General TOF-MS System for Gas Analysis

This TOF-MS system is designed to add-on to other apparatus to provide TOF analysis of a molecular gas stream emerging from that apparatus. It can be supplied with all the components and electronics to control and take data from the TOF-MS. This system is ideal for laboratories wishing to add high sensitivity TOF-MS capability to an experiment

The system comprises:

1. An analytical chamber with six ports, housing the gas ioniser and TOF source. As well as ports for mounting the TOF analyser and for connecting the analytical chamber to your system, there are additional ports for extra pumping (in the event of a high gas load) and also orthogonal ports for additional techniques, such as laser ablation.

2. An emission-stabilised electron impact (EI) gas ionisation source designed for operation at 70eV, featuring a repeller and focussing electrodes designed to inject a sheet of high flux electrons into the TOF source.

3. A multi-electrode TOF source in which ions are extracted and accelerated to their flight energy in such a way as to come to a sharp time focus at an adjustable position some way down the 'field-free' flight tube that follows. An external trigger pulse from the TDC triggers the flange-mounted fast pulser electronics to create the extraction pulse.

4. Floating X and Y deflector plates: Since we extract ions orthogonally from the gas stream, there will be a small component of momentum in the direction of the original molecular beam, and this can result in a small tilt angle of the extracted ion packet. Kore utilises X and Y deflector plates that are separated along the beam axis, allowing a greater part of the extracted beam to be transferred into the spectrometer. We use the Y deflector plate to steer the ion beam towards the offset detector assembly.

5. A floating 'field-free' liner: Ions are created at or near ground potential, and then accelerated in the TOF source to their flight potential. Thereafter, the ions fly within a 'field-free' region, the drift space. In this type of instrument, the field- free region of the TOF spectrometer must float at a potential approximately equal to the kinetic energy required in the drift space, usually a few kilovolts. To achieve this, we fit the flight tube with a floating inner liner.

6. A 150mm diameter flight tube (vacuum vessel) housing the floating inner liner.

7. A compact, dual slope R-500-6 reflectron. It is housed in a 150mm vacuum housing that fits onto the end of the flight tube.

8. A dual microchannelplate detector. This can be configured with either 40mm diameter or 25mm diameter channelplates.

9. A flange-mounted detector pre-amplifier.

10. A TOF-MS Voltage Controller (manual control) with all relevant power supplies for the reflectron, detector, deflector plates, electron source.

11. A 2ns multi-stop Time-to-Digital (TDC) Converter - histogramming unit.

12. A data acquisition computer with TOF mass analysis software.

13. Cable set.

A new version of this instrument has been delivered to Professor Chris Binns, head of the Condensed Matter Physics Group of Leicester University (September 2005). This TOF-MS has been fitted with a different detector system, comprising a large-area, discrete dynode electron multiplier. In order to improve the detection efficiency of metal clusters, the conversion dynode of the detector is automatically floated down to -5kV with the capability of extending this to -10kV. Professor Binns is assembling new apparatus in his group this autumn for the generation and characterisation of large metal clusters