CERN antiproton target: Hydrocode analysis of its core material dynamic response under proton beam impact

Abstract

Antiprotons are produced at CERN by colliding a 26 GeV=c proton beam with a fixed target made of a 3 mm diameter, 55 mm length iridium core. The inherent characteristics of antiproton production involve extremely high energy depositions inside the target when impacted by each primary proton beam, making it one of the most dynamically demanding among high energy solid targets in the world, with a rise temperature above 2000°C after each pulse impact and successive dynamic pressure waves of the order of GPa's. An optimized redesign of the current target is foreseen for the next 20 years of operation. As a first step in the design procedure, this numerical study delves into the fundamental phenomena present in the target material core under proton pulse impact and subsequent pressure wave propagation by the use of hydrocodes. Three major phenomena have been identified, (i) the dominance of a high frequency radial wave which produces destructive compressive-to-tensile pressure response (ii) The existence of end-ofpulse tensile waves and its relevance on the overall response (iii) A reduction of 44% in tensile pressure could be obtained by the use of a high density tantalum cladding.

Scaled prototype of a tantalum target embedded in expanded graphite for antiproton production: Design, manufacturing, and testing under proton beam impacts

“…Figure 7 shows the pressure response at the center of core rods 2, 4, 7 and 10 estimated by AUTODYN® simulation following a similar methodology as in Ref. [2]. As anticipated, a compressive-to-tensile pressure wave with a period of 2.7 μs (corresponding to a radial mode of vibration) dominates the response, reaching up to 5 GPa in tension.…”

“…II. These parameters were selected in such a way as to excite the radial vibration mode of the core, subjecting it to the compressive-to-tensile pressure states taking place in the AD-Target [2]. Figure 6 shows the estimated temperature profile in a quarter of the target's geometry as a consequence of a proton pulse impact.…”

“…Advanced numerical tools such as hydrocodes were used to study the dynamic response of the core material each time it is impacted by the primary proton beam [2]. These simulations showed that a maximum temperature rise of 2000°C takes place in the target core in less than 0.5 μs (the duration of a pulse burst), as a consequence of the sudden deposition of energy by the primary proton beam.…”

Development of a Neutron Imaging Station at the n_TOF Facility of CERN and Applications to Beam Intercepting Devices

“…This non-uniform contour along the core of the proton irradiated AD-Target is therefore a clear indication of its fragmentation and internal damage due to the extreme stress waves induced by the proton beam impact during operation, as suggested by numerical simulations in Ref. [15,16] and verified after target opening (detailed in a forthcoming paper). In Figure 11, the inner tantalum rods of the HiRadMat-42 target assembly experienced permanent plastic deformation and are slightly bent due to excitation of bending modes induced by the thermo-mechanical load of the proton beam impact.…”

“…This leads to a huge and fast energy deposition in the bulk of target material, with its subsequent sudden increase of temperature and appearance of violent stress waves, which can eventually fracture it [15]. This phenomena has been extensively studied both numerically [16] and experimentally [17,18]. For the latter, tests using real proton beams were carried out under the described conditions using CERN's HiRadMat facility [7].…”