No Arabic abstract
A novel interferometric method is presented for the measurement of the absolute energy of electron beams. In the year 2016, a pioneering experiment was performed using a 195 MeV beam of the Mainz Microtron (MAMI). The experimental setup consisted of two collinear magnetic undulators as sources of coherent optical synchrotron light and a high-resolving grating monochromator. Beam energy measurements required the variation of the relative undulator distance in the decimeter range and the analysis of the intensity oscillation length in the interference spectrum. A statistical precision of 1 keV was achieved in 1 hour of data taking, while systematic uncertainties of 700 keV were present in the experiment. These developments aim for a relative precision of $10^{-5}$ in the absolute momentum calibrations of spectrometers and high-precision hypernuclear experiments. Other electron accelerators with beam energies in this regime such as the Mainz Energy Recovering Superconducting Accelerator (MESA) might benefit from this new method.
To solve the discharge of the standard Bulk Micromegas and GEM detector, the GEM-Micromegas detector was developed in Institute of High Energy Physics. Taking into account the advantages of the two detectors, one GEM foil was set as a preamplifier on the mesh of Micromegas in the structure and the GEM preamplification decreased the working voltage of Micromegas to reduce the effect of the discharge significantly. In the paper, the performance of detector in X-ray beam was studied at 1W2B laboratory of Beijing Synchrotron Radiation Facility. Finally, the result of the energy resolution under various X-ray energies was given in different working gases. It indicated that the GEM-Micromegas detector had the energy response capability in all the energy range and it could work better than the standard Bulk-Micromegas.
This article includes the description of the geometric parameter gage device prototype for synchrotron radiation of HERA collider (DESY). The system construction which capable to measure photo current, caused by such a radiation in a refractory metal, described here. The system component parts are: measuring heads and photo current measuring electronics designed by IHEP, stepper motor by Vacuum Generators with HEDS-550X encoder by Hewlett Packard, PCI-STEP-4CX 4-Axis Closed Loop Step controller by National Instruments. The device is controlled by means of Microsoft Visual Basic program using Value Motion Windows Libraries. The device prototype was tested in the beam of the DORIS storage ring.
A novel interferometric method for absolute beam energy measurement is under development at MAMI. At the moment, the method is tested and optimized at an energy of 195 MeV. Despite the very small statistical uncertainty of the method, systematic effects have limited the overall accuracy. Recently, a measurement has been performed dedicated to the evaluation of these effects. This report comprises a description of the method and results of the recent data taking period.
We have performed a novel comparison between electron-beam polarimeters based on M{o}ller and Compton scattering. A sequence of electron-beam polarization measurements were performed at low beam currents ($<$ 5 $mu$A) during the $Q_{rm weak}$ experiment in Hall C at Jefferson Lab. These low current measurements were bracketed by the regular high current (180 $mu$A) operation of the Compton polarimeter. All measurements were found to be consistent within experimental uncertainties of 1% or less, demonstrating that electron polarization does not depend significantly on the beam current. This result lends confidence to the common practice of applying M{o}ller measurements made at low beam currents to physics experiments performed at higher beam currents. The agreement between two polarimetry techniques based on independent physical processes sets an important benchmark for future precision asymmetry measurements that require sub-1% precision in polarimetry.
The interest in using the radiation detectors based on high resistive chromium-compensated GaAs (GaAs:Cr) in high energy physics and others applied fields has been growing steadily due to its numerous advantages over others classical materials. High radiation hardness at room temperature stands out and needs to be systematically investigated. In this paper an experimental study of the effect of 20.9 MeV electrons generated by the LINAC-200 accelerator on some properties of GaAs:Cr based sensors is presented. In parallel, Si sensors were irradiated at the same conditions, measured and analyzed in order to perform a comparative study. The target sensors were irradiated with the dose up to 1.5 MGy. The current-voltage characteristics, resistivity, charge collection efficiency and their dependences on the bias voltage and temperature were measured at different absorbed doses. An analysis of the possible microscopic mechanisms leading to the observed effects in GaAs:Cr sensors is presented in the article.