Superconduttivita` e Criogenia per LHC

Transcript

Superconduttivita’ e Criogenia
XXII Giornate di Studio sui Rivelatori
Torino, 15 Giugno 2012
Amalia Ballarino
European Organization for Nuclear Research (CERN), Geneva
 Introduction
 Superconductivity for high energy physics
 Part I
 Cryogenics for LHC
 Part II
 Superconductivity in LHC
 PART III
 Superconductivity & Cryogenics in LHC Upgrades
Amalia Ballarino
 Introduction
 Part I
 Part II
 Superconductivity in LHC
 PART III
 Superconductivity & Cryogenics in LHC Upgrades
Amalia Ballarino
Introduction
What is cryogenics ?
Cryogenic: for Greek “kryos", which means cold or freezing, and
"genes" meaning born or produced.
“In physics, cryogenics is the study of the production of very
low eye temperature (below –150 °C, –238 °F or
123 K) and the behavior of materials at those temperatures”
from Wikipedia
The lowest natural temperature ever recorded on earth was in 1983
in Antartica: -89.2 oC or 183.8 K
What is superconductivity ?
“Superconductivity is a phenomenon occurring in certain materials at
very low temperatures , characterized by exactly zero electrical
resistance and the exclusion of the interior magnetic field (the
Meissner effect)
from Wikipedia
Amalia Ballarino
Introduction
Resistance (Ohm) vs Temperature (K)
of Hg – K. Onnes, 1911
Amalia Ballarino
Introduction
Cryogenics
Particles accelerator
Superconductivity
Amalia Ballarino
Introduction
Accelerator: Instrument of High Energy Physics
h/p
1 TeV  10-18 m
Amalia Ballarino
Introduction
Accelerator Energy and Magnetic Field
Particles are produced by converting the collision energy into mass
Synchrotron:
E[GeV]=0.29979 B[T] R[m]
High energy  High field magnets
Energy (TeV)
100.00
r=10 km
LHC
10.00
r=1 km
r=0.3 km
1.00
Tevatron
SSC
UNK
LHC
0.10
Colliding beams: ECM~2E
r=3 km
HERA
RHIC
LEP
0.01
0
5
10
15
Dipole field (T)
Amalia Ballarino
Introduction
Resistive magnets
 The most economical designs are iron-dominated;
 The upper field limit for iron-dominated magnets is ~2 T due to iron
saturation;
 Most resistive accelerator magnet rings are operated at low field (~
1 T), to limit power consumption ( B R).
Superconducting magnets
 Significant reduction in power consumption (cryogenic power  R);
 Higher current density in the magnet coils.
Amalia Ballarino
Introduction
Economical savings due to superconductivity
 The LHC has a circumference of 27 km, out of which some 20 km
of main superconducting magnets operating at 8.3 T and
1.9 K. Cryogenics will consume about 40 MW electrical power
from the grid.
If the LHC were not superconducting:
 Using resistive magnets operating at 1.8 T (limited by iron
saturation), the circumference should be about 100 km, and the
electrical consumption 900 MW, leading to prohibitive capital
and operation costs.
Amalia Ballarino
Introduction
The Energy Frontier
Amalia Ballarino
Introduction
Large Superconducting Accelerators
Tevatron
FermiLab
HERA
DESY
RHIC
BNL
LEP
CERN
LHC
CERN
Type
p -p
e-p
Heavy
ion
e+ - e-
p-p
Radius (m)
768
569
98
2801
2801
Energy per beam (TeV)
1
0.9
0.1
0.104*
7
Op. temperature (K)
4.6
4.5
4.6
RT-4.5 K*
1.9
Dipole field (T)
4.4
4.68
3.46
0.135
8.33
Dipole Current (kA)
4.4
5.03
5.09
4.5
11.8
Commissioning
1883
1990
19992000
1989
20072008
* Upgrade with sc cavities to achieve the mass of the pair of W particles
Amalia Ballarino
 Introduction
 Part I
 Part II
 Superconductivity for LHC
 PART III
 Superconductivity & Cryogenics for LHC Upgrades
Amalia Ballarino
Part I
Cryo-history
1848: Determination of existence of zero absolute (Lord Kelvin)
1853: Discovery of Joule-Thomson effect (cool-down of a compressed
gas during adiabatic expansion)
1877: Liquefaction of oxygen below 320 atmospheres (R. P., Pictet)
1895: First liquefaction of air (Carl von Linde)
1898: Liquefaction of hydrogen (Dewar)
1908: Liquefaction of helium @ 4.2 K (*K. Onnes, Leiden Univ., ND)
1911: Discovery of superconductivity (K. Onnes)
1938 : Discovery of superfluid helium (He II). 1978: Kapitza, Nobel
Price in Physics
1971: Use of superfluid helium at atmospheric pressure (Roubeau)
1990: Use of pressurized superfluid helium in large-scale projects
(Claudet and Aymar)
2008: Start-up of LHC, with the world’s largest cryogenic system
(superfluid helium for cooling the superconducting magnets)
*1913:Noble Price in Physics “for his investigations on the properties of matter at low
temperatures which led, inter alia, to the production of liquid helium”
Amalia Ballarino
Part I
Standard P-T and T-v Phase diagrams
Cryogenic fluids
Cryogen
Triple
point
(K)
Normal
Boiling
point
(K)
Critical
point
(K)
Oxygen
54.4
90.2
154.6
Argon
83.8
87.2
150.9
Nitrogen
63.1
77.3
126.2
Saturated
Vapor/liquid
Temperature
24.6
27.1
44.4
Hydrogen 13.8
20.4
33.2
Neon
Helium
2.2
4.2
(-point)
5.2
Saturated vapor
curve
Saturated liquid
curve
Amalia Ballarino
Part I
Helium
Second lightest elemental gas, after hydrogen
Smallest of all molecules
Colorless, odorless, inert and non-toxic
Lowest boiling point of any element (-268.9°C, 4.2 K)
Helium is produced continually by the radioactive decay of uranium
and other elements, gradually working its way into the atmosphere
Commercial extraction from air is impractical because helium's
concentration is only about five parts per billion. Commercially, helium
is obtained from the small fraction of natural gas deposits that contain
helium volumes of 0.3 percent or higher
Unusual characteristics:
Helium remains liquid to absolute zero
At 2.1 K, liquid helium exhibits super fluidity or virtually zero viscosity
(Helium II), defies gravity to flow up container walls and becomes
nearly a perfect heat conductor
Amalia Ballarino
Part I
Phase diagram of helium (He4)
10000
SOLID
Pressure [kPa]
1000
-line
He II
SUPERCRITICAL
He I
CRITICAL
POINT
Tc=5.19 K
SATURATED He I pc=2.2 bar
100
PRESSURIZED He II
(Subcooled liquid)
10
VAPOUR
T=2.17 K
p=50 mbar
-point
SATURATED He II
1
0
1
2
3
4
5
6
Temperature [K]
Amalia Ballarino
Part I
Specific heat of saturated helium
Amalia Ballarino
Part I
Viscosity of He II
Allen and Misener
Keesom
Two fluid model:
rn, n, sn
rs, s=0, ss=0
Amalia Ballarino
Part I
Equivalent thermal conductivity of He II
2000
Helium II
Y(T) ± 5%
KT,q   q 2.4  YT
1500
dT q 3.4

dX Y(T)
1000
q in W / cm2
T in K
X in cm
500
T
OFHC copper
0
1.3
1.4
1.5
1.6
1.8
1.7
1.9
2
2.1
2.2
T [K]
Conduction in a tubular conduit
Amalia Ballarino
Part I
Superconductor performance at 4.2 K and 1.9 K
Critical current density of NbTi as a function of
Magnetic field at 4.2 K and 1.9 K
Amalia Ballarino
Part I
Saturated and pressurized He II at 1.9 K
10000
SOLID
Pressure [kPa]
1000
-line
He II
SUPERCRITICAL
He I
CRITICAL
POINT
100
PRESSURIZED He II
(Subcooled liquid)
SATURATED He I
10
VAPOUR
-point
SATURATED He II
1
0
1
2
3
4
5
6
Temperature [K]
Amalia Ballarino
Part I
Large scale He II systems
Use of saturated superfluid helium.
By lowering the pressure of the vapor when pumping on LHe, the
boiling temperature is reduced.
Liquid helium vapor pressure equilibrium and latent heat of vaporization
T (K)
1.6
1.7
1.8
1.9
2
2.1
2.17
4.22
P (kPa)
0.74
1.12
1.63
2.29
3.12
4.14
5.04
101.32
L (J g-1)
22.93
23.19
23.36
23.44
23.4
23.19
-
20.72
Amalia Ballarino
Part I
Large scale He II systems
Sat.
He
Pres.
He
Air inleak
prevention
-
+
Dielectric
strength
-
+
Pump-down
time
-
+
Enthalpy margin
for transient
-
+
Technical
simplicity
+
-
10000
SOLID
Pressure [kPa]
1000
-line
He II
SUPERCRITICAL
He I
CRITICAL
POINT
100
PRESSURIZED He II
(Subcooled liquid)
SATURATED He I
10
VAPOUR
-point
SATURATED He II
1
0
1
2
3
4
5
6
Temperature [K]
Amalia Ballarino
Part I
Refrigeration
Refrigerator: machine that extracts heat (Qc) from a low temperature
source (Tc) by adsorbing mechanical work (W); by doing so, it rejects
heat (Qh) to the high temperature source (Th, usually equal to
room temperature)
W = Qh-Qc
COP = benefit/cost = Qc/W =
1/((Qh/Qc)-1)
COP ≤ Tc/(Th-Tc)
COP= Cofficient of
Performance
Amalia Ballarino
Part I
Carnot cycle
The Carnot cycle is the most efficient refrigeration cycle operating
between two temperature levels
COP = Tc/(Th-Tc)
Tc (K)
77 (LN2)
20 (LH2)
4.2 (LHe)
1.8 (LHe)
W/Qc*
2.8
13.5
68.7
161.8
COP
0.3
0.07
0.004
0.0006
Tc/(Th-Tc)
0
Tc
0
*Figure of merit
1-2
2-3
3-4
4-1
Isothermal expansion
Isentropic compression
Isothermal compression
Isentropic expansion
T
QH
4
1
3
2
QC
s
Amalia Ballarino
Part I
Hypothetical Carnot cycle for He refrigeration
Amalia Ballarino
Part I
Claudet cycle
Widely used in refrigeration technology. It combines isenthalpic and
isentropic expansion. A refrigerator based on the Claudet cycle
comprises a compressor at RT, a series of heat exchangers, an
expansion turbine and a Joule-Thomson valve.
Amalia Ballarino
Part I
Refrigeration
Cooling methods:
 Heat transfer – counter flow heat exchangers
 External work – engine work (usually via turbine expanders, with
reduction of the gas temperature and pressure)
 Isenthalpic expansion (Joule-Thomson effect)
Amalia Ballarino
Part I
Joule-Thompson inversion temperature: temperature above which
expansion at constant enthalpy causes the temperature to rise,
and below which such expansion causes cooling
Joule–Thomson (Kelvin) coefficient:
JT=(T/p)h (K/Pa)
JT > 0
JT < 0
T<Tin
T>Tin
Joule-Thomson effect: adiabatic expansion of a gas (constant enthalpy)
Amalia Ballarino
Part I
Amalia Ballarino
Part I
Efficiency of refrigerators and liquefiers as a function
refrigeration capacity
30
(W/Qc)CARNOT,4.2K = 68.7
(Q/Qc) = 68.7/0.3 230
Amalia Ballarino
Part I
The cryogenic system for the LHC machine
0.999999991c
Amalia Ballarino
Part I
LHC layout
Sector=3.3 km
SSS=528 m
Amalia Ballarino
Part I
From the LEP to the LHC machine
8000
Amalia Ballarino
Part I
Layout of LHC cryogenic system
• 5 Cryogenic islands
• 8 Refrigerators:
- 2 at P4, P6 and P8
- 1 at P2
- 1 at P1.8
• 1 Refrigerator serves 1 Sector
(3.3 km)
• Possibility of coupling two
refrigerators via the
interconnection box
Amalia Ballarino
Part I
Performance of 4.5 K refrigerators at CERN
LHC:
COP= 230 W/W
 = 29  CARNOT
Electrical input power installed 4.5 MW/refrigerator
Amalia Ballarino
Gas storage tanks
Part I
Cooling the LHC ring
Total refrigeration capacity: 144 kW at 4.5 K (8×18 kW @ 4.5 K,
600 kW liquid nitrogen pre-cooler liquid used during cool-down) and
20 kW at 1.9 K (82.4 kW @ 1.9 K) distributed around the ring.
Amalia Ballarino
Part I
Principle of LHC cooling scheme
In the LHC, heat is conducted from the superfluid helium to the a heat
exchanger pipe containing a mixture of saturated vapor and superfluid
helium (p16 mbar) arranged in a series of 107 m cooling loops all around
the ring.
Amalia Ballarino
Part I
Schematic of cooling system
SHe supply (4.6 K, 3 bar)
GHe pumping (15 to 19 mbar)
Bayonet heat exchanger
Saturated LHeII
TT
Hydraulic
plug
TT
TT
Magnet
TT
TT
Ps0
TT
Wetted length (Lw)
Magnet cell (107 m)
Amalia Ballarino
TT
JT
TT
Dried length (Ld)
Pressurised
LHeII
Slope
Part I
Cryogenic flow scheme of an LHC cell (107 m)
107 m
Amalia Ballarino
Part I
Temperature levels in the LHC cryogenic system
In view of the high cost of refrigeration at 1.8 K, the main heat
influx in intercepted at higher temperatures. The temperature levels are:
 50 K to 75 K for thermal shielding of the cold masses;
 4.6 K to 20 K for cooling of the beam screens and lower temperature
interception;
 1.9 K quasi-isothermal superfluid helium for the magnets;
 4 K helium at very low pressure for transporting the superheated
helium flow coming from the 1.8 K heat exchanger tubes across the
sector length to the 1.8 K refrigeration unit;
 4.5 K saturated helium for some insertion magnets, RF cavities, and
the bottom end of the HTS leads;
 20 K to 300 K cooling for the resistive upper section of the HTS leads.
Amalia Ballarino
Part I
Cryogenic block diagram
4
Amalia Ballarino
Part I
Thermodynamic states of He in LHC cryogenic system
Amalia Ballarino
Part I
Process flow diagram of
LHC 18 kW cryoplant
E1
T1
E3
E4
T2
20 K - 280 K loads
M
Pa
M
Pa
0.
1
1.
9
LN2
Precooler
0.
4
M
Pa
(LHC current leads)
201 K
50 K - 75 K loads
E6
T1
T3
from LHC loads
(LHC shields)
T2
E7
75 K
T3
E8
T4
49 K
Adsorber
LHC shields
32 K
E9a
T4
20 K
E9b
13 K
10 K
E10
4.5 K - 20 K loads
T5
T7
from LHC loads
T7
(magnets + leads + cavities)
T6
9K
T8
4.4 K
0.
3
M
Pa
E11
T5
To LHC loads
E12
T6
E13
Amalia Ballarino
T8
Part I
Adsorbers
Turblne
CCB WCS
4.5 K
Refrigerator
Cold compressors
1.8 K Refrigeration Unit
1.8 K He refrigeration system
D
C
0.13 MPa,
20 -30 K
0.3 MPa
4.6 K
B
LHC Sector
Load
LHe 1.8 K
Q1.8K
Installed pumping capacity
125 g/s at 15 mbar
(i.e. ~2.4 kW @ 1.8 K)
Amalia Ballarino
Part I
LHC Distribution system
 The refrigerating helium of the magnets and cavities have to
be distributed over the 27 km of the accelerator, in the
LHC tunnel, 100 m below ground level.
 Due to the size of the experiment, ultra high performance
cryogenic lines have been specially designed for the LHC project.
 The achieved performance of the line is: about 0.05 W/m on
each of the 4.5 K tubes of the transfer line, a performance around
10 times better than usually achieved
Amalia Ballarino
Part I
LHC Cryogenic line in the LHC tunnel
Amalia Ballarino
Part I
Connection via service
module and jumper
Supply and recovery of
helium with 26 km long
cryogenic distribution
line
Static bath of superfluid
helium at 1.9 K in cooling
loops of 110 m length
Amalia Ballarino
Part I
Transverse cross section of the LHC tunnel
Amalia Ballarino
Part I
Cool-down of LHC machine
 Removal of air in circuit by evacuation and He filling (1 week);
 Removal of dust and debris by flushing the helium circuits with
high helium flow at 300 K (1 to 2 week per sector) ;
 Cool-down of 4625 t per sector over 3.3 km:
From 300 to 80 K: 600 kW pre-cooling with LN2, up to ~5 t/h, 6 LN2
trailer per day during 10 days (1250 t of LN2 in total);
From 80 to 5 K: Cryoplant turbo-expander cooling;
LHe filling: 15 t of LHe in total (4 trailers);
LHe filling and cool-down completion by using the 1.8 K refrigeration
unit (1 week/sector)
Amalia Ballarino
Part I
Cool-down of Sector 7-8
80 K
20 K
Temperature evolution during cool-down of the first LHC Sector
From RT to 80 K, from 80 K to 20 K, from 20 K to 4.5 K, from 4.5 K
to 1.9 K with LHe filling. Electrical test are performed at each plateau.
The time for cooling one Sector is about 3 weeks (3.3 km, 1250 tons
LN2, 18 tons of He, 800 g/s of He, 4600 tons of material in the Sector)
Amalia Ballarino
Part I
Amalia Ballarino
Part I
Cryogenic instrumentation
Type
Thermometers
(Cernox 1.7 - 300 K)
Thermometers
(Pt100, Thermocouple)
Quantity
700*
500*
Location
Magnet cold mass, QRL, DFB
Current lead, cryo-heater, thermal
shield
SSS phase separator, DFB,
standalone magnet
Magnet cold mass, DFB, QRL, beam
screen
Level gauges
70
Cryo-heaters
300
Cryogenic control valves
180
QRL
Warm control valves (DFB)
150
Current lead
Total per sector
1900
Amalia Ballarino
Part I
Heat load and cryostat design
 Heat inleaks
– Radiation
– Residual gas conduction
– Solid conduction
 Joule heating
– Superconductor splices
70 K shield, MLI
Vacuum < 10-4 Pa
Non-metallic supports
Heat intercepts
Resistance < a few nW
 Beam-induced heating
– Synchrotron radiation (0.6 W/m)
– Beam image currents (0.8 W/m)
– Localized heat due to loss of particles
(e.g particles escaping collimations)
Amalia Ballarino
}
} 5-20 K beam screens
}
Part I
Cryostat of LHC dipole
Amalia Ballarino
Part I
Thermal shield
Amalia Ballarino
Part I
Multi-layer insulation
Amalia Ballarino
Part I
 Horizontal tanks for storage of He gas (250 m3) at 2 MPa
 Vertical dewars (100 m3) for liquid nitrogen
He gas
Amalia Ballarino
Part I
LHC Control Room
Amalia Ballarino
Part I
The CERN accelerator network
Amalia Ballarino

Superconduttivita` e Criogenia per LHC

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