A stationary target for the CERN-neutrino-factory

As production target for Neutrino Factories, free mercury jets with high axial velocity of about 20 m/s are being studied. For the CERN-Neutrino-Factory proposal with a 4 MW beam power, but with a relatively large beam size at 2.2 GeV/c and pulsed at 50 Hz, maximum energy deposition densities of below 20 J/g and average power densities of about 1 kW/g are expected in the target. Therefore, a study has been made which discusses the feasibility and limits of a stationary target. It is proposed to use densely packed solid spheres of heavy material and with diameters in the millimeter range. These spheres are confined inside a Titanium container and cooled by an efficient water circuit or possibly by He-gas. Dynamic response, as pressure pulses and vibrations are greatly reduced in the small target granules due to relatively long beam bursts, each with a duration of 3.3 μs. The encouraging results achieved in this assessment justify to pursue further experimental tests, in particular of the cooling of the target, its lifetime under repetitive thermal cycles (4.3 Mio/day) and of radiation damage, to validate this proposal. It is expected that the lifetime of this target will be adequate for the operation of the CERN-Neutrino-Factory, at least over its initial phase below 4 MW beam power.