Transcript LHC Accelerator Upgrade J.-P. Koutchouk CERN/AT 11/7/2015 Talk to IoP/JPK Outline 1. 2. 3. 4. Introduction Goals (phases I and II, energy upgrade) Phase I: the consolidation Phase II: the luminosity upgrade • • • • • How.

LHC Accelerator Upgrade
J.-P. Koutchouk
CERN/AT
11/7/2015
Talk to IoP/JPK
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Outline
1.
2.
3.
4.
Introduction
Goals (phases I and II, energy upgrade)
Phase I: the consolidation
Phase II: the luminosity upgrade
•
•
•
•
•
How to increase further the luminosity?
Increasing the beam current
Focusing more
Luminosity issues
Technological challenges
5. The energy upgrade
6. Conclusions
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1- Introduction
The present focus of the accelerator sector is
obviously the baseline LHC.
Planning the upgrade is nevertheless timely as it is
largely technology-driven with lead times of 5 to
15 years, depending on goals and complexity.
Yet, several choices require LHC results (machine and
physics)
Hence upgrade studies aim primarily at identifying the
necessary hardware to launch in time the R&D
programmes and give clear goals to the action of
CERN partners (US-LHC, CARE-HHH and NED)
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2a- The goals
Phase I:
LHC+
(or SLHC1)
Phase II:
SLHC
tentative goal
planning
2012
Triplet consolidation for high integrated
luminosity; Luminosity 1 to  2;
no interference with detectors
2016
Luminosity  10:
2020-25
energy doubler or tripler
(or SLHC2)
Phase III:
LHC-D or
LHC-T
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2b- The goals: the luminosity profile
Evolution
2008
2009
1.4 10
1.2 10
cm 2s
luminosity
8 10
with
2013
no upgrade
2014
2015
yellow , Phase II
2016
2017
2018
green , Phase I
2019
2020
2021
II
red
2022
2023
2019
2022
35
35
•LHC baseline
35
1
1 10
of peak luminosity
2010
2011
2012
• SLHC
34
•LHC+ & SLHC
6 10
4 10
2 10
34
34
34
2008
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2009
2010
2011
2012
2013
2014
2015
2016
time
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2017
2018
2020
2021
2023
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3a- Phase I (LHC+)
1. Motivations:
•
•
Facilitate reaching the ultimate luminosity of
2.31034cm-2s-1 (made difficult following increase
of crossing angle, introduction of a beam screen
and collimator impedance)
Improve the running efficiency at nominal
performance & create margins if some of the
design parameters would not be reached.
1. Boundary conditions:
•
•
•
no interference with detectors,
fastest implementation: Nb-Ti s.c. technology;
fast performance increase: no new beam dynamics
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3b- Phase I (LHC+)
1. Solution: change the IR1 & IR5 triplets (70mm)
for larger aperture ones (130mm). This gives the
potential to recover the “ultimate” luminosity with
a safety margin of ~50%. D1 may have to be
changed. The superconducting cable is available
(spare LHC dipole cable).
2. Status:
•
•
•
•
•
Feasibility studies done
Included in Proposal SLHC-PP to FP7-Infrastr.-2007-1
coord. L. Evans, issued in May 2007.
Project coordinator appointed (R. Ostojic) to evaluate
cost and manpower requirements.
Timescale: operational in 2012
Budget: remains to be found
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4a- Phase II (SLHC)
• Challenge: LHC baseline was pushed to
“maximum” in the competition with SSC. Going
beyond requires creative solutions.
• Luminosity goal: ~ 101034cm-2s-1
• Boundary conditions: For such a significant
upgrade, the added complexity should be minimized
for a fast progress of performance and the risks
mitigated for a graceful degradation in case of
unexpected.
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4b- P.II: The luminosity formula
 

L  F  c  * , kb , N b ,  s ,  * ,  N
crossing angle

  *  kb  N b2

H 
  *

 s N
standard
Variation of β along bunch
F decreases with decreasing *, increasing kb, Nb and
s. H is in the range {0.9, 1} for practical *.
A constraint is the “beam-beam limit”, usually given
by:
Nb
Qbb  F
 QbbMAX
N
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4c- P.II: The strategies
Luminosity at the
beam-beam limit:
L   form Qbb
1

*
 N b k b 
Two main tracks:
•
Luminosity increase by increasing the beam
current
•
Luminosity increase by lowering *
•
+ work on form factors and beam-beam limit
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4d- P.II: Increase of beam current
Strategy:
1. Increase significantly the bunch charge Nb (*4).
2. Respect the beam-beam limit (that would be exceeded) by a
change of regime: lengthen the bunch to reach a quasi
coasting beam regime by longitudinal emittance blow-up.
3. Reduce the number of bunches (50 ns spacing) to control ecloud and image current heat deposition & beam stability.
4. Recover the lost factor of 2 by reducing beta* by a factor of 2
(25 cm)
5. Reduce the crossing angle by wire compensation
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4e- P.II: Increase of beam current
Merits: no elements in detectors; quasi nominal insertion beam
optics with small chromatic aberrations; higher average luminosity
per run.
Challenges: new beam dynamics: novel beam-beam regime
not experienced at this level of performance; higher peak beam
current coupling to machine elements, sophisticated rectangular
beam distribution; machine protection: higher bunch/beam power;
higher collimator robustness required; radiation protection:
protection to be re-assessment when exceeding the ultimate beam
current in the LHC (INB). injectors: new beam preparation;
injectors’ upgrade for full operational performance: Linac4, PS2,
SPS improvement.
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4f- P.II: Increase of beam current
Investments: new triplet (*= 25 cm) & D1, install the 200 MHz
RF system, possibly more resistant collimators, upgrade of dumping
system, extend the dynamic range of some beam instruments, upgrade
radiation protection, upgrade of injectors (SPS, PS, Booster and
Linac).
What if: - if beam current cannot be reached or if new beam-beam
regime inefficient or if injectors not ready, return to 25 ns spacing to
recover the Phase I performance (nominal  1 to 2)
-Could then gain +30% luminosity with additional crab crossing.
-Recover Phase II performance if new triplet is *= 10cm type AND if
larger angle crab crossing would be successful.
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4g- P.II: Decrease of beta*
To improve significantly the luminosity by a * reduction, a
modification of the crossing scheme or parameters is mandatory
(Sep1 = 3)
(Sep1 = 3)
(Sep1 = 5)
PAC07
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4h- P.II: Early separation
D0
Full Early Separation
(50 ns only if D0 not in
inner detector)
D0
First encounter
D0
Partial Early
Separation
(25 or 50 ns)
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First encounter
D0
We need a residual crossing angle
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4i- P.II: Detector geometrical constraints
We cannot put the D0 in the inner detector.
There are potential slots starting at 3.5 m and 6.8 m (ATLAS).
A “partial” early separation should be considered
Courtesy of M. Nessi, ‘Machine upgrade, ATLAS considerations’, June 2006
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4j- P.II: Decrease of beta*
Merits: modification of LHC only in IR’s with no consequence
for the global machine; no beam current increase beyond the agreed
LHC & INB programs (collimation, machine and radiation
protection); same beam dynamics mode and operations strategy;
easy luminosity leveling, expected faster build-up of performance
related to a lower complexity; compatible with 25 and 50 ns spacing
(with reduced performance by 2), mild upgrade of injectors but
benefits from an injector upgrade program.
Challenges: installation of dipoles deep inside the detectors,
higher chromatic aberrations, a few encounters at a reduced beam
separation, lower integrated luminosity per run.
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4k- P.II: Decrease of beta*
Investments: {new triplet (*= 10 cm), D1}, D2, one matching
quad?, 4 early sep. dipoles, optional crab cavities and electron
lenses, improvements in injectors.
What if: - if reduced separation not acceptable: full recovery
possible but using new untested solutions: i) e-lens compensation or
ii) increase separation and use crab or iii) turn to 50 ns operation
with a loss by  2, that could be compensated by some current and
bunch length increase (other strategy).
- if chromatic aberrations too large: fast decrease with increase of
beta*, reduction of l*, Q0, or achromatic collimation insertions?
-If conceptual problem, turn to intensity increase with same
hardware in IR’s.
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parameter
symbol
transverse emittance
 [mm]
protons per bunch
25 ns, small *
50 ns, long
3.75
3.75
Nb [1011]
1.7
4.9
bunch spacing
t [ns]
25
50
beam current
I [A]
0.86
1.22
Gauss
Flat
longitudinal profile
rms bunch length
z [cm]
7.55
11.8
beta* at IP1&5
* [m]
0.08
0.25
full crossing angle
c [mrad]
0
381
Piwinski parameter
f=cz/(2*x*)
0
2.0
0.86
0.99
hourglass reduction
peak luminosity
L [1034 cm-2s-1]
15.5
10.7
tL [h]
294
2.2
403
4.5
peak events per
crossing
initial lumi lifetime
effective luminosity
(Tturnaround=5 h)
Leff [1034 cm-2s-1]
3.6
3.5
Trun,opt [h]
4.6
6.7
1.04 (0.59)
0.36 (0.1)
e-c heat SEY=1.4(1.3)
P [W/m]
SR heat load 4.6-20 K
PSR [W/m]
0.25
0.36
image current heat
PIC [W/m]
0.33
0.78
gas-s. 100 h (10 h) tb
Pgas [W/m]
0.06 (0.56)
0.09 (0.9)
extent luminous region
l [cm]
3.7
5.3
comment
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D0 + crab
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two draft
upgrade
scenarios
(courtesy F.
Zimmermann,
Valencia 2006)
compromises
between
heat load
and # pile up
events
wire comp.
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IP1& 5 luminosity evolution for 25-ns and 50-ns spacing
F. Zimmermann
25 ns
spacing
50 ns
spacing
average
luminosity
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initial luminosity peak
may not be useful for physics
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(set up & tuning?)
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4n-P.II: Luminosity leveling
The relatively fast luminosity decay and high multiplicity
call for Luminosity Leveling.
…but the issue is how to do it efficiently:
• dynamic beta*: uses existing hardware; probably complex
due to large number of side-effects in IR’s AND arcs.
• dynamic bunch length: needs new RF; possible side
effects in whole machine related to modification of peak
current.
• dynamic crossing angle: using the early separation
hardware, no side effects identified. Even better: use crab.
EXCEPT, valid for all, a modulation of the length of the
luminous region.
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4p-P.II: Luminosity leveling
Multiplicity
around 50
G. Sterbini
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4p-P.II: Learning period
Performance rise depends on complexity. Statistical law by V.
Shiltsev. Using/extending his approach yields:
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2018
2019
2020
2021
2022
2023
ISR31
2008
2009
2010
2011
Luminosity
2012
2013
profile
2014
over
2015
15 years without upgrade
2016
2017
2018
2019
2020
2021
2022
2023
complexity
4
1.4 10
35
HERA1
35
8 10
6 10
4 10
2 10
34
Complexity
luminosity
cm 2s
1
1 10
35
years
1.2 10
34
34
3
HERA2
RHIC
2
SppS
ISR26
34
TEV2a
2008
2009
2010
2011
2012
2013
2014
2015
2016
time
2017
2018
2019
2020
2021
2022
2023
1
TEV1b
luminosity
2008
2009
2010
2011
2012
2013
2014
2015
2016
time
2017
The strategy with beam current increase requires about 3 years
after Phase I (4 years without).
In the ISR, a comparable beta* decrease (/7) took a few weeks
at reduced current; one year for the LHC at full current?
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4q- P.II: LHC technological challenges
• Triplets: the key issue (challenge, lead time, cost) The
most promising technology is Nb3Sn for larger field (50%)
and larger temperature margin. A very recent success for this
delicate technology: US-LARP TQS02a reached ~ 11T peak.
The aperture barrier of 90 to 110 mm is being jumped (stress
limit) and the required length (~9 m) should not cause an
additional problem.
Fall-back solution: very large and long low gradient Nb-Ti
triplet for larger temperature margin & ability to collect the
collision debris on masks; presently considered for *≥ 25
cm but might be pushed further (?)
• Energy
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deposition: being included in magnet design
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4r- P.II: LHC technological challenges
• Early separation dipoles: feasibility study done
(e-m and power deposition). It appears so far technically
doable. Before further studies, an assessment of its impact
on the detection of particles is needed for ATLAS
(organized) and CMS (to be organized).
• Wire compensation: promising results in SPS;
implemented in RHIC by US-LARP and under study.
• Crab crossing: under test at KEK (electrons); being
considered for US-LARP R&D: accuracy challenging.
• Electron lenses: implemented at Tevatron;
considered for installation in RHIC and support by USLARP: very challenging for full beam-beam compensation.
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5-The energy upgrade
The progress of super-conducting magnet technologies opens
the possibility to consider doubling the LHC energy with
Nb3Sn (25 TeV c.m.) or perhaps tripling it with emerging
technologies based on HTS superconductors.
This would be a major upgrade of the CERN accelerator
complex that requires feasibility studies yet to be done.
The first and critical element is the availability of collider
quality high-field superconducting magnets that can stand
or are shielded from the emitted synchrotron radiation.
The phase II studies do not include the energy upgrade but
should be used to prepare and e.g. foster external contributions
if the physics motivation is expressed/confirmed.
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Conclusion
The upgrade of the LHC luminosity is a natural and necessary
development for such a unique facility; it is very challenging. A
two-phase strategy minimizes the increments in complexity.
Two roads are considered to reach the second phase with ~10 in
peak luminosity. They are both promising with different
challenges and risks. One should aim, if possible, at combining
both for a robust solution.
A tight collaboration with the experimentalists and sharing of
risks is needed, e.g. for an early separation scheme, for the
luminosity leveling options,…
The technology needed requires the R&D program proposed in
the White Paper and the joint effort of the community: USLARP, CARE and, of course, the Experimenters…
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Annexes
1. Variation of the luminous region with dynamic c
2. Expression of the F factor
3. Nominal LHC parameters
4. Minimum crossing angle
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Variation of the luminous region with dynamic c
Sterbini
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luminosity reduction factor from crossing angle
 c z
R =
; 
2 x
1  2
1
Piwinski angle
nominal LHC
Zimmermann
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Ruggiero
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