cryogenics for the large hadron collider (lhc): design ......easitrain school 2, cea saclay 1st...
TRANSCRIPT
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Cryogenics for the Large Hadron Collider (LHC):design, construction, operation & upgrade
Philippe LebrunCERN retired
EASITrain School 2, CEA Saclay
1st October 2019
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Contents
• Technical challenges of the LHC
• He II magnet cooling scheme
• Cryostat design and heat loads
• Refrigeration at 4.5 K and 1.8 K
• Specific He II technologies
• Instrumentation and controls
• Operation
• Upgrade
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Superconductivity and cryogenics are key technologies to the LHC and its large, multipurpose detectors
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A new territory in energy and luminosity
ISR
SppS
TeVatron
LEP1
LEP2 HERA
LHC
1.E+30
1.E+31
1.E+32
1.E+33
1.E+34
1.E+35
10 100 1000 10000 100000
Lu
min
osity [cm
-2.s
-1]
Center-of-mass energy [GeV]
x 100
x 7
Ph. Lebrun EASITrain School 2 Saclay 2019 4
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1232 twin-aperture superconducting dipolesBnom = 8.33 T, Inom = 11850 A
Ph. Lebrun EASITrain School 2 Saclay 2019 5
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Superfluid helium coolingenhances performance of Nb-Ti superconductor at high field
Ph. Lebrun EASITrain School 2 Saclay 2019 6
10
102
103
104
0 5 10 15 20 25
Engi
ne
eri
ng
Cri
tica
l Cu
rre
nt
De
nsi
ty (
A/m
m²,
4
.2K
)
Magnetic Field (T)
Nb₃Sn: Internal Sn RRP®
Nb₃Sn: High Sn Bronze
Nb-Ti: LHC 1.9 K
Nb-Ti: LHC 4.2 K
Nb-Ti: Iseult/INUMAC MRI 4.22 K
High-Jc Nb3Sn
Bronze Nb3Sn
Nb-Ti
High-Jc Nb3Sn
Bronze Nb3Sn
Nb-Ti
Normal-
conducting
magnets
LHCTeVatron
RHIC HERA
FCC
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Specific power consumption of particle collidersSuperconductivity and high fields
allow strong reduction of the power bill!
Ph. Lebrun EASITrain School 2 Saclay 2019 7
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The beam screenA multi-function component required by thermodynamics and beam physics
• Interception of beam-induced heat loads at 5-20 K (supercritical helium)
• Shielding of the 1.9 K cryopumpingsurface from synchrotron radiation (pumping holes)
• High-conductivity copper lining for low beam impedance
• Low-reflectivity sawtooth surface at equator to reduce photoemission and electron cloud
Ph. Lebrun EASITrain School 2 Saclay 2019 8
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Functions and constraints of LHC cryogenics
Functions
• Maintain all magnets at operating temperature below 1.9 K
• Handle dynamic heat loads due to magnet powering and circulation of beams
• Cooldown/warmup magnets (37’500 tons) from/to room temperature in less than 3 weeks
• Handle magnet resistive transitions without loss of helium and recoverfrom them in few hours
Constraints
• Produce refrigeration in imited numberof points (5) around machine circumference
• Re-use four 18 kW @ 4.5 K refrigerators from LEP2 project
• Distribute refrigeration in 3.3 km long sectors
• Tunnel slope 1.4 % leading to elevation differences of 150 m acrossthe ring
• Minimize power consumption
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Contents
• Technical challenges of the LHC
• He II magnet cooling scheme
• Cryostat design and heat loads
• Refrigeration at 4.5 K and 1.8 K
• Specific He II technologies
• Instrumentation and controls
• Operation
• Upgrade
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Thermophysical properties of superfluid heliumand engineering applications
• Temperature < 2.17 K superconductor performance
• Low effective viscosity permeation
– 100 times lower than water at normal boiling point
• Very high specific heat stabilization
– 105 times that of the conductor by unit mass
– 2x103 times that of conductor by unit volume
• Very high thermal conductivity heat transport
– 103 times that of OFHC copper
– Peaking at 1.9 K
– Still, insufficient for transporting heat over large distances across small temperature gradients
0,00001
0,0001
0,001
0,01
0,1
1
10
100
0 1 2 3 4 5
Temperature [K]
Spe
cific
he
at
[J/g
.K]
LHe
Cu
0
500
1000
1500
2000
1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2
T [K]
Y(T
) ±
5%
T
K T,q q Y T
dT
dX
q
Y(T)
q in W / cm
T in K
X in cm
2.4
3.4
2
Copper OFHC
Helium II
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Pressurized vs saturated He II
1
10
100
1000
10000
0 1 2 3 4 5 6
Temperature [K]
Pre
ssure
[kP
a]
SOLID
VAPOUR
He IHe IICRITICAL
POINT
PRESSURIZED He II
(Subcooled liquid)
SATURATED He II
SUPER-
CRITICAL
SATURATED He I
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Advantages & drawbacks of He II p
• Advantages– limits the risk of air inleaks and
contamination in large and complex cryogenic systems
– for electrical devices, limits the risk of electrical breakdown at fairly low voltage due to the bad dielectric characteristics of helium vapour (Paschen curve)
• Drawbacks– one more level of heat transfer
– additional process equipment (pressurized-to-saturated helium II heat exchanger)
Paschen curve for helium
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Cooling LHC magnets with He II p
1
10
100
1000
10000
0 1 2 3 4 5 6
Temperature [K]
Pre
ssure
[kP
a]
SOLID
VAPOUR
He IHe IICRITICAL
POINT
PRESSURIZED He II
(Subcooled liquid)
SATURATED He II
SUPER-
CRITICAL
SATURATED He I
LHC
Ph. Lebrun EASITrain School 2 Saclay 2019 14
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Heat transfer across electrical insulationof LHC superconducting cable
Conduction in polyimide
Double wrap with partial overlap maintainsporosity and percolation paths in electricalinsulation of superconducting cable
Conduction in He II
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Steady-state conduction in He II p from 1.9 to 1.8 K
0
5
10
15
20
25
30
35
40
45
50
0 50 100 150 200
Length, L [m]
Qto
t [W
]
1 W/m 0.5 0.3
0.2
0.1
0.4
50
65
80
100
40
DN
Linear distributed heat load
1.8 KHe II Pres.
Cold sourceHe II Sat.(1.75 K)
Qtot= .L
SC magnet string
DNL
1.9 K (W/m)
1.8 KHe II Pres. 1.9 K
L
Cold sourceHe II Sat.(1.75 K)
Q
Superconductingdevice
DN
Lumped heat load 45 T hybrid magnet at NHMFL
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Cooling magnet strings with superfluid heliumGetting the best of helium transport properties
• Fixed temperature
• Small flow, no pump
• Monophase
• Excellent thermal conductivity
• Good dielectric strength
Ph. Lebrun EASITrain School 2 Saclay 2019 17
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18
LHC magnet string cooling scheme
107 m
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3.3 km
Cryogenic operation of LHC sector
Ph. Lebrun EASITrain School 2 Saclay 2019 19
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Contents
• Technical challenges of the LHC
• He II magnet cooling scheme
• Cryostat design and heat loads
• Refrigeration at 4.5 K and 1.8 K
• Specific He II technologies
• Instrumentation and controls
• Operation
• Upgrade
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LHC cryostat cross-section
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Thermal insulation techniquesMulti-layer reflective insulation
10 layers around cold mass at 1.9 K
30 layers around thermal shield at 50-75 K
Cold surface area in LHC ~ 9 hectares!
Thermal radiation from 290 K (black-body) ~ 400 W/m2 = 4 MW/ha
Heat flux from 290 K across 30 layers MLI ~ 1 W/m2 = 10 kW/ha
Ph. Lebrun EASITrain School 2 Saclay 2019 22
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Thermal insulation techniquesLow-conduction non-metallic support posts
LHC cold mass to be supported = 37’500 tons
Conduction length = support height ~ 0.2 m
At a compressive stress of 50 N/mm2, this requires a total support cross-section of 7.5 m2, representing a large thermal conduction path
100 kN
~ 70 K
5 K cooling line (SC He)
Aluminium strips to thermal shield at 50-75 K
Aluminium intercept plates glued to G-10 column
Reflecting layer on section exposed to 300 K radiation 290 K
5 K
1.9 K
0.2 m
0.01
0.1
1
10
100
1 10 100 1000
Temperature [K]
k [
W/m
.K]
Stainless steel
Titanium
G-10
Ph. Lebrun EASITrain School 2 Saclay 2019 23
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Distributed steady-state heat loads [W/m](Cryomagnets & distribution line in LHC arc)
Temperature 50-75 K 4.6-20 K 1.9 K LHe 4 K VLP
Heat inleaks* 7.7 0.23 0.21 0.11
Resistive heating 0.02 0.005 0.10 0
Beam-induced nominal** 0 1.58 0.09 0
Beam-induced ultimate** 0 4.36 0.11 0
Total nominal 7.7 1.82 0.40 0.11
Total ultimate 7.7 4.60 0.42 0.11
* no contingency
** Breakdown nominal ultimate
Synchrotron radiation 0.33 0.50
Image current 0.36 0.82
Beam-gas Scattering 0.05 0.05
Photoelectron 0.89 3.07
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25
Heat inleak measurements on full sectorsconfirm thermal budget
LHC sector (3.3 km)
TPhmQ ,
Measured
He property tables
0100200300400500600700800
DR Meas. DR Meas. DR Meas. DR Meas. DR Meas.
Sector 1-2 Sector 4-5 Sector 5-6 Sector 6-7 Sector 8-1
[W]
Continuous cryostat IT 1 IT 2
On average, measured values 20 % lower thandesign estimates
Ph. Lebrun EASITrain School 2 Saclay 2019
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Contents
• Technical challenges of the LHC
• He II magnet cooling scheme
• Cryostat design and heat loads
• Refrigeration at 4.5 K and 1.8 K
• Specific He II technologies
• Instrumentation and controls
• Operation
• Upgrade
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Layout of the LHC cryogenic system
• 5 cryogenic islands
• 8 cryogenic plants, each serving adjacent sector, interconnected when possible
• Cryogenic distribution line feeding each sector
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28
18 kW @ 4.5 K helium refrigerators
33 kW @ 50 K to 75 K 23 kW @ 4.6 K to 20 K 41 g/s liquefaction
High thermodynamic efficiency
COP at 4.5 K: 220-230 W/W
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Challenges of high-power 1.8 K refrigeration
1
10
100
1000
10000
0 1 2 3 4 5 6
Temperature [K]
Pre
ssure
[kP
a]
SOLID
VAPOUR
He IHe IICRITICAL
POINT
PRESSURIZED He II
(Subcooled liquid)
SATURATED He II
SUPER-
CRITICAL
SATURATED He I
Pressure ratio > 80
• Compression of large mass flow-rate of He vapor across high pressure ratio
intake He at maximum density, i.e. cold
• Need contact-less, vane-less machine hydrodynamic compressor
• Compression heat rejected at low temperature thermodynamic efficiency
Ph. Lebrun EASITrain School 2 Saclay 2019 29
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Warm pumping unit for LHC magnet tests3 stages of Roots + 1 stage rotary-vane pumps
6 g/s @ 10 mbar (1/160 of LHC!)
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Cycles for refrigeration below 2 K
LHeCC
CC
CC
CC
CC
4.5
K r
efr
ige
rato
rHeat load
HP
MP
LP
CC
CC
CC
LHe
Sub-atmosphericcompressor
4.5
K r
efr
ige
rato
r
Heat load
HP
MP
LP
1
2
3
“Integral Cold”Compression
“Mixed”Compression
LHe
Sub-atmosphericcompressor
4.5
K r
efr
ige
rato
r
Heat load
HPLP
Ele
ctr
ica
lh
ea
ter
“Warm”Compression
Sub-cooling
heat exchanger
~ 2 kPa
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32
2.4 kW @ 1.8 K refrigeration unitsCold hydrodynamic compressors
Electric drive 6’000 to 48’000 rpm, active magnetic bearings
1.8 K Refrigeration Unit Cycles
CC
He
at
Inte
rcepts
Air Liquide Cycle IHI-Linde Cycle
4 K, 15 mbar124 g/s
20 K, 1.3 bar124 g/s
0.35 bar
4.75 bar
4 K, 15 mbar124 g/s
20 K, 1.3 bar124 g/s
0.59 bar
9.4 bar
4.6 bar
CC
CC
CC
CC
CC
CC
CC
T
T
T
Adsorber
Adsorber
WC
WC
WC WC
HX
HX
HX
HX
Ph. Lebrun EASITrain School 2 Saclay 2019
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Specific features of LHC cold compressors
Axial-centrifugalImpeller (3D)
Fixed-vanediffuser
3-phase inductionElectrical motor(rotational speed: 200 to 700 Hz)
Activemagneticbearings
300 K
under
atm
osp
here
Cold
under
vacu
um
Inlet
Outlet
Pressure ratio2 to 3.5
Spiral volute
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Performance of LHC cold compressors
0
10
20
30
40
50
60
70
80
1985 1993 2000Year of construction
Isentr
opic
eff
icie
ncy [
%]
Tore Supra
CEBAF
LHC
12
12'is
HH
HHη
Tem
per
atur
e (T
)
Entropy (s)
P1
P2
1
2
2'
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Warm sub-atmospheric screw compressors
Compound two-stage screw compressor
WCS at CERN:125 g/s @ 0.6 bar
or4600 m3/h @ 15 °C
Mycom
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Warm sub-atmospheric screw compressors
Kaeser
WCS at CERN:125 g/s @ 0.35 bar
or2 x 3900 m3/h @ 15 °C
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Isothermal efficiencyof warm subatmospheric compressors
0
10
20
30
40
50
60
0 20 40 60 80 100Suction pressure [kPa]
Iso
the
rma
l e
ffic
ien
cy [
%]
Tore Supra
LHC Supplier #1
LHC Supplier #2
TESLA
Liquid ring pump
Screw compressors
comp
1
20
thQ
P
PlnTRn
η
Isothermalefficiency
T0 = 300 KP1
P2
Qcomp.
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C.O.P. of LHC cryogenic plants
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Contents
• Technical challenges of the LHC
• He II magnet cooling scheme
• Cryostat design and heat loads
• Refrigeration at 4.5 K and 1.8 K
• Specific He II technologies
• Instrumentation and controls
• Operation
• Upgrade
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Efficiency of Joule-Thomson expansion
Sub-cooling T1’ [K] H3-H2 [J/g] H3-H0 [J/g] [%]
without 4.5 12.6 23.4 54
with 2.2 20.4 23.4 87
Sub-cooling efficiency :03
23sc
HH
HH
sc
expansion
valve
m.
Q.
LHe
Sat. He II
1.8 K, 16 mbar
expansion
valve
m.
Q.
LHe
Sat. He II
1.8 K, 16 mbar
sub-cooling
HX
1
23
1
1'
23
1'
Enthalpy of pure liquid
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Subcooling before J-T expansion
1
10
100
1000
0 10 20 30 40
Enthalpy [J/g]
Pre
ssu
re [
kP
a]
Sub-cooled liquid @ 2.2 K
Saturated liquid @ 4.5 K
Saturation dome
13 % of GHe produced in expansion
46 % of GHe produced in expansion
1
22
1’
30
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Subcooling HX technologies for LHC
Stainless steel sheet
Perforatedcopper plateswith SS Spacers
SS coiled tubes
Mass-flow: 4.5 g/sP VLP stream: < 1 mbarSub-cooling T: < 2.2 K
DATE
SNLS
Romabau
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Protection against air inleaks
• Motor shaft of warm sub-atmospheric compressors placed at thedischarge side to work above atmospheric pressure.
• For sub-atmospheric circuits which are not under guard vacuum or notcompletely welded, apply helium guard protection on dynamic seal ofvalves, on instrumentation ports, on safety relief valves and on criticalstatic seals
I
VLP circuitsSafety valves Instrumentation and components
not completely welded,without double O-ring joints
Static sealwith double O-ring joints
HP helium
PT
Evacuationfor periodic rinsing
He guard header
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Contents
• Technical challenges of the LHC
• He II magnet cooling scheme
• Cryostat design and heat loads
• Refrigeration at 4.5 K and 1.8 K
• Specific He II technologies
• Instrumentation and controls
• Operation
• Upgrade
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Local Cryogenic
control room
Central Control Room
OWS [1..x]
PVSS DS Sector
OWS
[1..x]
PROFIBUS DP
networks
PROFIBUS PA networks
WFIP
Networks (7)
RadTol
electronics
UNICOS
PLC
S7-400
Siemens
FECs
(FESA)
RM sector 81
RM sector 78 RM sector 78
PLC
QUIC
Schneider
Return
Module
Cryo instrumentation expert tool
PVSS DS
TT, PT, LT, DI, EH CV
Controls for LHC cryogenics21300 AI, 7000 AO, 18400 DI, 4200 DO
4700 analog control loops
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Cryogenics in CERN Accelerator Control Centre
On shift 24/7
Process synoptics and control
Trend curves
Fixed displays
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Display of cryogenic operation indicators
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Contents
• Technical challenges of the LHC
• He II magnet cooling scheme
• Cryostat design and heat loads
• Refrigeration at 4.5 K and 1.8 K
• Specific He II technologies
• Instrumentation and controls
• Operation
• Upgrade
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LHC temperature history 2009-2019(D. Delikaris)
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Cooldown to 80 K: 600 kW per sector with up to ~5 tons/h liquid nitrogen
Precooling 37’500 t magnets with 10’000 t liquid nitrogen
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Helium inventory management
Total He inventory of LHC accelerator: 135 tonsOn-site storage: 125 tons« Virtual » storage contract: 60 tons
Storage capacity GHe @ 2 MPa, Tambient:- 58 x 250 m3 tanks- 40 x 80 m3 tanks
Storage capacity LHe @ 0.1 MPa, 4.5 K:- 6 x 120’000 liter vacuum-insulated vessels
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Availability of LHC cryogenics 2010-2018(D. Delikaris)
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LHC helium losses 2007-2019(D. Delikaris)
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Contents
• Technical challenges of the LHC
• He II magnet cooling scheme
• Cryostat design and heat loads
• Refrigeration at 4.5 K and 1.8 K
• Specific He II technologies
• Instrumentation and controls
• Operation
• Upgrade
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The HL-LHC projectObjectives and contents
• Determine a hardware configuration and a set of beam parameters that will allow the LHC to reach the following targets:
– enable a total integrated luminosity of 3000 fb-1
– enable an integrated luminosity of 250-300 fb-1 per year
– design for m 140 ( 200) (peak luminosity of 5 (7) 1034 cm-2 s-1)
– design equipment for ‘ultimate’ performance of 7.5 1034 cm-2 s-1 and 4000 fb-1
Ph. Lebrun EASITrain School 2 Saclay 2019 55
Major intervention on 1.2 km of LHC ring
• New IR-quads using Nb3Sn superconductor
• New 11 T Nb3Sn (short) dipoles
• Collimation upgrade
• Cryogenics upgrade
• Crab Cavities
• Cold powering
• Machine protection
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Paths to high luminosity
Beam-beam effect precludes too low crossing angle
Ph. Lebrun EASITrain School 2 Saclay 2019 56
𝑳 = 𝒏𝒃𝑵
𝟐𝒇𝒓𝒆𝒗𝟒𝝅 𝜷∗ 𝜺𝒏
𝑹; 𝑹 = ൗ𝟏 𝟏 +𝜽𝒄 𝝈𝒛𝟐𝝈
Increase bunch population
Reduce beta at collision Reduce emittance
Increase R = reduce crossing angle?
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The HL-LHC projectFrom accelerator physics to technology
Ph. Lebrun EASITrain School 2 Saclay 2019 57
Increase bunch population
Reduce beta at collision
Reduce emittance
Reduce crossing angle
Increase intensity & brightness of injectors:
the LIU project
More powerful cryogenicsImproved collimation
Improved machine protection Stronger R to E relocation
New low-beta quadrupoles
Limit beam-beam effect
“Crab” cavities
Acce
lera
tor
ph
ysic
s
Acce
lera
tor
tech
no
log
y
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Additional cryogenics for HL-LHC(S. Claudet)
P7
P8
P6
P5
P4
P3
P2
P1
Existing cryoplant
New HL-LHC cryoplant
+
P1 and P5
o 2 new cryoplants (~15 kW @ 4.5 K incl. ~3 kW @ 1.8 K)
o 2 x 750m cryo-distribution for high-luminosity insertions
P4
o upgrade (+2 kW @ 4.5 K) of existing LHC cryoplant (18 kW @ 4.5 K)
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Some references
• Ph. Lebrun, Cryogenics for the Large Hadron Collider, IEEE Trans. Appl. Supercond. 10 (2000) 1500-1506
• Ph. Lebrun, Industrial technology for unprecedented energy and luminosity: the Large Hadron Collider, EPAC9 Lucerne, JACoW (2004) 6-10
• LHC Design Report, vol.1, The LHC Main Ring, CERN-2004-003-V-1 (2004)
• Ph. Lebrun, Advanced technology from and for basic science: superconductivity and superfluid Helium at the Large Hadron Collider, Inaugural Lecture of the Academic Year 2007-2008 -Politechnika Wroclawska/Wroclaw University of Technology, CERN-AT-2007-030 (2007)
• Ph. Lebrun, Commissioning and First Operation of the Large Hadron Collider, Proc. ICEC23 Wroclaw (2011) 41-48
• Ph. Lebrun, The LHC accelerator: performance and technology challenges, in LHC physics, Scottish Graduate Series, Taylor & Francis, ISBN 978-1-1398-3770-2 (2012) 179-195
• D. Delikaris et al., The LHC cryogenic operation: availability results from the first physics run of three years, IPAC4 Shanghai, JACoW (2013) 3585-3587
• Ph. Lebrun & L. Tavian, Cooling with superfluid helium, Proc. CERN Accelerator School Erice 2013, CERN-2014-005 (2014) 453-476
• S. Claudet et al. Helium inventory management and losses for LHC cryogenics: strategy and results for Run 1, Phys. Procedia 67 (2015) 66-71
• Ph. Lebrun, Twenty-three kilometres of superfluid helium cryostats for the superconducting magnets of the Large Hadron Collider, in J. Weisend (ed.) Cryostat design, Springer, ISBN 978-3-319-31150-0 (2016) 67-94
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