On a possibility of constructing a high-intensity, monochromatic, polarized gamma source at PETRA

A possibility of constructing a high-intensity, tunable, monochromatic, polarized γ-source at the PETRA storage ring is discussed. It is proposed to produce γ-quanta by means of Compton backscattering of laser photons on the electrons. The laser light wavelength is chosen in such a way that after the scattering the electron does not leave the separatrix. Since the probability of the scattering is rather small, energy oscillations are damped prior to the next scattering. As a result, the proposed source can operate in a “parasitic” mode not interfering with the main mode of the accelerator operation. It is proposed to install at PETRA a tunable free-electron laser operating in the 20–50 μm wavelength band with peak and average output power ∼ 10 MW and ∼ 1 kW, respectively. This will result in the intensity of the γ-source ∼ 3 × 1012s−1 with tunable γ-quantum energy up to 60 MeV. Gamma sources with a similar principle of operation could be constructed also at other storage rings such as HERA, TRISTAN, LEP(LEP 2), ESRF, SPring-8. Such γ-sources could reveal unique possibilities for precision investigations in nuclear physics.