Bolz, Philipp (2023)
Analyzation of radiation resistance of carbon-based materials for accelerator components.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00023113
Ph.D. Thesis, Primary publication, Publisher's Version
Abstract
Functional materials in high-dose environments have to withstand extreme radiation conditions but factors that limit their radiation hardness are poorly understood. An example are materials for components in particle accelerators such as beam dumps, targets and collimators. With increasing energy and pulse intensities of new accelerator facilities, these beam intercepting devices are exposed to loads with high strain rates. To secure the safe operation of future facilities, the suitability of materials exposed to extreme pulsed beam conditions need to be tested. This work mainly concentrates on graphitic materials including isotropic graphite, carbon fibre reinforced carbon, highly oriented pyrolytic graphite and flexible graphite. The mechanical properties and material changes with increasing ion fluence are investigated using nano- and microindentation and nanoimpact measurements. Samples are irradiated at the universal linear accelerator UNILAC of the GSI Helmholtz Centre for Heavy Ion Research. The experiments are performed with various types of ions of MeV to GeV energies achieving fluences up to 2e14 ions/cm². In isotropic graphite and carbon fibre reinforced carbon, large changes in Young’s modulus of up to 300 % and in hardness by more than 1000 % compared to the pristine values are observed. These pronounced material modifications occur if the energy loss of the ions surpasses approximately 18 keV/nm. By nanoimpact measurements hardening is revealed, leading to embrittlement at fluences above 3e13 ions/cm². Raman spectroscopy indicates that these severe changes of mechanical properties are related to beam-induced allotropic transformation of the graphite structure into a disordered structure similar to glassy carbon. To obtain further information about the dynamic response of the materials to ion impacts, in-situ measurements during the irradiation are required. Disc-shaped samples are exposed to short pulses of uranium ions corresponding to a deposited power density of ~3 MW/cm³. The resulting thermal stress produces pressure waves in the samples. The velocity of the respective motion of the target surface is monitored by laser Doppler vibrometry. The velocity signal recorded as a function of time reveals bending modes as the dominant components. With accumulated radiation damage, the bending mode frequency shifts toward higher values. Based on this shift, the Young’s modulus of irradiated isotropic graphite and carbon fibre reinforced carbon are determined by comparison with FEM simulations. Young’s modulus values deduced from microindentation measurements are similar confirming the validity of the method. Beam-induced stress waves remain in the elastic regime and no large-scale damage effects are observed in graphite. Tungsten and copper show no beam-induced changes while glassy carbon and hexagonal boron nitride have lower radiation resistance evident by chipping and cracks risking material failure when applied in high dose environment.
Item Type: | Ph.D. Thesis | ||||
---|---|---|---|---|---|
Erschienen: | 2023 | ||||
Creators: | Bolz, Philipp | ||||
Type of entry: | Primary publication | ||||
Title: | Analyzation of radiation resistance of carbon-based materials for accelerator components | ||||
Language: | English | ||||
Referees: | Trautmann, Prof. Dr. Christina ; Wilde, Prof. Dr. Gerhard | ||||
Date: | 2023 | ||||
Place of Publication: | Darmstadt | ||||
Collation: | x, 138 Seiten | ||||
Refereed: | 19 July 2022 | ||||
DOI: | 10.26083/tuprints-00023113 | ||||
URL / URN: | https://tuprints.ulb.tu-darmstadt.de/23113 | ||||
Abstract: | Functional materials in high-dose environments have to withstand extreme radiation conditions but factors that limit their radiation hardness are poorly understood. An example are materials for components in particle accelerators such as beam dumps, targets and collimators. With increasing energy and pulse intensities of new accelerator facilities, these beam intercepting devices are exposed to loads with high strain rates. To secure the safe operation of future facilities, the suitability of materials exposed to extreme pulsed beam conditions need to be tested. This work mainly concentrates on graphitic materials including isotropic graphite, carbon fibre reinforced carbon, highly oriented pyrolytic graphite and flexible graphite. The mechanical properties and material changes with increasing ion fluence are investigated using nano- and microindentation and nanoimpact measurements. Samples are irradiated at the universal linear accelerator UNILAC of the GSI Helmholtz Centre for Heavy Ion Research. The experiments are performed with various types of ions of MeV to GeV energies achieving fluences up to 2e14 ions/cm². In isotropic graphite and carbon fibre reinforced carbon, large changes in Young’s modulus of up to 300 % and in hardness by more than 1000 % compared to the pristine values are observed. These pronounced material modifications occur if the energy loss of the ions surpasses approximately 18 keV/nm. By nanoimpact measurements hardening is revealed, leading to embrittlement at fluences above 3e13 ions/cm². Raman spectroscopy indicates that these severe changes of mechanical properties are related to beam-induced allotropic transformation of the graphite structure into a disordered structure similar to glassy carbon. To obtain further information about the dynamic response of the materials to ion impacts, in-situ measurements during the irradiation are required. Disc-shaped samples are exposed to short pulses of uranium ions corresponding to a deposited power density of ~3 MW/cm³. The resulting thermal stress produces pressure waves in the samples. The velocity of the respective motion of the target surface is monitored by laser Doppler vibrometry. The velocity signal recorded as a function of time reveals bending modes as the dominant components. With accumulated radiation damage, the bending mode frequency shifts toward higher values. Based on this shift, the Young’s modulus of irradiated isotropic graphite and carbon fibre reinforced carbon are determined by comparison with FEM simulations. Young’s modulus values deduced from microindentation measurements are similar confirming the validity of the method. Beam-induced stress waves remain in the elastic regime and no large-scale damage effects are observed in graphite. Tungsten and copper show no beam-induced changes while glassy carbon and hexagonal boron nitride have lower radiation resistance evident by chipping and cracks risking material failure when applied in high dose environment. |
||||
Alternative Abstract: |
|
||||
Status: | Publisher's Version | ||||
URN: | urn:nbn:de:tuda-tuprints-231136 | ||||
Classification DDC: | 500 Science and mathematics > 500 Science | ||||
Divisions: | 11 Department of Materials and Earth Sciences 11 Department of Materials and Earth Sciences > Material Science 11 Department of Materials and Earth Sciences > Material Science > Ion-Beam-Modified Materials |
||||
Date Deposited: | 25 Jan 2023 13:01 | ||||
Last Modified: | 26 Jan 2023 06:28 | ||||
PPN: | |||||
Referees: | Trautmann, Prof. Dr. Christina ; Wilde, Prof. Dr. Gerhard | ||||
Refereed / Verteidigung / mdl. Prüfung: | 19 July 2022 | ||||
Export: | |||||
Suche nach Titel in: | TUfind oder in Google |
Send an inquiry |
Options (only for editors)
Show editorial Details |