FCC-hh Luminosity Evolution and Ultimate
Parameters
Daniel Schulte, Michael Benedikt, Frank Zimmermann
CERN December 2014
Motivation
•
Baseline parameters are based on reasonable assumptions
• Many technology and beam studies are required to establish validity
of current baseline, e.g. magnets, beam power issues, …
• Simplifications made for baseline parameters
•
Need to explore how far the beam parameters can be pushed
• To achieve higher performance
• To improve cost and relax specifications
•
For both a simplified model of the luminosity evolution and the average
luminosity is required, including
• Beam-beam limits, beam burn-off, beam lifetime (e.g. beam-gas
scattering), emittance damping, synchrotron radiation heating, intrabeam scattering, …
• Xavier is developing this tool
•
Need also to guide the parameter exploration
FCC-hh Ultimate Parameters
Daniel Schulte
CERN, December 2014
2
Parameter Sets
•
To focus the parameter exploration studies we introduce an additional
“ultimate” parameter set
• Goal is that one can reasonably hope to achieve this performance
after some operational experience with FCC and by improving the
hardware, e.g. introducing crab cavities
• Similar concept has been followed for LHC
•
This will lead to two parameter sets: baseline and ultimate.
•
Further parameter sets might come
• E.g. for staging scenarios
• or for further exploration of the parameter space
•
But the stable centre will be the baseline set (=promise) and the ultimate
parameter set (=reasonable hope)
• Those will be the ones shown in a general FCC presentation
FCC-hh Ultimate Parameters
Daniel Schulte
CERN, December 2014
3
FCC-hh Baseline
A baseline parameter list exists: http://indico.cern.ch/event/282344/material/3/
A somewhat conservative first approach, will now make a conceptual design and
optimise the parameters and look at alternative parameters
LHC
HL-LHC
FCC-hh
Cms energy [TeV]
14
14
100
Luminosity/IP [1034cm-2s-1]
1
5
5
Bunch distance [ns]
25
25
25
Background events/bx
27
135
170
Bunch length [cm]
7.5
7.5
8
•
Two main experiments sharing the beam-beam tuneshift
• Two reserve experimental areas not contributing to tuneshift
•
80% of circumference filled with bunches
FCC-hh Ultimate Parameters
Daniel Schulte
CERN, December 2014
4
Baseline Beam Parameters
LHC
HL-LHC
HE-LHC
FCC-hh
Bunch charge [1011]
1.15
2.2
1
1 (0.2)
Norm. emitt. [mm]
3.75
2.5
1.38
2.2(0.44)
IP beta-function [m]
0.55
0.15
0.35
1.1
IP beam size [mm]
16.7
7.1
5.2
6.8 (3)
RMS bunch length [cm]
7.55
7.55
7.55
8
•
•
Values in brackets for 5ns spacing
Same values for 16T and 20T design
•
•
Beam-beam tuneshift for two IP 0.01
Beta-function at IP scaled with sqrt(E) from one LHC insertion line design
with 0.4m (some safety margin)
Time to fully burn beam at full luminosity TB=19.2h (=nN/(LIPNIP s))
•
FCC-hh Ultimate Parameters
Daniel Schulte
CERN, December 2014
5
1
0.95
0.9
0.85
0.8
0.75
0.7
0.65
0.6
0.55
0.5
2.2
e [mm]
2
1.8
1.6
1.4
1.2
0
2
4
6
8 10 12 14
t [h]
Keep beam-beam tune shift constant
Control emittance as e~L
Luminosity decays exponentially
Optimum run time 12.1h for 5h turn-around
Relation TB/Tturn-around=a/(1-a+a ln(a))
a=<L>/L0
FCC-hh Ultimate Parameters
Daniel Schulte
CERN, December 2014
L, <L> [1035cm-2s-1]
N [1011]
Simplified Example Luminosity Evolution
1
0.50
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
2
4
6
8 10 12 14
t [h]
L
<L>
0
2
4
6
8 10 12 14
t [h]
6
Ultimate Parameter Choice Rational
Luminosity is given by
Beam current increase would also increase the radiation heat load
Turn-around time requires an improved injector
• currently value is 5h
• Would burn the beam in almost TB=4.8h at full luminosity
• Need to reduce it slightly => 4h
A smaller design for beta-function exists, but detailed studies required
based on lattice studies assume 1.1m => 0.3m
The beam-beam tuneshift is somewhat conservative (total 0.01)
Assume 0.01 => 0.03
 Use beta-function and beam-beam tuneshift
FCC-hh Ultimate Parameters
Daniel Schulte
CERN, December 2014
7
Ultimate Beam Parameters
•
•
LHC
HL-LHC
Base
Ultimate
Luminosity [1034cm-2s-1]
1
5
5
20
Bunch distance [ns]
25
25
25
25 (5)
Background events/bx
27
135
170
680 (136)
Bunch charge [1011]
1.15
2.2
1 (0.2)
1 (0.2)
Norm. emitt. [mm]
3.75
2.5
2.2(0.44)
2.2(0.44)
IP beta-function [m]
0.55
0.15
1.1
0.3
IP beam size [mm]
16.7
7.1
6.8 (3)
3.5 (1.6)
RMS bunch length [cm]
7.55
7.55
8
8
Turn-around time [h]
5
4
Crossing angle [s]
12
Crab. Cav.
Values in brackets for 5ns spacing, would be good for background
Maximum beam-beam tuneshift for ultimate for two IPs is 0.03
FCC-hh Ultimate Parameters
Daniel Schulte
CERN, December 2014
8
t [h]
FCC-hh Ultimate Parameters
Daniel Schulte
CERN, December 2014
2.5
2
e [mm]
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
3 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
2.8
t [h]
2.6
2.4
2.2
2
1.8
1.6
1.4
1.2
1
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
1.5
1
0.5
L, <L> [1035cm-2s-1]
x [0.01]
N [1011]
Simplified Example Luminosity Evolution
0
2.2 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
2
t [h]
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
L
0.2
<L>
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
t [h]
9
Note: Circumference, Magnets, Energy
For the civil engineering studies we maintain the 93km and 100km tunnels
(3.5 and 3.75 times the LHC circumference)
We will maintain a baseline parameter list for 100km and regard 93km as
an alternative until these studies come to a conclusion
Rarc=(C-16.8km-16*(1-a)*Ldisp)/(2p)
Ldisp=0.4km
a=0.75
Reffective=0.805 Rarc
This allows to reach Ecms=100TeV with 16T magnets
93km would lead to Ecms=91.5TeV
FCC-hh Ultimate Parameters
Daniel Schulte
CERN, December 2014
10
Note: Availability
Assumptions:
• Three year operating cycles
• Two years of operation
• One year of shut-down
• i.e. 720 in three years
• One quarter used for commissioning, MDs, …
• 540 days of scheduled luminosity operation
• 70% of actual luminosity operation
• 378 days of effective operation
• i.e. 126 per year
• i.e. 1.08864x107 s/year
• L0=5x1034cm-2s-1 <L>/L0=0.46 leads to 250fb-1 per year
FCC-hh Ultimate Parameters
Daniel Schulte
CERN, December 2014
11
Conclusion
Luminosity evolution model is important
• A number of simplification made sofar
• E.g. neglected beam heating by IBS and synchrotron radiation
• E.g. neglected beam loss through other processes than luminosity
• …
 Include relevant effects and check their importance/define budgets
Parameter space exploration is important
• To make sure we do not inhibit later performance improvements
• To identify potential to relax specifications
• To understand margins
We are introducing an ultimate parameter set to focus parameter space
exploration
Good test case for luminosity evolution studies
FCC-hh Ultimate Parameters
Daniel Schulte
CERN, December 2014
12