1. FCC-he Parameters Daniel Schulte, O. Brüning, M. Klein, F. Zimmermann
Rome, April 2016

2. Basis for FCC-he Design
Infrastructure does not aim for FCC-ee and FCC-hh being in the tunnel at the same time
FCC-he will be based on using the LHeC recirculating energy recovery electron linacs with the FCC-hh collider ring
FCC-he will operate at the same time as the two main FCC experiments and potentially more experiments
It must not significantly compromise the main experiments
D. Schulte
FCC-he parameters, Rome, April 2016

3. FCC-he parameters, Rome, April 2016
FCC-hh Parameters
House two main and two additional experiments
For baseline will run all experiments
For ultimate parameters may run main experiments only
Use dipole magnets of up to 16T
Assuming 80% dipole filling factor in arcs we need about 82km of arcs
Current baseline of 3.75 corresponds to C=99.971km
Baseline
Ultimate
CMS energy [TeV]
100
Luminosity [1034cm-2s-1] 5 20
Bunch distance [ns]
25 (5)
Background events/bx
170 (34)
680 (136)
Bunch charge [1011]
1 (0.2)
Norm. emitt. [mm]
2.2(0.44)
RMS bunch length [cm] 8
IP beta-function [m]
1.1
0.3
IP beam size [mm]
6.8 (3)
3.5 (1.6)
Max ξ for 2 IPs
0.01
(0.02)
0.03
D. Schulte
FCC-he parameters, Rome, April 2016

4. FCC-he parameters, Rome, April 2016
Luminosity Evolution
Example of ultimate parameters shown
1.5 years shutdown, 1 year of MDs and stops, 2.5 years of luminosity operation at 70% efficiency
Can reach >8fb-1 with ultimate for ξ=0.03
5000fb-1 per 5 year run
Beam is burned quickly
Another reason to have enough charge stored
Ultimate example, 25ns, no luminosity levelling
8fb-1/day
Turn-around time
D. Schulte
FCC-he parameters, Rome, April 2016

5. FCC-he parameters, Rome, April 2016
Baseline ERL Layout
Circumference will have to be adapted to the FCC circumference
C=CFCC/n
Reasonable choice could be n=11
About 2% larger circumference than LHeC
D. Schulte
FCC-he parameters, Rome, April 2016

6. Parameter Choice for FCC-he
For matched electron and proton beam sizes:
Electron beam current
Fill pattern matching
Proton beam brilliance
Proton ring design
Hourglass effect
Beam-beam effect
D. Schulte
FCC-he parameters, Rome, April 2016

7. Proton Beamsize Evolution
Assumed 15cm beta-function for proton beam
Agressive number because of high energy
May be a bit tight for the aperture
hh beta-function is 1.1m-0.3m
But can gain some factor
to be studied in detail
The beam emittance varies strongly during run (baseline parameters)
Try to follow with electron beam
Luminosity is almost constant
σ=2.5μm
σ=1.7μm
D. Schulte
FCC-he parameters, Rome, April 2016

8. FCC-he parameters, Rome, April 2016
Electron Current
Can likely tolerate 4x109 electrons per bunch (LHeC review 2014)
Corresponds to maximum of 26mA
About 100MW, only for injectors and synchrotron radiation compensation
Use 15mA, 2.3x109
FCC-hh ring beam filling factor is only 80%
Will lose 20% luminosity
Could avoid accelerating these bunches (RF fluctuates a tiny bit or use beam with 11-fold symmetry in FCC-hh)
Need to have ion clearing gaps
May lose 1/3 of the bunches
Could add the charge in other buckets
Need to review single bunch limitation
LHC circumference
D. Schulte
FCC-he parameters, Rome, April 2016

9. Note: Electron Beam Emittance
Initial emittances could be of the order of a few μm (e.g. typical for TTF)
Synchrotron radiation in arcs:
Δεx≈7.4μm and Δεy≈0.8μm
(agrees with theory)
Other sources to be added
Emittance goals:
20μm appears reasonable
10μm appears aggressive
D. Pellegrini
A. Latina
Questions to address:
Could we consider flat beams to collide with the protons?
Is there an advantage by making the beam round at collision using a small horizontal and a large vertical beta-function?
Could we couple the planes to share the growth?
D. Schulte
FCC-he parameters, Rome, April 2016

10. Scaling LHeC to FCC-eh Parameters
protons
electrons
beam energy [GeV] 60
Luminosity [1033cm-2s-1]
1 6.8/8.2
normalized emittance gex,y [mm]
50->20/10
IP beta function b*x,y [mm]
120 -> 36/72
rms IP beam size s*x,y [mm]
7 2.5
7 2.5
beam current [mA]
bunch spacing [ns]
25 (50) 25
bunch population [1010]
17 10
0.1 (0.2) 0.23
Effective crossing angle
0.0
Beam-beam not included, no gap for ions assumed, Hcoll=0.8
D. Schulte
FCC-he parameters, Rome, April 2016

11. Including Beam-beam Effect
protons
electrons
beam energy [GeV]
50000 60
Luminosity [1033cm-2s-1]
6.8/ /11.7
normalized emittance gex,y [mm]
2.2
20/10
IP beta function b*x,y [mm]
150
36/72
rms IP beam size s*x,y [mm]
2.5
beam current [mA]
500 15
bunch spacing [ns] 25
bunch population [1010] 10
0.23
Effective crossing angle
0.0
Beam-beam not included, no gap for ions assumed, Hcoll=0.8
D. Schulte
FCC-he parameters, Rome, April 2016

12. FCC-he parameters, Rome, April 2016
End of the Run
protons
electrons
beam energy [GeV]
50000 60
Luminosity [1033cm-2s-1]
8.4/11.7 -> 4.7/8.3
normalized emittance gex,y [mm]
2.2 -> 1.1
20/10
IP beta function b*x,y [mm]
150
36/72-> 18/36
rms IP beam size s*x,y [mm]
2.5 -> 1.7
2.5 ->1.7
beam current [mA]
500 -> 250 15
bunch spacing [ns] 25
bunch population [1010]
10->5
0.23
Effective crossing angle
0.0
D. Schulte
FCC-he parameters, Rome, April 2016

13. FCC-he parameters, Rome, April 2016
Effective Beam Size
Do the electron and proton transverse beam sizes have to be matched?
In LHeC the sizes are not matched along the collision
Strong pinching of electrons
Not obvious why beam sizes do need to match
Scan for optimum electron beam size and waist position
Electron beam shrinks during collision
Increases beam-beam tune shift for protons
D. Schulte
FCC-he parameters, Rome, April 2016

14. FCC-he parameters, Rome, April 2016
Scan Results
E. Nissen
Scans performed with GUINEA-PIG
Strong-strong simulation
Waist [μm]
Start of a run
End of a run
Waist [μm]
β [mm]
Identified optimum beta-function and waist shift for perfect head-on collisions
β [mm]
D. Schulte
FCC-he parameters, Rome, April 2016

15. Optimised Beam-beam Effect
protons
electrons
beam energy [GeV]
50000 60
Luminosity [1033cm-2s-1]
(8.4/11.7) 10.8/13.7
normalized emittance gex,y [mm]
2.2 -> 1.1
20/10
IP beta function b*x,y [mm]
150
(36/72) 44/42
rms IP beam size s*x,y [mm]
2.5
(2.5/2.5) 2.7/1.9
Waist shift [mm]
(0/0) 65/65
beam current [mA]
500-> 250 15
bunch spacing [ns] 25
bunch population [1010]
10 -> 5
0.23
Smaller electron emittance is helpfull
D. Schulte
FCC-he parameters, Rome, April 2016

16. Including Beam-beam Effect
protons
electrons
beam energy [GeV]
50000 60
Luminosity [1033cm-2s-1]
10.8/13.7->7.3/10.7
normalized emittance gex,y [mm]
2.2 -> 1.1
20/10
IP beta function b*x,y [mm]
150
44/42 -> 48/52
rms IP beam size s*x,y [mm]
2.5
2.7/1.9 -> 2.9/2.1
Waist shift [mm]
65/65 -> 60/70
beam current [mA]
500-> 250 15
bunch spacing [ns] 25
bunch population [1010]
10 -> 5
0.23
O( fb-1) per 5-year period
Assuming no Ion gaps
D. Schulte
FCC-he parameters, Rome, April 2016

17. FCC-he parameters, Rome, April 2016
Baseline Summary
An integrated luminosity of O( fb-1) per 5-year period of operation appears potentially possible
What is the electron bunch charge limit?
Could lose 1/3 of the luminosity due to ion clearing
Electron current depends on Hcoll and clearing gaps
Is the proton beta-function of 30cm possible without making the proton-electron experiment the tightest spot for the proton beam?
Can the electron beta-function be achieved?
Is the impact of the beam-beam effects on both beams acceptable? …
D. Schulte
FCC-he parameters, Rome, April 2016

18. FCC-he parameters, Rome, April 2016
FCC-hh Ultimate Run
σ=2.5μm
Same beta-function in main and proton-electron experiments
Could attempt to push proton beta-function in eh
Very difficult to reach <1μm with electron beam
σ=0.7μm
For 5ns spacing sizes can go down to about 0.35μm
D. Schulte
FCC-he parameters, Rome, April 2016

19. Ultimate Parameters, 25ns
protons
electrons
beam energy [GeV]
50000 60
Luminosity [1033cm-2s-1]
14.1 (-> 22.4) -> 11.1
normalized emittance gex,y [mm]
2.2 -> 0.15 10
IP beta function b*x,y [mm]
150
45 -> 45
rms IP beam size s*x,y [mm]
2.5 -> 0.7
1.9 -> 1.9
beam current [mA]
500 -> 100 15
bunch spacing [ns] 25
bunch population [1010]
10 -> 2
0.23
Effective crossing angle
0.0
O(>320fb-1) per 5-year period
Assuming no Ion gaps
D. Schulte
FCC-he parameters, Rome, April 2016

20. Ultimate Parameters, 5ns
protons
electrons
beam energy [GeV]
50000 60
Luminosity [1033cm-2s-1]
6.1 -> 2.6
normalized emittance gex,y [mm]
0.44->0.044 10
IP beta function b*x,y [mm]
150
40 -> 40
rms IP beam size s*x,y [mm]
1.1-> 0.35
1.6 -> 1.6
beam current [mA]
500-> 150 15
bunch spacing [ns] 5 25
bunch population [1010]
2->0.6
0.23
Effective crossing angle
0.0
O(>110fb-1) per 5-year period
Assuming no Ion gaps
D. Schulte
FCC-he parameters, Rome, April 2016

21. FCC-he parameters, Rome, April 2016
Conclusion
Target parameter sets for FCC-he presented
Need to take into account emittance damping during luminosity run
The operation mode of FCC might change …
Uncertainties from gaps in both beams, …
Parameters appear reasonable for FCC-hh baseline
But need to verify beta-functions for protons and electrons
More difficult for the ultimate parameters
25ns are probably OK (O(320fb-1/5years))
5ns spacing most difficult (O(110fb-1/5years))
Explore limits for the electron emittance (flat beams?) and proton beta-function
More work is needed to verify parameter sets
Interaction region layout
Ion studies
Electron beam gaps and RF …
D. Schulte
FCC-he parameters, Rome, April 2016

22. FCC-he parameters, Rome, April 2016
Reserve
D. Schulte
FCC-he parameters, Rome, April 2016

23. Machine Protection and Friends
8GJ kinetic energy per beam
Airbus A380 at 720km/h
2000kg TNT per beam
O(20) times LHC
Machine protection
This machine protection risk must not be increased by FCC-he
Do not create a new bottleneck
High risk at injection and extraction
Instrumentation to detect failures
Interlock system
Passive protection and collimation system
Machine protection strategy
O(160GJ) in magnets
O(20) times LHC
Serious protection issue
D. Schulte
FCC-he parameters, Rome, April 2016

24. FCC-he parameters, Rome, April 2016
Collimation System
S. Redaelli
Efficiency is important
Robustness in case of fast beam loss (in a few minutes)
Materials, …
Main impedance at collision energy
=> Optics, materials, …
D. Schulte
FCC-he parameters, Rome, April 2016

25. FCC-he parameters, Rome, April 2016
Power Consumption
Luminosity is limited by allowed power consumption (100MW)
Synchrotron radiation loss compensation RF
20 MW -> 40MW
Can be calculated reliably
Include cryogenics etc for this part of the linacs
Cryo power of linacs
21 MW -> ?
Depends on cavity (Q0) and gradient
RF power to control linacs
24 MW -> ?
QL due to microphonics, phase stability, …
Injector and other consumers are less important
Depends on injection energy, hence wakefields etc.
D. Schulte
FCC-he parameters, Rome, April 2016

26. FCC-he parameters, Rome, April 2016
Interaction Region
Will not discuss detail here Integration of machine and detector is challenging
Proton optics design focus has been on b=10cm
Chromatic correction studied
Achieved b=8cm with L*=10m
Achieved b=10cm with L*=18m
Had a design for CDR
Significant design work is required for new design
Can relax electron beta-function if we aim for smaller emittance
E. Cruz-Alaniz, M. Korostelev, D. Newton (Cockcroft),
R. Tomás
D. Schulte
FCC-he parameters, Rome, April 2016

27. Beam Pulse and Fast Beam-ion Instability
Fast beam-ion instability may require a long gap
All ions are trapped in continuous beam (fc<flimit)
Beam will become unstable before neutralisation is reached
Gaps of different turns need to overlap
Fix LHeC circumference to be 1/n of LHC
Each LHC bunch always or never collides with electron bunches
Would increase bunch charge by 50% to 3x109
Needs to be reviewed
CDR
Stronger trapping with high luminosity parameters
But better clearing in gap
LHC circumference
D. Schulte
FCC-he parameters, Rome, April 2016

28. FCC-he parameters, Rome, April 2016
FBII Rise Length
Rise length in linacs for 10-11hPa:
CH4+: 14km -> 2.5km
H2+: 25km -> 4km
Total distance in linacs 12km
Measured
1x10-11 (HERA, B. Holzer), 0.05x10-11 hPa (LHC, V. Baglin)
In arcs for p=10-9hPa
H2+: 70km -> 12km
N2+,CO+:50km -> 8km
CO2+: 60km -> 10km
Total distance traveled 33km
Probably OK
But simulations will be required
Tool is under development
Use a few shorter gaps?
D. Schulte
FCC-he parameters, Rome, April 2016

29. FCC-he parameters, Rome, April 2016
Impact on Proton Beam
Strong variation of tune shift along the bunch
->time dependent quadrupole
Also position changes with time
Calculate tune shift for each slice of proton beam at the location of the collision with the electron beam
Effective tune shift in worst slice
is about
strong variation along the bunch
-> Smaller than in LHC collision points
-> opposite sign
-> small linear region
D. Schulte
FCC-he parameters, Rome, April 2016

30. FCC-he parameters, Rome, April 2016
Beam-beam Effect
The proton beam emittance growth due to beam-beam effects is of concern
Change of normalised emittance at the end of the ultimate run is O(-1a/s)
Aim for growth of <O(0.1a/s)
Growth rate
Δϵxn (x10-10)(m)
Turn Number
Predicted rate x10-14
Mean calculated rate 4.046x10-14
Δϵxn/Δt=7.095x10-9(σjitter/σx)²m/s
Doubling time 1 day σjitter/σx=5.99%
D. Schulte
FCC-he parameters, Rome, April 2016

31. High-luminosity Insertions
The allocated length is consistent with the required performance
Achieve beta-function goal
Provide less beam stay clear than HL-LHC
Pushed beta-function
More shielding in magnet
Collimation system
Hopeful to be able to handle radiation into the final triplet
Enough space for the detector
Do currently not expect large variations of the required length
D. Schulte
FCC-he parameters, Rome, April 2016

32. FCC-he parameters, Rome, April 2016
Betatron Collimation
Need to adapt to smaller beam stay clear in experiment triplets
Secondaries from showers in primary collimators will be much harder to catch
smaller scattering angles
more energy in showers
Optics scaling from HL-LHC:
rC =(50TeV/7TeV)1/2 x 0.4m/0.3m x (59mm/49mm)2
=> rC ≈ 5.2 ≈ 2 r
=> LC=2.8km
Normal scaling (r)
IP beta-function (increases beta-function in triplets)
Aperture reduction due to shielding
Have a scaled lattice of 2.7km
seems to give adequate inefficiencies
gaps are consistent with experimental insertion beam stay clear
Now need to verify the performance
In particular for secondaries
D. Schulte
FCC-he parameters, Rome, April 2016

33. First Collimation Studies
First betatron collimation system scaled from LHC
Gaps as in HL-LHC
But 2.7km long
Starting point for exploration
Fix issues from LHC design
R. Tomas
LHC
M. Fiascari,
S. Redaelli
D. Schulte
FCC-he parameters, Rome, April 2016

34. FCC-he parameters, Rome, April 2016
5 ns Spacing
protons
electrons
beam energy [GeV]
50000 60
Luminosity [1033cm-2s-1]
2.3->0.97 (1.06)
normalized emittance gex,y [mm]
0.44->0.044 10
IP beta function b*x,y [m]
0.30
0.036-> (0.009)
rms IP beam size s*x,y [mm]
1.56-> 0.5
beam current [mA]
500-> 150
6.5
bunch spacing [ns] 5 25
bunch population [1010]
2->0.6
0.125/1.875
Effective crossing angle
0.0
D. Schulte
FCC-he parameters, Rome, April 2016

35. FCC-he parameters, Rome, April 2016
LHeC Parameters
protons
electrons
beam energy [GeV]
7000 60
Luminosity [1033cm-2s-1] 1
normalized emittance gex,y [mm]
3.75 50
IP beta function b*x,y [m]
0.10
0.12
rms IP beam size s*x,y [mm] 7
beam current [mA]
(860) 430
6.5
bunch spacing [ns]
(25) 50
bunch population
1.7x1011
(1x109) 2x109
Effective crossing angle
0.0
D. Schulte
FCC-he parameters, Rome, April 2016

36. Parameter Choice for FCC-he
For matched electron and proton beam sizes:
Note: CDR electron current is 6.5mA
Corresponds to x109 particles per bunch at 25ns spacing (filling pattern)
Could be doubled adding 23MW of power consumption
Further increase remains to be studied
LHC circumference
D. Schulte
FCC-he parameters, Rome, April 2016