THE NEXT LINEAR COLLIDER DAMPING RING COMPLEX
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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

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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.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).

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 = 21.5kG (probably too high)

  • Keep x and w reasonably small (x  4.5 m, w= 27 cm)

  • Choose Fwfor ‘large’ p (Fw = 2.3, p = 6.610–4)

  • 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 < 18 kG requiresmc2 > 2.8 GeV (RF costs , z),therefore, at 1.98 GeV (a = n+1/2), we need a longwiggler.

  • 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...

AsFwincreases...

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 chooseFw= 2.3, which sets Lw = 46.2 m andB0 = 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

wiggler’s

emittance

asymptotes


RF Cavity

Technology

The arc TME-cell...

THE NEXT LINEAR COLLIDER DAMPING RING COMPLEXErnest Orlando Lawrence Berkeley National Laboratory and Stanford Linear Accelerator Center

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 lengthLT/6,

drifts of lengthLT/6

–C

LT

( 1.7 mm)  Need at

least Cw-correction for

‘wiggler-off’ and also for

unexpected errors.

Emittance increase ~1.3% @

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


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