Sumio Kumashiro

Computer simulation of the quadrupole mass filter

Abstract A computer program, called MMFCODE, has been developed to analyze numerically the dynamics of ion beams in a Quadrupole Mass Filter (QMF). The motion of the ions can be known by solving the three-dimensional equation of motion. A harmonic expansion of the electric field is introduced to get a reasonable computing time. For the incident beam, more than 10 4 ions are generated by a Monte Carlo method. After the mass scan line was determined with the condition that ΔM = const. at two different mass numbers ( M ), the mass spectrum and the acceptance can be simulated. By using MMFCODE, the simulation of a real dimension can be done without neglecting the fringing field or using the model field. In this paper, a model of a QMF with an RF-only pre-filter, called the delayed DC ramp [W. Brubaker, U.S. patent 3,371,204 (1968)], was analyzed by using MMFCODE. By our simulation, the transmittance was oscillated with respect to the pre-filter length in the case of a low mass number as reported by C. Trajber et al. [Rapid Commun. Mass Spectrom. 6 (1992) 459], but was not oscillated in the case of a high mass number. This is probably because the distribution of the axial velocities is narrow in the case of a low mass number but broad in the case of a high mass number. This discrepancy is caused by the influence of the fringing field at the pre-filter entrance.

Two-dimensional problems of acousto-optic tunable filter

Since acousto-optic tunable filter (AOTF) is one of the volume gratings that has an extremely small dielectric constant (or index of refraction) modulation it needs the grate volume (about mm or cm-order thickness) to attain the sufficient diffraction efficiency. If the width or the coherence length of incident light beam is much smaller than the width of the volume gratings, AOTF needs to be treated by 2-dimensional (2D) coupled mode theory to study the amplitude distributions of the transmission and the diffraction light waves, the spatial resolving power of the Bragg diffraction imaging, and the trace of energy flow, which cannot be obtained by 1D-model. Among the above- mentioned 2D problems, we theoretically studied the trace of energy flow of AOTF made of TeO2 crystal, taking account of being an optically anisotropic medium.

Simulation software BEAMISH for the design of charged-particle optical instruments

The versatile software package BEAMISH has been developed for the design and optimization of charged particle optical instruments. It is possible to pre- and detailed design using this software. There are five distinct features in this software, namely: (1) the optical properties of the same one instrument are calculated by plural computational methods; (2) it is easy to get hold of the optical properties of the instrument by using the various graphical representations; (3) the optimization design can be carried out automatically by the computer; (4) using the Monte Carlo simulation and 3D analysis; it is able to simulate the optical instrument as very real as possible; (5) the optical database is used for the arrangement of computed electromagnetic fields. To realize foregoing distinct features this software package includes the following sub-programs; (a) computations or real or model electromagnetic fields; (b) raytracing and aberration calculations for estimating the optical properties of the instruments; (c) optimization program to minimize the merit functions of the instruments; (d) optical database and its handling programs; (e) graphical interfaces of various computational results and optical properties. In this paper the outline of this software is described and an example (the analysis of Pierce 5B type electron gun) is shown.