Facility for antiproton and ion research

The design of a high-resolution asymmetric von Hamos spectrometer for low energy X-ray spectroscopy experiments at the electron cooler of CRYRING [1] in the international Facility for Antiproton and Ion Research (FAIR) in Darmstadt is presented in this document. The spectrometer will allow to measure, with a high resolution of down to 100 meV, the low-energy X-rays (5-10 keV) from radiative recombination (RR) of stored bare or few-electron heavy ions interacting with cooling electrons. X-ray tracing simulations show that the energies of the X-ray transitions can be measured with relative precision of a few ppm, which gives access to study the QED effects for mid-Z bare ions with a high precision. For these ions the nuclear size effect is much smaller than one-loop QED corrections. The proposed asymmetric von Hamos spectrometer benefits from the unique features of RR X-ray emission in the electron cooler of CRYRING, namely, the extremely long-linear (∼ 1 m x 1 mm) X-ray source accepted by von Hamos geometry and very cold electron beam temperature of about meV. This is achieved by application of adiabatic magnetic expansion of the electron beam, which increases substantially the intensities of RR X-rays and, consequently, the precision of determination of X-ray energies. In order to control the Doppler effect, two copies of the asymmetric von Hamos spectrometer will be installed next to the dipole magnets on both sides of the electron cooler to detect blue/red (0◦/180◦) shifted RR X-rays, what allows to eliminate completely the influence of Doppler effect on measured X-ray energies. The X-rays diffracted by the cylindrically bent crystal will be measured by a novel type of position sensitive semiconductor detector having nanoseconds time resolution, what will be crucial to eliminate non-RR X-ray background by counting photon-downcharged-ion coincidences. The spectrometers will be mounted to the dedicated intermediate vacuum chambers on the e-cooler axis. EDMS 2384915 v.LATEST status In Work access Public GSI_TDR_VonHamos_CRYRING_online.pdf modified 2020-06-15 13:00