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Time-of-flight mass spectrometer for plasma ion mass and energy measurements

Photo of system

We have supplied the Ioffe Physical Technical Institute, High Temperature Plasma Physics Lab in St. Petersburg, Russia with an orthogonal TOF-MS for the customer to characterise their development of a RF plasma ion source. This Russian group develops mirrors for Thompson scattering diagnostics that will be used at ITER (International Thermonuclear Experimental Reactor). The international nuclear fusion research and engineering project in France. These mirrors are located in an area that is subjected to a high concentration of contaminants resulting in deposition induced loss of mirror reflectivity. Therefore protective cleaning techniques such as plasma ion sources need to be developed.

The instrument's primary purpose is to investigate the identity and energy of ions that might strike the mirror surface in a plasma generated by the client's equipment. The identity is assessed by measuring the mass to charge ratio, using mostly pre-existing Kore designs for an orthogonal injection, time-of-flight mass spectrometer (TOFMS). The advantage of TOFMS, in this context, is that it is able to measure a wide range of masses simultaneously with good sensitivity. The energy of ions is measured by arranging things in such a way that, at a given setting, only a relatively narrow range of ion energies at the entrance will yield a signal. The settings can then also be adjusted to vary the ion energy that is transmitted, over the range of energies of interest, to yield an energy profile.

A secondary experiment is to be able to assess the neutral gas composition in the plasma chamber. For this purpose, a simple small electron impact ion source is also included.


Energy scan using calibration source

The energy scan shown above was taken when using the simple surface ionisation source supplied for commissioning purposes. The full-width-half-maximum resolution is about 1.8eV, which is achieved at low cost and without compromise to the sensitivity. For users requiring more resolution, tighter apertures could be fitted, at the expense of sensitivity.


13:43 15/07/2013

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