Ramsey Research GroupThe University of North Carolina at Chapel Hill

Department of Chemistry

High Pressure Ion Detectors

Much progress has been made in the miniaturization of ion trap mass spectrometers but the development of small, lightweight, and power efficient systems remains challenging. Reducing the pumping requirements for these systems will eliminate much of their size, weight, and power consumption but will require operation at higher pressures.  Less progress has been made in the area of high pressure ion detection.  Conventional scale mass spectrometers almost exclusively use some form of cascade electron multiplier achieving current gains up to 107.  Unfortunately, operation of such detectors at high pressures is limited to ~10 mTorr for even the most robust electron multipliers.  A simple Faraday cup and charge sensitive amplifier scheme is attractive in that it is inherently pressure tolerant up to and exceeding atmospheric pressure and operates without the need for high voltages.

Towards this end we are currently developing a variety of Faraday cups with integrated amplifiers.  Through collaboration with the University of Arizona we are working on integrating several prototypes into our miniaturized mass spectrometry systems.  Work is also ongoing in the use and modification of commercial amplifiers to serve the same purpose.

Faraday Cupfaraday cup circuit

The figure on the left shows a Faraday cup detector with integrated amplifier that can be inserted into the high pressure mass spectrometer. A potential signal processing circuit diagram is shown on the right.