Transcript Pergine-Presentation

LHC beam performance and
luminosity upgrade scenarios
performance limitations, possible scenarios
and milestones for the LHC upgrade
triplet magnets
http://care-hhh.web.cern.ch/care-hhh/
See also slides on Measurements, ideas, curiosities
F. Ruggiero
CERN
Univ. “La Sapienza”, Rome, 20–24 March 2006
Outline
•
•
•
•
•
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Time scale and potential of an LHC upgrade
LHC commissioning strategy and beam parameters
Machine performance limitations
Luminosity optimization and upgrade paths
Luminosity lifetime: peak vs integrated luminosity
LHC luminosity upgrade scenarios:
•
•
•
•
•
ultimate performance without hardware changes
upgrade of the Interaction Regions
new bunch-shortening RF system and cryogenic loads
collimation, beam-beam compensation and crab cavities
milestones and baseline design
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Time scale of an LHC upgrade
radiation
damage limit
~700 fb-1
time to halve error
integrated L
L at end of year
ultimate
luminosity
design
luminosity
courtesy J. Strait
•
•
•
the life expectancy of LHC IR quadrupole magnets is estimated to be
<10 years owing to high radiation doses
the statistical error halving time will exceed 5 years by 2011-2012
therefore, it is reasonable to plan a machine luminosity upgrade based
on new low-ß IR magnets before ~2015
CERN
F. Ruggiero
LHC beam performance and luminosity upgrade scenarios
luminosity versus energy upgrade
Courtesy of Michelangelo Mangano
03 November 2005 - LHC seminar
F. Ruggiero & W.Scandale, LHC luminosity upgrade - report from LHC-LUMI-05
CARE-HHH
4
Chronology of LHC Upgrade studies
•
•
•
•
Summer 2001: two CERN task forces investigate physics potential (CERN-TH2002-078) and accelerator aspects (LHC Project Report 626) of an LHC
upgrade by a factor 10 in luminosity and 2-3 in energy
March 2002: LHC IR Upgrade collaboration meeting
http://cern.ch/lhc-proj-IR-upgrade
October 2002: ICFA Seminar at CERN on
“Future Perspectives in High Energy Physics”
2003: US LHC Accelerator Research Program (LARP)
•
2004: CARE-HHH European Network on High Energy
High Intensity
Hadron Beams
•
November 2004: first CARE-HHH-APD Workshop (HHH-04) on
“Beam Dynamics in Future Hadron Colliders and Rapidly
Cycling High-Intensity Synchrotrons”, CERN-2005-006
•
September 2005: CARE-HHH Workshop (LHC-LUMI-05) on
“Scenarios for the LHC Luminosity Upgrade”
http://care-hhh.web.cern.ch/CARE-HHH/LUMI-05/
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
The CARE-HHH Network
CARE-HHH
Mandate
Coordinate and integrate the activities of the accelerator and particle
physics communities, in a worldwide context, towards achieving superior
High-Energy High-Intensity Hadron-Beam facilities for Europe
•
Roadmap for the upgrade of the European accelerator infrastructure
(LHC and GSI accelerator complex)
o
o
o
o
•
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luminosity and energy upgrade for the LHC
pulsed SC high intensity synchrotrons for the GSI and LHC complex
R&D and experimental studies at existing hadron accelerators
select and develop technologies providing viable design options
Coordinate activities and foster future collaborations
Disseminate information
• HHH coordination: F. Ruggiero (CERN) & W. Scandale (CERN)
1. Advancement in Acc. Magnet Technology (AMT): L. Rossi (CERN) & L. Bottura (CERN)
2. Novel Meth. for Acc. Beam Instrumentation (ABI): H. Schmickler (CERN) & K. Wittenburg (DESY)
3. Accelerator Physics and Synchrotron Design (APD): F. Ruggiero (CERN) & F. Zimmermann (CERN)
3 November 2005 - LHC seminar
F. Ruggiero & W.Scandale, LHC luminosity upgrade - report from LHC-LUMI-05
6
Nominal LHC parameters
collision energy
dipole peak field
injection energy
Ecm
B
Einj
protons per bunch
bunch spacing
average beam current
Nb
∆t
I
stored energy per beam
radiated power per beam
2x7
8.3
450
1.15
25
0.58
362
3.7
TeV
T
GeV
1011
ns
A
MJ
kW
normalized emittance
rms bunch length
n
z
3.75
7.55
beam size at IP1&IP5
beta function at IP1&IP5
full crossing angle
*
b*
c
16.6
0.55
285
mm
m
mrad
luminosity lifetime
peak luminosity
events per bunch crossing
L
L
15.5
h
cm-2s-1
∫ L dt
66.2
integrated luminosity
F. Ruggiero
CERN
1034
19.2
mm
cm
fb-1/year
LHC beam performance and luminosity upgrade scenarios
LHC upgrade paths/limitations
longer bunches
5
4
I=1.72 A
3
2
I=0.86 A
ultimate
bb limit
I=0.58 A
1
0
1
2
3
4
5
number of bunches nb 1000
F. Ruggiero
•
Peak luminosity at the
beam-beam limit L~ I/b*
•
Total beam intensity I
limited by electron cloud,
collimation, injectors
•
Minimum crossing angle
depends on beam intensity:
limited by triplet aperture
•
Longer bunches allow
higher bb-limit for Nb/n:
limited by the injectors
•
Less ecloud and RF heating
for longer bunches: ~50%
luminosity gain for flat
bunches longer than b*
•
Event pile-up in the physics
detectors increases with Nb
•
Luminosity lifetime at the
bb limit depends only on b*
⇒ reduce Tturnaround to
increase integrated lumi
more bunches
nominal
bunch population Nb 1011
6
CERN
6
LHC beam performance and luminosity upgrade scenarios
Expected factors for the LHC
luminosity upgrade
The peak LHC luminosity can be multiplied by:
 factor 2.3 from nominal to ultimate beam intensity (0.58  0.86 A)
 factor 2 (or more?) from new low-beta insertions with ß* = 0.25 m
Tturnaround~10 h  ∫Ldt ~ 3 x nominal ~ 200/(fb*year)
Major hardware upgrades (LHC main ring and injectors) are needed to exceed
ultimate beam intensity. The peak luminosity can be increased by:
 factor 2 if we can double the number of bunches (maybe impossible due
to electron cloud effects) or increase bunch intensity and bunch length
Tturnaround~10 h  ∫Ldt ~ 6 x nominal ~ 400/(fb*year)
Increasing the LHC injection energy to 1 TeV would potentially yield:
 factor ~2 in peak luminosity (2 x bunch intensity and 2 x emittance)
 factor 1.4 in integrated luminosity from shorter Tturnaround~5 h
thus ensuring L~1035 cm-2 s-1 and ∫Ldt ~ 9 x nominal ~ 600/(fb*year)
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Challenge of a Cold Machine
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
LHC Cleaning System (R. Assmann)
Two-stage cleaning (phase 2)
Two-stage cleaning (phase 1)
43
Single-stage cleaning
No collimation
Pilot
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Collimation & Machine Protection
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Constraints for LHC commissioning
 Only 8/20 LHC dump dilution kickers available during the first two years
of operation  total beam intensity in each LHC ring limited to 1/2 of
its nominal value
 According to SPS experience and to electron cloud simulations, the
initial LHC bunch intensity Nb can reach and possibly exceed its nominal
value for 75 ns bunch spacing, while it may be limited to about 1/3 of
its nominal value for 25 ns spacing
 Machine protection and collimation favours initial operation with lower
beam power and lower transverse beam density. Simple graphite
collimators may limit maximum transverse energy density to about 1/2
of its nominal value
 Emittance preservation from injection to physics conditions will require
a learning curve  do not assume transverse emittance smaller than
nominal, even for reduced bunch intensity
 Initial operation with relaxed parameters is strongly favoured
ß*, reduced crossing angle, and fewer parasitic collisions
F. Ruggiero
CERN
 higher
LHC beam performance and luminosity upgrade scenarios
LHC beam commissioning
Mike Lamont, Chamonix 2005 workshop
43 on 43 with 3 to 4 x 1010 ppb to 7 TeV
•
No parasitic encounters
•
•
•
•
•
•
Instrumentation
Good beam for RF, Vacuum…
Lower energy densities
•
•
•
•
No crossing angle
No long range beam-beam
Larger aperture
Reduced demands on beam dump system
Collimation
Machine protection
Luminosity
•
•
F. Ruggiero
1030 cm-2s-1 at 18 m
2 x 1031 cm-2s-1 at 1 m
CERN
LHC beam performance and luminosity upgrade scenarios
LHC beam commissioning
Mike Lamont, Chamonix 2005 workshop
Phase
R1/2
Time [days]
Total
1
Injection
2
1
2
2
First turn
2
3
6
3
Circulating beam
2
3
6
4
450 GeV: initial commissioning
2
4
8
5
450 GeV: detailed measurements
2
4
8
6
450 GeV: 2 beams
1
2
2
7
Nominal cycle
1
5
5
8
Snapback – single beam
2
3
6
9
Ramp – single beam
2
4
8
10
Single beam to physics energy
2
2
4
11
Two beams to physics energy
1
3
3
12
Establish Physics
1
2
2
13
Commission squeeze
2
4
4
14
Physics partially squeezed
TOTAL
F. Ruggiero
CERN
60
LHC beam performance and luminosity upgrade scenarios
Steps to reach nominal LHC luminosity
parameter units
75 ns spacing
25 ns spacing
nominal
2808
0.4
2808
1.15
number of bunches nb
protons per bunch Nb
[1011]
936
0.9
normalized emittance n
rms bunch length z
rms energy spread E
[µm]
[cm]
[10-4]
3.75
7.55
1.13
3.75
7.55
1.13
3.75
7.55
1.13
135
1.0
250
304
0.55
285
106
0.55
285
luminosity lifetime L [h]
peak luminosity L [1034cm-2s-1]
events per crossing
22
0.12
7.1
26
0.12
2.3
15
1.0
19.2
∫ over 200 runs L dt
9.3
9.5
66.2
IBS growth time xIBS [h]
beta at IP ß* [m]
full crossing angle c [mrad]
Lint [fb-1]
Possible scenarios with 75 ns and 25 ns bunch spacing for early LHC runs
with integrated luminosity of about 10 fb-1 in 200 fills, assuming an average
physics run time Trun = 14 h and Tturnaround=10 h.
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Luminosity optimization
   b 
L
•
•
•
transverse beam size at IP
nb f rev N b2
4
2
 Nb

I
*
4b  n
Nb/n beam brightness
2
 n    
b
peak luminosity for head-on collisions
round beams, short Gaussian bunches
•
•
•
•
head-on beam-beam
space-charge in the injectors
transfer dilution
normalized emittance
I = nbfrevNb total beam current
Collisions with full crossing angle c
reduce luminosity by a geometric factor F
long range beam-beam
collective instabilities
synchrotron radiation
stored beam energy
  
F  1 / 1   c *z 
 2 
2
maximum luminosity below beam-beam limit
⇒ short bunches and minimum crossing angle (baseline scheme)
H-V crossings in two IP’s ⇒ no linear tune shift due to long range
total linear bb tune shift also reduced by F
F. Ruggiero
CERN
Qbb  x   y 
N b rp
2n
F
LHC beam performance and luminosity upgrade scenarios
If bunch intensity and brightness are not limited by the injectors
or by other effects in the LHC (e.g. electron cloud) ⇒ luminosity
can be increased without exceeding beam-beam limit Qbb~0.01
by increasing the crossing angle and/or the bunch length
Express beam-beam limited brilliance Nb/εn in terms of maximum
total beam-beam tune shift Qbb, then
 Qbb I f rev Q n 
L
 2
*
2rp b
rp
b
2
bb b n
*
 c z 
1 
* 
 2 
2
At high beam intensities or for large emittances, the performance
will be limited by the angular triplet aperture
2
*




A
/


1
1


tripl


L
Qbb I min  * , 


2rp
 b   20  c /  θ  
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Minimum crossing angle
Beam-Beam Long-Range collisions:
•
perturb motion at large betatron
amplitudes, where particles come
close to opposing beam
•
cause ‘diffusive’ (or dynamic)
aperture, high background, poor
beam lifetime
•
increasing problem for SPS,
Tevatron, LHC, i.e., for operation
with larger # of bunches
dynamic aperture caused by npar parasitic collisions around two IP’s
npar N b 3.75mm
c
c
I 3.75mm

3


6

3
 θ
32 1011  n
θ
0.5A  n
d da

θ 
b*
angular beam
divergence at IP
F. Ruggiero
CERN
higher beam intensities or smaller b*
require larger crossing angles to preserve
dynamic aperture and shorter bunches to
avoid geometric luminosity loss

baseline scaling: c~1/√b* , z~b*
LHC beam performance and luminosity upgrade scenarios
Schematic of a super-bunch collision, consisting of ‘head-on’
and ‘long-range’ components. The luminosity for long bunches
having flat longitudinal distribution is ~1.4 times higher than for
conventional Gaussian bunches with the same beam-beam tune
shift and identical bunch population (see LHC Project Report 627)
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Schematic of reduced electron cloud build up for a long
bunch. Most electrons do not gain any energy when
traversing the chamber in the quasi-static beam potential
negligible heat load
F. Ruggiero
CERN
[after V. Danilov]
LHC beam performance and luminosity upgrade scenarios
Scenarios for the luminosity upgrade
 ultimate performance without hardware changes (phase 0)
 maximum performance with only IR changes (phase 1)
 maximum performance with “major” hardware changes (phase 2)
Nominal LHC performance


•
•
•
•
beam-beam tune spread of 0.01
L = 1034 cm-2s-1 in ATLAS and CMS
Halo collisions in ALICE
Low-luminosity in LHCb
Phase 0: steps to reach ultimate performance without hardware changes:
1) collide beams only in IP1 and IP5 with alternating H-V crossing
 L = 2.3 x 1034 cm-2 s-1
increase the dipole field to 9T (ultimate field)  Emax = 7.54 TeV
2) increase Nb up to the beam-beam limit
3)
The ultimate dipole field of 9 T corresponds to a beam current limited by
cryogenics and/or by beam dump/machine protection considerations.
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Scenarios for the luminosity upgrade
Phase 1: steps to reach maximum performance with only IR changes
1)
2)
3)
4)
5)
Modify the insertion quadrupoles and/or layout  ß* = 0.25 m
Increase crossing angle c by √2  c = 445 µrad
Increase Nb up to ultimate intensity  L = 3.3 x 1034 cm-2s-1
Halve z with high harmonic RF system  L = 4.6 x 1034 cm-2s-1
Double the no. of bunches nb (and increase c )  L = 9.2 x 1034 cm-2s-1
excluded by electron cloud?
Step 5 belongs to Phase 2
 Step 4) requires a new RF system providing




an accelerating voltage of 43 MV at 1.2 GHz
a power of about 11 MW/beam
longitudinal beam emittance reduced to 1.8 eVs
horizontal Intra-Beam Scattering (IBS) growth time decreases by ~ √2
 Operational consequences of step 5)  exceeding ultimate beam intensity
 upgrade LHC cryogenics, collimation, RF and beam dump systems
 the electronics of all LHC beam position monitors should be upgraded
 possibly upgrade SPS RF system and other equipment in the injectors
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
luminosity upgrade: baseline scheme
0.58 A
1.0
c>mindue
increase Nb
restore F
  
F  1   c *z
  2

bb
limit?
no
0.86 A
yes
4.6
2 1 / 2




BBLR
compensation
or decouple crab
cavities
L and F
reduce c
(squeeze b*)
2.3
reduce b* by new IR
factor ~2
magnets
0.86 A
if e-cloud, dump &
impedance ok



to LR-bb
reduce z
by factor ~2
using higher
frf & lower ||
(larger c ?)
increase nb by
factor ~2
peak luminosity gain 9.2
beam current 1.72 A
use large c
& pass each beam
through separate
magnetic channel
simplified IR design
with large c
24
luminosity upgrade: Piwinski scheme
reduce b* by new IR
factor ~2
magnets
1.0
0.58 A
decrease F
superbunches?
  
F  1   c *z
  2

flatten profile?



2 1 / 2




increase zc
increase Nb
reduce #bunches
to limit total
current?
2 n
Nb 
Qbb
rp F
no
?
yes
7.7
0.86 A
15.5
1.72 A
luminosity gain
beam current
25
Various LHC upgrade options
parameter
symbol
nominal
ultimate
shorter
bunch
longer
bunch
no of bunches
nb
2808
2808
5616
936
proton per bunch
Nb [1011]
1.15
1.7
1.7
6.0
bunch spacing
∆tsep [ns]
25
25
12.5
75
average current
I [A]
0.58
0.86
1.72
1.0
normalized emittance
n [µm]
3.75
3.75
3.75
3.75
Gaussian
Gaussian
Gaussian
flat
longit. profile
rms bunch length
z [cm]
7.55
7.55
3.78
14.4
ß* at IP1&IP5
ß* [m]
0.55
0.50
0.25
0.25
full crossing angle
c [µrad]
285
315
445
430
Piwinski parameter
c z/(2*)
0.64
0.75
0.75
2.8
peak luminosity
L [1034 cm-2 s-1]
1.0
2.3
9.2
8.9
19
44
88
510
44.9
42.8
21.8
36.2
events per crossing
luminous region length
F. Ruggiero
lum [mm]
CERN
LHC beam performance and luminosity upgrade scenarios
Heat loads per beam aperture
for various LHC upgrade options
nominal
ultimate
shorter
bunch
longer
bunch
Nb [1011]
1.15
1.7
1.7
6.0
bunch spacing
∆tsep[ns]
25
25
12.5
75
average current
I [A]
0.58
0.86
1.72
1.0
Gaussian
Gaussian
Gaussian
flat
7.55
7.55
3.78
14.4
1.07
(0.44)
1.04
(0.59)
13.34
(7.85)
0.26
(0.26)
parameter
symbol
protons per bunch
longitudinal profile
rms bunch length
z [cm]
Average electron-cloud heat load at
4.6–20 K in the arc for R=50% and
δmax=1.4 (in parentheses for
δmax=1.3)
Pecloud [W /m]
Synchrotron radiation heat load at
4.6–20 K
P [W /m]
0.17
0.25
0.50
0.29
Image currents power at 4.6–20 K
PW [W /m]
0.15
0.33
1.87
0.96
Beam-gas scattering heat load at
1.9 K for 100-h beam lifetime (in
parentheses for a 10-h lifetime).
It is assumed that elastic scattering
(~40% of the total cross section)
leads to local loss.
Pgas [W /m]
0.038
(0.38)
0.056
(0.56)
0.113
(1.13)
0.066
(0.66)
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Events per bunch crossing and beam
lifetime due to nuclear p-p collisions
events
L  bb

X - ing nb f rev
bb=60 mb total inelastic cross section
beam intensity halving time due to
nuclear p-p collisions at two IP’s with
total cross section TOT=110 mb
n N /L
N  b b
2 TOT
L
f rev Qbb

nb N b 2rp b *
L 
1
2
x
IBS

1
2
 gas

nuclear scattering lifetime
at the beam-beam limit
depends only on b* !
1.54
N
luminosity lifetime: assumes radiation
damping compensates diffusion
exponential luminosity lifetime
due to nuclear p-p interactions
F. Ruggiero
CERN
( e  1) N 
N
1.54
LHC beam performance and luminosity upgrade scenarios
Optimum run time and effective luminosity
 L  Trun  Tturnaround
 e
L
Trun
Trun
1.4
1.2
1
0.8
0.6
0.4
0.2
L
The optimum run time and the
effective luminosity are universal
functions of Tturnaround/L
Trun
L
 1 
Tturnaround
L
 ProductLog [-1,-e
Leff
L
Leff L
1
0.8
0.6
0.4
0.2
-1-
Tturnaround

L
L
Tturnaround
0.5
]
L
 L  Trun  Tturnaround

1
1.5
2
L
1
-1-
ProductLog [-1,-e
Tturnaround
L
where w  ProductLog [ z ]  z  wew
Tturnaround
0.5
1
F. Ruggiero
1.5
2
CERN
L
When the beam lifetime is
dominated by nuclear protonproton collisions, then L~N/1.54
and the effective luminosity is a
universal functions of
Tturnaround/b
LHC beam performance and luminosity upgrade scenarios
]
Effective luminosity for various upgrade options
parameter
symbol
nominal
ultimate
shorter
bunch
longer
bunch
protons per bunch
Nb [1011]
1.15
1.7
1.7
6.0
bunch spacing
∆tsep [ns]
25
25
12.5
75
average current
I [A]
0.58
0.86
1.72
1.0
Gaussian
Gaussian
Gaussian
flat
longitudinal profile
rms bunch length
z [cm]
7.55
7.55
3.78
14.4
ß* at IP1&IP5
ß* [m]
0.55
0.50
0.25
0.25
full crossing angle
c [µrad]
285
315
445
430
Piwinski parameter
c z/(2*)
0.64
0.75
0.75
2.8
peak luminosity
L [1034 cm-2 s-1]
1.0
2.3
9.2
8.9
19
44
88
510
events per crossing
IBS growth time
xIBS [h]
106
72
42
75
nuclear scatt. lumi lifetime
N/1.54 [h]
26.5
17
8.5
5.2
luminosity lifetime (gas =85 h)
L [h]
15.5
11.2
6.5
4.5
effective luminosity
Leff [1034 cm-2 s-1]
0.4
0.8
2.4
1.9
Trun [h] optimum
14.6
12.3
8.9
7.0
Leff [1034 cm-2 s-1]
0.5
1.0
3.3
2.7
Trun [h] optimum
10.8
9.1
6.7
5.4
(Tturnaround=10 h)
effective luminosity
(Tturnaround= 5 h)
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Interaction Region upgrade
goal: reduce b* by at least a factor 2
options: NbTi ‘cheap’ upgrade, NbTi(Ta), Nb3Sn
new quadrupoles
new separation dipoles
maximize magnet aperture,
factors driving IR design:
minimize distance to IR
• minimize b*
• minimize effect of LR collisions
• large radiation power directed towards the IRs
• accommodate crab cavities and/or beam-beam
compensators. Local Q’ compensation scheme?
• compatibility with upgrade path
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
IR ‘baseline’ schemes
triplet magnets
short bunches &
minimum crossing angle &
BBLR
F. Ruggiero
CERN
crab cavities &
large crossing angle
LHC beam performance and luminosity upgrade scenarios
alternative IR schemes
dipole magnets
dipole first &
small crossing angle
reduced # LR collisions
collision debris hit D1
F. Ruggiero
CERN
triplet magnets
dipole
triplet magnets
dipole first &
large crossing angle &
long bunches or crab cavities
LHC beam performance and luminosity upgrade scenarios
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Dipoles first and doublet focusing
Features
Q1
• Requires beams to be in
separate focusing channels
• Fewer magnets
D2
• Beams are not round at the IP
Q2
IP
D1
D2
Focusing symmetric about IP
Tanaji Sen,
Doublet optics
• Polarity of Q1 determined by
crossing plane – larger beam
size in the crossing plane to
increase overlap
• Opposite polarity focusing at other
IR to equalize beam-beam tune shifts
• Significant changes to outer triplet
magnets in matching section.
35
Flat beams
•
•
•
•
•
Interesting approach, flat beams could increase luminosity
by ~20-30% with reduced crossing angle
Symmetric doublets studied by J. Johnstone (FNAL)
require separate magnetic channels, i.e. dipole-first, Crab
cavities or special quads
Tune footprints are broader than for round beams, since
there is only partial compensation of parasitic beam-beam
encounters by the H/V crossing scheme. More work
needed to evaluate nonlinear resonance excitation.
Probably requires BBLR compensation
Recently S. Fartoukh has found a more interesting flat
beam solution with anti-symmetric LHC baseline triplets
F. Ruggiero
CERN
LHC upgrade scenarios
Beam aspect ratio vs triplet aperture (1/5)
• Beam screen orientation for H/V scheme
 In both cases, H-separation of
about 9.5*max(x,b1 ,x,b2)
Effect of decreasing the
beam aspect ratio at the IP
(and increasing the vert. X-angle)
 In both cases, V-separation of
about 9.5*max(y,b1 ,y,b2)
Effect of increasing the
beam aspect ratio at the IP
(and decreasing the vert. X-angle)
Find the optimum matching between
37
beam-screen and beam aspect ratio
S. Fartoukh, ABP-RLC meeting, 28-10-2005
Pushing the luminosity by 10-20%
bx* [cm]
by* [cm]
a *[mrad]
n1 in the
triplet
Geometric loss
factor [%]
L/Lnom
Nominal
r=1.0, b55cm
55.00
55.00
285
~7
83.9
1.00
Flat
r=2.0, b55cm
110.00
27.50
201
~7
95.1
1.13
Flat
r=1.6, b55cm
88.00
34.37
225
~7.5
92.7
1.10
Flat
r~1.7, b~51cm
88.00
30.00
225
~7
92.7
1.18
Case
All these cases being allowed by the nominal LHC hardware:layout,
power supply, optics antisymmetry, b.s. orientation in the triplets
(only changing the present H/V scheme into V/H scheme)!
38
S. Fartoukh, ABP-RLC meeting, 28-10-2005
‘cheap’ IR upgrade
in case we need to double LHC luminosity earlier than foreseen
triplet magnets
short bunches &
minimum crossing angle &
BBLR
each quadrupole individually optimized (length & aperture)
reduced IP-quad distance from 23 to 22 m
conventional NbTi technology: b*=0.25 m is possible
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Several LHC IR upgrade options are being explored :
•
•
•
•
•
•
quadrupole-first and dipole-first solutions based on
conventional NbTi technology and on high-field Ni3Sn
magnets, possibly with structured SC cable
energy deposition, absorbers, and quench limits
schemes with Crab cavities as an alternative to the baseline
bunch shortening RF system at 1.2 GHz to avoid luminosity
loss with large crossing angles
early beam separation by a “D0” dipole located a few metres
away from the IP (or by tilted experimental solenoids?) may
allow operation with a reduced crossing angle. Open issues:
compatibility with detector layout, reduced separation at first
parasitic encounters, energy deposition by the collision debris
local chromaticity correction schemes
flat beams, i.e. a final doublet instead of a triplet. Open
issues: compensation of long range beam-beam effects with
alternating crossing planes
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Crab cavities vs bunch shortening
RF Deflector
( Crab Cavity )
HER
LER
Electrons
Positrons
1.44 MV
Head-on
Collision
Crossing Angle
(11 x 2 m rad.)
1.41 MV
1.44 MV
1.41 MV
Comparison of timing tolerances
Crab cavities combine advantages
KEKB
of head-on collisions and large
crossing angles
x* 100 mm
require lower voltages compared
to bunch shortening RF systems
c +/- 11
but tight tolerance on phase jitter
mrad
to avoid emittance growth
t
6 ps
F. Ruggiero
CERN
SuperKEKB
ILC
SuperLHC
70 mm
0.24 mm
11 mm
+/-15
mrad
+/-5
mrad
+/- 0.5
mrad
3 ps
0.03 ps 0.08 ps
LHC beam performance and luminosity upgrade scenarios
Crab Cavities
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Motivation of Beam-Beam
compensation studies
•
•
Provide more LHC luminosity earlier
Space is reserved in the LHC for the wires. An
early test in RHIC will determine the effectiveness
of the compensation and possibly address the
challenges to the compensation. If effective, will
allow a smaller crossing angle and more beam
intensity.
Provide direction to an IR upgrade path
If compensation is proven to be effective, then
the quadrupole-first option, possibly with flat
beams, seems to be a more natural path for the
IR upgrade. Otherwise, the dipole-first option will
be more attractive.
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Lessons from the SPS experiments
No wires activated
•
•
•
•
•
•
Nearly perfect compensation
Both wires on
F. Ruggiero
1 wire on
CERN
Compensating 1 wire with
another wire at nearly the
same phase “works”
Compensation is tune
dependent
Current sensitivity
Alignment sensitivity
Equivalent crossings in the
same plane led to better
lifetimes than alternating
planes
Beam lifetime  ~ d3
d is the beam-wire distance
Higher power law expected
given the proximity of high
order resonances
LHC beam performance and luminosity upgrade scenarios
2nd prototype BBLR in the CERN SPS
has demonstrated benefit of compensation
CERNJ.-P. Koutchouk, F. Zimmermann et al.
G. Burtin,
J. Camas,
LHC beam performance and luminosity upgrade scenarios
F. Ruggiero
Lessons from RHIC experiment
•
•
•
•
•
•
F. Ruggiero
CERN
Study at injection energy
with 1 bunch and 1
parasitic interaction per
beam
There is an effect to
compensate, even with
1 parasitic
Drop in lifetime seen for
beam separations < 7 σ
Effect is very tune
dependent
How important are
machine nonlinearities
and other time
dependent effects?
Did they change with the
beam-beam separation?
LHC beam performance and luminosity upgrade scenarios
Wire compensation at RHIC
•
Proposed wire location
•
•
•
Location of parasitic
F. Ruggiero
CERN
Compensation of 1 wire
by another wire worked
well in the SPS under
LHC conditions.
Real test of the
compensation principle
requires 2 beams
Beam studies in RHIC
show that parasitic
interactions have strong
influence on beam loss
Favorable location for
wire has been found in
IR6, phase advance to
parasitic ~6 degrees at
top energy
LHC beam performance and luminosity upgrade scenarios
Milestones for future LHC Upgrade
machine studies
•
•
•
•
•
2006: installation and test of a beam-beam long
range compensation system at RHIC to be
validated with colliding beams
2006/2007: new SPS experiment for crystal
collimation, complementary to Tevatron results
2006: installation and test of Crab cavities at
KEKB to validate higher beam-beam limit and
luminosity with large crossing angles
2007: if KEKB test successful, test of Crab
cavities in a hadron machine (RHIC?) to validate
low RF noise and emittance preservation
2007-2009: LHC running-in and first machine
studies on collimation and beam-beam
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Tentative conclusions for
the LHC IR Upgrade
•
•
•
We do need a back-up or intermediate IR
upgrade option based on NbTi magnet
technology. What is the maximum luminosity?
A vigorous R&D programme on Nb3Sn
magnets should start at CERN asap, in parallel
to the US-LARP programme, to be ready for
1035 luminosity in ~2015
Alternative IR layouts (quadrupole-first, dipolefirst, D0, flat beams, Crab cavities) will be
rated in terms of technological and operational
risks/advantages
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Towards a baseline design
Following the approach proposed by Barry Barish
for the ILC, we propose to:
•
•
•
Define a Baseline, i.e. a forward looking
configuration which we are reasonably confident
can achieve the required LHC luminosity
performance and can be used to give an accurate
cost estimate by mid-end 2006 in a “Reference
Design Report”
Identify Alternative Configurations and rate them
in terms of technological and operational
risks/advantages
Identify R&D (at CERN and elsewhere)
•
•
To support the baseline
To develop the alternatives
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Reference LHC Luminosity Upgrade:
workpackages and tentative milestones
accelerator
WorkPackage
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
after 2015
LHC Main Ring Accelerator Physics
High Field Superconductors
High Field Magnets
Magnetic Measurements
Cryostats
Cryogenics: IR magnets & RF
RF and feedback
Collimation&Machine Protection
Beam Instrumentation
Power converters
SPS
SPS kickers
Tentative Milestones
Other Tentative Milestones
Beam-beam
compensation
test at RHIC
Crab cavity test
at KEKB
SPS crystal LHC collimation LHC collimation Install phase 2
collimation test
tests
tests
collimation
Low-noise crab LHC Upgrade
cavity test at
Conceptual
RHIC
Design Report
LHC tests:
collimation &
beam-beam
LHC Upgrade Nominal LHC
Technical Design luminosity
Report
10^34
Install new SPS new IR magnets
kickers
and RF system
Ultimate LHC
luminosity
2.3x10^34
Double ultimate
beam-beam
LHC luminosity
compensation
4.6x10^34
LHC Upgrade
Reference
Design Report
Reference LHC Upgrade scenario: peak luminosity 4.6x10^34/(cm^2 sec)
Integrated luminosity 3 x nominal ~ 200/(fb*year) assuming 10 h turnaround time
new superconducting IR magnets for beta*=0.25 m
phase 2 collimation and new SPS kickers needed to attain ultimate LHC beam intensity of 0.86 A
beam-beam compensation may be necessary to attain or exceed ultimate performance
new superconducting RF system: for bunch shortening or Crab cavities
hardware for nominal LHC performance (cryogenics, dilution kickers, etc) not considered as LHC upgrade
R&D for further luminosity upgrade (intensity beyond ultimate) is recommended: see Injectors Upgrade
R&D - scenarios & models
specifications & prototypes
construction & testing
installation & commissioning
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
LHC upgrade scenarios
Summary
• The upgrade scenario currently assumed as baseline
includes a reduction of b* to 0.25 m, an increased
crossing angle and a new bunch-shortening RF system.
• The corresponding peak luminosity with ultimate beam
intensity is 4.6x1034 cm-2 s-1 at two IP’s. Electron cloud
effects and/or cryogenic heat loads may exclude the
possibility to double the number of bunches.
• Milestones for future LHC Upgrade machine studies
include RHIC tests on Long Range Beam-Beam
compensation and possibly on crab cavity operation,
after KEKB tests, SPS and Tevatron studies on crystal
assisted collimation, as well as collimation, electron
cloud, and beam-beam studies at the LHC itself.
• Several LHC IR upgrade options are currently being
explored: we need to converge to a baseline
configuration and
CERN identify a few alternative options.
F. Ruggiero
LHC beam performance and luminosity upgrade scenarios
Additional Slides
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Alternative ways to avoid
luminosity loss
1) Reduce crossing angle and apply “wire”
compensation of long range beam-beam effects
2) Crab cavities ⇒ large crossing angles to avoid long
range bb effects w/o luminosity loss. Potential of
boosting the beam-beam tune shift (factor 2-3 predicted
for KEKB, what about LHC?)
3) Early beam separation by a “D0” dipole located a
few metres away from the IP, as recently
suggested by JPK at the LHC-LUMI-05 workshop.
The same effect could be obtained by tilted experimental
solenoids, but the experiments don’t seem to like the idea.
A potential drawback of 2) and 3) is that Qbb is no longer
reduced by the geometric factor F ⇒ lower beam-beam limit?
F. Ruggiero
CERN
LHC upgrade scenarios
Back to the Xing angle issue
An “easy” way to reduce
or cancel the Xing angle
at the IP and gain 20%
to 50% in luminosity.
Orbit
corrector
Q1
Q3
Is it possible for the
detectors?
Q2
J.-P. Koutchouk, LHC-LUMI-05
55
New idea: D0 magnet a few
meters away from the IP
Advantages
•
•
•
Cheap and elegant solution to increase luminosity
No need of a new bunch shortening RF system
Cleans collision debris from Q1?
Possible drawbacks
•
•
•
Reduced separation at first few parasitic encounters?
Collision debris and background in the experiments?
Compatibility with detector layout and integration
into the experiments
F. Ruggiero
CERN
LHC upgrade scenarios
LR beam-beam compensation:
remarks and open issues
•
•
•
•
•
Simulations of LR compensation with 2 wires indicate that lifetime is
recovered over a wide tune range but not for all tunes.
The measured SPS lifetime is 5 ms x (d/)5. Extrapolation to LHC
beam-beam distance (9.5 ) would predict 6 minutes beam lifetime!
Tevatron observations with electron lens show cubic dependence.
Further SPS tests at different energy are needed.
Lifetimes predicted by simulation codes are much larger than those
observed, even though sensitivity to parameters seems correct.
Needs further understanding and beam tests, e.g. at RHIC.
For extreme PACMAN bunches there is overcompensation which
causes the footprint to flip over or to increase instead of shrinking.
To avoid degraded lifetime for PACMAN bunches, the wire
should be pulsed train by train. It is rather challenging to make a
pulsed wire for BB compensation: the required average pulse rate is
439 kHz and the turn-by-turn amplitude stability 10-4.
Experiments at RHIC (Fischer) with a single LR encounter show
that the BB effect is visible starting from a 5 separation,
consistent with Tevatron and Daphne observations, but contrary to
LHC simulations and possibly earlier observations at the SPS collider.
F. Ruggiero
CERN
LHC upgrade scenarios
RHIC experiment
•Studied at injection energy with 1
bunch and 1 parasitic interaction
per beam
:   (d/)5
SPS
•There is an effect to
compensate, even with 1
parasitic
Tevatron:  ~ d3
•Drop in lifetime seen for beam
separations < 7 σ
RHIC
•Effect is very tune dependent
:  ~ d4 or d2
[measured 04/28/05, scan 4]
58
LHC-LUMI-05 workshop: some
conclusions on the IR Upgrade
•
Local correction à la Raimondi, via dispersion inside triplet
magnets and two pairs of sextupoles, can correct
chromaticity and geometric aberrations  look for a
solution that can be implemented and removed
anytime by varying quads and sexupole strengths
•
Three IR layout options were identified that should be
studied in more detail:
1) dipole-first based on Nb3Sn technology with ℓ* = 19 m
2) quad-first layout based on Nb3Sn technology ℓ * = 19 m
3) low gradient quad-first layout based on NbTi technology
•
Still need to fix ℓ* and required length for TAS upgrade.
Agreement to assume ℓ* = 19 m as a reasonable estimate
•
CARE-HHH web repository with optics solutions is very
desirable  we should all use the same input (MADX)
•
Update the 3 proposals by the end of 2005
F. Ruggiero
CERN
LHC upgrade scenarios
Energy Deposition Issues in
LHC IR Upgrades, N. Mokhov (FNAL)
•
•
•
•
•
All three aspects, i.e. i) quench limit, ii) radiation damage
(magnet lifetime), and iii) dynamic heat load on the cryo
system should be simultaneously addressed in the IR
magnet design. i) and ii) are linked
Peak power deposition at non-IP end of IR magnets
~proportional to ∫Bdℓ  FDFD “quadruplet” focusing?
Estimated dipole field with TAS in quad-first option to reduce
peak energy deposition “well below” quench limits
 15-20 Tm for magnetic TAS
Estimated thickness of internal absorbers  a 5 mm thick
SS absorber reduces peak power by a factor ~2
Impact of orbit corrector D0 inside the experiment on energy
deposition in downstream magnets, including detector
solenoid field
 more work needed, modest impact of solenoid
field on energy deposition (more from fringe fields)
F. Ruggiero
CERN
LHC IR Upgrades, LARP Workshop, WG1 summary
•
•
•
•
•
Action items/comments on energy
deposition, Nikolai Mokhov
Refine and test scaling law for energy deposition in IR
magnets with MARS simulations (including dependence on ℓ*)
Introduce quench limits to JPK’s spreadsheet for NbTi and
Nb3Sn
Address radiation damage/lifetime issues in all IR magnet
design analyses: 7 years at 1034 become 8 months at 1035
with currently used materials  new (ceramic type) materials
for 1035?
Launch R&D program on beam tests for SC and insulating
materials asap: BNL, FNAL, MSU
Arrive at a clear picture on Dynamic Heat Load limits. How
serious is the current 10 W/m limit or 120 W on each side of
IR? This becomes 100 W/m and 1.2 kW for 1035. Cooling
scheme? Cryoplant capability?
F. Ruggiero
CERN
LHC IR Upgrades, LARP Workshop, WG1 summary
Potential impact of novel magnet
technology for IR elements, Peter McIntyre
•
•
•
•
Designs have been suggested for novel magnet technology to mitigate
limitations from heat deposition and radiation damage from deposition of
secondary particles in the quadrupole triplet and separation dipole. One
example is an ironless quadrupole using structured-cable Nb3Sn
conductor, which could provide 390 T/m gradient at a location as close as
12 m from the IP, and compatibility with supercritical helium flowing
throughout the coils. A second example is a 9 T levitated-pole dipole for
D1, which would open the transverse geometry so that secondaries are
swept into a room-temperature flux return.
In order to evaluate the potential benefit of these concepts it is necessary
to model the heat deposition and radiation damage in the more compact
geometries, and to examine potential interference with the performance
of the detectors.
Of particular importance is to undertake a consistent examination of the
impact of reducing ℓ* on the ensemble of issues that impact achievable b*
the interface of the IR with the machine lattice (chromaticity and
dispersion, multipole errors, orbit errors, etc.), and the strategy for
accommodating long-range beam-beam effects.
Also of interest is to evaluate the pros and cons of the alternatives for
operating temperature (superfluid, two-phase, or supercritical cooling) for
the IR elements that must operate with substantial heat loads.
F. Ruggiero
CERN
LHC IR Upgrades, LARP Workshop, WG1 summary
Latest design: 9 Tesla @ 4.5 K
All windings
are
racetracks.
Only pole tip
winding is
Nb3Sn.
All others are
NbTi.
Support each pole piece using tension struts
63
(low heat load).
56 mm clear aperture
Dipole-First optics (R. De Maria)
•
matched optics solution for dipole-first layout for Beam1 and
Beam2 with squeeze and tunability study:
•
•
•
•
•
•
18 km b-max requires additional Q’ correction
dispersion of 15 cm from D1/D2 arrangement for free
could be increased for D’ ≠ 0 at the IP
dispersion changes sign left and right from IP
S. Fartoukh proposed a `kissing scheme’ could allow equal signs of
D but vertical D is quite small
optics study relies on Nb3Sn technology:
•
•
•
 10 m long dipole magnets with B = 15 T
 quadrupole magnets with 260 T/m and 80 mm
aperture  11 T coil field
 IR layout provides magnetic TAS for “free”
F. Ruggiero
CERN
LHC upgrade scenarios
Alternative Dipole-First optics (O.Brüning)
proposal of a low-gradient solution that could be
realized with NbTi technology
•
•
•
•
18 km b-max requires additional Q’ correction
maximum gradient of 70 T/m allows more than
200 mm diameter with a peak coil field of 5.5 T
Dispersion inside the triplet could be increased for
D’ ≠ 0 at the IP
Layout still requires an improved TAS absorber
F. Ruggiero
CERN
LHC upgrade scenarios
CERN: the World’s Most Complete
Accelerator Complex (not to scale)
F. Ruggiero
CERN
LHC beam performance and luminosity upgrade scenarios
Injector chain for 1 TeV proton beams
injecting at 1 TeV into the LHC reduces dynamic effects of persistent currents, i.e.:
 persistent current decay during the injection flat bottom

snap-back at the beginning of the acceleration
 easier beam control
 decreases turn-around time and hence increases integrated luminosity
Trun

Trun  Tturnaround
1
 e L

L

Trun (optimum)  Trun
 Ldt  L0  Trun  Tturnaround


 L Trun  Tturnaround   L
0
L0
L
Tturnaround
Trun
[cm-2s-1]
[h]
[h]
[h]
1034
1034
15
15
10
5
14.6
10.8
1035
6.1
10
1035
6.1
5
F. Ruggiero
CERN
with gas = 85 h and
xIBS= 106 h (nom)  40 h (high-L)
∫200 days L dt [fb1]
gain
66
85
x1.0
x1.3
8.5
434
x6.6
6.5
608
x9.2
LHC beam performance and luminosity upgrade scenarios
Injector chain for 1 TeV proton beams
injecting in LHC more intense proton beams with constant brightness,
within the same physical aperture
 will increase the peak luminosity proportionally to the proton intensity
n f rep
 c z 
L  Q
1  * 
2 *
rp b
 2 
2
bb
2
d sep

 c
b
n
*
• at the beam-beam limit, peak luminosity L is proportional to normalized
emittance n = , unless limited by the triplet aperture
• an increased injection energy (Super-SPS) allows a larger normalized
emittance n in the same physical aperture, thus more intensity and
more luminosity at the beam-beam limit.
• the transverse beam size at 7 TeV would be larger and the relative
beam-beam separation correspondingly lower: long range beam-beam
effects have to be compensated.
F. Ruggiero
CERN
LHC upgrade scenarios
LHC injector complex upgrade
•
•
•
•
CERN is preparing a road map for an upgrade of its
accelerator complex to optimize the overall proton
availability in view of the LHC luminosity upgrade and of
all other physics users
Scenarios under consideration include a new proton linac
(Linac 4, 160 MeV) to overcome space charge limitations
at injection in the PS Booster and a new
Superconducting PS reaching an energy of 50-60 GeV
This would open the possibility of a more reliable
production of higher-brightness beams for the LHC, with
lower transmission losses in the SPS thanks to the
increased injection energy
It would also offer the opportunity to develop new fast
pulsing SC magnets in view of a Super-SPS, injecting at
1 TeV into the LHC
F. Ruggiero
CERN
LHC upgrade scenarios