G. A. Naumenko

Feasibility of optical diffraction radiation for a non-invasive low-emittance beam diagnostics

Abstract A “proof-of-principle” experiment on the optical diffraction radiation (ODR) as a single-pulse beam profile monitor is planned using an electron beam extracted from the KEK-ATF damping ring. The main goals of this experiment are the following: (i) To measure the yield and the angular distributions of the optical diffraction radiation from a large-size target at different wavelengths, impact parameters and beam characteristics for a comparison with analogous characteristics of optical transition radiation from a foil with identical optical parameters and for a verification of the model assumption (perfectly conducting semi-infinite target). (ii) To investigate the ODR angular distributions from a tilted target with a slit for observing the interference effects. (iii) To compare the results obtained by simulations based on classical approaches, taking into account the optical characteristics of the equipment and the beam parameters. (iv) To estimate the prospects of using ODR as a new non-invasive tool for ultrarelativistic beams. We estimated that the ODR photon yield in 10% bandwidth for 500 nm is about 106 photons/bunch with an impact parameter of 100 μm . This indicates that the ODR monitor is a promising candidate for single-pulse beam-profile measurements, and that it will be an extremely useful instrument for future linear colliders (JLC, NLC, TESLA and CLIC).

Investigation of positron generation by relativistic electrons in aligned crystals

Abstract An experiment to investigate the positron production efficiency by electrons moving in axially oriented tungsten and silicon single crystals has been conducted. The electron energy was 1.2 GeV. The positron yield from the aligned crystal ∼0.35 r.l. in thickness was 2.8 times that from the randomly oriented crystals for tungsten and 1.8 times higher for silicon. A simple model has been designed to simulate positron production by coherent bremsstrahlung (CB) photons. Comparison of the calculation with the experiment has shown that most contribution to the positron production in thick crystals comes from CB.

Resonant diffraction radiation from an ultrarelativistic particle moving close to a tilted grating.

A simple model for calculating the diffraction radiation characteristics from an ultrarelativistic charged particle moving close to a tilted ideally conducting strip is developed. Resonant diffraction radiation (RDR) is treated as a superposition of the radiation fields for periodically spaced strips. The RDR characteristics have been calculated as a function of the number of grating elements, tilted angle, and initial particle energy. An analogy with both the resonant transition radiation in an absorbing medium and the parametric x-ray radiation is noted.

Experimental comparison of parametric X-ray radiation and diffracted bremsstrahlung in a pyrolytic graphite crystal

Abstract Spectral characteristics of diffracted bremsstrahlung (DB) and parametric X-ray radiation (PXR), that can be treated as a diffraction of the own field of a charged particle moving through a crystal, were measured under similar experimental conditions. The target used was a pyrolytic graphite crystal with a mosaic factor of ∼3 mrad. It is shown that for the thickness of a mosaic graphite target ∼0.01 rad length and ω⩾γωp, the contribution from diffraction of real photons into spectrum measured is comparable with that from PXR. For DB, the yield ratio falls well within the diffraction theory of X-rays in mosaic crystals, taking into account the effect of suppression of bremsstrahlung. For PXR, the yield ratio may be satisfactory explained following the kinematic theory, taking into account the PXR photon diffraction and correlation between DB and PXR intensity.

Observation of the stimulated coherent diffraction radiation in an open resonator at LUCX facility

We present an initial test of a new type of a pre-bunched beam pumped free electron maser based on Stimulated Coherent Diffraction Radiation (SCDR) generated in an open resonator. A fast Schottky Barrier Diode (time response o1 ns) has enabled us to investigate the properties of the radiation stored in the cavity as well as the intrinsic properties of the cavity itself. We observed a turn-by-turn SCDR generated by a multibunch beam. When the cavity length was exactly a half of the bunch spacing a clear resonance was observed. Moreover, turn-by-turn measurements revealed the cavity quality factor of 72.88, which was rather high for an open resonator in the wavelength range of 3–5 mm. An exponential growth of the photon intensity as a function of the number of bunches was also demonstrated.

Status of optical diffraction radiation experiment at KEK-ATF extraction line

Abstract At KEK-ATF extraction line detailed investigation of backward optical diffraction radiation (ODR) and its implementation to transversal beam parameter diagnostics is planned. We designed and constructed a target chamber with a precise target movement mechanism, a precise laser alignment system and an optical system. The first step to achieve success in the experiment is the tuning of the optical system using backward optical transition radiation (OTR). We believe that, if we are able to measure OTR spectral-angular characteristics with a proper accuracy, we may obtain good results for ODR measurements as the OTR effect is well experimentally and theoretically studied. Therefore, the first stage of our experiment assumes the measurements of backward OTR to analyze all possible types of radiation coming from the target, which could be obstacles for the ODR measurements. In the first series of experiments we have found that the angular distribution of the detected optical radiation is strongly asymmetric. One of the possible reasons for the asymmetry is the synchrotron radiation contribution from bending or steering magnets.

The investigation of a model of an EM calorimeter on NaBi (WO4)2 crystals

We have constructed a mock-up model consisting of nine elements to evaluate the space and energy resolution of the NaBi(WO4)2 crystal electromagnetic calorimeter. The characteristics of the mock-up model have been studied with a 700 MeV electron beam. It is shown that with cell dimensions of about 2.4 cm one can achieve an accuracy of < 4 mm in measuring the coordinates. The investigations have shown that the calorimeter has fast operation, satisfactory energy resolution and good space resolution characteristics.

Development of microwave and soft X-ray sources based on coherent radiation and Thomson scattering

Compact, high-brightness and reliable sources in the VUV and the soft X-ray region may be used for numerous applications in medicine and biochemistry. We propose a new approach to produce the intense beams of X-rays in the range of ≤ 500 eV based on compact electron accelerator. We present our first experimental results obtained in the Laser Undulator Compact X-ray facility (LUCX) at KEK: High Energy Accelerator Research Organization devoted to the development of a compact microwave and soft X-ray source based on coherent diffraction radiation and Thompson scattering processes.

Soft Component of Emission from Channeled Electrons in a Silicon Crystal

The Tomsk synchrotron has been used to measure the emission spectrum and orientation dependences of the yield of photons with energies much smaller than the emission energy of channeled electrons. The measurements have been performed with a crystal-diffraction spectrometer. For electrons incident along the (110) axis, the radiation intensity in the energy range 30 ≤ ω ≤ 360 keV exceeds the bremsstrahlung one by almost an order of magnitude. The shape of the emission spectrum does not coincide with that of the bremsstrahlung spectrum. The radiation intensity increases smoothly with the photon energy. The bremsstrahlung spectrum from a disoriented crystalline target is satisfactorily described by the existing theory with phenomenological consideration of the polarization of the medium.

Grating optical diffraction radiation – Promising technique for non-invasive beam diagnostics

Abstract Two simple approaches for evaluating the transversal beam size using a slit and a grating are presented. A model for calculating the resonant diffraction radiation (RDR) characteristics from grating consisting of perfectly conducting strips spaced by vacuum gaps is developed. The proposed model allows calculating the RDR characteristics for a beam passing through a big slit between two gratings. It is noted that quasimonochromatic maxima appear in the RDR spectral–angular distribution, whose position is determined by the grating’s period and observation geometry. The peak shape depends on the beam parameters. Having measured the RDR angular distribution at a fixed wavelength, one may evaluate the beam size using simple formulas obtained.