High Power RFTS

A complete RF transmitter chain of 3 MW peak power is implemented in ESS Bilbao with a pulse width of 1.5 ms/3.5 ms and 30 Hz/14 Hz of frequency repetition rate at a central frequency of 352.21 MHz. The RFTS includes the same subsystems required for linac operation.

  • Modulator: generates the high voltage pulse for powering the klystron with 110 kV and 60 A (manufactured by Jema Energy).


  • Klystron: amplifies the power from the driver up to 3 MW peak power (manufactured by CPI).


  • Driver: preamplifiers the low-level signal from the signal generator up to the peak power required by the klystron, hundreds of W. It is an ESS Bilbao development.

Driver test

  • Timing Box: generates the trigger and pulse signals for synchronizing correctly all the RF chain components (ESS Bilbao development).

Timing box

  • Circulator and high power load: the circulator protects the klystron for the possible reflections. It is a full power circulator and controlled by temperature control unit and manufactured by AFT. The high power water loads, in this cases, dissipate the reflected and the forward power of the klystron, since there is no cavity to deliver the power.


High power load

  • WR 2300 components: passive components, which transmit and sample the reflected and forward RF power signals (manufactured by local workshops).

WR 2300 components

  • Slow interlock system: protects the complete chain from any failure in the slow signal such us: water cooling signal and klystron auxiliary components. It has been implemented in PLC technology due to the required time reaction (>10 us).

Slow interlock system

  • Fast interlock system: protects the complete chain from any failure in the fast failure (vacuum, high power levels, etc). The time response required is less than 10 usec and it has to shutdown the RF drive or modulator depending of the type of failure. This subsystem has been based in electronic circuits with logic gates.

Fast interlock system

  • The human safe system: is the subsystmen responsible of the human safety and based on the PILZ. safety relays.

The human safe system

  • Control system: monitories every RFTS signals and as well as control the remote operation of the different components and instruments. The control system has been implemented in Labview and also manages the state machine of the RFTS as well of the GUI.

Control system

  • Cooling system: refrigerates all the RF components providing the specific quality water required for each RF component, achieving the quality water control under the next parameters: type II water with a 0.5- 1uS/cm conductivity, a filtered water with 10-50 um particles size and an oxygen concentration of <0.5 ppm.

Cooling system


The main objectives of the high-power test stand are:
  • Klystron re-conditioning for long pulse operation (from 1.5 ms up to 3.5 ms of pulse width) for a pulse repetition rate of 14Hz.
  • Validation, optimization, conditioning and integration of each of the components and subsystems of the high-power RF chain: modulator, amplifier, RF distributions system, LLRF, control and interlock system
  • Create a high-power laboratory specialised in measurements, characterization and conditioning of resonant cavities and high power devices.