Klystron Modulators

The European Spallation Source in collaboration with Lund University researchers have successfully brought a new high-voltage modulator design to series production. The cost savings and reduced footprint for these large machines mean a paradigm shift for the linear particle accelerator (LINAC) power supply worldwide. They developed a prototype of the Stacked Multi-Level (SML) Modulator for ESS. ESS decided to launch an internal R&D project aiming at developing a new class of modulators, particularly suited for long pulse and high-power applications. 

The LINAC at ESS is required to have capability of delivering a proton beam with a peak power of 125MW, a pulse width of 2.86 ms and a pulse repetition rate of 14Hz. The required klystrons will be fed by 33 high power long pulse modulators, each rated for 115 kV/100A; 3.5 ms/14Hz.


  • Completed the high-risk R&D effort successfully and the concept is proven with the first installation.
  • The invention can benefit ESS and the member states in many different directions.
  • In parallel to the R&D activity, a matured and trusted vendor for supply is identified and prepared.
  • The designed is compliant with the specification and follow an open solution concept where:
    • Renewable energy can be incorporated and used efficiently,
    • Solid state switch mode technology, allowing varying pulse length up to continuous operation is a possibility in the design.
  • Test, installation and integration is running according to plan.


  • The further commercial potential will be explored and the first Future and Emerging Technologies (FET) open call under Horizon 2020 has been addressed.
  • ESS will seek partners for further technology upgrade e.g. possible feasibility study together with ITER and maybe other ERICs.
  • Possible spin-out of unique knowledge and competence to a commercial company to maintain resources and impact in the field. ESS will support this effort.
  • Possibility to add to the “Green ESS” identity by enabling external sustainable power. A study and concept will need to be identified to plan the way ahead.
  • As the klystron modulators are complete according to ESS specification, further funding for the exploitation need to be found.