Multi-MW accelerator target material properties under proton irradiation at Brookhaven National Laboratory linear isotope producer

Abstract

The effects of proton beams irradiating materials considered for targets in high-power accelerator experiments have been studied using the Brookhaven National Laboratory's (BNL) 200 MeV proton linac. A wide array of materials and alloys covering a wide range of the atomic number (Z) are being scoped by the high-power accelerator community prompting the BNL studies to focus on materials representing each distinct range, i.e. low-Z, mid-Z and high-Z. The low range includes materials such as beryllium and graphite, the midrange alloys such as Ti-6Al-4V, gum metal and super-Invar and finally the high-Z range pure tungsten and tantalum. Of interest in assessing proton irradiation effects are (a) changes in physiomechanical properties which are important in maintaining high-power target functionality, (b) identification of possible limits of proton flux or fluence above which certain materials cease to maintain integrity, (c) the role of material operating temperature in inducing or maintaining radiation damage reversal, and (d) phase stability and microstructural changes. The paper presents excerpt results deduced from macroscopic and microscopic post-irradiation evaluation (PIE) following several irradiation campaigns conducted at the BNL 200 MeV linac and specifically at the isotope producer beam-line/target station. The microscopic PIE relied on high energy x-ray diffraction at the BNL NSLS X17B1 and NSLS II XPD beam lines. The studies reveal the dramatic effects of irradiation on phase stability in several of the materials, changes in physical properties and ductility loss as well as thermally induced radiation damage reversal in graphite and alloys such as super-Invar.

120 GeV neutrino physics graphite target damage assessment using electron microscopy and high-energy x-ray diffraction

“…The evolution of graphite strength with irradiation has also been a subject of study [3,13,21]. It has been assessed that graphite strength, under both neutrons and energetic protons, increases with the fluence up to a threshold (∼6.0 × 10 20 cm −2 ).…”

“…Several studies [20][21][22][23][24] focusing on energetic proton irradiation effects on the physiomechanical properties and the changes in the microstructure have been conducted in recent years. This is prompted by the fact that graphite, in its various grades including POCO ZXF-5Q of the NuMI target, has been used in several neutrino experiment initiatives (NuMI/MINOS, T2K, and CNGS) as a low-Z material producing a desired pion spectrum.…”

“…Section II summarizes relevant results of past studies [21][22][23][24] on the POCO ZXF-5Q and other isotropic graphites from high neutron and proton fluences. We shall use these data as the basis for interpreting the changes induced by the 120 GeV proton beams.…”

Design of the upstream decay pipe window of the long baseline neutrino facility

“…Beryllium is widely used in X-ray windows for photon sources [10] and drift detectors [11]. With the increasing beam intensities of future multi-mega-watt accelerator facilities, beryllium and AlBeMet (a metal matrix made of 62% beryllium and 38% aluminum by weight) have received increasing attention in the design of the hadron beam window because of their good beam transparency, high thermal conductivity, high strength and thermal stability [12], good resistance against ductility loss from irradiation [13], and good thermal shock resistance [14]. The downstream target window at NuMI was specially constructed using a combination of beryllium and aluminum.…”

“…In pursuit of lower disturbances in particle propagation, beryllium is selected as the base material. In addition, beryllium has higher thermal-mechanical properties and better resistance against ductility loss from irradiation compared with AlBeMet [13]. This paper describes the structure optimization of the window, as well as the thermal-mechanical response induced by beam shock in the case of accidents.…”