ALBA Synchrotron
The RadioFrequency (RF) systems of ALBA are responsible of the electrons acceleration in the Booster and the Storage Ring. In the Booster, the energy of the electrons is increased from 100 MeV to 3 GeV. In the Storage Ring, the RF systems just restore the energy that the electrons lose due to synchrotron radiation (1.1 MeV/turn maximum).
The acceleration is accomplished creating high electric fields in the path of the electrons. The electric fields are created in resonant cavities which are fed by RF Amplifiers.
The different elements that can be found on each RF plant are: RF Amplifier (IOT), CaCo (Cavity Combiner), Circulator, Waveguide System, Cavity and Low Level RF.
The main parameters of the RF system of the ALBA Storage Ring and Booster are summarized in following table.
Booster | storage ring | |
|---|---|---|
Frequency | 499.654 MHz | 499.654 MHz |
# Cavities | 1 | 6 |
RF voltage per cavity | 1000 kV | 600 kV |
Energy loss per turn | 627 keV/turn | 1.1 MeV/turn |
RF Power per cavity | 25 kW | 90 kW |
RF Transmitter | SSPA: 1 x 50 kW | IOT: 2 x 80 kW |
Synchrotron frequency | 9.4 – 13.7 kHz | 1.5 - 9.5 kHz |
Overvoltage factor - q | 2.7 | |
Maximum Current | 4 mA | 400 mA |
RF Amplifier: IOT
IOT stands for Inductive Output Tube. The IOT is a High frequency high power amplifier. It magnifies the low power coming from the control system up to a factor of 1E6. The IOT 4444-C from L3 is used in the Storage Ring and it can provide up to 80 kW of RF power.
RF Amplifier: SSPA
SSPA stands for Solid State Power Amplifier. Like the IOT, the SSPA is used as an RF amplifier. Instead of using a vacuum tuve for the amplification, the SSPA is based in transistors. Since each transistor is only capable of delivery hundreds of Watts, in order to reach the kW rango, several units, up to 100, are used and the power is combimed inside the SSPA to reach 50 kW.
CaCo: cavity combiner
Each Cavity of the Storage Ring is powered by two IOTs, whose power is combined in CaCo, a cavity combiner device design at ALBA, a more compact design compared to standard magic tees or hybrid combiners.
Circulator
The output of CaCo is sent to a circulator, a three port device whose function is to protect the amplifiers from reflected power of the cavity. The circulator has some ferrites and coils in its body that will force any RF power coming from port 1 to be sent to port 2, power coming from port 2 to port 3 and power coming from port 3 to port 1, like in a roundabout.
Waveguides and watrax
The RF Power is transported from the IOTs to the cavity through standard WR1800 waveguides. The input power couplers to the Storage Ring and Booster cavities of ALBA have a standard 6 1/8” coaxial interface. In addition, the Storage Ringcavity (Dampy) is tilted 60º respect the vertical. And finally, it has to stand 160 kW of power. A specific WAveguide TRansition to coaxial (WATRAX) had to be designed by ALBA to meet these requirements.
Storage ring cavity: DAMPY
Dampy cavities are based in the normal conducting HOM damped cavity designed by BESSY (Germany) following the EU design. Their main parameters are:
Type | Single cell |
|---|---|
Resonant frequency | 500 MHz ± 1 |
Insertion length | 0.5 m |
Shunt Impedance | > 3.1 MΩ |
Longitudinal HOMs | < 2 MΩ·MHz |
Transverse HOMs | < 60 kΩ/m |
Input power coupler | > 150 kW |
Cooling capacity | > 80 kW |
Maximum Voltage | 700 kV |
Booster cavity
The booster cavity is based on the 5-cell Petra-II cavity design and its main parameters are:
Type | 5-cell |
|---|---|
Resonant frequency | 500 MHz ± 3 |
Insertion length | 1.65 m |
Shunt Impedance | 15 MΩ |
Maximum Input power | 75 kW |
Maximum Voltage | 1000 kV |
Digital Low Level RF
The main task of the Low Level RF is to control the RF Voltage of the cavity, keeping its phase and amplitude constant respect to the beam. Commercial digital boards with fast ADCs, DACs and FPGA processor have been used to implement this signal. It also keeps constant the resonance frequency of the cavity by moving a plunger inwards/outwards the cavity body to compensate thermal drifts.
The main parameters of this system are:
Digital boards | SAFRAN:
|
Based on IQ Modulation/demodulation technique | |
Amplitude precision | < 0.05% peak to peak |
Phase Loop Resolution | < 0.1º peak to peak |
Loops bandwidth | > 10 kHz |
Dynamic range | > 30 dB |
Extra utilities |
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