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Idaho National Laboratory

Envisioning Ions with SIMION
Photo of Saturn

Instruments designed using SIMION are on their way to Saturn and it's moon, Titan.

A program written by Dave Dahl is helping solve mysteries from this side of the Solar System to its far reaches. Three instruments now hurtling toward Saturn aboard the spacecraft Cassini will analyze cosmic dust and the atmosphere of Titan, Saturn’s largest moon. Dave’s award-winning ion optics simulation program, SIMION for the PC, helped design the instruments. Here on Earth, other instruments with ion optics elements designed with the help of SIMION analyze environmental contaminants, decode DNA, and even uncover illegal drugs in urinalysis samples. SIMION has also been used to analyze components used in semiconductor manufacturing, indirectly improving the production of the very computers it runs on.

"It’s kind of pervasive," said David Dahl, a consulting engineer/scientist in the Chemistry Department of the Idaho National Laboratory (INL).

Photo of David Dahl

David Dahl with his ASMS Award for Distinguished Contribution in Mass Spectrometry

SIMION is so pervasive, and so influential that the American Society for Mass Spectrometry recognized that "the application of SIMION has been invaluable to the design of mass spectrometers (the kinds of machines that SIMION simulates)for the last decade." The Society awarded Dave its 1998 ASMS Award for a Distinguished Contribution in Mass Spectrometry.


Dave likes to think of SIMION as an "enabling technology." Because the program is very user-friendly and intuitive, it helps people design the ion optics of instruments creatively and explore options they may not have conceived of without the insights gained from using SIMION.

He feels that creating enabling technology is a particularly appropriate niche for a national lab. "This represents exactly the kind of thing a national lab ought to be doing," he said, "producing, developing and vigorously proliferating technology so that the maximum number of people will benefit from the taxpayer’s investment."

Users say SIMION’s beauty lies in its intuitiveness. The program makes ions coursing through electromagnetic fields as easy to visualize as golf balls rolling across a putting green. The user chooses some ions, chooses a field to simulate, finds a comfortable viewing perspective, and lets the ions fly. The simulated ions whose "flight" paths the user can trace mimic real ions inside a mass spectrometer. Mystery ions, whether in cosmic dust, environmental contaminant samples, or a drug-user’s bodily fluids, can be identified by mass spectrometers based on how the particles move through the machine.

SIMION screen shot

SIMION simulates how ions travel within an Ion Cyclotron Resonance Fourier Transform Mass Spectrometer (ICR FTMS). The color-coded lines trace the virtual ions' paths as they enter the test cell (blue), become excited (red), and then stabilize at their cyclotron frequencies (green).

With the click of a mouse button, a user can rotate the SIMION display in all three dimensions, zoom in and out, and cut out walls of the virtual mass spectrometer in order to observe the ions in action. The user can change the ions’ masses and the qualities of the electromagnetic field as the simulation is running, can choose to watch the ions as dots or with lines tracing where they have moved, and can modify the ion optic geometry at will to optimize the virtual mass spectrometer’s performance. Universities, national laboratories, and corporations use the versatile program to better understand and/or improve the performance of the ion optical elements in their instruments.


Dave’s SIMION odyssey began in 1985, when he re-wrote the original Australian version of the program. He made it compatible with personal computers, re-wrote the user interface, and improved the numerical methods that the program uses to calculate each ion’s trajectory.

Each generation of SIMION and he is now on Version 6 has been faster and more powerful. Dave said, "This is an example of what you can accomplish if you stick with something for a long time.

Michael McIlwain, (208) 526-8130,
David L. Miller, (208) 526-9052,