THE NEXT LINEAR COLLIDER DAMPING RING COMPLEX J.N. Corlett, S. Marks , R. Rimmer, R. Schlueter Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA, 94720 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, 94309 . 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 http://www-project.slac.stanford.edu/lc/nlc-tech.html. [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 m 273 . 297 ) MHz 714 /( ) 708 ( / m 27 . 295 1 c f hc C N cN C RF k b b t m 03 . 0 1 2 2 0 N ye N y y e e 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, y0 150 m, sets the number of damping times required per train, N ... Equilibrium y-emittance and y-tolerances r r N r y y y ye 1 ln 2 1 ... 0 Vertical alignment tolerances scale as ~r 1/2 , so push r1 yet with reasonably small damping, N . NLC MDR… y 0 / y = 5000 , r = 2/3 , ye = 0.02 m , N = 4.8 y0 / y = 5000, y0 / y = 3333, y0 / y = 1667 Layout of Rings and Transport Lines M ain Rings Pre-Ring Energy G eV 1.98 1.98 Circ.m eter 297 214 T p M H z (1/ T 0 ) 1.01 1.401 RF (M H z) 714 714 h 708 510 b (bunch spacing) 2.80 ns 2.80 ns Fillpattern (# trains N T ,/# bunches) N T =3/95 3 gaps68 ns N T =2/95 2 gaps100 ns x,y (m s) < 5.21 < 5.21 N m ax /bunch 1.6x10 10 1.9x10 10 I m ax (Am p) 0.75 0.80 N orm alized extracted emittance x / y < 3/.03 m- rad <100 m -rad x / y <800/8 pm -rad <25 nm -rad G ap voltage V g (M V) 1.5 (3 cells) 2 (4 cells) Loss/turn U 0 750 K eV 400 K eV M omentum compaction p 6.6 x 10 -4 0.0051 Injected em ittance x 0 ,y 0 150 m -rad > 0.06 m -rad (A cceptance) Bunch length z 4.0 m m 8.4 m m Energy acceptance +/-1.9% +/-1.3% Parameter table: Vertical damping time-constant, y , is set by repetition rate, f , trains stored, N t , and the store time per train, N , as... Damping Time-Constant of Ring 2 12 0 0 kG 10 2.9 msec 2 . 5 ) Hz 120 ( 8 . 4 3 B T f N N t y B 0 < 18 kG requires mc 2 > 2.8 GeV (RF costs , z ), therefore, at 1.98 GeV (a = n+1/2), we need a long wiggler. loss/tur energy arcs loss/t energy wiggler , 1 2 1 2 2 2 0 a w w w k b b I I F F N N f B Wiggler at 1.98 GeV kG 21.5 ˆ @ m 33 1 ˆ 6 2 3 2 w w w w y e w B F F B c r B C L 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/sect ion 51-m full wiggler physical length 27-cm period ... 2- cm gap ... Effects of more wiggler damping... w w w F F L 1 ~ 3 / 5 ) 1 ( ~ w p F w x w w F J F 0 ~ w F ~ B 1 1 0 wiggler length asympto tes wiggler’ s emittanc e asymptot es momentum compaction increases arc bend field decrea ses 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 = 6.610 –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...