非傍轴双光束势阱产生的辐射力

分析了两束相对传输的非傍轴高斯光束相干叠加形成的双光束势阱对瑞利粒子产生的辐射力,并作了数值计算,结果表明,与傍轴双光束势阱相比,非傍轴双光束势阱的辐射力有明显的不同,纵向辐射力和横向辐射力都增大,y方向平衡点数目由一个增加到多个,且势阱更深,横向辐射力变化趋势更陡,更有利于微粒的精确定位,与非傍轴单光束势阱相比,势阱更深,所产生的辐射力更大,因而更利于控制瑞利粒子。     

Electron beam density imaging system at Beam study using a portable slit the Shanghai Electron Ion Trap

In this work, a portable slit imaging system is developed to study both the electron beam diameter and the profile of the newly developed Shanghai Electron Beam Ion Trap （Shanghai EBIT）. Images are detected by a charge coupled device （CCD） sensitive to both X rays and longer wavelength photons （up to visible）. Large scale ray tracings were conducted for correcting the image broadening effects caused by the finite slit width and the finite width of the CCD pixels. A numerical de-convolution method was developed to analyse and reconstruct the electron beam density distribution in the EBIT. As an example of the measured beam diameter and current density, the FWHM （full width at half maximum） diameter of the electron beam at 81 keV and 120 mA is found to be 76.2 μm and the density 2.00 × 10^3 A.cm-2, under a magnetic field of 3 T, including all corrections.     

Electron beam density study using a portable slit imaging system at the Shanghai Electron Beam Ion Trap

In this work,a portable slit imaging system is developed to study both the electron beam diameter and the profile of the newly developed Shanghai Electron Beam Ion Trap (Shanghai EBIT).Images are detected by a charge coupled device (CCD) sensitive to both X rays and longer wavelength photons (up to visible).Large scale ray tracings were conducted for correcting the image broadening effects caused by the finite slit width and the finite width of the CCD pixels.A numerical de-convolution method was developed to analyse and reconstruct the electron beam density distribution in the EBIT.As an example of the measured beam diameter and current density,the FWHM (full width at half maximum) diameter of the electron beam at 81 keV and 120 mA is found to be 76.2 μm and the density 2.00 × 10 3 A·cm 2,under a magnetic field of 3 T,including all corrections.     

Propagation of Plasma Generated by Intense Pulsed Ion Beam Irradiation

Taking the calculation results based on the established two-dimensional ablation model of the intense-pulsed-ionbeam （IPIB） irradiation process as initial conditions, we build a two-dimensional hydrodynamic ejection model of plasma produced by an IPIB-irradiated metal titanium target into ambient gas. We obtain the conclusions that shock waves generate when the background pressure is around 133 mTorr and also obtain the plume splitting phenomenon that has been observed in the experiments.     

Study of Intense Electron Beams Produced by High-Voltage Pulsed Glow Discharges

We report the generation of high-current-density (20 A/cm2) pulsed electron beams from high-voltage (48-100 kV) glow discharges using cathodes 7.5 cm in diameter. The pulse duration was determined by the energy of the pulse generator and varied between 0.2 ?s and several microseconds, depending on the discharge current. The largest electron beam current (900 A) was obtained with an oxidized aluminum cathode in a helium-oxygen atmosphere. An oxidized magnesium cathode produced similar results, and a molybdenum cathode operated at considerably lower currents. A small-diameter (<1 mm) well-collimated beam of energetic electrons of very high current density (>1 kA/cm2) was also observed to develop in the center of the discharge. Electrostatic probe measurements show that the negative glow plasma density and the electron beam current have a similar spatial distribution. Electron temperatures of 1-1.5 eV were measured at 7 cm from the cathode. The plasma density (8.5 · 1011 cm-3 at 450 A) was found to depend linearly on the discharge current. In discharges at high currents a denser and higher temperature plasma region was observed to develop at approximately 20 cm from the cathode. We have modeled the process of electron beam generation and predicted the energy distribution of the electron beam. More than 95 percent of the electron beam energy is calculated to be within 10 percent of that corresponding to the discharge voltage.     

The Canadian Penning Trap Spectrometer at Argonne

The Canadian Penning Trap (CPT) mass spectrometer is a device used for high-precision mass measurements on short-lived isotopes. It is located at the ATLAS superconducting heavy-ion linac facility where a novel injection system, the RF gas cooler, allows fast reaction products to be decelerated, thermalized and bunched for rapid and efficient injection into the CPT. The CPT spectrometer and its injection system will be described in detail and its unique capabilities with respect to its initial physics program, concentrating on isotopes around the N=Z line with particular emphasis on isotopes of interest to low-energy tests of the electroweak interaction and the rp-process, will be highlighted. This revised version was published online in July 2006 with corrections to the Cover Date.     

Diode Feedback Effects in Intense Relativistic Electron Beam Oscillators

The general operation of intense relativistic electron beam oscillators is described. These oscillators employ the well-known reflex triode phenomenon to plug the ends of a magnetically confined beam drift region by setting up efficient electron reflexing between the real cathode of an accelerator and a downstream virtual cathode. For a variety of magnetic traps and experimental conditions, it is shown that the inherent electron beam feedback from the drift region can be effectively utilized to reduce the electronion diode impedance and thereby permit good matching and energy transfer between the diode and a sub-ohm particle accelerator. A theoretical model is presented to interpret the observed phenomena.     

Charge Flow and Plasma Behavior in Intense Ion Beam Diodes

Intense ion beams are produced in high-power vacuum diodes of various configurations and are believed to be useful for applications in inertial confinement fusion and plasma confinement. Using magnetically insulated diodes, we investigated spatial nonuniformities of the diode plasmas, plasma expansion, ion transverse velocities in the diode gap, electron flow to the anode, and the charge distribution in the gap. Various time-dependent diagnostic techniques including recently developed spectroscopic methods have been used. We observed rapid closure of the diode gap, resulting from fast expansion of the electric field-excluding anode plasma early in the pulse. This contributes significantly to the measured ion current density enhancement. The electron cloud in the gap was seen to spread towards the anode beyond the region of the theoretical electron sheath. This is consistent with observed ion current densities being larger than the values calculated using the actual diode gap. The ion angular spread was found to increase locally due to nonuniform expansion of the cathode plasma for one class of phenomena and of the anode plasma for the other two classes. Part of these phenomena were associated with electron flow to the anode. The ion divergence angle in the gap was observed to be independent of the ion mass and to be significantly smaller than angles previously observed outside the diode.     

渡越辐射在强流电子束诊断中的应用

文中描述了渡越辐射用于束流诊断的理论依据,介绍了利用渡越辐射对18MeV,2.7kA的强流脉冲电子束进行诊断的实验方案,介绍了在强流束测量中遇到的困难和解决方法.实验中获得了渡越辐射的特征图案,并对特征图案进行了分析,得到了测量时应该使用偏振片的结论.据此,利用渡越辐射测量了强流脉冲束的剖面、能量、发散角.并采用渡越辐射与切伦科夫辐射相结合的方法，用切伦科夫辐射测量束剖面,用渡越辐射测量能量和发散角,在同一次实验中获得了强流脉冲束的归一化发射度.     

The Electrostatic Trapping of an Intense Relativistic Electron Beam in a Magnetic Mirror

Observations of rapid axial oscillations of an intense relativistic electron beam in a magnetic mirror are reported. The mirror field primarily provides radial confinement of the relativistic electrons. The axial confinement was achieved by placing thin aluminized mylar foils at the conjugate mirror field maxima. The region between these foils was filled with a few Torr air to provide a beam induced plasma for charge and current neutralization. The regions outside these foils were maintained at ~10-4 Torr. One foil formed the anode of a space-charge limited relativistic electron diode which launched the beam into the mirror. When the beam passed through the second foil it was no longer charge neutralized. In a manner quite similar to the anode foil oscillations observed by others, a space-charge limited electrostatic well was established which stopped the electrons and re-accelerated them through the foil-thereby reflecting the beam. When the reflected electrons re-entered the diode, they were once again "electrostatically" reflected. This process continued until the oscillating beam was either lost through the "virtual cathodes" outside the foils, dissipated in the drift region or quenched in the diode plasma after gap closure.     

EBIT装置零蒸发低温超导磁体系统的研制

介绍了EBIT(Electron Beam Ion Trap,电子束离子阱)装置零蒸发低温超导磁体系统的研制过程与超导磁体的性能测试结果。该系统中超导磁体由一对上下布置的分离线圈组成,中心最大磁场强度可达4.5T,在中心轴线上±10mm内磁场均匀度优于2×10-4,磁场衰减系数在8h小于1×10-4;同时其低温杜瓦系统采用双冷屏结构,并通过二级G-M制冷机冷却冷屏来降低液氦的蒸发量。超导磁体的性能测试结果表明满足用户基本要求。     

Theory of Microwave Emission by Velocity-Space Instabilities of an Intense Relativistic Electron Beam

The stability of waveguide modes in a waveguide along which is propagated an unneutralized, intense beam of relativistic electrons guided by an applied axial magnetic field is considered. It is found that the waveguide mode can interact unstably with the beam by resonating with the Doppler shifted cyclotron frequency of the beam. This instability appears to be the mechanism by which microwaves are produced in some recent experiments which are discussed.     

Towards a Measurement of the n=2 Lamb Shift in Hydrogen-like Nitrogen Using an Electron Beam Ion Trap

Hyperfine Interactions - Using a 14C16O2 laser the 2s 1/2–2p 3/2 (fine structure – Lamb shift) transition has been induced in 14N6+ ions trapped in an electron beam ion trap. Prospects...     

Ion Beam Probe Measurements of Electron Temperature

The technique for measuring electron temperature with an ion beam probe has been refined, the time resolution reduced and the limitations evaluated. The technique involves sequentially probing the same volume of plasma with beams of different ion species and using the observed secondary ion currents and the known ionizing cross sections to evaluate the electron temperature. Spatial resolution is less than 0.1 cm3 and the time required to obtain a radial temperature profile is presently 10 msec. Detailed measurements have been made on a hollow cathode discharge and the results compared with Langmuir probe and spectroscopic data. Quantitative results can only be obtained with K+ -Na+ beams due to the lack of cross sections for other ion species. Better experimental data has been obtained with Rb+ and Cs+ beams but they cannot be reduced to Tee Theoretical cross sections provide qualitative indications of the system behavior but are not sufficiently accurate to permit quantitative data reduction.     

Numerical Simulation on Expansion Process of Ablation Plasma Induced by Intense Pulsed Ion Beam

We present a one-dimensional time-dependent numerical model for the expansion process of ablation plasma induced by intense pulsed ion beam （IPIB）. The evolutions of density, velocity, temperature, and pressure of the ablation plasma of the aluminium target are obtained. The numerical results are well in agreement with the relative experimental data. It is shown that the expansion process of ablation plasma induced by IPIB includes strongly nonlinear effects and that shock waves appear during the propagation of the ablation plasma.     

脉冲光电子枪中光电子束性能研究

利用新设计的脉冲光电子枪,研究了光电子束的能量分布,光数密度与激光强度的关系和光电子在电离区内的滞留时间。大部分电子的能量为光发射电子的剩余能量,但量由于电子的空间电荷效应,电子能量分布具有加宽现象。每个激光脉冲发射到电离区内的光电子数密度在１０＾９／ｃｍ＾３以上。     

Deceleration of Metastable Li~+ Beam by Combining Electrostatic Lens and Ion Trap Technique

Ion deceleration has played a critical role in ion-related research when the ions are produced in the form of a high-energy beam.We present a deceleration method combining electrostatic lens and ion trap technique,which can effectively decelerate ions to energy below the trapping potential of a typical ion trap.The experiments were performed on metastable 1s2s³S₁Li⁺ ions,and demonstrated that the kinetic energy could easily be reduced from ～450 e V to a few e V,w...     

聚焦电子/离子束技术的原理及应用

总结近几年来聚焦电子/离子束双束技术的发展概况和主要应用领域,主要对双束系统的结构、原理及其在刻蚀、沉积、离子注入、显微成像和能谱分析等几方面的应用发展进行介绍,讨论双束技术未来发展的趋势。