Measurement of Longitudinal Wakefields in the SLC Collider Arcs K.L.F. Bane, P. Emma, M. Minty, F. Zimmermann Stanford Linear Accelerator Center Stanford, CA 94309 USA

1
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 gex 3
mm-rad and gey 0.03 mm-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.h
tml. 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).
Layout of Rings and Transport Lines
Parameter table
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, N??y , as...

• For simplicity, use bend with no gradient (Jx0 ?
  1)
• Use Bw 21.5 kG (probably too high)
• Keep ??x? and ?w reasonably small (??x? ? 4.5 m,
  ?w 27 cm)
• Choose Fw for large ?p (Fw 2.3, ?p
  6.6?104)
• Solve ? for ??x 3 ?m (? 12)
• Calculate arc bend field for ?y 5.2 msec (B0
  11.2 kG)
• Find total number of cells ( Nc 2?/? 30)
• Get length of arc bends ( LB ?(B?)/B0 1.23 m)
• Set TME-cell length (Lc (C 2Lw ?Lmatch)/Nc
  6 m)
• Build the arc TME-cell...

Extracted vertical emittance ...
B0 lt 18 kG requires ? mc2 gt 2.8 GeV (RF costs ?,
?z ?), therefore, at 1.98 GeV (a? n1/2), we
need a long wiggler.

• 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
Wiggler at 1.98 GeV
Effects of more wiggler damping...
As Fw increases...
Vertical alignment tolerances scale as r1/2, so
push r?1 yet with reasonably small damping, N?.
For increased momentum compaction (see next
slides) we choose Fw 2.3, which sets Lw 46.2
m and B0 11.2 kG.
momentum compaction increases
20 wiggler sections
8 periods/section
wiggler length asymptotes
2-cm gap
...
...
?y0/?y 5000, ?y0/?y 3333, ?y0/?y 1667
NLC MDR ?y0/?y 5000 , r 2/3 ,
?ye 0.02 ?m , N? 4.8
arc bend field decreases
2.2 m
27-cm period
51-m full wiggler physical length
wigglers emittance asymptotes
2
THE NEXT LINEAR COLLIDER DAMPING RING
COMPLEXErnest Orlando Lawrence Berkeley National
Laboratory and Stanford Linear Accelerator Center
RF Cavity
Technology
The arc TME-cell...
Injection/Extraction Kicker
QD
QD
BEND
QF
QF
See paper TUP11
See paper MOP60
?x /m
?x , ?y /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

Wiggler
Circumference adjustment...
Vacuum System
Wiggler switched on extends circumference by...
?C
bends of length LT/6, drifts of length LT/6
?C
LT
(? 1.7 mm) ? Need at least ?Cw-correction
for wiggler-off and also for unexpected errors.
Emittance increase 1.3 _at_ ?C 2 mm for
chicane length of LT 3.6 m (2 mm ?C range).
Other parameters, ?p, ?y, ?z, ...etc., are
changed insignificantly.
See paper FRA23
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