Superconducting Magnets for a Muon Collider

Superconducting Magnets for a Muon Collider Michael A. Green Ernest Orlando Lawrence Berkeley National Laboratory University of California Berkeley CA. 94720 The existence of a muon collider will be dependent on the use of superconducting magnets. Superconducting magnets for the µ - µ + collider will be found in the following locations: the π - π + capture system, the muon phase rotation system, the muon cooling system, the recirculating acceleration system, the collider ring, and the collider detector system. This report describes superconducting magnets for each of these sections except the detector. In addition to superconducting magnets, superconducting RF cavities will be found in the recirculating accelerator sections and the collider ring. The use of superconducting magnets is dictated by the need for high magnetic fields in order to reduce the length of various machine components. The performance of all of the superconducting magnets will be affected the energy deposited from muon decay products. 1 . INTRODUCTION The proposed muon collider[1-5] consists of the following components: 1) a 10 GeV proton source that generates about 1.5 x 10 1 5 protons per second, 2) a target section that produces and captures pions, 3) a section where the pions decay to muons that are phase rotated to compact bunch, 4) a muon cooling section where the muon emitance is reduced three orders of magnitude, 5) several rings to accelerate muons to 2 TeV, 6) the collider ring, and 7) the detector. Superconducting magnets will be found in all of these sections except for the proton source. This report describes the superconducting solenoids in the pion capture system around the target. A brief description of the solenoids needed in the phase rotation and the muon cooling sections is presented. Dipole and quadrupoles for the recirculating accelerator rings and the collider ring are also described. This report does not include any discussion about superconducting magnets that are part of the detector system around the collider collision point. A muon decays to two neutrinos and electron or positron (depending on the charge state of the original muon). Roughly forty percent of the muon energy ends up in the decay electron or positron. The energy in the electron or positron can be deposited in various parts of the muon collider and its subsystems. The problem of muon decay is at its worst in the collider ring, but it is a problem for superconducting magnets and RF cavities throughout the muon collider subsystems. Muons have a life time that is dictated by its energy. The mean life of a muon at rest is about 2.197 µs. At the collider full energy the of 2 TeV, the muons will have a mean life of 41.6 ms. This means that the repetition rate for the muon collider must be of the order of the muon life time in the collider ring if high colliding ring luminocities are to be maintained. In order to maintain a luminocity of 10 3 5 cm -2 s -1 in a collider ring with a ∫* of 3 mm at the collision point, over 1.2 x 10 1 4 muons per second must be created and stored in a ring with 7 T bending magnets. The collider ring must have two bunches (one of each charge state) of 2x10 1 2 muons per bunch at a repetition rate of 30 Hz in order to have the desired luminocity at the collision point. This work was performed with the support of the Office of High Energy and Nuclear Physics, United States Department of Energy under contract number DE-AC03-76SF00098.