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Manuscript Title: Ion trajectory analysis program (ITAP).
Authors: D.L. Youchison, M.D. Nahemow
Program title: ITAP
Catalogue identifier: ABTZ_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 64(1991)167
Programming language: Fortran.
Computer: IBM 3090-400E.
Operating system: OS/VS2, MS-DOS.
RAM: 1110K words
Word size: 32
Keywords: Ion-optics, Trajectories, Ion, Electron, First-order, Matrix, Transport, Prism, Optimization, Paraxial, Accelerators, Size, Divergence, Dispersion.
Classification: 7.10, 19.2.

Nature of problem:
The first approach in the design of any beam transport system is the preliminary modelling of the ion-optics to select and optimize the focal properties of the beamline components. Charged particle trajectories must be calculated through the system to determine the excitations, thicknesses, and gaps required on the lens to produce a desired image size and divergence from a given set of object conditions.

Solution method:
ITAP utilizes analytical solutions to the equations of motion in matrix form for the first-order design of charged particle transport systems. As many as 10 rays (30 rays in PC version) may be followed, generating an R-theta or X-Y mapping of the trajectory. The transfer matrices are rewritten as a product of entrance drift space, a principal plane, and an exit drift space. These matrices are then discretized into interval matrices for each increment along the beam axis and multiplied together in the main program to form a new composite matrix at each new increment.

Only first-order design is possible. Only electrons and singly charged ions can be analyzed. All equations are linear with a no-space-charge approximation. Problem size is limited to 10 rays with 400 steps on the mainframe version and 30 rays with 400 steps on the PC version. For reliable results, the ray divergence should be less than 5 degrees. The focal length should be at least ten times the lens thickness, and the thickness should be at least three times the aperture diameter.

Unusual features:
ITAP possesses a unique design option which uses an iterative bisection method to perform the design algorithm "programmed" at input by the user. The ability to customize a design run gives the user enormous flexibility. A detailed procedure for the lens design can be input directly, and multiple design sequences performed in one run. It allows the user to clearly see how different ion-optical elements can be intergrated with one another to create the desired pseudo-image. ITAP also has an extensive graphics capability which may be applied as desired. A complete reference manual is available from CPC.

Running time:
Running times vary depending on the complexity of the problem. The quadrupole sample problem with 6 rays and 303 steps without graphics required 2.81 s: 1.76 s on the VS compiler and 1.05 s in execution. The PC version required 5 min and 42 s excluding graphics. Full graphics display required an additional 5 min and 38 s, minimum.