Main Accelerator

ELBE is a high-frequency linear accelerator that operates at a wavelength of 23 cm. The main accelerator consists of two identical accelerator modules. Each module contains two 9-cell cavity resonators (cavities) made of the niobium. The operating temperature is 1.8 K (superfluid helium). Due to the superconducting technology, the power dissipation in the accelerator resonators is very small (maximum 20 W per cavity). This enables continuous wave (CW) operation. The acceleration of the electron bunches coming from the injector to energies of up to 20 Mega electron volts (MeV) per module at beam currents of up to 1.6 mA (CW operation) is achieved by the electric field component of the electromagnetic alternating field (accelerating E-field) in the niobium resonators pointing in the direction of flight of the electron beam. The high-frequency power is amplified by transistor power amplifiers, transported by waveguides and coupled into the cavities via antennas.

                                                                  Accelerator module ELBE ©Copyright: Dr. Büttig, Hartmut

ELBE accelerator module

The electron bunches of maximum 1.6 mA beam current (CW) coming out of the thermionic injector at about 74% of the speed of light are accelerated to about 10 MeV per 9-cell cavity. Up to 20 kW RF power can be coupled into each 9-cell cavity resonator and transferred to the electron beam.

                                       EM field inside the accelerator cavity ©Copyright: Dr. Büttig, Hartmut

Acceleration in a high-frequency field

Acceleration takes place in TM 010 mode (transverse magnetic) of the cavity resonator. In this monopole mode, the electric field lines are parallel to the trajectory of the electron beam