analytical model to reconstruct the spread-out Bragg peak (SOBP) using laser-accelerated proton beams. Firstly, we present a modified weighting formula for protons of different energies. Secondly, a theoretical model for the reconstruction of SOBPs with laser-accelerated proton beams has been built. It can quickly calculate the number of laser shots needed for each energy interval of the laser-accelerated protons. Finally, we show the 2D reconstruction results of SOBPs for laser-accelerated proton beams and the ideal situation. The final results show that our analytical model can give an SOBP reconstruction scheme that can be used for actual tumor therapy. [ABSTRACT FROM AUTHOR]

A compact laser plasma accelerator that is a novel accelerator based on the interaction of ultra-intense laser and plasmas is being built now at Peking University. According to the results of experiments and numerical simulations, a beam line combining the advantages of quadrupole and analyzing magnets is designed to deliver proton beams with energy ranging from 1 to 44 MeV, energy spread within ±5% andprotons per pulse. It turns out that the existence of space charge force of protons can be ignored for the increase of transverse and longitudinal envelopes even in the case of 10protons in one pulse. To cope with the challenge to obtain a uniform distribution of protons at the final experiment target in laser acceleration, we manipulate the envelope beam waist in the Y direction to a proper position and obtain a relatively good distribution uniformity of protons with an energy spread of 0±5%. [ABSTRACT FROM AUTHOR]

The stability and reliability of an ion source and its beam availability are extremely significant for any accelerator, especially for those high current long term CW operation ones like ADS. Although the first high quality 306-hours continuous wave (CW) operating curve at 50 mA@35 keV has been successfully obtained with a standard compact 2.45 GHz ECR ion source at Peking University (PKU), but the uncertainties that caused beam trips before are unacceptable during an accelerator real operation and should be eliminated. Meanwhile, no permission will be given when the beam power is upgraded from 50 mA@35 keV to 50 mA@50 keV. To improve the PKU CW proton source quality, several upgrades were done recently. After those improvements, a new long term CW proton beam experiment at 50 mA@50 keV was carried out in June 2016. The total running time is 300.5 hours, including near 6 hours ion source preparation and 294 hours non-disturb continuous operation. Within the continuous 13 days operation, no beam-off happened, no spark was observed, no beam drop appeared, no interrupting action was needed, and only a few beam fluctuations caused by the air conditional failure occurred. Beam availability and reliability within the 294 hours is 100%. The root-mean-square (RMS) emittance of this 50 mA@50 keV CW proton beam is about 0.186 π.mm.mrad. A careful inspection of the ion source was done after this long term operation and no obvious damage was found. The restart experimental results obtained after the ion source inspection prove the high repeatability of PKU PMECRIS. In addition, a 130-mA H+ beam was obtained at 50 kV with duty factor of 10% (100 Hz/1 ms) with this source. Details will be presented in this paper. [ABSTRACT FROM AUTHOR]

During the laser foil interaction, the output ion beam quality including the energy spread and beam divergence can be improved by the target ablation, due to the direct laser acceleration (DLA) electrons generated in the ablation plasma. The acceleration field established at the target rear by these electrons, which is highly directional and triangle-envelope, is helpful for the beam quality. With the help of the target ablation, both the beam divergence and energy spread will be reduced. If the ablation is more sufficient, the impact of DLA-electron-caused field will be strengthened, and the beam quality will be better, confirmed by the particle-in-cell simulation. [ABSTRACT FROM AUTHOR]