Lattice design and expected performance of the Muon Ionization Cooling Experiment demonstration of ionization cooling

Muon beams of low emittance provide the basis for the intense, well-characterized neutrino beams necessary to elucidate the physics of flavor at a neutrino factory and to provide lepton-antilepton collisions at energies of up to several TeV at a muon collider. The international Muon Ionization Cooling Experiment (MICE) aims to demonstrate ionization cooling, the technique by which it is proposed to reduce the phase-space volume occupied by the muon beam at such facilities. In an ionization-cooling channel, the muon beam passes through a material in which it loses energy. The energy lost is then replaced using rf cavities. The combined effect of energy loss and reacceleration is to reduce the transverse emittance of the beam (transverse cooling). A major revision of the scope of the project was carried out over the summer of 2014. The revised experiment can deliver a demonstration of ionization cooling. The design of the cooling demonstration experiment will be described together with its predicted cooling performance.

Figure 1

Layout of the lattice configuration for the cooling demonstration. The red rectangles represent the solenoids. The individual coils in the spectrometer solenoids are labeled E1, C, E2, M1 and M2. The ovals represent the rf cavities and the blue rectangles the absorbers. The various detectors (time-of-flight hodoscopes [29, 30], Cerenkov counters [31], scintillating-fibre trackers [32], KLOE Light (KL) calorimeter [27, 33], electron muon ranger [34]) used to characterize the beam are also represented. The green-shaded box indicates the cooling cell.

Figure 2

Design of the movable frame for the secondary absorber (front) and the lead radiation shutter (back). The half discs of the lead shutter (grey) can be seen together with the rails (white) inside the vacuum chamber (yellow).

Figure 3

Transverse 4D beta-function versus longitudinal coordinate $z$ in the cooling-demonstration lattice for $200\mathrm{MeV}/c$ settings with a phase advance of $2\pi \times 1.75$ (dashed blue line), $2\pi \times 1.81$ (solid red line) and $2\pi \times 1.86$ (dot-dashed green line). The vertical dashed lines with labels show the positions of the tracker reference planes and the centers of the absorbers, rf cavities, and focus coil modules.

Figure 4

4D emittance evolution in the cooling-demonstration lattice for $200\mathrm{MeV}/c$ settings with a phase advance of $2\pi \times 1.75$ (dashed blue line), $2\pi \times 1.81$ (solid red line) and $2\pi \times 1.86$ (dot-dashed green line). The vertical dashed lines with labels show the positions of the tracker reference planes and the centers of the absorbers, rf cavities, and focus coil modules.

Figure 5

Magnetic field $B_z$ on-axis versus the longitudinal coordinate $z$ for the cooling-demonstration lattice design for $200\mathrm{MeV}/c$ (solid black line), $140\mathrm{MeV}/c$ (dashed purple line), and $240\mathrm{MeV}/c$ (dot-dashed blue line) settings. The vertical dashed lines with labels show the positions of the tracker reference planes and the centres of the absorbers, rf cavities, and focus coil modules.

Figure 6

${\beta }_{\perp }$ versus the longitudinal coordinate $z$ for $200\mathrm{MeV}/c$ (solid black line), $140\mathrm{MeV}/c$ (dashed purple line) and $240\mathrm{MeV}/c$ (dot-dashed blue line) in the cooling-demonstration lattice. The vertical dashed lines with labels show the positions of the tracker reference planes and the centers of the absorbers, rf cavities, and focus coil modules.

Figure 7

Mean energy of the beam versus longitudinal coordinate ($z$) in the cooling-demonstration lattice. Top: the $140\mathrm{MeV}/c$ configuration for initial emittance ${ϵ}_{\perp }=4.2\mathrm{mm}$. Middle: the $200\mathrm{MeV}/c$ configuration for initial emittance ${ϵ}_{\perp }=6\mathrm{mm}$. Bottom: the $240\mathrm{MeV}/c$ configuration for initial emittance ${ϵ}_{\perp }=7.2\mathrm{mm}$. The vertical dashed lines with labels show the positions of the tracker reference planes, and the centers of the absorbers, rf cavities, and focus coil modules.

Figure 8

Emittance variation versus the longitudinal coordinate ($z$) for the cooling-demonstration lattice design. Top: $140\mathrm{MeV}/\mathrm{c}$ beam with initial ${ϵ}_{\perp }=4.2\mathrm{mm}$ with an rms momentum spread of $6.7\mathrm{MeV}/c$ (rms spread 4.8%, solid line) and $2.5\mathrm{MeV}/c$ (rms spread 1.8%, dashed line). Middle: $200\mathrm{MeV}/\mathrm{c}$ beam with initial ${ϵ}_{\perp }=6\mathrm{mm}$ (rms spread 4.0%). Bottom: $240\mathrm{MeV}/\mathrm{c}$ beam with initial ${ϵ}_{\perp }=7.2\mathrm{mm}$ (rms spread 3.6%). The vertical dashed lines with labels show the positions of the tracker reference planes, and the centers of the absorbers, rf cavities, and focus coil modules.

Figure 9

Transmission (defined as the ratio of good muons observed downstream of the cooling cell, $N_{\mathrm{down}}$, to those observed upstream, $N_{\mathrm{up}}$) in percent versus initial emittance (${ϵ}_{\perp \mathrm{in}}$) for the cooling-demonstration lattice. The transmission of the $140\mathrm{MeV}/c$, $200\mathrm{MeV}/c$, and $240\mathrm{MeV}/c$ lattices are shown as the purple-dashed, solid black, and dot-dashed blue lines respectively. The error bars indicate the statistical precision that would be achieved using a sample of 100,000 muons.

Figure 10

Fractional change in emittance versus initial emittance (${ϵ}_{\perp \mathrm{in}}$) for the cooling-demonstration lattice design measured at the tracker reference planes. The fractional change in emittance of the $140\mathrm{MeV}/c$, $200\mathrm{MeV}/c$, and $240\mathrm{MeV}/c$ lattices are shown as the purple-dashed, solid black, and dot-dashed blue lines, respectively. The error bars indicate the statistical precision that would be achieved using a sample of 100,000 muons.