1. Recent Progress Toward a Muon Recirculating Linear Accelerator S.A.Bogacz, V.S.Morozov, Y.R.Roblin 1, K.B.Beard 2, A. Kurup, M. Aslaninejad, C. Bonţoiu, J.K. Pozimski 1 Jefferson Lab, Newport News,VA, 2 Muons, Inc., Batavia, IL, 3 Imperial College of Science and Technology, London, UK INTERNATIONAL DESIGN STUDY The International Design Study for the Neutrino Factory (IDS-NF) baseline design involves a complex chain of accelerators including a single-pass prelinac, two recirculating linacs (RLA) and a fixed field alternating gradient accelerator (FFAG).[1] Muons, Inc. ABSTRACT Both Neutrino Factories (NF) and Muon Colliders (MC) require very rapid acceleration due to the short lifetime of muons. After a capture and bunching section, a linac raises the energy to about 900 MeV, and is followed by one or more Recirculating Linear Accelerators (RLA), possibly followed by a Rapid Cycling Synchnotron (RCS) or Fixed-Field Alternating Gradient (FFAG) ring. A RLA reuses the expensive RF linac section for a number of passes at the price of having to deal with different energies within the same linac. Various techniques including pulsed focusing quadruopoles, beta frequency beating, and multipass arcs have been investigated via simulations to improve the performance and reduce the cost of such RLAs. 3 GeV 1.8 GeV 1.2 GeV 3.6 GeV 244 MeV 900 MeV 2.4 GeV RLA I RLA II Pre-linac 244 MeV900 MeV 3.6 GeV 0.9 GeV 3.6 GeV 12.6 GeV 86 m 0.6 GeV/pass 202 m 255 m 2 GeV/pass RLA II (arcs not shown) prelinac RLA I * Funding: Supported in part by US DOE STTR Grant DE-FG02-08ER86351. Notice: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE- AC05-06OR23177. 2020 26 0 0 Size_X[cm] Size_Y[cm] Ax_betAy_betAx_dispAy_disp 24 short cryos 26 medium cryos (2.5) 2   = 30 mm rad (2.5) 2   p  z /m  c  = 150 mm 78.91030 15 0 5 0 BETA_X&Y[m] DISP_X&Y[m] BETA_XBETA_YDISP_XDISP_Y quad gradient 389.3020 30 0 5 0 BETA_X&Y[m] DISP_X&Y[m] BETA_XBETA_YDISP_XDISP_Y 1.2 GeV 0.9 GeV 3.0 GeV 2.4 GeV 1.8 GeV 3.6 GeV Arc 4 Arc 3 Arc 2 Arc 1  x = 3.2 m  y = 6.0 m  x =-1.1  y =1.5  x,y →  x,y  xy →  xy  x,y →  x,y  xy →  xy  x,y →  x,y  xy →  xy  x,y →  x,y  xy →  xy  x = 6.3 m  y = 7.9 m  x =-1.2  y =1.3  x = 7.9 m  y = 8.7 m  x =-0.8  y =1.3  x = 13.0 m  y = 14.4 m  x =-1.2  y =1.5 1 m 1.75 m -H V -V 2 cells 4 cells -V V 30.50 Beta_X&Y[m ] DISP_X&Y[m] BETA_XBETA_YDISP_XDISP_Y H -H V H -V 2 cells 4 cells Double achromat Optics -V V β x β y D x D y 0 20 +1 PRELINAC Accelerates μ ± from about 244 to 900 MeV total energy and accepts a high emittance beam about 30 cm wide with a 10% energy spread. PRELINAC TO RLA CHICANE The current chicane separates the μ ± with a dipole, then each is directed down 1.75m into the plane of RLA I, then directed by dipoles into the middle of the linac. On subsequent passes, the injection dipole separates the returning μ ±, so a mini-chicane in the linac is used to correct the paths. FUTURE PLANS The neutrino factory baseline is being redesigned in light of recent experimental results; it is anticipated that only ~10 GeV is required, so the prelinac and RLAs will need be reoptimized and will feed a decay ring directly. Beta function beating in the RLA I linac. Beta functions in RLA I arcs 1 & 3 MULTIPASS ARCS By combining two arcs into one multipass arc, it is possible to greatly simplify the RLA by eliminating one arc’s chicanes and most of the switchyard. While pulsed quadrupoles could allow as many as 7 ½ passes, they aren’t needed for 4 ½ passes. The arc’s cells are constructed of linear combined-functions magnets with variable dipole and quadrupole field components. Unlike a fixed field alternating gradient design, opposing bends are not required.