# Presentation: 193993

## Welcome to Fermilab

- Tom Peterson

- 6 March 2005

## Cryogenics – Why Fermilab Has Caught the Uncommon Cold 

- March 6, 2005
- Tom Peterson
- Cryogenic Engineer, Fermilab
- Tommy@fnal.gov

## What Fermilab does -- accelerate subatomic particles for physics experiments

- Tom Peterson

- 6 March 2005

## Fermilab is the world’s highest energy particle accelerator

- Tom Peterson

- 6 March 2005

## Slide 5

- Tom Peterson

- 6 March 2005

## Linac

- A view of the
- linear accelerator
- or “linac”

- Tom Peterson

- 6 March 2005

## Linac

- Radio-frequency
- accelerating cavities
- or  “RF cavities”
- RF cavities
- accelerate the
- particle beam

- Tom Peterson

- 6 March 2005

## 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

- Tom Peterson

- 6 March 2005

## Tevatron

- A view in the
- tunnel of the
- final stage of
- acceleration --
- the Tevatron
- Electro-magnets
- steer and focus
- the particle
- beam

- Tom Peterson

- 6 March 2005

## The DZero detector

- Tom Peterson

- 6 March 2005

## Collider Detector (CDF) particle tracks

- Tom Peterson

- 6 March 2005

## electric current creates a magnetic field that steers and focuses the particle beam like a lens  

- 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

- Tom Peterson

- 6 March 2005

## A “conventional” accelerator magnet

- 22” / 559mm

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

*Iron*

*Copper, carrying *
*electric current*

*Particle beam*

- Tom Peterson

- 6 March 2005

## A superconducting accelerator magnet

*Thermal *
*Shield*

*Cold Mass*

*Heat Exchanger*

*Vacuum Vessel*

*Support*

*Beam tube*

*Helium pipes*

- Tom Peterson

- 6 March 2005

## A superconducting accelerator magnet

- 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

*Iron*

*Superconducting*
*Cable*

*Liquid helium cooling channels*

*Particle*
*beam*

- Tom Peterson

- 6 March 2005

## 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

- Tom Peterson

- 6 March 2005

## Superconductors only work cold

- Tom Peterson

- 6 March 2005

## Superconductors only work cold

- Chicago’s 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)
- Fermilab’s superconducting magnets are cooled to as low as -456 F (1.8 K)
- Absolute zero is -459.67 F (0 K)

- Tom Peterson

- 6 March 2005

## Superconductors only work cold

- Tom Peterson

- 6 March 2005

## Coldest liquids

- Tom Peterson

- 6 March 2005

## Cryogenics

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

- Tom Peterson

- 6 March 2005

## 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 world’s largest cryogenic systems

- Tom Peterson

- 6 March 2005

## 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.

- Tom Peterson

- 6 March 2005

## 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

- Tom Peterson

- 6 March 2005

## Photographic tour of a cryostat--here assembly has just started

- Tom Peterson

- 6 March 2005

## Liquid helium vessel will hang from thin rods

- Tom Peterson

- 6 March 2005

## Helium vessel is hung, some piping is done

- Tom Peterson

- 6 March 2005

## More piping is done

- Tom Peterson

- 6 March 2005

## Wrap vessel and piping, cover with copper thermal shield

- Tom Peterson

- 6 March 2005

## Wrap the copper thermal shield

- Tom Peterson

- 6 March 2005

## Weld a vacuum-tight steel container around it

- Tom Peterson

- 6 March 2005

## A super-

- conducting
- magnet built
- by Fermilab
- for LHC at
- CERN in
- Geneva,
- Switzerland
- Illustrates the same layers as just shown--inner pipes, thermal insulation, steel vacuum container

- Tom Peterson

- 6 March 2005

## 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”).

- Tom Peterson

- 6 March 2005

## A conceptual refrigerator

- Tom Peterson

- 6 March 2005

## Now make the process continuous

- Tom Peterson

- 6 March 2005

## A simplified refrigeration cycleKlaus D. Timmerhaus and Thomas M. Flynn, Cryogenic Process Engineering, p.126

- Compressor

- Expander

- Tom Peterson

- 6 March 2005

## 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

- Tom Peterson

- 6 March 2005

## A flow scheme for a cryogenic refrigerator Expanders are red, compressors are blue, heat exchangers are yellow

- Tom Peterson

- 6 March 2005

## Photographic tour of the Magnet Test Facility helium liquefier

- Tom Peterson

- 6 March 2005

## Helium compressor (1000 Horsepower!)

- Tom Peterson

- 6 March 2005

## Compressor cooling water--this is where the heat goes!

- Tom Peterson

- 6 March 2005

## Pipes!  Lots of pipes, and gas vessels

- Tom Peterson

- 6 March 2005

## Heat exchangers (hidden in a vacuum container), expanders (also hidden) and dozens of valves

- Tom Peterson

- 6 March 2005

## 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%

- Tom Peterson

- 6 March 2005

## A heat exchanger assembly container in better view--on its side, we are looking at valves on top

- Tom Peterson

- 6 March 2005

## More valves, pipes, control racks, gauges

- Tom Peterson

- 6 March 2005

## End of the line--a magnet being tested

- Tom Peterson

- 6 March 2005

## End of the line--a magnet being tested

- Tom Peterson

- 6 March 2005

## 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 Fermilab’s Magnet Test Facility (but not in the Tevatron)

- Tom Peterson

- 6 March 2005

## 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!

- Tom Peterson

- 6 March 2005

## Other applications of cryogenics

- Liquefied Natural Gas (LNG)

- Tom Peterson

- 6 March 2005

## 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

- Tom Peterson

- 6 March 2005