1. Constraints on Working with Two IRs
Tom Markiewicz/SLAC
LCWS 2002 Jeju, Korea
28 August 2002

2. List of Constraints Physics / Politics Geometry Choice
One IR vs. Two IRs
Geometry Choice
Luminosity vs. Energy given fixed angles
Simultaneous Operation
Beamlines
Klystrons
Damping Rings
Simultaneous Occupation
Vibration Sensitivity
Radiation Safety
Muon Flux from Collimation System
Beam Containment
Beam Dump Radiation

3. Physics / Politics One vs. Two IRs Current NLC Baseline Model
Discussion: Physics Justification, Politics, Cost
WG Leaders: Jan 5, 2001  NLC Baseline model:
Other Possibilities
One Detector
Two Push-Pull Detectors in One Large IR hall
Two Detectors in One Large IR Hall with separate beamlines to each
Current NLC Baseline Model
One IR w/ qC=20mrad and one with qC =30 mrad
Very short combined function COLLIMATION + FF allows for independent post-linac beamlines to each IR
LINAC BYPASS lines allow (in principle) for any energy up to E_max

4. Injector Systems for 1.5 TeV
NLC at Snowmass 2001
Bypass Lines
50, 175, 250 GeV
Low Energy IR
(0.09 – 1TeV)
32 km
Length for
500 GeV/beam
High Energy IR
(250 GeV to multi-TeV)
Injector Systems for 1.5 TeV

5. TESLA Post-Linac Layout

6. Tunnel Constraints Ds Enough length for magnets
Bends per unit length low enough to keep SR-caused emittance growth below desired limit given maximum forseen beam energy
IRs separated Ds enough so vibration is not a concern
Ds ~ 0.5 x DR circumference
Minimize tunnel length for cost Ds FF FF
LINAC
LINAC
BB+COLL
COLL
If e- leaves one turn early and e+ leaves at normal time, e+ arrives at z=0 when e- arrives at z=300m; each continues until they collide at 150m;
TESLA has single bunch extraction so can tune this independently.
NLC has 3 trains in ring at a time and must extract entire train in one go.
COLL
COLL FF FF

7. NLC 2002 Layout e+ e- IP Separation  150 m IP2 c = 30 mrad IP1
Skew Correction / Emittance Diagnostics
Interaction Region Transport (High Energy)
Interaction Region Transport (Low Energy)
Collimation / Final Focus
(High Energy)
Collimation / Final Focus
(Low Energy)
IP Separation  150 m
IP2
c = 30 mrad
IR Hall (Low Energy)
IR Hall (High Energy)
IP1
c = 20 mrad
Collimation / Final Focus
(Low Energy)
Collimation / Final Focus
(High Energy)
Interaction Region Transport (Low Energy)
Interaction Region Transport (High Energy)
Skew Correction / Emittance Diagnostics e-

8. Luminosity versus Energy
Over most of E range, Luminosity  E
At Highest Energies, Luminosity  E-2.5
Synchroton Radiation causes horizontal emittance growth
Final Focus Bends (part of the “Chromatic Correction System”)
“Big” Bend required to transport beam to a 2nd IR
For constant De, length of Big Bend scales as E_max
For fixed geometry, x-emittance scales as E6 so Luminosity scales as g-2.5
For constant dq/ds, De scales as q3
Lum =sqrt(E (from e_y))/sqrt(E6 (from e_x))

9. L=Calculated for lattice
Lum to Hi-E IR: NLC 2002
Ls=Scale Bends down
L0=Geometric
L=Calculated for lattice
Y. Nosochkov et al, SLAC Pub 9254
E>1.5 TeV possible by reoptimizing Final Doublet length

10. The harder the bend to get Dx, the more e-growth
e+ is the short arm %
The harder the bend to get Dx, the more e-growth
e- is the long arm
x-emittance increases ~20% for 30 mrad qC

11. Approximate LEIR Luminosity Relative to HEIR: NLC 2002
In NLC 2001 example to right, LEIR length/optics optimized for 500 GeV cms with an 80 mrad bend
0.92

12. Engineering Constraints
Magnet & vacuum apertures set by lowest beam energy
Since ex and ey scale as 1/E, you can only go down in E with b constant until beam spot fills the beam pipe, then you must scale the beta functions by 1/E. This keeps divergence constant, but Lum falls faster than before
Hard to meet Power Supply sensitivity requirements (~10-5) without limiting range
X4 in Energy range has been rule of thumb

13. Simultaneous Operation Layout Issues
2002 design HAS separate collimation & FF for each IR
Other hardware
Bypass line for E<E_linac
To operate at DIFFERENT energies simultaneously would require
Pulsed extraction to bypass line
Different energy beams in linac could affect performance
Polarization must be longitudinal at BOTH IRs
Need to develop pulsed magnet to rotate polarization vector
Not much thought has been given to any of this

14. Simultaneous Operation 180 Hz Operation
Rate1*Energy1 + Rate2*Energy2 limited by site power
~ Gev 120 hz
Rate1+Rate2 limited by
Maximum rate klystrons can handle
Max CW power before meltdown or cracked windows
180 Hz has been held mentioned as an option
Share as desired: 90/90, 120/60 etc.
Minimum acceptable time e-,e+ stay in damping rings to get to design emittance
Two 200m 90 hz DRs in 1 vault OK
$$ but easier rings than 300m DR
MPS looks at ORBIT every 1/120sec and requires that all magnet & movers move slow enough that the orbit cannot change much in the interval. Current system would probably work at 60 Hz as well. Not fundamental, but much cheaper than building a system to look at hardware.

15. Vibration Constraints NLC Coll/FF Lattice Sensitivity
Layout provides enough transverse space so that the IR halls don’t run into the tunnels and enough longitudinal space to both hold the beamlines and to isolate the sensitive magnets in one hall/beamline from the other
Longitudinal separation chosen as a multiple of (DR-circumference =300m)/2 so beams can collide at both IPs SIMULTANEOUSLY
Extra tunnel length is always possible if you pay for it

16. How do we know any given IR separation is good enough
How do we know any given IR separation is good enough? We don’t know really yet!
If you believe in your feedback or other vibration suppression schemes, don’t worry at all!
If your tunnels are deep and in solid strata
Cultural surface noise does not penetrate easily
~70% energy carried by “Rayleigh waves that like to travel on surface and almost do not penetrate to ~100m depth.
Correlation will be good
“Slow” motion will be smaller
Amplitude of Rayleigh surface waves from “cultural noises” decrease exponentially with depth
Best to measure the relevant Xfer Functions in representative sites that bring “cultural noise” from one IR to the other?

17. Planned Vibration Transmission Measurements in Santa Monica Metro Tunnels & at SLAC Work in Progress
Thump Ground, Measure Linac tunnel response
SLD pit
Babar-SLD measurements would be useful

18. Radiation Safety Aspect of Collimator System Muons
Can you occupy IR2 when IR1 is running?
Can you occupy IR1 when IR2 is running?
This is the more difficult case
Shorter COLL/FF makes this more difficult than before
Betatron
Betatron Cleanup
Energy

19. YES
But you need the Magnetized 18m Steel Wall often mention in connection with limiting detector backgrounds
ABE
AB3,4,5

20. Analysis Use current lattice to IR1 Tunnel to IR2 holds just FF2
Not important; need to iterate; worse case
Run both 250 and 500 GeV beams with full charge (1.7E14e-/sec) and assume 0.1% Halo
Muon Source Terms on Collimators
1st stage Betatron: 0.1% e- make muons
2nd stage Betatron: 0.01% e- make muons
E-slit: % e- make muons
SLAC Rad Safety Rules:
0.5 mrem/hr for normal operation
25 rem/hr (3 rem max dose) for max credible accident
Run MUCARLO and find maximum dose in any 80cmx80cm area

21. Muon Dose Rates in IR1 and IR2 when other IR has beam
1.0 TeV CM
No Spoiler
18m Mag z=321m
Source
Halo
IR1 (mr/hr)
IR2 (mr/hr)
10-3
2.54
0.016
0.015
0.070
2.45
0.041
0.13
0.71
10-4
0.12
0.005
0.011
0.002
0.34
0.082
0.013
0.007
Total for 2 beams
10.9
0.29
0.61
0.15
Total for 2 GeV
4.5
0.13
0.12
0.01
If do nothing and halo=10-3, dose is 10-20x SLAC 0.5 mrem limit
18m mag spoiler buys you x20 to 40; IR2 looks OK in any event
Max credible accident only dumps 103 more beam, limit is 50E3 higher

22. Beam Containment stoppers
Forget muons, how would you like to be staring at 10 MW of electrons that are supposed to bend over to IR2?
Each bend has protection collimator and there are two in-line stoppers
Each protection collimator and stopper is seen by an ion chamber that trips beam if > few kW
Each protection collimator and stopper has a burn through monitor which can crash machine
Additionally:
Toroid comparators in beamline and at dump
Interlocked Bend power supplies that trip if current out of range
stoppers

23. Dump Neutrons will NOT be seen by other IR or beamline
Ground water activation limits (2E-5 microCi/cc ) require 5.5m concrete around dump

24. Conclusions
Design is flexible and can accommodate whatever constraints the physics program puts on it.
There appear to be no show stoppers if two IRs are indeed desired