Abstract
We demonstrate efficient transverse compression of a 12.5 MeV/c muon beam stopped in a helium gas target featuring a vertical density gradient and crossed electric and magnetic fields. The muon stop distribution extending vertically over 14mm was reduced to a 0.25mm size (rms) within 3.5 μs. The simulation including cross sections for low-energy μ^{+}-He elastic and charge exchange (μ^{+}↔ muonium) collisions describes the measurements well. By combining the transverse compression stage with a previously demonstrated longitudinal compression stage, we can improve the phase space density of a μ^{+} beam by a factor of 10^{10} with 10^{-3} efficiency.
Highlights
We demonstrate efficient transverse compression of a 12.5 MeV=c muon beam stopped in a helium gas target featuring a vertical density gradient and crossed electric and magnetic fields
At the Paul Scherrer Institute, we are developing a novel device that reduces the full phase space of a surface [12] (28 MeV=c momentum) μþ beam by 10 orders of magnitude with 10−3 efficiency [13]. This so-called muCool device is placed inside a 5 T magnetic field, pointing in the þz direction (Fig. 1)
In the muCool device, the muons collide with He gas atoms with an average frequency νc, which depends on the gas density, elastic μþ-He cross section, and muon energy
Summary
We demonstrate efficient transverse compression of a 12.5 MeV=c muon beam stopped in a helium gas target featuring a vertical density gradient and crossed electric and magnetic fields. Throughout this drift, the collisional energy loss is balanced by the acceleration in the electric field, so that ∼20 keV=c momentum spreads σpx;py;pz are maintained; combined with the spatial compression in the y direction we obtain transverse (σyσpy) phase-space compression.
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