Transcript Measurement of Longitudinal Wakefields in the SLC Collider

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.
Layout of Rings and
Parameter table:
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).
Energy GeV
Circ. meter
Tp MHz (1/T0)
RF (MHz)
h
b (bunch spacing)
Fill pattern (# trains
NT, /# bunches)
x,y (ms)
Nmax /bunch
Imax (Amp)
Normalized extracted
emittance gex / gey
ex / ey
Gap voltage Vg (MV)
Loss/turn U0
Momentum
compaction p
Injected emittance
gex0,y0
Bunch length z
Energy acceptance
Main Rings
1.98
297
1.01
714
708
2.80 ns
NT=3/ 95
3 gaps 68 ns
< 5.21
1.6x1010
0.75
< 3/.03 mmrad
<800/8 pm-rad
1.5 (3 cells)
750 KeV
6.6 x 10-4
Pre- Ring
1.98
214
1.401
714
510
2.80 ns
NT =2/ 95
2 gaps 100 ns
< 5.21
1.9x1010
0.80
<100mm-rad
150 mm-rad
> 0.06 m-rad
(Acceptance)
8.4 mm
+/- 1.3%
4.0 mm
+/- 1.9%
Transport Lines
<25 nm-rad
2 (4 cells)
400 KeV
0.0051
Circumference and Store Time
Require at least 3 trains (Nt  3) for reasonable cell packing.
Circumference is then, C = cT0 ...
Damping Time-Constant of Ring
C  cN t  Nb  1 b   k   295.27 m
Vertical damping time-constant, y , is set by repetition rate, f
, trains stored, Nt , and the store time per train, Ny , as...
C  hc / f RF  (708)c /(714 MHz )  297.273 m
Extracted vertical emittance ...



Nt
2.9 1012 kG T0
3
y 

 5.2 msec 
N f 4.8  (120 Hz )
B0g 2

e y  e y 0 e 2 N  e ye 1  e 2 N  0.03 mm
• Keep equilibrium y-emittance large (sets y-tolerances)
• Initial y-emittance, gey0  150 mm, sets the number of
damping times required per train, N ...
B0 < 18 kG requires g mc2 > 2.8 GeV (RF costs , z ),
therefore, at 1.98 GeV (ag = n+1/2), we need a long wiggler.
B0 
f N  N b  1 b   k 
2g 2 1  Fw 
I 2 w wiggler energy loss/turn
, Fw 

I 2a
arcs energy loss/turn
Equilibrium y-emittance and y-tolerances
 B 
1  e y0 e y  r 
1 r
2
Fw
ˆ w  21.5 kG
Lw  6C


33
m
@
B
rec yg 3 Bˆ w2 1  Fw


Vertical alignment
tolerances scale as
~r1/2, so push r1
yet with reasonably
small damping, N.
NLC MDR…
ey0/ey = 5000 ,
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10–4)
Solve  for gex = 3 mm ( = 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...
Wiggler at 1.98 GeV
r  e ye e y ...
N  ln 
2 
•
•
•
•
•
•
•
•
•
•
For increased momentum compaction (see next slides) we
choose Fw = 2.3, which sets Lw = 46.2 m and B0 = 11.2 kG.
ey0/ey = 5000, ey0/ey = 3333, ey0/ey = 1667
r = 2/3 ,
eye = 0.02 mm ,
N = 4.8
20 wiggler sections
~8 periods/section
2.2 m
27-cm period
...
51-m full wiggler physical length
2-cm
gap
...
Effects of more wiggler damping...
As Fw increases...
momentum
5/3
compaction  p ~ (1  Fw )
increases
wiggler
length
asymptotes
Fw
Lw ~
1  Fw
arc bend
field
decreases
1
B0 ~
1  Fw
wiggler’s
emittance
asymptotes
Fw
e w ~
J x 0  Fw
THE NEXT LINEAR COLLIDER DAMPING RING COMPLEX
Ernest Orlando Lawrence Berkeley National Laboratory and Stanford Linear Accelerator Center
RF Cavity
The arc TME-cell...
QD
Technology
Injection/Extraction
Kicker
QD
BEND
QF
QF
See paper TUP11
x /m
x , y /m
See paper MOP60
• mx = 108°, my = 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...
+C
bends of length LT/6,
drifts of length LT/6
–C
Wiggler switched on
extends circumference by...
Cw 
LT
Vacuum System
N s Bw2 3w
3072 B 
2
8 N  1
( 1.7 mm)  Need at
least Cw-correction for
‘wiggler-off’ and also for
unexpected errors.
τ x βx γ6
Δγε x  393  Cq re c
C
ΔC 5
L9T
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 ey-blowup)
Wiggler radiation deposition problem
Termite inspection
Lots more...
* Full skew correction is available immediately after extraction in 1st bunch compressor
E(GeV)
I (mA)
CIRCUMFERENCE -- TOTAL M)
DIPOLE BEND RADIUS (M)
NO. BEND MAGNETS
POWER PER BEAM (KW)
KW PER METER
PER DIPOLE (KW)
Spear 3
3
500
234
7.5
34
478
2
14.1
NLC
2
800
295
5.8
SLC DR
1.2
136.2
35
2
32
230
1
7.2
40
13
0.4
0.3
ALS
Spear 2
1.7
3
500
200
197
234
4
12.7
24
115
0.6
4.8
36
113
0.5
3.1
APS
1.9
400
1104
38.9
80
1,639
1.5
20.5
Bessy
HER
7
300
240
10.3
9
3000
2200
165
LER
3.1
3000
2200
30.6
32
36
0.1
1.1
192
10,557
4.8
55
192
802
0.4
4.2
PEP I
15
92
2200
165.5
192
2,490
1.1
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-05
GAS 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)
PUMP SPEED REQUIRED
Actual pump speed (arc)
PUMP SPEED/METER
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
145,440
77440
7,990
36,845
622
397
227
187
29,088
29,520
124
101,808
20,604
92
86
130,896
173,760
59
90,173
42,240
41
33,451
165,000
15