Welcome to Fermilab

1
Welcome to Fermilab
2
Cryogenics Why Fermilab Has Caught the Uncommon
Cold

• March 6, 2005
• Tom Peterson
• Cryogenic Engineer, Fermilab
• Tommy_at_fnal.gov

3
What Fermilab does -- accelerate subatomic
particles for physics experiments
4
Fermilab is the worlds highest energy particle
accelerator
5
(No Transcript)
6
Linac A view of the linear accelerator or
linac
7
Linac Radio-frequency accelerating cavities or
RF cavities RF cavities accelerate the
particle beam
8
Main Injector (and Recycler)

• A view in the
• tunnel of the
• next-to-final
• stage of
• acceleration --
• Main Injector
• Electro-magnets
• steer and focus
• the particle
• beam

9
Tevatron A view in the tunnel of the final
stage of acceleration -- the Tevatron
Electro-magnets steer and focus the particle
beam
10
The DZero detector
11
Collider Detector (CDF) particle tracks
12
How the magnets work-- electric current creates
a magnetic field that steers and focuses the
particle beam like a lens
Particle beam in a dipole (bending or steering)
magnet
13
A conventional accelerator magnet
Copper, carrying electric current

• Electric current in copper bars
• Magnet enclosed in iron
• Particle beam in central, evacuated beam tube

Iron
Particle beam
22 / 559mm
14
A superconducting accelerator magnet
Support
Heat Exchanger
Helium pipes
Thermal Shield
Cold Mass
Beam tube
Vacuum Vessel
15
A superconducting accelerator magnet
Liquid helium cooling channels

• The cold mass in the previous slide contains
  the actual magnet
• Cross-section of the cold mass is shown here it
  looks a lot like the conventional magnet
• The magnet structure within and outside of the
  cold mass is complicated by the requirement of
  very low temperatures

Particle beam
Superconducting Cable
Iron
16
Superconductivity

• Accelerator magnets must be very powerful
• Superconductors can carry more electric current
  than copper
• Superconducting magnets can be more powerful than
  the strongest conventional (copper and iron)
  electromagnets

17
Superconductors only work cold
18
Superconductors only work cold

• Chicagos record cold -27 F (Jan 20, 1985)
• Dry ice -109 F
• Lowest recorded temperature on earth -129 F
  (Vostok, Antarctica, July 21, 1983)
• Liquid natural gas (LNG) -256 F (113 K)
• Liquid air -321 F (77 K)
• Liquid helium -452 F (4.2 K)
• Fermilabs superconducting magnets are cooled to
  as low as -456 F (1.8 K)
• Absolute zero is -459.67 F (0 K)

19
Superconductors only work cold
20
Coldest liquids
21
Cryogenics

• The science of generating extreme cold, generally
  defined as LNG temperature
• (-256 F) and lower, is called Cryogenics

22
The Tevatron Cryogenic System

• 4 miles of superconducting magnets
• Over 10,000 gallons of liquid helium
• Even more liquid nitrogen
• Over 8 megawatts of input power
• About 20 kW of cooling at liquid helium
  temperature (heat always leaks in, which we
  have to remove)
• One of the worlds largest cryogenic systems

23
Problems at low temperatures

• Brittle materials
• Lubricants freeze solid
• Water and even air freeze and plug pipes
• Must minimize heat into the liquid helium
• Need to measure temperatures, pressures, flows,
  etc.

24
How do we handle the cold stuff?

• Stainless steel
• Some plastics are OK
• Vacuum insulation
• Multi-layer insulation
• Optimized supports
• Very clean helium
• Special methods for measurements

25
Photographic tour of a cryostat--here assembly
has just started
26
Liquid helium vessel will hang from thin rods
27
Helium vessel is hung, some piping is done
28
More piping is done
29
Wrap vessel and piping, cover with copper
thermal shield
30
Wrap the copper thermal shield
31
Weld a vacuum-tight steel container around it
32
A super- conducting magnet built by Fermilab
for LHC at CERN in Geneva, Switzerland Illust
rates the same layers as just shown--inner pipes,
thermal insulation, steel vacuum container
33
How do we make the cold?

• The fundamental knowledge needed for
  refrigeration came out of 19th century efforts to
  understand the relationships among temperature,
  pressure and energy in gases, particularly how to
  harness steam for work.
• The key gas cools when it expands (when it does
  work).

34
A conceptual refrigerator
35
Now make the process continuous
36
A simplified refrigeration cycleKlaus D.
Timmerhaus and Thomas M. Flynn, Cryogenic
Process Engineering, p.126
Compressor
Expander
37
A typical modern helium cycle(but simplified,
from Linde Kryotechnik, AG)

• The Claude process, shown to the right,
  includes intermediate temperature expanders
• Modern cryoplants follow this pattern
• Modern cryogenic plants each have many
  turboexpanders

38
A flow scheme for a cryogenic refrigerator
Expanders are red, compressors are blue, heat
exchangers are yellow
39
Photographic tour of the Magnet Test Facility
helium liquefier
40
Helium compressor (1000 Horsepower!)
41
Compressor cooling water--this is where the heat
goes!
42
Pipes! Lots of pipes, and gas vessels
43
Heat exchangers (hidden in a vacuum container),
expanders (also hidden) and dozens of valves
44
Helium Turbo-expander

• Linde turbine at right
• Expansion turbines are typically used in helium
  refrigerators larger than about 500 W.
• Real efficiencies (relative to isentropic) are
  60 to 80

45
A heat exchanger assembly container in better
view--on its side, we are looking at valves on top
46
More valves, pipes, control racks, gauges
47
End of the line--a magnet being tested
48
End of the line--a magnet being tested
49
Superfluid helium

• In liquid helium at 2.17 K viscosity disappears
• Thermal conductivity becomes much better than
  pure copper
• The fountain effect results
• Superfluid helium is used for cooling accelerator
  components, including at Fermilabs Magnet Test
  Facility (but not in the Tevatron)

50
Other cryogenic particle accelerators

• HERA (Hamburg, Germany)
• Jefferson Lab (Newport News, VA)
• RHIC (Brookhaven National Lab, NY)
• SNS (Oak Ridge, TN)
• LHC (at CERN, Geneva, Switzerland)
• But Tevatron was the first!

51
Other applications of cryogenics

• Liquefied Natural Gas (LNG)

52
Other applications of cryogenics

• MRI in hospitals
• Fast freezing of food
• Preservation of medical specimens
• Cryo-surgery
• Liquid nitrogen shattered the shape-shifting
  cyborg in Terminator 2 (but he came back)
• The silent drive in Hunt for Red October used a
  superconducting magnet