Gamma System Department

Variable Energy Gamma (VEGA) System at ELI-NP

Short description

The Variable Energy Gamma (VEGA) System is a dedicated system for delivering gamma-ray beams to users. The implementation of the VEGA System is currently underway at ELI-NP.

The system will deliver gamma-rays with energy continuously variable from 1 MeV up to 19.5 MeV covering the energy range relevant for low-energy nuclear physics and astrophysics studies, as well as applied research in materials science, management of nuclear materials, and life sciences. The beams will be quasi-monochromatic by having a relative energy bandwidth better than 0.5%, high intensity with a spectral density higher than 0.5 x 10⁴ photons/eV/s and high degree of linear polarization at more than 95%. With these parameters, the VEGA System will be the most advanced gamma-ray source in the world having about one order of magnitude higher gamma-ray flux and at least a factor of two smaller relative bandwidth than the current state-of-the-art.

The VEGA System is based on the use of a storage ring and a high-finesse Fabry-Perot cavity. The parameters of the electron beam and of the interaction laser are optimized at the interaction point such to provide gamma-rays with the features discussed above. The electron beam system will operate in the range of 234 MeV to 742 MeV. For a given interaction laser wavelength, this electron energy range allows at least a factor of 10 in gamma-ray energy continuous tunability. Two separate optical cavity laser systems, one at ~1 μm ('IR') and one at ~0.5 μm ('Green') wavelengths, will be provided to cover the gamma ray energy range from 1 MeV to 19.5 MeV. The laser systems use a passive, high-finesse Optical Cavity to resonantly build-up pulsed laser power. The Optical Cavity provides gains of 5,000-10,000 in laser power, which reduces the complexity of the interaction laser drive system.

VEGA main parameters:

Quantity	Specification
Maximum Photon Energy	≥ 19.5 MeV
Tunability of the Photon Energy	Steplessly variable
Linear Polarization of Gamma-Ray Beam	≥ 95%
Divergence at Full Width Half Maximum (FWHM) of Beam Spot	≤ 1.5 x 10^-4 rad
Average Relative Bandwidth of Gamma-Ray Beam (FWHM)	≤ 5.0 x 10^-3
Total Photon Flux	≥ 1.0 x 10¹¹ 1/s
Time-Average Spectral Density at Peak Energy	≥ 5.0 x 10³ 1/(s eV)
Average Spectral Off-Peak Gamma-Ray Background Density	≤ 1.0 x 10^-2 1/(s eV)
Angular Spectral Flux Density	≥ 1.0 x 10⁹ 1/(s mrad² 0.1%W)

Variable Energy Gamma (VEGA) System at ELI-NP

Project Milestones

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