Researchers prove Cherenkov radiation can be used for non-invasive beam diagnostics

An experiment carried out by scientists proved that Cherenkov radiation occurs when a beam of charged particles travels nearby a transparent dielectric (quartz prism) rather than passing through it as in the traditional studies and meantime its power is enough to characterize the beam itself. Although it was believed that this effect is insignificant and not of interest.

Photo: A glow caused by Cherenkov radiation at the TPU nuclear reactor

An international team of scientists from Switzerland (CERN), USA, Great Britain and Russia (Tomsk Polytechnic University) published its study results in Physical Review Letters (IF 8.839; Q1). The researchers reported on the first observation and systematic study of incoherent Cherenkov diffraction radiation in a visible range.

Cherenkov radiation was discovered by Russian physicist Pavel Cherenkov. In 1958, he together with another scientist who had explained this phenomenon received the Nobel Prize. The radiation occurs when a charged particle passes through a transparent dielectric (e.g. water) at the velocity surpassing the phase velocity of light in this medium. Cherenkov radiation is visually observed, for example, as a blue glow in the pool of a nuclear reactor.

The radiation is extremely useful in particle physics as it helps to measure characteristics of charged particles that pass through the dielectric. Detectors based on the effect are currently utilized both in laser-plasma laboratories, tokamaks (installations to produce controlled thermonuclear fusion power – ed.) and accelerators, e.g. at the Large Hadron Collider (LHC). When particles pass through the medium, they are scattered and the energy is lost.

A co-author of the study, Prof. Alexander Potylitsyn from the TPU Research School of High-Energy Physics says:

‘Non-invasive methods of diagnosing particle beams produced by modern accelerators are necessary in cases when the energy losses of particles might not be neglected when they are scattered out at passing the medium.’

Earlier, in the scientific community, it was believed that Cherenkov radiation which occurs when particles pass in the immediate vicinity of the dielectric, rather than cross it, is too small to take into account. The outcomes of modeling carried out by Tomsk Polytechnic University scientists and the experiment conducted at the Cornell University accelerator disproved this opinion.

During the experiment, a beam of positrons passed near the quartz prism at a distance less than 1 mm.

The generated Cherenkov radiation from the prism was reflected by a mirror and collected by a lens, and then it was detected by a sensitive camera. According to the characteristics of the fixed light spot, the parameters of the initial positron beam can be identified.

‘The results of the experiment showed that the generated Cherenkov radiation does not significantly affect on the beam parameters. The results are well described by our model,’ notes Prof. Potylitsyn.

At the next stage of research, the scientists plan to diagnosis submicron beams that is impossible to perform with the existing tools. 

They plan to conduct an experiment at the High Energy Accelerator Research Organization (KEK) in Tsukuba. The Japanese accelerator has necessary beam parameters to prove the possibility of using Cherenkov radiation in such a non-perturbing format for the diagnosis of submicron beams. The results to be obtained can be used for the creation of a facility comparable in scale to the LHC, i.e. an International Linear Collider in Japan. 

The supposed method of beam diagnosis is rapid, i.e. online.

‘Such online diagnosis will allow operators monitoring beam characteristics to make quick decisions for its correction,’ says Alexander Potylitsyn.