Free surface and splashing simulation of a windowless target concept for ESS
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Data
2011-05-03
Autori
Massidda, Luca
Moreau, Vincent
Class, Andreas
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Abstract
The international collaboration for the future European Spallation Source (ESS) required the formation of a Target Station Concept Selection (TSCS) working group, with the task to re-evaluate the potential target concepts, moving away from the short pulse experiences of the last decade, and re-considering many of the concepts already studied in the past. The main targetry concern for recent pulsed spallation neutron sources (ESS, SNS, JSNS) focused on the effects and mitigation of the pressure wave caused by the quasi-instantaneous deposition of large amounts of energy in a few litres of Hg. In ESS, a long pulse solution was chosen to mitigate these effects, the 2 mA spallation beam at 2.5 GeV is pulsed with a repetition rate of 16,67Hz and a pulse length 2ms. The spallation target must dissipate about 2.8MWth within a relatively short space (with a conservative 56\% thermal efficiency). In the PDS-XADS FP5 project, a windowless channel like target has already been dimensioned and simulated for a relatively similar proton beam: 2.4 MWth, 5 mA and 600 MeV. In the framework of this project, the spallation target was conceived by Ansaldo and developed mainly by CRS4 and ENEA. Starting from this concept we investigated the feasibility of a windowless design for the ESS conditions, by scaling PDS-XADS design for the ESS beam properties and relaxing the constraints of the 2003 design. We focused on the numerical simulation of the flow to verify the stability of the free surface, the thermohydraulic performance of Hg and LBE, and the response to dynamic pulses. At the same time KIT investigated the possibility to fit a windowless target concept within the design limits of the target station and accelerator and developed the WITA concept. The CFD simulations we present have been successfully completed thanks to the use of a specific surface sharpening algorithm, developed in the framework of the THINS FP7 project, and lacking the usual rigidifying defect of common sharpening algorithms. The dynamic effects of proton beam deposition on the free surface windowless target are then investigated numerically with a smoothed particle hydrodynamic simulation through a specifically developed code, allowing to identify the pressure waves in the liquid and estimate the splashing phenomena at the free surface.
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Keywords
windowless target , ESS , CFD , SPH