The design, construction and performance of the MICE target

Abstract

The pion-production target that serves the MICE Muon Beam consists of a titanium cylinder that is dipped into the halo of the ISIS proton beam. The design and construction of the MICE target system are described along with the quality-assurance procedures, electromagnetic drive and control systems, the readout electronics, and the data-acquisition system. The performance of the target is presented together with the particle rates delivered to the MICE Muon Beam. Finally, the beam loss in ISIS generated by the operation of the target is evaluated as a function of the particle rate, and the operating parameters of the target are derived.

The liquid-hydrogen absorber for MICE

“…The muons for MICE were created from the decay of pions produced when a target dipped into the circulating proton beam in the ISIS synchrotron at the STFC Rutherford Appleton Laboratory (RAL) [19,20]. A beamline of nine quadrupoles, two dipoles, and a superconducting 'decay solenoid' collected each burst of particles (a 'spill') and transported the momentum-selected particles to the experiment [21].…”

The design and performance of an improved target for MICE

“…As described in [7], the 24 coils are wired in three phases, A B & C in a repeating pattern. Each coil in a phase is connected in series, with one end of the phase connected to a power lead and the other connected to a common star-point.…”

“…The previous target [7] operated successfully on ISIS from 2011, performing over half a million actuations during three years. However, variability in performance between different examples of the target mechanism, and the need to generate the absolute minimum of abraded material (which could enter the accelerator vacuum space) due to wear have led to a programme of improvements which are reported in this publication.…”

“…It has been suggested that poorer performance could be due to off-axis forces, due to misalignments between the stator coils in the body of the drive and permanent magnets mounted on the titanium shaft the tip of which constituted the target. The previous target mechanism employed a stator containing 24 pre-wound and potted coils which were then assembled on the tube forming the vacuum barrier and down which the shaft passed [7]. Section 2 describes a new construction technique which allows the coils to be wound and potted in situ on a special tube which also acts as a former.…”

“…Section 3 describes improvements to the control circuitry. Our previous publication [7] explained how the stator coils are connected in three banks, with two being powered at any one time; the new controller allows currents to flow through all three banks simultaneously when this provides a greater driving force on the target. The user interface to the target controller has been upgraded to allow greater functionality and easier operation by both experts and other users; this is documented in section 4.…”