New target solution for a muon collider or a muon-decay neutrino beam facility: The granular waterfall target

A new target solution, the granular waterfall target, is proposed here for a muon collider or a muon-decay neutrino beam facility, especially for the moment which adopts a 15 MW continuous-wave (cw) superconducting linac. Compared to the mercury jet target, the granular waterfall target works by a much simpler mechanism which can operate with a much more powerful beam, which are indicated by the detailed investigations into the heat depositions and the evaluations of the temperature increases for different target concepts. By varying proton beam kinetic energy and the geometrical parameters of the waterfall target, an overall understanding of the figure of merit concerning muon production for this target concept as the target solutions of the long-baseline neutrino factory and the medium-baseline moment is obtained. With 8 GeV beam energy and the optimal geometrical parameters, the influence on muon yield by adopting different beam-target interaction parameters is explored. Studies and discussions of the design details concerning beam dumping are also presented.

Figure 1

Schematic outline of a granular waterfall target in the grain loop system with heat exchanger, grain filter, lift, and degassing/cleansing devices.

Figure 2

Schematic representation of beam-target interaction for a granular waterfall target. The velocity variance of the waterfall is shown.

Figure 3

Different regions for the comparison between the liquid mercury/powdery tungsten jet and the grain waterfall. The regions are marked in transverse sections of the targets ($A\in B\in C$).

Figure 4

Temperature rises in different regions (within beam profiles) for the three targets.

Figure 5

Total production of charged pions (per proton per GeV) produced in target body of proton beams with various kinetic energies simulated using different hadronic models.

Figure 6

Medium density (relative factor) distributions (in x-y plane) for the grain waterfalls with 2, 3, and 4 cm target width.

Figure 7

Medium density (relative factor) distributions (in y direction, at $x=0$ height) for the grain waterfalls with 2, 3, and 4 cm target width.

Figure 8

Magnetic field profile distribution on axis along the field tapering section for the simulations for the NF and MOMENT.

Figure 9

Desired (pions and) muons yields (per proton per GeV) for different target widths for the neutrino factory as a function of beam energy.

Figure 10

Desired (pions and) muons yields (per proton per GeV) of 8 GeV proton beam for different target widths for the neutrino factory as a function of target length.

Figure 11

Desired muons yields (per proton per GeV) for different jet widths for MOMENT as a function of beam energy.

Figure 12

The momentum distribution of the useful pions produced in the target calculated using INCL and FTF model.

Figure 13

Same as for Fig. 11 except for choosing INCL model for all simulation.

Figure 14

Desired muons yields (per proton per GeV) of 8 GeV proton beam for different outlet widths for MOMENT as a function of target length.

Figure 15

The beam-target geometry for the waterfall target.