Muon Acceleration in a Neutrino Factory Orbit Correction in a nonscaling FFAG

1. Muon Acceleration in a Neutrino Factory Orbit Correction in a nonscaling FFAG D. J. Kelliher, ASTeC, STFC Rutherford Appleton Laboratory, Harwell, Didcot, Oxfordshire, OX11 0QX It is a requirement of the proposed Neutrino Factory (NF) that, due to their short decay time and large emmitance, the muons are rapidly accelerated to a kinetic energy of at least 20GeV. It is proposed that this is achieved by a chain of non-scaling Fixed Field Alternating Gradient (FFAG) accelerators. EMMA is a prototype electron model nonscaling FFAG to be built at Daresbury. Topics examined in this poster will include the difficulties in orbit correction due to the large transverse tune excursion in a non-scaling FFAG. Failure of harmonic correction • Advantages of FFAG for neutrino factory • Very rapid acceleration rate (as no synchronisation is required between magnets and rf) • Large acceptance (muon beam will have large emittance) • Reuse of rf cavities (cost-effective) Effect of kicker varies since the phase advance between the kicker and any point in the lattice changes as the momentum increases. Therefore, conventional harmonic correction of error source with kickers is not possible in a nonscaling FFAG. Optimising initial conditions Figure shows how the orbit distortion rms depends on the initial vertical tune (i.e. injecting at different momenta). In general, the closed orbit co-ordinates at the injection momentum do not give optimal initial conditions. A scan over the initial phase space (x,x’,y,y’) allows the distortion to be optimised. Latest acceleration scheme of International Scoping Study [1] Local correction of magnets It will be necessary to realign magnets to correct misalignments. In EMMA there are horizontal sliders on each magnet to allow for this. In the absence of other error sources, by placing simulated kickers in each magnet, and adjusting their strengths until 2 is minimized, the magnet displacements can be inferred from the BPM measurements. The algorithm can be generalised to include other error sources (as in the storage ring code LOCO [3]). EMMA nonscaling FFAG comprises 42 shifted quadrupole doublets. The energy range is 10-20 MeV. Orbit distortion due to alignment errors Many integral tunes are crossed over the energy range. While there are peaks in closed orbit distortion near the integral tunes (black curve), when acceleration is included, this correlation is not evident (red curve). We may surmise that the beam does not see the effects of resonance, instead the distortion is due to the random kicks imparted by the quad misalignment [2]. • References • “International scoping study of a future Neutrino Factory and super-beam facility”, www.hep.ph.ic.ac.uk/iss/ • S. Machida and D.J. Kelliher, ‘Orbit and optics distortion in fixed field alternating gradient muon accelerators’,submitted to Phys. Rev. STAB • J. Safranek, ‘Experimental determination of storage ring optics using orbit response measurements’, Nucl. Inst. And Meth. A388, 27 (1997) CERN accelerator school 2007, Daresbury