Oct 5 – 10, 2014
Capri-Naples, Italy
Europe/Rome timezone

PS2-09: Experimental Investigation of Interference Effects on Transverse Beam Profile Measurements using OTR Imaging

Oct 7, 2014, 5:00 PM
1h 30m
Hotel La Residenza

Hotel La Residenza


Dr Pavel Karataev (Royal Holloway, Unviersity of London)


Optical Transition Radiation appearing when a charged particle crosses a boundary between two media with different dielectric properties has widely been used for transverse beam size, energy spread, position, and emittance diagnostics. Recent developments have demonstrated an ability to achieve sub-micrometre resolution for transverse beam size measurements [1]. However, a high power beam might generate a serious background (e.g. synchrotron radiation). The background is difficult to predict. On the other hand it might significantly distort the measured beam profile and create a false opinion about the beam parameters. At higher energies the situation might be even more severe. The integral OTR photon yield logarithmically depends on the beam energy, however the background radiation dependence could be much stronger, e.g. SR power depends on the beam energy as E4. We propose to shield the OTR screen from any background radiation with a thin metallic film placed in front of the screen. However, the beam will generate forward OTR from the film, which might destructively interact with backward OTR from the screen distorting its characteristics. The initial interference of the backward and forward OTR were demonstrated in [2] and is known as Wartski interferometer. In [3], where the authors studied diffraction radiation interference, they demonstrated that if the distance L between two screens is much less than a critical distance Lc = γ^2 λ/2π known as coherence or radiation formation length, the radiation photon yield is significantly suppressed. However, in this experiment the electron energy is low such that when the distance satisfies the requirement, it becomes comparable to the measured wavelength. In that case classical Wartski approach does not work. On the other hand, in [4] the authors have studied a possibility to use multi-OTR screens for single short emittance measurements at 3 GeV beam of Diamond booster synchrotron. They did not observe any affect on the beam profile by forward OTR from upstream screens. We decided to investigate experimentally the effect of forward OTR on the beam size measurements in conventional OTR monitors at the CTF3 facility at CERN. The test will elucidate the mechanisms of OTR interference over a range of distances from “zero” up to approximately twice the coherence length LC. In addition, it will serve as a simulation benchmark for the more complicated ODR case. We shall represent the hardware status, theoretical expectations, and the near future experimental plan. References 1. K Kruchinin, et al., Journal of Physics: Conference Series 517 (2014) 012011 2. L. Wartski et al., Journal of Applied Physics 46 (8) 1975, 3644. 3. G. Naumenko, et al., Journal of Physics: Conference Series 236 (2010) 012004. 4. C. Thomas, et al., Journal of Instrumentation 6 (2011) P07004.

Primary author

Dr Pavel Karataev (Royal Holloway, Unviersity of London)


Dr Enrico Bravin (CERN) Dr Stefano Mazzoni (CERN) Dr Thibaut Lefevre (CERN) Dr Thomas Aumeyr (Royal Holloway, University of London)

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