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
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.
We report progress on the design of the Next Linear Collider (NLC) Damping Rings complex (DRC) . The purpose of the DRC is to provide 120 Hz, low emittance electron and positron bunch trains to the NLC linacs . 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 gex = 3 mm-rad and gey = 0.03 mm-rad. The preliminary optical design, performance specifications and tolerances are given in . Key subsystems include 1) the 714 MHz RF system , 2) the 60 ns risetime injection / extraction pulsed kicker magnets , 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.
 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.
 V. Bharadwaj, et.al., The NLC Injector System, PAC99, FRA27.
 R.A.Rimmer,et.al., The Next Linear Collider Damping Ring RF System, PAC 99, (MOP60).
 C. Pappas and R. Cassel, Damping Ring Kickers for the Next Linear Collider, presented at PAC 99, (TUP11).
Layout of Rings and
Circumference and Store Time
Damping Time-Constant of Ring
Require at least 3 trains (Nt 3) for reasonable cell packing.
Circumference is then, C = cT0 ...
Vertical damping time-constant,y , is set by repetition rate, f , trains stored,Nt , and the store time per train,Ny , as...
Extracted vertical emittance ...
B0 < 18 kG requiresmc2 > 2.8 GeV (RF costs , z),therefore, at 1.98 GeV (a = n+1/2), we need a longwiggler.
Equilibrium y-emittance and y-tolerances
Wiggler at 1.98 GeV
Effects of more wiggler damping...
Vertical alignment tolerances scale as ~r1/2, so push r1 yet with reasonably small damping, N.
For increased momentum compaction (see next slides) we chooseFw= 2.3, which sets Lw = 46.2 m andB0 = 11.2 kG.
20 wiggler sections
y0/y= 5000, y0/y= 3333, y0/y= 1667
y0/y= 5000 , r = 2/3 , ye= 0.02 m , N= 4.8
51-m full wiggler physical length
The arc TME-cell...
See paper TUP11
See paper MOP60
x , y/m
Wiggler switched on
extends circumference by...
bends of lengthLT/6,
drifts of lengthLT/6
( 1.7 mm) Need at
least Cw-correction for
‘wiggler-off’ and also for
Emittance increase ~1.3% @
C = +2 mm for chicane length
of LT = 3.6 m (±2 mmC range).
Other parameters, p, y,z, ...etc., are changed insignificantly.
See paper FRA23
* Full skew correction is available immediately after extraction in 1st bunch compressor