Phase locking the spin precession in a storage ring

This letter reports the successful use of feedback from a spin polarization measurement to the revolution frequency of a 0.97 GeV/$c$ bunched and polarized deuteron beam in the Cooler Synchrotron (COSY) storage ring in order to control both the precession rate ($\approx 121$ kHz) and the phase of the horizontal polarization component. Real time synchronization with a radio frequency (rf) solenoid made possible the rotation of the polarization out of the horizontal plane, yielding a demonstration of the feedback method to manipulate the polarization. In particular, the rotation rate shows a sinusoidal function of the horizontal polarization phase (relative to the rf solenoid), which was controlled to within a one standard deviation range of $\sigma = 0.21$ rad. The minimum possible adjustment was 3.7 mHz out of a revolution frequency of 753 kHz, which changes the precession rate by 26 mrad/s. Such a capability meets a requirement for the use of storage rings to look for an intrinsic electric dipole moment of charged particles

Development of a Rogowski coil beam position monitor for electric dipole moment measurements at storage rings

One of the unsolved phenomena in physics is the matter-over-antimatter dominance in our universe. The known CP violating processes of the Standard Model of particle physics are not sufficient to explain this asymmetry. Therefore, additional CP violating sources beyond the Standard Model are required. One of these sources can be manifest themselves in permanent electric dipole moments (EDMs) of elementary particles. For neutral particles investigations for EDMs started already 60 years ago. Up to now all results of the EDM measurements are compatible with a vanishing EDM value. Complementary EDM measurements for charged particles like protons and deuterons in dedicated electrical storage rings are suggested of different collaborations worldwide. As a first step towards dedicated storage ring, feasibility studies are performed by the JEDI (Jülich Electric Dipole moment Investigations) collaboration at the magnetic storage ring COSY (COoler SYnchotron) at Forschungszentrum Jülich in Germany. A first direct deuteron EDM measurement is planned in the years 2017 to 2019. To create a vertical polarization build-up proportional to the EDM, a radio frequency Wien filter is used. However, this polarization build-up can also be caused by interactions of the magnetic dipole moment with magnetic fields for a not centred beam in the accelerator. Therefore, the orbit of the particle beam has to be centred in all accelerator elements. An important device for this orbit detection is a beam position monitor (BPM) with high accuracy and high resolution.The existing BPM system at COSY has a resolution of 1 μm (for 4096 data points) by a beam current of 〖10〗^9 particles and an accuracy of 0.1 mm. This accuracy value is the main source for systematic uncertainties and limits this deuteron EDM measurement to 5⋅〖10〗^(-20) e cm. Due to these demanding requirements for the beam position detection a development started towards an ultra precise SQUID (Superconducting QUantum Interference Device) based Rogowski coil BPM. As a first step we investigated normal conducting Rogowski coils with the option to increase sensitivity by cooling the system and applying SQUIDs. The theoretical and experimental basis for a normal conducting Rogowski coil BPM is investigated in this thesis. A model for the induced voltage of a segment for different Rogowski coil configurations has been developed. Also a model-based calibration algorithm has been developed, which takes into account an offset between the electrical and geometrical centre, a rotation of the coil itself and different segment weights. A comparison between the calculated model and a numerical simulation of a bidirectional Rogowski coil has been performed. The calibration algorithm is also tested on a numerical simulation of bidirectional Rogowski coil, which is rotated, offset and has different segment weights. With this model-based calibration algorithm an accuracy of 15 μm has been achieved. A dedicated testbench has been constructed and a grid measurement calibration of a bidirectional Rogowski coil BPM has been performed with respect to an arbitrary reference point. As readout electronics for the induced voltages lock-in amplifiers were used. The resolution of 1.25 μm for a single measurement setup is the theoretical limit of the measurement setup of the Rogowski coil BPM and lock-in amplifier for room temperature. The accuracy for the model-based position reconstruction is 150 μm.Beam position measurements in COSY with an uncalibrated unidirectional and two uncalibrated bidirectional Rogowski coil BPMs were performed and the data were analysed. The resolution for both experiments is about 4.4 μm for a single position measurement. A beam-based calibration has been performed with one bidirectional Rogowski coil BPM and an accuracy of 150 μm is achieved with respect to an arbitrary reference point. In both experiments orbit bump measurements were performed to measure the response of the Rogowski coil BPMs

Studies for a BPM Upgrade at COSY

For the planned Electric Dipole Moment (EDM) precursor experiment at the COSY synchrotron and storage ring an accurate control of the beam orbit is crucial. The required beam position measurement accuracy demands an upgrade of the BPM readout electronics. The BPM system currently in operation is described. The required performance and the possible upgrade scenarios are discussed

Measurement of deuteron carbon vector analyzing powers in the kinetic energy range 170–380 MeV

A measurement of vector analyzing powers in elastic deuteron-carbon scattering has been performed at the Cooler Synchrotron COSY of Forschungszentrum Jülich, Germany. Seven kinetic beam energies between 170 and 380 MeV have been used. A vector-polarized beam from a polarized deuteron source was injected, accelerated to the final desired energy and stored in COSY. A thin needle-shaped diamond strip was used as a carbon target, onto which the beam was slowly steered. Elastically scattered deuterons were identified in the forward direction using various layers of scintillators and straw tubes. Where data exist in the literature (at 200 and 270 MeV), excellent agreement of the angular shape was found. The beam polarization of the presented data was deduced by fitting the absolute scale of the analyzing power to these references. Our results extend the world data set and are necessary for polarimetry of future electric dipole moment searches at storage rings. They will as well serve as an input for theoretical description of polarized hadron-hadron scattering