Charge accumulations on the wall of the chunnels in field emission devices are analyzed with the Monte Carlo method. The chunnel's wall is dielectric, and secondary electrons are generated when electrons hit the chunnel's wall. Under the electron bombardment, the secondary emission induces charging on the wall. It is implied that in the field emission process, the upper part of the chunnel's inside wall is positively charged, while the lower part of the chunnel's inside wall and the chunnel's underside wall are negatively charged. Four models with different forms of chunnels are studied. We analyze the effect of charge accumulation in different models by comparing the potential distributions near the cathode and the current density distributions of the cathode, respectively. The results show that increasing the slope of the chunnels will reduce charge accumulations at the chunnel's underside wall. Also, the energy distributions of electrons arriving at the anode are analyzed, and it suggests that the chunnel's slope may decrease the ratio of primary electrons directly on the anode to all the electrons on the anode.

In the manufacture of electron optical system, the dimension and alignments of the electrodes may have some small perturbations. The performance of the electron optical system is affected by these tolerances. It is important to analyse the in#uence of the tolerance. Usually, the perturbations of the potential and the trajectory are obtained by the difference of parameters at various positions of the movable electrode. Because the value of the tolerance is usually very small, it is diffcult to estimate the acceptable tolerance. Serious numerical error may also be introduced in this method. This paper proposes another method to determine the acceptable tolerance in the manufacture. In this method, the derivative of the potential versus the displacement vector is obtained from the unperturbed field. Then the derivative of trajectory is calculated with the RK method from the normal result. According to the first-order approximation, the acceptable tolerance can be determined. This paper analyses some typical perturbations in the main lens of CRT. (1999 Elsevier Science B.V. All rights reserved.

The fabrication of carbon nanotube emitters with excellent emission properties is described. The multi-walled carbon nanotubes (MWNTs) produced by chemical vapor deposition (CVD) method were purified with oxidation method and mixed with organic binding pastes and then screen-printed on glass substrates with ITO film. We applied anode voltage gradually to refine the emission behavior of the emitter by cleaning the top surface of screen-printed carbon nanotubes (CNTs). The density of the carbon nanotubes is about 2:5 108/cm2. Diode field emission experiments were performed in dynamic vacuum system to study the emission current, the emission uniformity, etc. Bright and stable character emission images were obtained in the diode structure and the emission current could approach 1 mA/cm2.

In the design of a charged particle optical system, many geometrical and electric parameters have to be optimized to improve the performance characteristics. In every optimization cycle, the electromagnetic field and particle trajectories have to be calculated. Therefore, the optimization of a charged particle optical system is limited by the computer resources seriously. Apart from this, numerical errors of calculation may also influence the convergence of merit function. This article studies how to improve the optimization of charged particle optical systems. A new method is used to determine the gradient matrix. With this method, the accuracy of the Jacobian matrix can be improved. In this paper, the charged particle optical system is optimized with a Message Passing Interface (MPI). The electromagnetic field, particle trajectories and gradients of optimization variables are calculated on networks of workstations. Therefore, the speed of optimization has been increased largely. It is possible to design a complicated charged particle optical system with optimum quality on a MPI environment. Finally, an electron gun for a cathode ray tube has been optimized on a MPI environment to verify the method proposed in this paper.