ERL-Mode

Establishment of the first Energy Recovery Linac (ERL) in Germany

On 9th August 2017 the first ERL measurements have been conducted successfully at the S-DALINAC, making it the first accelerator in Germany running in this mode.

Figure 1 shows the path of the electron beam for this special setting. The beam is produced by a thermionic gun and pre-accelerated in the injector accelerator to a kinetic energy of 2.5 MeV (energy chosen for this setting). The beam then gains additional 20 MeV (energy chosen for this setting) during the first main accelerator passage before travelling through the second recirculation beam line. After the recirculation, the beam can be guided a second time through the main accelerator in order to accelerate the electrons a second time and achieve a final energy of 42.5 MeV. The beam can then be dumped in the E0F1-Cup (blue mark in Fig. 1). Alternatively, the electrons ca be decelerated while passing the main accelerator the second time. In this case the kinetic energy of the electrons, which have for example been used as a source for radiation, can be recovered, since the energy of the electrons will be given to the cavities while decelerating. The energy can then be used to accelerate subsequent electrons. This is the so called ERL mode. Due to the loss of energy by the deceleration process, the electrons will be stronger deflected in a dipole magnet and therefore dumped in the “ERL-Cup” (green mark in Fig. 1).

Figure 1: This diagram shows the beam path in a once recirculating setting (marked in red). Depending on the mode, the end of the beam path is either highlighted in green (ERL operation) or blue (twice accelerating mode). Elements needed for the ERL measurements (first main LINAC cavity in yellow, both cups in green and blue) are mentioned.

The change from a twice accelerated mode to ERL operation is conducted actively in the second recirculation. An increase or decrease of the distance travelled by the bunches, shift the phase of the beam relatively to the RF phase by 180°. Figure 2 illustrates the principle of an ERL operation applied to the S-DALINAC layout.

Figure 2: Principle of ERL operation applied to the S-DALINAC. The first beam in the main accelerator is accelerated (red particles) while the second beam gets decelerated (green particles) due to a phase shift of 180°.