• C.J. Densham, M. Baldwin, M.D. Fitton, V.B. Francis, M.T. Rooney, M.L. Woodward
  STFC/RAL, Chilton, Didcot, Oxon
• A. Ichikawa
  Kyoto University, Kyoto
• T. Nakadaira, T. Sekiguchi
  KEK, Ibaraki

Funding: Science and Technology Facilities Council

The T2K experiment will utilise the highest pulsed power proton beam ever built to generate an intense beam of neutrinos. This uses the conventional technique of colliding the 0.75 MW 30 GeV proton beam with a graphite target and using a magnetic horn system to collect pions of one charge and focus them into a decay volume where the neutrino beam is produced. The target is a two interaction length (900 mm long) graphite target supported directly within the bore of the first magnetic horn which generates the required field with a pulsed current of 300 kA. This paper describes the design and development of the target system required to meet the demanding requirements of the T2K facility. Challenges include radiation damage, shock waves resulting from a 100 K temperature rise in the graphite material during each beam spill, design and optimisation of the helium coolant flow, and integration with the pulsed magnetic horn. Conceptual and detailed engineering studies were required to develop a target system that could satisfy these requirements and could also be replaced remotely in the event of a target failure.

• M.T. Rooney, C.J. Densham
  STFC/RAL, Chilton, Didcot, Oxon
• Y. Yamada
  KEK, Ibaraki

The target station of the T2K neutrino facility requires a beam window to separate the target chamber, containing helium at atmospheric pressure, from the secondary beam line, which is maintained at ultra high vacuum. In addition to withstanding this differential pressure, the window must survive induced stresses due to intense heating resulting from interaction with a 0.75 MW pulsed proton beam. The design consists of a hemispherical double window with forced convection helium cooling in the volume enclosed, manufactured from titanium alloy. Preliminary analysis suggested that 'shock' waves induced by the pulsed nature of the beam will form the dominant mode of stress. The finite element software ANSYS Mechanical (V10) has been used to simulate the effect of beam impingement on a variety of window thicknesses in an attempt to find the optimum geometry. Results have shown that through thickness stress waves can be amplified if successive bunches arrive in phase with the waves generated by previous bunches. Therefore, thickness has been shown to be a critical variable in determining the window’s resistance to induced thermal shock.