Radio Frequency

Radio Frequency System

The Radio Frequency (RF) system is used to accelerate the electrons in the accelerator, consequently increase their energy to the required value. At the operational energy where electrons’ energy should be fixed to 2.5 GeV in SESAME case, the main role of the RF system is to compensate the energy lost by the electrons in terms of synchrotron radiation. The operation frequency of the RF systems at SESAME are 3GHz in the Microtron and 500MHz in the booster and the storage ring.

The RF system accelerates electrons using the electric field component in the microwave, i.e. using alternative voltage.  

The electron bunch passes through the RF cavity to match the sinusoidal electrical field at a specific phase (called synchronous phase) to gain the exact lost energy.

Booster RF System

The beam is injected to the booster at almost 20MeV and ramped in energy up to 800MeV by the magnets and RF system. The RF voltage starts from 7KV up to 80KV in 650ms as can be seen on the oscilloscope in yellow. The blue, green and pink curves belong to the dipole current, quadrupole current, and stored electron beam current respectively. The 80KV ensures enough lifetime to allow for efficient extraction to the storage ring.

The booster RF system uses a digital low level RF (D-LLRF) control system to regulate the power amplitude, phase and frequency of the RF wave sent to the RF cavity in order to overcome any errors due to the passage of the beam in the RF cavity. The implemented RF loops inside the D-LLRF keeps the stability of amplitude and phase to better than 0.1%, and the stability of the frequency tuning system is within the required limits to keep the RF cavity tuned. The RF regulated signal is then fed to the booster solid state amplifier (SSA) which can deliver a power from a few watts up to 2KW to the RF cavity through an inductive coupler which in turn will excite the RF cavity to generate an axial electric field in the center and in a direction parallel to the beam passage. The schematic below describes the block diagram for the booster RF system.

Storage Ring

The extracted beam from Booster is transferred by Transfer line TL2 and injected and accumulated in the storage ring at a rate of one shot / second at a total RF voltage of 520kV. When the target current is reached, the RF system is ramped, in parallel with beam energy, to the final total voltage of 1.8kV.

The storage ring RF system is the same as the booster’s one, but differs in the higher generated RF power, and in having more restricted interlock system for more protection since the excessive forward or reflected power would certainly cause a severe damage for the RF subsystems.

The main parameters for the RF system are: