Ricerc@Sapienza

In high-brightness LINear ACcelerators (LINACs), electron bunch length can be measured indirectly by a radio frequency deflector (RFD). In this paper, the accuracy loss arising from non-negligible correlations between particle longitudinal positions and the transverse plane (in particular the vertical one) at RFD entrance is analytically assessed. Theoretical predictions are compared with simulation results, obtained by means of ELEctron Generation ANd Tracking (ELEGANT) code, in the case study of the gamma beam system (GBS) at the extreme light infrastructure—nuclear physics (ELI-NP).

The Gamma Beam System (GBS) is a high brightness LINAC to be installed in Magurele (Bucharest) at the newELI-NP (Extreme Light Infrastructure — Nuclear Physics) laboratory. The accelerated electrons, with energiesranging from 280 to 720 MeV, will collide with a high power laser to produce tunable high energy photons(0.2–20 MeV ) with high intensity (1013photons/s), high brilliance and spectral purity (0.1%BW), through theCompton backscattering process. This light source will be open to users for nuclear photonics and nuclear physicsadvanced experiments.

Optical Transition Radiation (OTR) screens are widely used for beam profile measurements. The radiation is emitted when a charged particle beam crosses the boundary between two media with different optical properties. The main advantages of OTR are the instantaneous emission process allowing fast single shot measurements (i.e. bunch by bunch measurements in a multi bunch machine), and the good linearity with the beam charge (if coherent effects can be neglected). Furthermore, OTR angular distribution strongly depends on beam energy.

We report on the optical commissioning of the high power laser beam circulator for the high brightness Compton γ-ray source Extreme Light Infrastructure for Nuclear Physics. Tests aiming at demonstrating the optical performances of the laser beam circulator have been realized with a low-power pulsed laser-beam system and without electron beam. We show that, with the developed alignment and synchronization methods coming from the laser beam circulator design study presented in the Dupraz et al. paper [Phys. Rev. Accel.

The effects of assumptions about bunch properties on the accuracy of the measurement method of the bunch length based on radio frequency deflectors (RFDs) in electron linear accelerators (LINACs) are investigated. In particular, when the electron bunch at the RFD has a non-negligible energy chirp (i.e. a correlation between the longitudinal positions and energies of the particle), the measurement is affected by a deterministic intrinsic error, which is directly related to the RFD phase offset.

A high brightness electron LINAC is being built in the Compton Gamma Source at the ELI Nuclear Physics facility in Romania. To achieve the design luminosity, a train of 32 bunches, 16 ns spaced, with a nominal charge of 250 pC will collide with a laser beam in two interaction points. Electron beam spot size is measured with Optical Transition Radiation (OTR) profile monitors. In order to measure the beam properties, the OTR screens must sustain the thermal and mechanical stress due to the energy deposited by bunches.

New generation of Compton sources are developing in different countries to take advantage of the photon energy amplification given by the Compton backscattering effect. In this framework the Eurogammas international collaboration is producing a very high brilliance gamma source for the Nuclear Physics pillar of the Extreme Light Infrastructure program (ELI-NP).