X-ray spectra of $K$-shell hollow krypton atoms produced in single collisions with 52–197-MeV/u $\mathrm{X}{\mathrm{e}}^{54+}$ 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 $K{\beta }_{1,3}^s$ 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.

The transmission of low-energy (1100eV-1500eV) electrons through SiO 2 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.

The collisions of the isocharged sequence ions of $q=6$ (${\text{C}}^{6+}$, ${\text{N}}^{6+}$, ${\text{O}}^{6+}$, ${\text{F}}^{6+}$, ${\text{Ne}}^{6+}$, ${\text{Ar}}^{6+}$, and ${\text{Ca}}^{6+}$), $q=7$ (${\text{F}}^{7+}$, ${\text{Ne}}^{7+}$, ${\text{S}}^{7+}$, ${\text{Ar}}^{7+}$, and ${\text{Ca}}^{7+}$), $q=8$ (${\text{F}}^{8+}$, ${\text{Ne}}^{8+}$, ${\text{Ar}}^{8+}$, and ${\text{Ca}}^{8+}$), $q=9$ (${\text{F}}^{9+}$, ${\text{Ne}}^{9+}$, ${\text{Si}}^{9+}$, ${\text{S}}^{9+}$, ${\text{Ar}}^{9+}$, and ${\text{Ca}}^{9+}$) and $q=11$ (${\text{Si}}^{11+}$, ${\text{Ar}}^{11+}$, and ${\text{Ca}}^{11+}$) with helium at the same velocities were investigated. The cross-section ratios of the double-electron transfer (DET) to the single-electron capture (SEC) ${\sigma }^{\text{DET}}∕{\sigma }^{\text{SEC}}$ and the true double-electron capture (TDC) to the double-electron transfer ${\sigma }^{\text{TDC}}∕{\sigma }^{\text{DET}}$ were measured. It shows that for different ions in an isocharged sequence, the experimental cross-section ratio ${\sigma }^{\text{DET}}∕{\sigma }^{\text{SEC}}$ varies by a factor of 3. The results confirm that the projectile core is another dominant factor besides the charge state and the collision velocity in slow ($0.35-0.49v_0$; $v_0$ denotes the Bohr velocity) highly charged ions (HCIs) with helium collisions. The experimental cross-section ratio ${\sigma }^{\text{DET}}∕{\sigma }^{\text{SEC}}$ is compared with the extended classical over-barrier model (ECBM) [A. Bárány et al., Nucl. Instrum. Methods Phys. Res. B 9, 397 (1985)], the molecular Coulombic barrier model (MCBM) [A. Niehaus, J. Phys. B 19, 2925 (1986)], and the semiempirical scaling laws (SSL) [N. Selberg et al., Phys. Rev. A 54, 4127 (1996)]. It also shows that the projectile core properties affect the initial capture probabilities as well as the subsequent relaxation of the projectiles. The experimental cross-section ratio ${\sigma }^{\text{TDC}}∕{\sigma }^{\text{DET}}$ for those lower isocharged sequences is dramatically affected by the projectile core structure, while for those sufficiently highly isocharged sequences, the autoionization always dominates, hence the cross-section ratio ${\sigma }^{\text{TDC}}∕{\sigma }^{\text{DET}}$ is always small.

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 O³⁺ ions and 2 keV electrons show that it can provide exact boundaries when a positive charged particle beam current distribution is measured.

We have developed a real-time beam current density meter for charged particle beams. It measures the mean current density by collimating a uniform and large diameter primary beam. The suppression of the secondary electrons and the deflection of the beam were simulated, and it was tested with a 105 keV Ar⁷⁺ ion beam.