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PANDA Target meets HESR Stochastic Cooling System in COSY

Jülich, September 2018. The High Energy Storage Ring (HESR) is the core storage ring for experiments with antiprotons and heavy ions at FAIR (Facility for Antiproton and Ion Research) in Darmstadt, Germany, on the campus of GSI. FAIR contracted FZJ for design, procurement and commissioning of the HESR (without buildings). The Institute for Nuclear Physics 4 (IKP-4) is coordinating the project, is responsible and carries out most of the work. Next largest support within FZJ is supplies by ZEA-1, which is responsible for the complete vacuum work package.

One of the key systems in HESR is the so-called stochastic cooling system. It is not only essential for enhancing the beam quality for the experiments but is also indispensable for the accumulation of antiprotons in HESR. At the core, stochastic cooling consists of broad band microwave control loops which measure the deviation of the circulating particles from their ideal flight path and feed this information back to the beam appropriately using low noise amplifiers, filters, actors and high power amplifiers. Thus the diameter of the circulating beam decreases everywhere in the accelerator.

Pickup-Tank of the stochastic cooling system in HESRVacuum vessel with microwave structures as antennae for the signals of the charged particles lassing by. On top of the tank the cryogenic pumps are mounted which have to cool the complete structure to about 20K.
Copyright: Forschungszentrum Jülich

Antennae of the stochastic cooling system in HESR with Combiner-BoardsThe ring like structures are the antennae. The signals are combined in the vacuum on dedicated boards to limit the number of vacuum feed-throughs.
Copyright: Forschungszentrum Jülich

Apart from the high power amplifiers, the core elements are the microwave signal detectors and the deflectors. IKP-4 developed completely new structures for that purpose and built them in close collaboration with ZEA-1. The first pick-up tank (detector) and the first kicker tank (deflector) were installed in COSY. First cooling tests were executed. The ultimate performance test for the complete feedback loop is possible when the beam is interacting with a target from the experimentalists.

The HESR originally has been optimized for the PANDA experiment (Proton ANtiproton Detector Array). The PANDA collaboration comprises more than 500 scientists coming from 20 countries. Their research is dedicated to fundamental physics research covering topics such as strong and weak interaction, exotic states of matter, and the structure of hadrons. One big contributor is IKP-1 of FZJ. In order to record as much information as possible from the antiproton - proton collisions a versatile detector is being built that allows precise track reconstruction, ernergy and momentum measurements, and efficient identification of charged particles. One of the required targets is being built by scientists at the Münster University. This cluster target has been installed and successfully commisioned in COSY during summer 2018. The stochastic cooling system performed excellent. For the first time simultanuous cooling of the horizontal, vertical and longitudinal particle motion has been shown. (Longitudinal cooling makes the individual particle velocities more similar). Energy loss and beam broadening in the cluster target could be compensated efficiently. In the diagram the beam current (=intensity), and the horizontal together with the vertical beam size are displayed evolving in time. At first the cooling is off, afterwards the cooling is on. The cycle time was 5 minutes. Systematic measurements to compare the real cooling process to the simulated one will follow.

Beam Intensity with and without HESR type stochastic coolingBeam intensity and beam size with and without stochastic cooling during the experiment cycle with cluster target switched on. The upper trace refers to the right axis, the lower traces refer to the left axis. Without cooling the circulating beam is broadened and its intensity decreases as particles are lost by hitting the vacuum chamber walls. With cooling the intensity for the user is higher, and the beam size throughout the accelerator is smaller.
Copyright: Rolf Stassen


Dr. Rolf Stassen, Institut für Kernphysikalische Großgeräte (IKP-4)

phone +49 2461 612352

email r.stassen@fz-juelich.de