Workshop on

Non-linear beam expander systems in high-power accelerator facilities

ISA, Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark

26th and 27th March 2012

The use of non-linear magnetic elements to shape the beam profile is, and has been, considered for several high power facilities. At ISA, Aarhus University in Denmark, we are designing the high-energy beam transport (HEBT) for the European Spallation Source (ESS), including a beam expander system to match the beam size and profile to the target. The ESS HEBT system will transport the 5 MW, 2.5 GeV proton beam from the linac to the spallation target, which will be a rotating tungsten wheel. The lifetimes of the target and the preceding Proton Beam Window depend critically on the maximum beam current density and the intensity gradient. Another concern in the high-power facility is the magnitude and extent of tails of the beam. For the ESS beam expander, we are presently favouring a system combining octupole beam folding and quadrupole expansion. However, many issues require careful attention before a detailed design can be frozen.

The aim of this workshop is to present the baseline ESS design, exchange knowledge, and review other beam expander systems, to assess the problems and constraints involved, in particular using magnetic multipoles. Issues for discussion include:

  • Beam optics optimization and transverse decoupling in the presence of space charge
  • Beam profile stability, both concerning the centroid position, the maximum current density, and the maximum intensity gradient
  • Unavoidable beam losses arising from over-focused beam halos, and how these losses compare to a linear expansion system
  • Magnet choices
    • Step-like field magnets versus conventional multipole magnets
    • Aperture choice, i.e. the tradeoff between large field gradients versus local losses

Related issues to be discussed are collimation and the interface to the target including diagnostics.

If you would like to give a talk at the meeting please include the title of your talk in the registration form.

Important Dates:

Registration deadline: Wednesday 29th February 2012



Last Modified 20 January 2012