The FN accelerator has a maximum accelerator voltage of 10 MV and is loaded via a pelletron. Measurement setups are available for nuclear structure physics, nuclear astrophysics, accelerator mass spectrometry and material investigations with ion beams. A duoplasmatron for helium beams and two sputter sources for negative ion beams (excluding noble gases) with different mass separations are available as sources on the low-energy side. In addition to a continuous beam, a pulsed beam with a maximum frequency of 2.5 MHz and packets of 2.5 ns is also possible. The highest possible beam energy is 120 MeV, provided the charge state is high enough and no molecule is injected. If you have any questions about whether a specific beam can be offered, please contact Christoph Fransen (fransen@ikp.uni-koeln.de).
Operating principle
A tandem accelerator consists of two electrostatic acceleration sections of reversed polarity, one behind the other, whose center (the terminal) is kept at positive high voltage by a Van de Graaff generator. The terminal is charged via two chains (Pelletron), which consist of metal cylinders insulated from each other. High voltages above 1-2 MV require the system to be installed in a pressure tank for insulation reasons. In the tandem Van de Graff accelerator, the terminal voltage is used several times. Negatively charged ions are injected on one side, which strip off some of their electrons in a stripper (usually a thin carbon film is used) in the terminal and are then accelerated further as positive ions on the other side. The achievable energy depends on the terminal voltage U and the charge state Z of the positively charged ions. In the first half of the tank, negatively charged ions are accelerated to the energy eU. After recharging in the terminal, the ions are then Z-fold positively charged and their total energy is (Z+1)eU. Protons, for example, can be accelerated to 20 MeV at the Cologne tandem.