1. NLC 2001 Beam Delivery Layout
Tom Markiewicz
Fermilab Meeting of Detector WG Leaders
05 January 2001

2. Summer 2000 Configuration

3. Summer 2000 Configuration Linacs point at each other
One <= 1 TeV Collimation section common to two IRs
Energy collimation with tune-up dumps
“Relaxed” Betatron collimation with consumable spoilers
+10 and –10 mrad Big Bends to get to each of two symmetric IRs
20 mrad crossing angle at each IP
Working assumption is “Large” and “Small” detector
Non-simultaneous delivery of beam to either detector
280m IP Stretch provides separation and vibration isolation of IR halls
New FF with L*=4.3m and magnet apertures designed for 1 TeV
Most magnets could be re-used up to 1.5 TeV
Length of FF tunnels compatible with 5 TeV
Either:
same FF lattice to each IR or
leave tunnel to IR2 empty (Lehman cost estimate)

4. Conceptual Problems with Symmetric Two IR Layout
Experimenters seem to want full luminosity at 90 GeV – 1 TeV, be able to “quickly” change energy and continually question the maximum energy reach of NLC X-band technology
“Big Bend” (designed for 1.5 TeV) limits upper range of energy for HE IR
Emittance growth due to SR ~ 5% by limiting strength of bends
Magnet apertures set by lowest energy
Magnet design set by aperture and highest energy
Ambiguous physics justification for two detectors given symmetric layout and fact that only one detector gets data at a time
As FF gets shorter, two FF tunnels merge into one
lateral displacement of IRs shrinks (44m in ZDR, 16m in CD4)
No design provision for gg, which needs larger crossing angle

5. Base Element of 2001 Layout
Emin, Enom, Emax = 250 GeV(?), 500 GeV, 1000 GeV
No Big Bend
New FF w/ L* = 4.3 m
Collimation lattice with dog-leg energy collimation
20 mrad crossing angle
One IR Hall with One Large Detector

6. The 2nd IR Hall in the 2001 Layout
Assume a 2nd IR is part of the baseline package
Questions: In order of importance
Emin, Enom, and Emax for “high luminosity” running
Sequential or simultaneous beam delivery
Crossing angle, hall size, and facilities infrastructure
Detector staging & spacing of halls for vibration isolation
Optimal tunnel layout for cost, flexibility, performance?
IR2
??m
IR1
Linac and bypass
One collimation system or two?

7. First “Working” Answers to IR2 Questions
Transverse and longitudinal spacing of halls for vibration isolation
Dx=100m Dz = 0m
Emin, Enom, and Emax for “high luminosity” beam delivery
90, 250, 500 GeV, respectively
Need to know Emax to before bend tunnels are dug
Sequential or simultaneous beam delivery
Sequential BUT supporting simultaneous operation if issues resolved
Polarized beam to each IR
2nd INDEPENDENT collimation system allows possibility of simultaneous operation at different energies
Crossing angle, hall size, and facilities infrastructure
30 mrad (20-40 possible; keep E(L*Bsq)5/2 < current value)
10mrad gg stay-free requires bigger angle
2nd detector? Precision?

8. Site Layout Dx=100m Dz = 0m

9. BDIR Detail: Dx=100m Dz = 0m
FF2
27mrad
Coll2+Bends
52mrad
Coll1
FF1

10. An Alternative Layout
Length of tunnels to IR#2 is just that required for bends that maintain good emittance beam at 500 GeV c.o.m.
110m of tunnel per 10mrad of bend for 5% dilution if Emax=500 GeV
Can we reduce IR separation and either reduce cost or increase program flexibility?
Reduce Dx to ~25m
Vibration, simultaneous occupation of halls, etc??
Use ONE collimation system for BOTH IRs
Need some “empty” IP-Stretch tunnel to make geometry work
Second collimation system in same tunnel also allows possibility of simultaneous operation at different energies
25 mrad big bend and NO reverse bend
Are there advantages to ONE big IR Hall?

11. Site Layout Dx=25m Dz = 0m One Collimation Tunnel per Side
FF2
0 mrad
Coll
Bend
25mrad
Stretch
FF1

12. Reversed Linac Angle, IR Separation = 25m and Separate Collimation Lattices and IR lead to Big Bend + Reverse Bend Angles ~ 21.8mrad

13. Another Possibility: Dx=25m Dz = 440m One Collimation Tunnel per Side
FF2
0 mrad
Coll
Bend
25mrad
Stretch
FF1

14. Site layout with Dx=25m Dz = 440m

15. VERY, VERY Rough Cost Estimate Length Scaling Only, NOT Parts counting

16. Summary It’s really a “User’s choice”: You get what you pay for
Model 0: One IR
Cheapest option: 251M$
Model 1: Dx=100m Dz = 0m
Most flexible?
Most bending, perhaps lowest maximum energy reach
Most expensive: 499M$
Model 2: Dx=25m Dz = 0m
Allows for flexibility in detector/IR staging. Is this interesting?
407M$ plus 60M$ for second collimation system (simultaneous running)
Model 3: Dx=25m Dz = 440m
Seems best suited to a low start up cost
Begin with one collimation system & sequential data taking
Better vibration isolation; same cost as Model 2
Is there another variation we are missing?

17. Conceptual Problems with Symmetric Two IR Layout
Experimenters seem to want full luminosity at 90 GeV – 1 TeV, be able to “quickly” change energy and continually question the maximum energy reach of NLC X-band technology
“Big Bend” (designed for 1.5 TeV) limits upper range of energy for HE IR
Emittance growth due to SR ~ 5% by limiting strength of bends
330m for 10mrad of bend at 750 GeV/beam
Length of Big Bend scales as E_max for constant De
For fixed geometry, emittance scales as E6; Luminosity as g-2.5
Magnet apertures set by lowest energy
Given aperture, once max beam divergence is reached, since emittance scales as 1/E, need to scale beta function by 1/E
Hard to meet PS sensitivity requirements (~10-5) without limiting range
Ambiguous physics justification for two detectors given symmetric layout and fact that only one detector gets data at a time
As FF gets shorter, two FF tunnels merge into one
lateral displacement of IRs shrinks (44m in ZDR, 16m in CD4)
No design provision for gg, which needs larger crossing angle

18. Luminosity Scaling with Energy
Assuming same injector, the luminosity scales as:
Luminosity in high energy FF scales linearly with energy between and 1 TeV
Low energy FF scales similarly but at lower energy!

19. Reversed Linac Angle Leads to Larger Bend and Reverse Bend to IR2 When IR Separation = 100m

20. Reverse Linac Angle and Common Use of Collimation Lattice when IR Separation is 25m leads to Bend and Reverse Bend Tunnel Angles Too Large to be Supported by Tunnel Length

21. Separate collimation systems & standard linac angle

22. Another Possibility: Dx=25m Dz = 300m

23. How About: Dx=25m Dz = 500m