Mingwu Zhang

Transmission of electrons through a tapered glass capillary

The transmission of high-current electrons through a tapered SiO2 capillary was investigated. The angular distribution and incident energy dependence of transmitted electrons were observed. We found that the transmitted fraction decreases with the incident energy. The transmitted electrons had significant energy loss but could not be focused by the tapered capillary.

Transmission of low-energy electrons through SiO2 tube

The transmission of low-energy (1100eV-1500eV) electrons through SiO2 tube was investigated, the distribution of transmitted beam current was observed. Results indicate that the intensity of transmitted electrons is proportional to the relative incident beam intensity and the angular divergence of the transmitted electrons is reduced when incident energy increased.

A 128-channel picoammeter system and its application on charged particle beam current distribution measurements

A 128-channel picoammeter system is constructed based on instrumentation amplifiers. Taking advantage of a high electric potential and narrow bandwidth in DC energetic charged beam measurements, a current resolution better than 5 fA can be achieved. Two sets of 128-channel strip electrodes are implemented on printed circuit boards and are employed for ion and electron beam current distribution measurements. Tests with 60 keV O(3+) ions and 2 keV electrons show that it can provide exact boundaries when a positive charged particle beam current distribution is measured.

Production and decay of K -shell hollow krypton in collisions with 52–197-MeV/u bare xenon ions

X-ray spectra of K-shell hollow krypton atoms produced in single collisions with 52 - 197 MeV/u Xe54+ ions are measured in a heavy-ion storage ring equipped with an internal gas-jet target. Energy shifts of the K{\alpha}_1,2^s, K{\alpha}_1,2^(h,s), and K\b{eta}_1,3^s transitions are obtained. Thus, the average number of the spectator L-vacancies presented during the x-ray emission is deduced. From the relative intensities of the K{\alpha}_1,2^s and K{\alpha}_1,2^(h,s) transitions, the ratio of K-shell hollow krypton to singly K-shell ionized atoms is determined to be 14 - 24%. In the considered collisions, the K-vacancies are mainly created by the direct ionization which cannot be calculated within the perturbation descriptions. The experimental results are compared with a relativistic coupled channel calculation performed within the independent particle approximation.

Electron beam guiding by grooved SiO2 parallel plates without energy loss

Using a pair of grooved SiO2 parallel plates, stably guided electron beams were obtained without energy loss at 800–2000 eV. This shows that the transmitted electrons are guided by a self-organized repulsive electric field, paving the way for a self-adaptive manipulation of electron beams.

One-dimension position sensitive MCP detector using a parallel strips readout anode

We have developed a one-dimension position sensitive MCP detector based on a new parallel micro-strips readout anode. The position resolution of the detector is 0.2mm.

Energy spectra of sputtering ions induced by Ar7, 9+ ions on graphite collisions

The Sputtering Ion Energy Spectra (SIES) produced by Ar7, 9+ ions at velocities of 0.9 vBohr, 1.35 vBohr and 1.8 vBohr bombardment at 45o to high oriented graphite target were obtained for the first time.

Guiding of high-current electron beam by macro-insulating units

Since the unexpected guiding effect of low energy ions by PET nanocapillaries was reported, considerable work [1, and references therein] has been done to investigate slow highly charged ions (SHCIs) interacting with inner surface of various insulating capillaries. Now it is clear that the preceding SHCIs will deposit positive charges on the surface, building up an electric field by forming a charged patch and therefore preventing the succeeding ions from close contact with the surface. The deposited charge patch more than one may be created until stable guiding is achieved. However, when an electron beam passes through an insulating capillary, besides the low energy secondary electrons, a notable portion of the transmitted electrons suffers significant energy loss, and the transmission efficiency is much lower than that of SHCIs. The current studies of electron guiding indicate that it is essentially different from that of SHCI [2, and references therein]. In our previous work [2], using a pair of grooved SiO2 parallel plates, we had obtained stably guided electron beams without energy loss in the incident energy range of 800-2000V. Different beam fluxes and different ground boundaries were employed to explore the discharge mechanisms, but no obvious influences have been observed. It shows that the self-organizing repulsive electric field played the dominant role to guide the electrons, by comparing with a pair of asymmetric parallel plates that were constructed by replacing one of the plates by a ground metal. This is similar to the case of SHCI beams. However, our results suggest that the complicated mechanisms involved in charging and discharging of insulators bombarded by electrons. Following the above investigation, we used several insulators which were all made into grooved plates as same as the above grooved SiO2 plates, to study the dependence relative to the guiding beams on different materials. As shown in Figure 1, it is very surprised that, because the conductivities of these materials may differ several magnitudes from each other, the guiding behaviors among these different insulators are quite same. Moreover, we found that the gap between two symmetric plates might play significant role in guiding process of electron beams. The present results suggest that the guiding effect of high-current electron beams by macro-insulating units may be due to the combined contributions of the individual atom scattering and the repulsive field on material surface. This work was supported by the National Natural Science Foundation of China (Nos. 11205224, 11275240, and U1332206).

Determination of internal-target thickness and experimental luminosity from beam energy loss at HIRFL-CSRe*

The target thickness for nitrogen was determined from the beam energy loss in HIRFL-CSRe during the experimental study of the K-REC process in 197 MeV/u Xe54+-N-2 collisions. Furthermore, the corresponding integrated luminosity of (1.15 +/- 0.06) x 10(30) cm(-2) was obtained. As an independent check on the energy-loss method, we have also determined the integrated luminosity by measuring the produced X-rays from the K-REC process with a known differential cross section. The values of (1.12 +/- 0.06) x 10(30) and (1.09 +/- 0.06) x 10(30) cm(-2) were obtained by using two high-purity germanium (HPGe) detectors which were oriented at 90 degrees and 120 degrees with respect to the beam path, respectively. The consistent results confirmed the feasibility of the energy-loss method, which may have an important impact on future internal target experiments at HIRFL-CSRe.

Double K-shell ionization of Kr induced by swift Xe54+ ions

Kα satellite and hypersatellite lines of Kr induced by 52-, 94-, 146-, and 197-MeV/u Xe54+ ions were measured. Experimental values were compared with theoretical ones obtained within the independent electron model (IEM) employing single electron probabilities calculated with the semi-classical approach (SCA). This comparison suggests that first order perturbation approximation is consistent well with the experimental result at 197-MeV/u projectile collision while breaks down for the lower energies.