THE NEXT LINEAR COLLIDER DAMPING RING COMPLEX

J.N. Corlett, S. Marks , R. Rimmer, R. SchlueterErnest 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.AbstractWe 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 27.2951

cfhcC

NcNC

RF

kbbt

m 03.01 220 N

yeN

yy ee

Require at least 3 trains (Nt 3) for reasonable cell packing. Circumference is then, C = cT0 ...

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

rr

N

r

yy

yye

1ln

21

...

0

Vertical alignment tolerances scale as ~r1/2, so push r1 yet with reasonably small damping, N.

NLC MDR…y0/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 LinesMain Rings Pre- Ring

Energy GeV 1.98 1.98Circ. meter 297 214Tp MHz (1/T0) 1.01 1.401RF (MHz) 714 714h 708 510b (bunch spacing) 2.80 ns 2.80 nsFill pattern (# trainsNT, /# bunches)

NT=3/ 953 gaps 68 ns

NT =2/ 952 gaps 100 ns

x,y (ms) < 5.21 < 5.21Nmax /bunch 1.6x1010 1.9x1010

Imax (Amp) 0.75 0.80Normalized extractedemittance x / y

< 3/.03 m-rad

<100m-rad

x / y <800/8 pm-rad <25 nm-radGap voltage Vg (MV) 1.5 (3 cells) 2 (4 cells)Loss/turn U0 750 KeV 400 KeVMomentumcompaction p

6.6 x 10-4 0.0051

Injected emittancex0,y0

150 m-rad > 0.06 m-rad(Acceptance)

Bunch length z 4.0 mm 8.4 mmEnergy acceptance +/- 1.9% +/- 1.3%

Parameter table:

Vertical damping time-constant, y , is set by repetition rate, f , trains stored, Nt , and the store time per train, Ny , as...

Damping Time-Constant of Ring

2

12

0

0kG 102.9msec 2.5)Hz 120(8.4

3

B

TfN

Nty

B0 < 18 kG requires mc2 > 2.8 GeV (RF costs , z ), therefore, at 1.98 GeV (a = n+1/2), we need a long wiggler.

loss/turnenergy arcs

loss/turnenergy wiggler , 12

1

2

220

a

ww

w

kbbIIF

F

NNfB

Wiggler at 1.98 GeV

kG 21.5ˆ @ m 331ˆ

6 23

2

w

w

w

wyew B

FF

BcrBCL

For increased momentum compaction (see next slides) we choose Fw = 2.3, which sets Lw = 46.2 m and B0 = 11.2 kG.

2.2 m

20 wiggler sections ~8 periods/section

51-m full wiggler physical length

27-cm period

...

2-cmgap

...

Effects of more wiggler damping...

w

ww F

FL1

~

3/5)1(~ wp F

wx

ww FJ

F0

~

wF~B

11

0

wigglerlengthasymptotes

wiggler’semittanceasymptotes

momentumcompactionincreases

arc bendfielddecreases

As Fw increases...

• 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 = 6.610–4)

• 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...

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

TechnologyRF Cavity

Wiggler

Injection/Extraction Kicker BEND

QD

QF 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

9

56393

T

xxeqx L

ΔCC

γβτcrCΔγε

18

3072 2

32 N

BBNC wws

w

Wiggler switched onextends circumference by...

( 1.7 mm) Need atleast Cw-correction for‘wiggler-off’ and also forunexpected errors.

Emittance increase ~1.3% @ C = +2 mm for chicane lengthof LT = 3.6 m (±2 mm C range).

LT

bends of length LT/6,drifts of length LT/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

Spear 3 NLC SLC DR ALS Spear 2 APS Bessy HER LER PEP IE(GeV) 3 2 1.2 1.7 3 1.9 7 9 3.1 15I (mA) 500 800 136.2 500 200 400 300 3000 3000 92CIRCUMFERENCE -- TOTAL M) 234 295 35 197 234 1104 240 2200 2200 2200DIPOLE BEND RADIUS (M) 7.5 5.8 2 4 12.7 38.9 10.3 165 30.6 165.5

NO. BEND MAGNETS 34 32 40 24 36 80 32 192 192 192POWER PER BEAM (KW) 478 230 13 115 113 1,639 36 10,557 802 2,490KW PER METER 2 1 0.4 0.6 0.5 1.5 0.1 4.8 0.4 1.1PER DIPOLE (KW) 14.1 7.2 0.3 4.8 3.1 20.5 1.1 55 4.2 13

PHOTON DESORPTION (MOL./PHOTON) 2.00E-06 2.00E-06 2.00E-06 2.00E-06 2.00E-05 2.00E-06 2.00E-06 2.00E-06 2.00E-06 2.00E-05GAS LOAD (T.L/S) 7.00E-05 7.74E-05 8.00E-06 4.00E-05 3.00E-04 1.00E-04 4.00E-05 1.00E-03 5.00E-04 7.00E-04

DESIGN PRESSURE (TORR) 5.00E-10 1.00E-09 1.00E-09 1.00E-09 1.00E-08 1.00E-09 2.00E-09 1.00E-08 5.00E-09 2.00E-08

PUMP SPEED REQUIRED 145,440 77440 7,990 36,845 29,088 101,808 20,604 130,896 90,173 33,451Actual pump speed (arc) 29,520 173,760 42,240 165,000PUMP SPEED/METER 622 397 227 187 124 92 86 59 41 15

Vacuum System