THE NEXT LINEAR COLLIDER DAMPING RING COMPLEX J.N. Corlett, S. Marks, R. Rimmer, R. Schlueter Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA, P. Bellomo, V. Bharadwaj, R. Cassel, P. Corredoura, P. Emma, R.K. Jobe, P. Krejcik, S. Mao, B. McKee, K. Millage, M. Munro, C. Pappas, T.O. Raubenheimer, S. Rokni, M.C. Ross, H. Schwarz, J. Sheppard, C.M. Spencer, R.C. Tighe, M. Woodley Stanford Linear Accelerator Center, Stanford, CA, Abstract We report progress on the design of the Next Linear Collider (NLC) Damping Rings complex (DRC) [1]. The purpose of the DRC is to provide 120 Hz, low emittance electron and positron bunch trains to the NLC linacs [2]. It consists of two 1.98 GeV main damping rings, one positron pre-damping ring, two pairs of bunch length and energy compressor systems and interconnecting transport lines. The 2 main damping rings store up to 0.8 amp in 3 trains of 95 bunches each and have normalized extracted beam emittances  x = 3  m-rad and  y = 0.03  m-rad. The preliminary optical design, performance specifications and tolerances are given in [1]. Key subsystems include 1) the 714 MHz RF system [3], 2) the 60 ns risetime injection / extraction pulsed kicker magnets [4], 3) the 40 m wiggler magnet system, 4) the arc and wiggler vacuum system, 5) the radiation management system, 6) the beam diagnostic instrumentation, 7) special systems used for downstream machine protection and 8) feedback-based stabilization systems. Experience at the SLAC Linear Collider has shown that the NLC damping rings will have a pivotal role in the operation of the high power linacs. The ring dynamics and instabilities will in part determine the design choices made for the NLC machine protection system. This paper includes a summary overview of the main ring design and key subsystem components. [1] T.O. Raubenheimer, et.al., Updated parameters can be found on the NLC Accelerator Physics Web pages found at [2] V. Bharadwaj, et.al., The NLC Injector System, PAC99, FRA27. [3] R.A.Rimmer,et.al., The Next Linear Collider Damping Ring RF System, PAC 99, (MOP60). [3] C. Pappas and R. Cassel, Damping Ring Kickers for the Next Linear Collider, presented at PAC 99, (TUP11). Abstract We report progress on the design of the Next Linear Collider (NLC) Damping Rings complex (DRC) [1]. The purpose of the DRC is to provide 120 Hz, low emittance electron and positron bunch trains to the NLC linacs [2]. It consists of two 1.98 GeV main damping rings, one positron pre-damping ring, two pairs of bunch length and energy compressor systems and interconnecting transport lines. The 2 main damping rings store up to 0.8 amp in 3 trains of 95 bunches each and have normalized extracted beam emittances  x = 3  m-rad and  y = 0.03  m-rad. The preliminary optical design, performance specifications and tolerances are given in [1]. Key subsystems include 1) the 714 MHz RF system [3], 2) the 60 ns risetime injection / extraction pulsed kicker magnets [4], 3) the 40 m wiggler magnet system, 4) the arc and wiggler vacuum system, 5) the radiation management system, 6) the beam diagnostic instrumentation, 7) special systems used for downstream machine protection and 8) feedback-based stabilization systems. Experience at the SLAC Linear Collider has shown that the NLC damping rings will have a pivotal role in the operation of the high power linacs. The ring dynamics and instabilities will in part determine the design choices made for the NLC machine protection system. This paper includes a summary overview of the main ring design and key subsystem components. [1] T.O. Raubenheimer, et.al., Updated parameters can be found on the NLC Accelerator Physics Web pages found at [2] V. Bharadwaj, et.al., The NLC Injector System, PAC99, FRA27. [3] R.A.Rimmer,et.al., The Next Linear Collider Damping Ring RF System, PAC 99, (MOP60). [3] C. Pappas and R. Cassel, Damping Ring Kickers for the Next Linear Collider, presented at PAC 99, (TUP11). Circumference and Store Time Require at least 3 trains (N t  3 ) for reasonable cell packing. Circumference is then, C = cT 0... Extracted vertical emittance... Keep equilibrium y-emittance large (sets y-tolerances) Initial y-emittance,  y 0  150  m, sets the number of damping times required per train, N ... Equilibrium y-emittance and y-tolerances Vertical alignment tolerances scale as ~r 1/2, so push r  1 yet with reasonably small damping, N . NLC MDR…  y 0 /  y = 5000, r = 2/3,  ye = 0.02  m, N  = 4.8  y 0 /  y = 5000,  y 0 /  y = 3333,  y 0 /  y = 1667 Layout of Rings and Transport Lines Parameter table: Vertical damping time-constant,  y, is set by repetition rate, f, trains stored, N t, and the store time per train, N   y, as... Damping Time-Constant of Ring B GeV (RF costs ,  z  ), therefore, at 1.98 GeV (a  = n+1/2), we need a long wiggler. Wiggler at 1.98 GeV For increased momentum compaction (see next slides) we choose F w = 2.3, which sets L w = 46.2 m and B 0 = 11.2 kG. 2.2 m 20 wiggler sections~8 periods/section 51-m full wiggler physical length 27-cm period... 2-cm gap... Effects of more wiggler damping... wiggler length asymptotes wiggler’s emittance asymptotes momentum compaction increases arc bend field decreases As F w increases... For simplicity, use bend with no gradient (J x 0  1) Use B w = 21.5 kG (probably too high) Keep  x  and w reasonably small (  x   4.5 m, w = 27 cm) Choose F w for ‘large’  p (F w = 2.3,  p = 6.6  10 –4 ) Solve  for  x = 3  m (  = 12°) Calculate arc bend field for  y = 5.2 msec (B 0 = 11.2 kG) Find total number of cells ( N c = 2  /  = 30) Get length of arc bends ( L B =  (B  )/B 0 = 1.23 m) Set TME-cell length (L c = (C – 2L w –  L match )/N c = 6 m) Build the arc TME-cell... For simplicity, use bend with no gradient (J x 0  1) Use B w = 21.5 kG (probably too high) Keep  x  and w reasonably small (  x   4.5 m, w = 27 cm) Choose F w for ‘large’  p (F w = 2.3,  p = 6.6  10 –4 ) Solve  for  x = 3  m (  = 12°) Calculate arc bend field for  y = 5.2 msec (B 0 = 11.2 kG) Find total number of cells ( N c = 2  /  = 30) Get length of arc bends ( L B =  (B  )/B 0 = 1.23 m) Set TME-cell length (L c = (C – 2L w –  L match )/N c = 6 m) Build the arc TME-cell...

THE NEXT LINEAR COLLIDER DAMPING RING COMPLEX Ernest Orlando Lawrence Berkeley National Laboratory and Stanford Linear Accelerator Center Technology RF Cavity Wiggler Injection/Extraction Kicker BEND QD QF QD  x,  y /m  x /m  x = 108°,  y = 45° 30 cells (28 full) 6-m cell length 25-cm quad length 4-cm quad bore 7-kG max. field 4 sextupoles/cell The arc TME-cell... Circumference adjustment... +C+C –C–C Wiggler switched on extends circumference by... (  1.7 mm)  Need at least  C w -correction for ‘wiggler-off’ and also for unexpected errors. Emittance increase  C = +2 mm for chicane length of L T = 3.6 m (±2 mm  C range). LTLT bends of length L T /6, drifts of length L T /6 Other parameters,  p,  y,  z,...etc., are changed insignificantly. Work remaining... Dynamic aperture (studied in ZDR but not for new ring) Abort kickers (not added yet) Skew quads (for correction * and/or fast MPS  y -blowup) Wiggler radiation deposition problem Termite inspection Lots more... * Full skew correction is available immediately after extraction in 1st bunch compressor See paper FRA23 See paper MOP60 See paper TUP11 Vacuum System