channeltron

see also:

channel photomultiplier (CPM), channel electron multiplier (CEM), continuous dynode, continuous dynode electron multiplier (CDEM), secondary electron multiplier

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Channeltrons (Channel Electron Multipliers, CEMs, or Channel Photomultipliers, CPMs) are highly sensitive secondary electron multipliers used to detect individual electrons, ions, and high-energy photons (e.g. VUV or X-ray radiation). They convert each incoming particle into an electron avalanche, thereby generating a measurable electrical pulse.

These detectors consist of structures formed within glass or ceramic bodies. Depending on the design, a Channeltron contains a straight, curved, or spiral-shaped electron channel whose inner wall is coated with a semiconducting material. When an electron strikes this surface, it is accelerated by the applied high voltage and, during subsequent collisions with the channel wall, initiates an avalanche of secondary electrons that can be measured as voltage pulses. The curved shape of the channel ensures that the secondary electrons generated at each wall impact strike the wall repeatedly, thereby releasing additional electrons and sustaining the multiplication process.

Their gain can reach up to 10⁸.

Channeltrons are widely used in mass spectrometry, surface analysis (e.g. Auger electron spectroscopy), and vacuum ultraviolet (VUV) detection. They are relatively insensitive to magnetic fields and mechanically more compact than photomultiplier tubes (PMTs). Typically, they require only a high-voltage supply (usually 1.5–3 kV) between the input and output.

The voltage pulses generated by a Channeltron have rise times of only a few nanoseconds, making them ideally suited for high-precision time measurements with Time-to-Digital Converters (TDCs). Applications such as TOF mass spectrometry, ToF-SIMS, and electron spectroscopy frequently combine Channeltron detectors with high-resolution cronologic TDCs to determine the arrival time of individual particles with picosecond precision. When additional information about pulse shape or pulse amplitude is required, high-speed ADC digitizers such as the Ndigo series are used.

Advantages

  • Single-particle detection
  • High gain
  • Low dead time
  • Compact design
  • Vacuum compatible
  • Less sensitive to magnetic fields than PMTs

Disadvantages

  • Limited lifetime due to aging of the emissive surface
  • Requires a high-voltage supply
  • No spatial resolution (in contrast to MCPs)

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Schematic illustration of the operating principle of a Channeltron, showing the electron avalanche, secondary electron multiplication, and the main components including the dynode, electron channel, collector, and high-voltage connection.

Operating principle of a Channeltron: A single electron striking the dynode initiates a cascade of secondary electrons. Repeated impacts on the semiconductive channel wall produce an exponentially growing electron avalanche, resulting in a measurable current pulse at the collector that can be captured with high precision using a TDC or ADC digitizer.