Tandem accelerator

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Tandem accelerator in the Maier-Leibnitz Laboratory in Garching near Munich
Stripper film

A tandem accelerator is a particle accelerator . It is a further development of the Van de Graaff accelerator , in which the acceleration voltage is used twice, in that the ions are reloaded inside the high-voltage electrode (terminal) after the first acceleration.

The tandem accelerator needs negative ions for the first acceleration stage. These are pre-accelerated by a high voltage of a few thousand volts and fed into the main acceleration section. In the middle of the accelerator is the terminal, which is charged to a positive electrical potential by a Van de Graaff generator or a pelletron . Depending on the design of the accelerator, the potential is from 1 MV (mega volt ) to 25 MV; even higher voltages are tested.

Inside the terminals passing through the ion beam , a carbon - film or generated by differential pumping gas line, the stripper (engl for "stripper".). Here the particles are converted into positive ions by stripping electrons. As a result, they are further accelerated in the second acceleration section from the terminal to the exit from the accelerator (to earth potential).

Without the change in charge, a particle would be decelerated back to the initial speed by the second acceleration stage. It is therefore not possible to use this accelerator to accelerate electrons .

Advantages over the simple Van-de-Graaff accelerator are:

  • the higher achievable ion energy at a given acceleration voltage; compared to other accelerators, the energy is twice as great with the same voltage and the same type of ion.
  • the arrangement of both “ends”, ion source and target , on earth potential and not in the high-voltage terminal.

One of the main drawbacks is the restriction on negative ions. Noble gases cannot be accelerated or can only be accelerated with difficulty (helium), since they do not form negative ions and cannot be extracted from the ion source as a chemical compound.

literature

  • SY Lee: Accelerator Physics. World Scientific Pub. Co., Singapore, 1999

Web links

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