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

Abstract

This study presents a further step within the ongoing R&D activities for the redesign of the CERN's Antiproton Decelerator Production Target (AD-Target). A first scaled target prototype, constituted of a sliced core made of ten Ta rods −8 mm diameter, 16 mm length-embedded in a compressed expanded graphite (EG) matrix, inserted in a 44 mm diameter Ti-6Al-4V container, has been built and tested under proton beam impacts at the CERN's HiRadMat facility, in the so called HRMT-42 experiment. This prototype has been designed following the lessons learned from previous numerical and experimental works (HRMT-27 experiment) aiming at answering the open questions left in these studies. Velocity data recorded on-line at the target periphery during the HRMT-42 experiment is presented, showing features of its dynamic response to proton beam impacts. Furthermore, x-ray and neutron tomographies of the target prototype after irradiation have been performed. These non-destructive techniques show the extensive plastic deformation of the Ta core, but suggest that the EG matrix can adapt to such deformation, which is a positive result. The neutron tomography successfully revealed the internal state of the tantalum core, showing the appearance of voids of several hundreds of micrometers, in particular in the downstream rods of the core. The possible origin of such voids is discussed while future microstructure analysis after the target opening will try to clarify their nature.

First prototypes of the new design of the CERN's antiproton production target

“…The simulations also suggest that the containing graphite matrix could be damaged by the generated stress wave propagating from the core . These results encouraged the execution of experimental studies (HiRadMat‐27 and HiRadMat‐42 experiments) aiming at validating these simulations and finding a core and matrix material configuration that could withstand these operating conditions.…”

“…The missing aspects of the HRMT‐27 experiment were then addressed by the HRMT‐42 experiment by irradiating in HiRadMat the assembly illustrated in Figure . This assembly was an upscaled prototype of a proposed new target core and matrix design, consisting in an 8‐mm diameter Ta core split into 16‐mm long rods surrounded by an EG matrix.…”

“…The idea was that the compressed EG could accommodate the radial wave and eventual plastic deformation of the core. The assembly of the HRMT‐42 target was carried out using a tailored tooling, which allowed one‐stage compression of the EG matrix in the Ti‐6Al‐4V capsule and the capsule sealing by electron beam welding (EBW) while maintaining the pressure, with the goal of achieving an EG compression ratio of 27% . The outcome of HRMT‐42 experiment can be summarized in three points: (1) The irradiation in HiRadMat and Post Irradiation Examinations (PIEs) validated the fact that EG can adapt to the changes in core due to permanent deformation.…”

“…From the point of view of the return of experience from the assembly procedure of this target, it was observed that the EG compression ratio when performing one‐stage compression was considerably non‐uniform due to friction with the walls of the Ti‐6Al‐4V container during compression. The achieved compression ratio of the EG disks in the bottom of the target was just 7%, while 40% in the upper disks was reached . For this reason, a new compression method was proposed for the PROTAD targets (described in Section ) aiming at achieving a constant compression ratio over the target length.…”

Beam impact tests of a prototype target for the beam dump facility at CERN: Experimental setup and preliminary analysis of the online results

“…The Beam Dump Facility conditions require slow extraction of the beam, therefore the HiRadMat facility at CERN [7] could not be used, as done for target technologies tests in the past [8][9][10][11][12][13]. The target prototype experimental setup was therefore located in the North Area target zone of CERN (TCC2), where the SPS proton beam is regularly sent under slow extraction with intensities up to 3-4·10 13 protons per pulse for physics experiments and test beams.…”