Development of Time-Of-Flight Gated Ion Mass Spectrometer Tof-Gims, 15-R9538

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Principal Investigators
Jim Cravens
Frédéric Allegrini
Philip Valek
Dave McComas
Jerry Goldstein

Oleg Vaisberg
Space Research Institute, Russian Academy of Sciences

Inclusive Dates:  04/01/05 – Current

Background - Measurements of mass composition and velocity distribution of space plasmas is of crucial importance for understanding the origin, the transport, and the acceleration of plasma populations in different environments of the solar system. Most of NASA's future missions will embark simple, lightweight, and robust plasma instruments for small or multispacecraft missions. Though several types of mass spectrometers have been successfully used in space experiments, there is a need for further development of mass-spectrometric techniques, especially in simpler mass spectrometers with high mass resolution and in the mass spectrometers used in combination with imaging instruments. We are developing a novel mass spectrometer that will have both high mass resolution and imaging capabilities. The combination of these two capabilities has a significant potential for further applications in space experiments.

Approach - Our approach is to design the mass spectrometer with simple planar geometry that can be used in a variety of plasma instruments. Unlike existing laboratory prototypes with one-chamber electric fields, we will use a two-chamber electric field geometry that provides much more flexibility in achieving a high mass resolution and provide imaging capabilities. This type of instrument is much simpler than existing linear electric field mass spectrometers and surpasses them in imaging capabilities. First, we will analytically explore this electric field geometry to find optimized configuration. Then, we will make extensive test of this configuration using SIMION™ simulation software to achieve sensible imaging capabilities in the model. Finally, we will build and test a laboratory prototype to verify the performed simulations and confirm the characteristics of proposed instrument. Our objectives in this internal research program are:

  • To run computer simulations to optimize the design and achieve the highest mass resolution of a two-chamber time-of-flight mass-spectrometer
  • To analyze the different gating regimes to optimize the detection of the desired ion species such as minor components of a plasma
  • To model a two-chamber gating time-of-flight mass-spectrometer with a diverging ion beam to optimize the mass measurement in conjunction with the imaging capability
  • To build a prototype of the two-chamber mass-spectrometer and to verify the results from the model.

Accomplishments - The modeling of the laboratory prototype was completed and delivered very promising results. All mechanical parts have been fabricated, and the laboratory prototype has been fully assembled. The gate represented our most technically challenging item of the prototype. The assembly and testing of auxiliary electronics are 75 percent complete. We have worked on the transmission lines and impedance matching networks required to transmit this pulse to the gate. We accurately measured the impedance of the gate and tried the component values for the matching network to exactly equal the transmission line impedance. We are very close to testing the laboratory prototype in the SwRIbvacuum facility with ion beam.

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