Hardware: ToF AMS Manual

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Instrument Hardware

  1. Lower Chamber

  2. ToF
  3. Tuning the Ion Source and ToF-MS
  4. Troubleshooting

Lower Chamber

Pumping
Work in Progress

Aerodynamic Lens
Work in Progress

Chopper
Work in Progress

Vaporization
Work in Progress

Ionization
Work in Progress

ToF

Details related to the Tofwerk Instrument are CONFIDENTIAL and password protected

Tuning the Ion Source and ToF-MS

Note: these are some notes on tuning put together by P. DeCarlo and J.L. Jimenez, and circulated via email to Tofwerk and some core users. The responses that we got via email are inserted in the original list. There appear to be different schools of thought on how to tune, so these are given here only as guidelines.

  1. ORDER OF TUNING
    • Tune ion source first for signal, then tune reflectron voltages for resolution, then tune Pulsers for detailed peak shape
      • Response from Achim T: The order of tuning you suggest is the one that works best.

  2. ION SOURCE:
    • The tuning appears to depend on the emission current (maybe really filament current?) in a way that we don't understand. So it is important to tune at the emission current that will be used during measurements (typically 2 mA)
    • Don't change ion chamber from design values for that ToF by more than 10% (design values = 49V for cToF, 35V for vToF, and 8.5 for wToF, from Katrin's email on 3/1/2006)
    • In general we don't tune the ion chamber. Rather we tune the heater bias, which will typically be a few volts lower than the ion chamber value.
      • Response from Achim T: Tuning the ion chamber makes a lot of sense. It affects the ion signal a lot by a better extraction of the ions into the Pulser region. In the moment we have no evidence that changes in a certain range (not up to 80 V) will lead to a loss of small ions. The post acceleration affects this loss in a similar way like the ion chamber voltage. By increasing it the ions get a higher velocity perpendicular to the ion extraction. This has the opposite effect to increasing the ion chamber voltage.
    • The difference between the ion chamber and the filament should be 70 V (this is the electron energy)
      • Response from Katrin F: This is somewhat flexible, since depending on where you set your extraction lens voltage you may have a range of potentials in the ion source (due to field penetration). The problem is that what you see on the tof detector will be a folding of the Energy acceptance of the TOF (which is on maximum at the 49eV for the C etc) And the energy distribution of the ions transferred in the TOF extraction. Depending on your LV settings you will get ions of different energies into the TOF extraction. To be sure that you have preferentially 70eV ions one would need to compare to a reference spectrum, and tune the LV until you reproduce the reference spectrum. In principle you should be fine if you use the same voltages relative to the ion source as with the quad settings (what voltages did you use there to get the 70eV reference spectra?) for filament, ion chamber, and extraction lens.
    • The ion energy into the ToF orthogonal extractor is determined by the ion chamber. Changing the ion energy will change the m/z-dependence of the extraction efficiency. This should not be changed during a campaign.
    • Deflector flange needs to walk with the deflector voltage, small changes between the two are okay, and fractional volts can help a lot
    • Electron Pusher is not connected and is disabled in recent TPS software versions.

  3. HIGH VOLTAGE:
    • Tune reflectron grid and backplane together. This is the best way to increase resolution.
      • Response from Katrin F: Just tuning RG is sufficient.
    • Lens: this was added to tune off V-mode ions in W-mode. It should be high (~2800 V) in W mode and low (~1000) in V-mode
      • Response from Achim T: Tuning the lens voltage helps a lot by reducing the vmode ions in W mode and by increasing the signal. The quoted numbers of 1000 V for Vmode and 2800 V for Wmade are typical but they vary a lot. There are instruments which have the best vmode performance with a lense voltage of 2300 V.
    • MCP and post-acceleration are NOT tuned, these are set for amplification depending on other considerations (saturation, signal-to-noise, etc.)
    • Hardmirror doesn't have much effect on signal or resolution, no need to tune much
      • Response from Katrin F: Yes, hardmirror should NOT be tuned
      • Response from Achim T: The hardmirror has an effect on the peak shape and signal height. But you may have to vary it by some hundred Volts. In a well tuned instrument it has really no effect.

  4. PULSERS
    • The three should be tuned together
      • Response from Katrin F: I would prefer in the future that the pulser is left at the settings I ship it. You can get the same effects by just tuning the LV.
    • These should NOT be set higher than 800V
    • Tuning these 3 together is the best way to tune out leading and tailing edges
    • U+Low is not connected and doesn't do anything


Troubleshooting

P-ToF Air Beam is Low

In GenAlt MS/PToF mode, the MS and PToF airbeam readings should be approximately equal. If the PToF airbeam is signifantly lower, try changing the value of "Timing offset between modes" is the ToF Parameter menu between values of 100 and 50. The mass calibration will need to be adjusted accordingly.

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