LNF:Technology: Difference between revisions

===2 MeV ELECTRON VAN DE GRAAFF ACCELERATOR===

This facility permits material irradiation either by a 2 MeV electron beam or by Bremsstrahlung induced by stopping the electron beam. In this way, radiation testing that is normally carried out using a Co-60 source can be undertaken more rapidly (producing a larger and better controlled dose rate) while allowing in-situ measurements. Irradiation parameters (temperature, vacuum pressure, gas environment, dose rate and beam energy) are well controlled. Moreover, irradiation of relatively large components or material samples is possible. The accelerator staff can design and develop different irradiation chambers and experimental set-ups depending on irradiation requirements. Such experimental systems permit performing optical, electrical and dielectrical measurements during irradiation ("in-beam"). This makes it a unique experimental radiation facility in which simultaneous optical, electrical and dielectrical measurements can be made in the range of Hz to GHz. For this, systems to measure optical absorption and radioluminescence, electrical conductivity and dielectric properties during irradiation (in-situ) are mounted on the accelerator beam line.

Electron energy: 0.25 to 2.0 MeV. Beam current: 10 pA to 150 µA

Sample size from ≈ 3 mm2 to about 20x20 cm2.

Unfocused beam diameter at target is ≈ 1 cm

Beam can be focused to ≈ 1 mm diameter (for small samples)

Beam can be defocused to ≈ 3 cm diameter  

Beam can be scanned over 20x20 cm2 (for large samples)

The facility has been used for studying insulators for which low displacement per atom (dpa) rates are required. The facility allows in-beam testing at a controlled temperature of the electrical, dielectric (RF), and optical properties of solid and gas insulators. Irradiation can be performed in high vacuum, air, or controlled atmospheres (such as N or He).

For insulator studies typical dpa rates range from about 10-12 to 10-8 dpa/s while ionization rates (Bremsstrahlung or direct electron irradiation) range form 0 to ≈ 104 Gy/s

For steels, about 10-3 dpa/day can be achieved in samples of approximately 3x3x1 mm3.

The facility is extremely flexible and has several unique in-beam systems for measuring electrical conductivity, dielectric loss and permittivity (Hz to GHz), and optical absorption and emission during irradiation over a wide range of dose rates and temperatures. Irradiations can be performed in high vacuum, air, or controlled atmosphere such as N or He. Simulation in electron accelerators offers important advantages, namely easy experimental parameter control  and high dose rates available (0 a ≈105 Gy/s).

To date a range of studies have been carried out on fusion candidate insulators. For instance, electrical, optical as well as hydrogen and helium diffusion properties are measured during irradiation.  These studies are carried out at a controlled temperature, from liquid nitrogen up to 1000 C. For these studies special irradiation chambers and sample holders have been designed by the accelerator staff and have been fabricated at the Ciemat workshops.