Radiation damage and thermal shock response of carbon-fiber-reinforced materials to intense high-energy proton beams

Abstract

A comprehensive study on the effects of energetic protons on carbon-fiber composites and compounds under consideration for use as low-Z pion production targets in future high-power accelerators and low-impedance collimating elements for intercepting TeV-level protons at the Large Hadron Collider has been undertaken addressing two key areas, namely, thermal shock absorption and resistance to irradiation damage. Carbon-fiber composites of various fiber weaves have been widely used in aerospace industries due to their unique combination of high temperature stability, low density, and high strength. The performance of carbon-carbon composites and compounds under intense proton beams and long-term irradiation have been studied in a series of experiments and compared with the performance of graphite. The 24-GeV proton beam experiments confirmed the inherent ability of a 3D C/C fiber composite to withstand a thermal shock. A series of irradiation damage campaigns explored the response of different C/C structures as a function of the proton fluence and irradiating environment. Radiolytic oxidation resulting from the interaction of oxygen molecules, the result of beam-induced radiolysis encountered during some of the irradiation campaigns, with carbon atoms during irradiation with the presence of a water coolant emerged as a dominant contributor to the observed structural integrity loss at proton fluences ≥5 × 10 20 p=cm 2 . The carbon-fiber composites were shown to exhibit significant anisotropy in their dimensional stability driven by the fiber weave and the microstructural behavior of the fiber and carbon matrix accompanied by the presence of manufacturing porosity and defects. Carbon-fiberreinforced molybdenum-graphite compounds (MoGRCF) selected for their impedance properties in the Large Hadron Collider beam collimation exhibited significant decrease in postirradiation loaddisplacement behavior even after low dose levels (∼5 × 10 18 p cm −2 ). In addition, the studied MoGRCF compound grade suffered a high degree of structural degradation while being irradiated in a vacuum after a fluence ∼5 × 10 20 p cm −2 . Finally, x-ray diffraction studies on irradiated C/C composites and a carbon-fiber-reinforced Mo-graphite compound revealed (a) low graphitization in the "as-received" 3D C/C and high graphitization in the MoGRCF compound, (b) irradiation-induced graphitization of the least crystallized phases in the carbon fibers of the 2D and 3D C/C composites, (c) increased interplanar distances along the c axis of the graphite crystal with increasing fluence, and (d) coalescence of interstitial clusters after irradiation forming new crystalline planes between basal planes and excellent agreement with fast neutron irradiation effects.

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

“…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.…”

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

“…Specifically, beryllium in various grades has been studied [1][2][3][4] under the effects of neutrons for use in nuclear fission or fusion reactors and proton effects [5][6][7][8] on beryllium and AlBeMet (a material metal matrix made of 62% beryllium and 38% aluminum by weight) for accelerator applications (targets and beam windows). Various grades of graphite have been explored over the decades for use as a nuclear reactor moderator material [9][10][11][12][13][14] and target in multi-MW proton accelerators [15,16]. Proton irradiation studies on graphite and carbon composites [15,16] revealed a crucial fluence threshold (∼5 × 10 20 p=cm 2 at low irradiation temperature 80°C-200°C) that could affect the ability of the graphite to maintain its structural integrity.…”

“…Various grades of graphite have been explored over the decades for use as a nuclear reactor moderator material [9][10][11][12][13][14] and target in multi-MW proton accelerators [15,16]. Proton irradiation studies on graphite and carbon composites [15,16] revealed a crucial fluence threshold (∼5 × 10 20 p=cm 2 at low irradiation temperature 80°C-200°C) that could affect the ability of the graphite to maintain its structural integrity. In addition, proton-induced damage has shown similarities with fast neutron-induced damage in terms of microscopic and macroscopic properties.…”

“…The low CTE is of interest to the particle accelerator community in that it minimizes thermal stresses upon interaction with intense proton beams. Limited irradiationinduced effects are available for this alloy [14][15][16][17][18]. Prompted by their superb properties [superelasticity, superplasticity, low elastic modulus and high strength as well as its Invar-like characteristics (low CTE) over an extended temperature regime as compared to Invar] interest in the multifunctional alloys, known as gum metals [19,20], has increased [16,21,22].…”