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Master’s thesis: Development of phase control to optimize a notch filter based on an optical delay line

Advertising institute: ZEA-2 - Electronic Systems
Reference number: D069/2014, electrical engineering or computer engineering

Job description:

The Central Institute for Electronics (ZEL) is a scientific and technical institute at Forschungszentrum Jülich GmbH. It implements research and development projects in cooperation with the institutes of Forschungszentrum Jülich and with external partners.
Work at ZEL focuses on the development of electronic and information technology system solutions in sensor and detector technology, signal and data processing, measuring technology as well as imaging and image processing.

Forschungszentrum Jülich operates the cooler synchrotron COSY for basic research in hadron, particle and nuclear physics. COSY generates polarized and unpolarized proton and deuteron beams with beam pulses between 300 MeV/c and 3.7 GeV/c and high phase space densities by means of electron and stochastic phase space cooling. The ongoing improvement of the beam parameters also involves optimizing the longitudinal stochastic cooling of COSY.
Stochastic cooling is a process used in particle accelerators to reduce the pulse uncertainty and transversal beam expansion of the particles by means of negative feedback. In the signal pickups, small groups of antenna measure the electromagnetic fields of the circulating particles in a frequency range of 1–3 GHz. After filtering and amplification, kickers then use similar antenna to generate electromagnetic correction fields to reduce both the pulse uncertainty and the transversal expansion.

In longitudinal cooling, the pickup signal is directed through a notch filter, which suppresses that part of the signal attributed to the expected particle, i.e. only particles outside of the expected frequency receive a corrective pulse, the size of which is determined by the deviation from the expected frequency.
The notch filter is based on a controllable optical delay, which is used to set the notch frequency. A correction signal is first optically converted via laser modulation and then split into two signal paths by an optical splitter – a direct path and a path adjusted by optical delay. The optical signals are then converted back into electrical signals and subtracted from each other in a hybrid. This leads to suppression of the frequency determined by the run-time difference and its harmonics.

A pilot pulse transmitted parallel to the useful signal is directed to a phase detector after filtering and provides the control signal for controlling a variable optical delay line. The master’s thesis involves designing and implementing a control algorithm, which readjusts the optical delay on the basis of the phase difference and thus stabilizes the notch frequency.

In addition to the requirements for COSY, this work will also be incorporated into research and development activities for the future high-energy storage ring HESR, which is part of the planned international accelerator complex FAIR in Darmstadt.

Work on the master’s will be conducted in Jülich as part of a cooperation between the Chair for Integrated Analog Circuits at RWTH Aachen University and the institutes ZEL and IKP at Forschungszentrum Jülich. A development system comprising modules from the JDSU WaveReady 3000 series including the necessary modulators, splitters and optical attenuators will be provided.


Master’s student studying electrical engineering or computer engineering.

Limited-term contract:

6 months

Dr. Stefan van Waasen
Central Institute for Electronics
Forschungszentrum Jülich GmbH
Tel: +49 2461 61-9400