Superconduttivita’ e Criogenia - Giornate di Studio … · Superconduttivita’ e Criogenia XXII...

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 XXII Giornate di Studio sui Rivelatori


Introduction


Part I

Cryogenics for LHC

Part II

Superconductivity in LHC

PART III

Superconductivity & Cryogenics in LHC Upgrades

“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 cryogenics ?

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

Cryogenic: for Greek “kryos", which means cold or freezing, and "genes" meaning born or produced.


Introduction


Introduction

Resistance (Ohm) vs Temperature (K) of Hg – K. Onnes, 1911

Cryogenics

Superconductivity

Particles accelerator


Introduction

Accelerator: Instrument of High Energy Physics

h/p

1 TeV 10-18 m


Introduction

Particles are produced by converting the collision energy into mass Synchrotron: E[GeV]=0.29979 B[T] R[m] High energy High field magnets Colliding beams: ECM~2E

Accelerator Energy and Magnetic Field


Introduction

0.01

0.10

1.00

10.00

100.00

0 5 10 15

Dipole field (T)

En

erg

y (

TeV

)Tevatron HERA

SSC RHIC

UNK LEP

LHC

r=10 km

r=3 km

r=1 km

r=0.3 km

LHC

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.


Introduction

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.

Economical savings due to superconductivity


Introduction

The Energy Frontier


Introduction

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 1999-2000

1989 2007-2008

Large Superconducting Accelerators

* Upgrade with sc cavities to achieve the mass of the pair of W particles


Introduction


Introduction


Part I

Cryogenics for LHC

Part II

Superconductivity for LHC

PART III

Superconductivity & Cryogenics for LHC Upgrades

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”


Part I

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

Neon 24.6 27.1 44.4

Hydrogen 13.8 20.4 33.2

Helium 2.2

(-point)

4.2 5.2

Standard P-T and T-v Phase diagrams

Temperature

Saturated Vapor/liquid

Saturated liquid curve

Saturated vapor curve


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


Part I

Phase diagram of helium (He4)

1

10

100

1000

10000

0 1 2 3 4 5 6

Temperature [K]

Pre

ssu

re [

kPa

]

SOLID

VAPOUR

He IHe IICRITICAL

POINT

PRESSURIZED He II

(Subcooled liquid)

SATURATED He II

SUPER-

CRITICAL

SATURATED He I

-line

-point

Tc=5.19 K pc=2.2 bar

T=2.17 K p=50 mbar


Part I

Specific heat of saturated helium


Part I

Viscosity of He II

Allen and Misener Keesom

Two fluid model: rn, n, sn

rs, s=0, ss=0


Part I

Equivalent thermal conductivity of He II

Conduction in a tubular conduit

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

OFHC copper

Helium II


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


Part I

1

10

100

1000

10000

0 1 2 3 4 5 6

Temperature [K]

Pre

ssu

re [

kPa

]

SOLID

VAPOUR

He IHe IICRITICAL

POINT

PRESSURIZED He II

(Subcooled liquid)

SATURATED He II

SUPER-

CRITICAL

SATURATED He I

-line

-point

Saturated and pressurized He II at 1.9 K


Part I

Use of saturated superfluid helium.

By lowering the pressure of the vapor when pumping on LHe, the boiling temperature is reduced.

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

Liquid helium vapor pressure equilibrium and latent heat of vaporization

Large scale He II systems


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 + -

1

10

100

1000

10000

0 1 2 3 4 5 6

Temperature [K]

Pre

ssu

re [

kPa

]

SOLID

VAPOUR

He IHe IICRITICAL

POINT

PRESSURIZED He II

(Subcooled liquid)

SATURATED He II

SUPER-

CRITICAL

SATURATED He I

-line

-point

1

10

100

1000

10000

0 1 2 3 4 5 6

Temperature [K]

Pre

ssu

re [

kPa

]

SOLID

VAPOUR

He IHe IICRITICAL

POINT

PRESSURIZED He II

(Subcooled liquid)

SATURATED He II

SUPER-

CRITICAL

SATURATED He I

-line

-point


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


Part I

The Carnot cycle is the most efficient refrigeration cycle operating between two temperature levels

Carnot cycle

1 2

3 4

T

s

QC

QH

COP = Tc/(Th-Tc) Tc/(Th-Tc) 0

Tc 0

1-2 Isothermal expansion 2-3 Isentropic compression 3-4 Isothermal compression 4-1 Isentropic expansion

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

*Figure of merit


Part I

Hypothetical Carnot cycle for He refrigeration


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.


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)


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 T<Tin JT < 0 T>Tin Joule-Thomson effect: adiabatic expansion of a gas (constant enthalpy)


Part I


Part I

Efficiency of refrigerators and liquefiers as a function

refrigeration capacity


Part I

(W/Qc)CARNOT,4.2K = 68.7 (Q/Qc) = 68.7/0.3 230

30

0.999999991c0.999999991c

The cryogenic system for the LHC machine


Part I

LHC layout

Sector=3.3 km SSS=528 m


Part I

From the LEP to the LHC machine

8000


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


Part I

Performance of 4.5 K refrigerators at CERN


Part I

LHC: COP= 230 W/W = 29 CARNOT

Electrical input power installed 4.5 MW/refrigerator

Gas storage tanks

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 (82.4 kW @ 1.9 K) distributed around the ring.


Part I

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 (p16 mbar) arranged in a series of 107 m cooling loops all around the ring.

Principle of LHC cooling scheme


Part I

Schematic of cooling system

Slope

MagnetSaturated LHeII

Magnet cell (107 m)

Bayonet heat exchanger

GHe pumping (15 to 19 mbar)

SHe supply (4.6 K, 3 bar)

Ps0

Wetted length (Lw) Dried length (Ld)

JT

Hydraulicplug

PressurisedLHeII

TT TT TT TT TT TT TT TT


Part I

Cryogenic flow scheme of an LHC cell (107 m)

107 m


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.


Part I

Cryogenic block diagram

4


Part I

Thermodynamic states of He in LHC cryogenic system


Part I

T54.5 K - 20 K loads

(magnets + leads + cavities)

T7

T1

T2

T3

T4

T8

T6

E1

E7

E3

E4

E6

E8

E9a

E9b

E10

E11

E12

E13

LN2Precooler

20 K - 280 K loads

(LHC current leads)

50 K - 75 K loads

(LHC shields)

Adsorber

T1

T3

T7

T4

T8

T5

T6

201 K

75 K

49 K

32 K

20 K

13 K

10 K

9 K

4.4 K

0.1

MPa

0.4

MPa

1.9

MPa

0.3

MPa

T2

LHC shields

To LHC loads

from LHC loads

from LHC loads

Process flow diagram of

LHC 18 kW cryoplant


Part I

1.8 K He refrigeration system

0.3 MPa4.6 K

0.13 MPa,20 -30 K

WC

S

1.8

K R

efr

igera

tio

n U

nit

LHe 1.8 K Q1.8K

CC

B

4.5 KRefrigerator

B

D

C

Cold

com

pre

ssors

Tu

rbln

e

Adsor-bers

LHC SectorLoad

Installed pumping capacity 125 g/s at 15 mbar (i.e. ~2.4 kW @ 1.8 K)


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


Part I

LHC Cryogenic line in the LHC tunnel


Part I

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

Connection via service module and jumper


Part I

Transverse cross section of the LHC tunnel


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)


Part I

Cool-down of Sector 7-8

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)

80 K

20 K


Part I


Part I

Type Quantity Location

Thermometers

(Cernox 1.7 - 300 K) 700* Magnet cold mass, QRL, DFB

Thermometers

(Pt100, Thermocouple) 500*

Current lead, cryo-heater, thermal

shield

Level gauges 70 SSS phase separator, DFB,

standalone magnet

Cryo-heaters 300 Magnet cold mass, DFB, QRL, beam

screen

Cryogenic control valves 180 QRL

Warm control valves (DFB) 150 Current lead

Total per sector 1900

Cryogenic instrumentation


Part I

Heat load and cryostat design

Heat inleaks

– Radiation 70 K shield, MLI

– Residual gas conduction Vacuum < 10-4 Pa

– Solid conduction Non-metallic supports Heat intercepts

Joule heating

– Superconductor splices Resistance < a few nW

Beam-induced heating

– Synchrotron radiation (0.6 W/m) }

– Beam image currents (0.8 W/m) } 5-20 K beam screens

– Localized heat due to loss of particles }

(e.g particles escaping collimations)


Part I

Cryostat of LHC dipole


Part I

Thermal shield


Part I

Multi-layer insulation


Part I

Horizontal tanks for storage of He gas (250 m3) at 2 MPa Vertical dewars (100 m3) for liquid nitrogen

He gas


Part I

LHC Control Room


Part I

The CERN accelerator network


Part I

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