How to measure ultra-small beam sizes?
Some of the smallest particle beams used in accelerators now have diameters in the nanometer range. It is extremely challenging to reliably characterize these beams.
Light generated by the beam itself as it passes through a screen, referred to as Optical Transition Radiation (OTR), is now routinely used as a powerful beam diagnostics tool at accelerator facilities around the world. However, the optical imaging system used to observe the beam via this route risks introducing errors that are larger than the beam size that shall be observed, leading to very large errors.
Image of a beam observed at KEK’s ATF2 facility.
An international collaboration between researchers from the QUASAR Group, the John Adams Institute, CERN and KEK has realized experimental and simulation studies using beams at the ATF2 facility in Japan to critically assess the relationship between simulation and experiment. They found that it is of critical importance to have detailed simulations to optimize any optical system and to predict the error made on measurement.
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B. Bolzon, A. Aryshev, T. Aumeyr, S. Boogert, P. Karataev, K. O. Kruchinin, T. Lefevre, S. Mazzoni, L. Nevay, M. Shevelev, N. Terunuma, J. Urakawa, and C. P. Welsch, “Very high resolution optical transition radiation imaging system: Comparison between simulation and experiment”, Phys. Rev. ST Accel. Beams 18, 082803 – Published 31 August 2015.