Initiatives in the Target Sector J. R. J. Bennett CCLRC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon. OX11 0QX, UK

Targets Current Target R&D Target Design - and influences of the rest of the NF ISS Baseline Design Summary R&D Required

Current High-Power Target R&D Free Jet Neutrino Factories Radioactive Beams Contained PSI SNS LIQUID METALSOLID IFMIF Low Thermal Expansion Small Spheres Re- circulating RAL Thermal Shock Radiation Damage Mechanics Target Station CERN Currently no R&D BNL Radiation Damage BNL, CERN, RAL, Japan MERIT Proof of principle experiment, with beam and magnetic field Radioactive Beams Neutrino Factories EURISOL RIA

The Proton Pulse macro-pulse micro-pulse Proton beam “macro-pulses” and “micro-pulses”.

The Design of the Solid and Jet Targets are influenced by:  the proton driver To reduce space charge it is best to have many and long micro- pulses, long macro-pulses and a high repetition rate.  the front end Need a micro-pulse of ~<3 ns for phase rotation. The beryllium windows will not stand a pulse longer than 160 μs.  the storage ring Should not exceed ~4 micro-pulses to limit the size of the storage ring.§ and of course the target itself:

 the target Solid Targets Prefer dc rather than pulsed beams to avoid thermal shock. Jet Targets i.Because the jet breaks up after the beam hits, the macro- pulse length should not be too long, ~<50  s. ii.Pulse repetition rates greater than 50 Hz will make re- establishment of the jet difficult. iii.Charge density –there may be a limit (not yet known) due to erosion of the container walls. This opposes i and ii. So, the proton driver and the solid target have a preference for low charge density.

The ISS Baseline Design § § § Free Mercury Jet Target

ParameterValueReason Beam Power4 MWBy definition Proton energy~10 GeVBased on calculated muon yield Beam repetition rate ~50 HzBased on Jet target(≤~50 Hz)/driver design Micro-pulse width~2 nsBased on muon yield (front end/phase rotation) Number of micro- pulses per macro- pulse ~4 (16  s spacing) Based on proton driver/front end design/size of storage ring Macro-pulse length~50  sBased on Jet target Target – Mercury Jet Based on advanced R&D/best choice Free Mercury Jet Target

ParameterValueReason Beam Power4 MWBy definition Proton energy~10 GeVBased on calculated muon yield Beam repetition rate~ 50 Hzdriver design/reduced thermal shock Micro-pulse width~2 nsBased on muon yield (front end/phase rotation) Number of micro- pulses per macro-pulse 4 (~60  s spacing) Based on proton driver/front end design size of storage ring Macro-pulse length120  s(beryllium window dissipation)/reduced thermal shock Target – Solid Tungsten Not chosen Shock studies incomplete Solid target

Target R&D Liquid Metal 1.Free Mercury Jet - After MERIT – may indicate further R&D needed. ???? 2.Improve/widen/increase experience with mercury jet and handling/safety. Consider low temperature eutectics as alternatives to Hg. 3.Contained, flowing liquid metal targets?

Solid Shock studies in solids – tantalum, tungsten and carbon –for targets (and at high temperatures) and windows. In-beam tests required. Investigate low thermal expansion metals? Produce a viable rotating/moving solid target design. Radiation Damage in solids –high temperatures - annealing.

Target Station 9. Design a target station and beam dump for Jet target and Solid target. Including remote handling, maintenance and replacement. 10. Produce a viable beam dump design for solid and free jet targets. 11. Safety aspects. Mercury presents special hazards.

Costs over a 3-4 year period #ITEMSTAFFCOST YearskEuro 1.Free Mercury Jet - After MERIT? Increase experience with mercury jet and handling/safety. Consider low temperature eutectics as alternatives to Hg Contained, flowing liquid metal targets - possibly combined with pulsed spallation neutron source research work? Shock studies in solids –tungsten and carbon –for targets (and at high temperatures) and windows In-beam tests required Investigate low thermal expansion metals Produce a viable rotating/moving solid target design Radiation Damage in solids –high temperatures - annealing Design a target station for Jet target and Solid target. Including remote handling, maintenance and replacement Produce a viable beam dump design for solid and free jet targets Safety aspects. Mercury presents special hazards Total Test Target Station with 4 MW proton beam ~ 50 MEuro