SUPERCONDUCTIVITY and ITS APPLICATION to PARTICLE ACCELERATORS

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SUPERCONDUCTIVITY and ITS APPLICATION to
PARTICLE ACCELERATORS

• Anthony J. Favale
• Chairman, Board of Directors
• SPAFOA
• July 30, 2009
• Presentation to US Congress

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What is Superconductivity?

• If Mercury is cooled below 4.1 K, it loses all
  electric resistance.
• Discovery of superconductivity by H. Kammerlingh
  Onnes in 1911 was followed by observation of
  other metals which exhibit zero resistivity below
  a certain critical temperature, Tc.
• The fact that the resistance is zero has been
  demonstrated by sustaining currents in
  superconducting rings for many years with no
  measurable reduction.
• One of the properties of a superconductor is that
  it will exclude magnetic fields a property called
  the Meissner effect

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What is Superconductivity ?

• The disappearance of electrical resistivity was
  modeled in terms of electron pairing in the
  crystal lattice, Cooper pairs, by John Bardeen,
  Leon Cooper, and Robert Schrieffer in what is
  commonly called BCS theory.
• A new era of superconductivity began in 1986 with
  the discovery of high critical temperature
  superconductors

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Critical Temperature for Superconductors

• Material Tc
  Material Tc
• Aluminum 1.2 K La-Ba-Cu
  oxide 30 K
• Tin 3.7 K
  Y-Ba-Cu oxide 92 K
• Mercury 4.2 K
  Tl-Ba-Cu oxide 125 K
• Lead 7.2 K
• Niobium 9.3 K
• Niobium Titanium 10 K
• Niobium Tin 17.9 K

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When a Superconductors Temperature is below its
Tc there is a Critical Magnetic Field above which
Superconductivity ceases
Normal conducting
Magnetic Field
Superconducting
Temperature
Tc
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The Prime Use of DC Superconductivity in
Accelerators is for Bending and Focusing Magnets

• If the 373 bending and 432 focusing
  superconducting magnets in Brookhavens RHIC
  accelerator were made of copper, they would
  consume hundreds of megawatts of electrical
  power. The RHIC magnets are cooled with liquid
  helium, the helium refrigerator consumes about 5
  megawatts. Superconducting magnets a no brainer

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RHIC Magnets
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Radio Frequency, RF, Superconductivity

• To accelerate charged particles one must apply an
  electric field to either a copper or a
  superconducting cavity. Today most accelerators
  utilize RF electric fields.
• For RF currents in a superconductor, dissipation
  exists for all temperatures gt 0 K, albeit very
  small compared to the normal state. The Cooper
  pairs of BSC theory do move without friction, but
  they have inertial mass and for AC currents to
  flow forces must be applied to bring about
  alternative directions of flow, hence an AC
  electric field will be present in the surface
  which will also accelerate the normal electrons
  which gives rise to dissipation.

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SRF Cavities
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RF Superconductivity

• Superconducting RF, SRF, cavities excel over
  those of copper for applications requiring
  continuous wave, CW, or long-pulse high voltage.
  Ohmic losses increase as the square of the
  accelerating voltage. Copper can become
  uneconomical when the demand for high CW voltage
  grows with particle energy.
• Superconductivity to the rescue !!
• For RF fields the RF current resides at the
  surface. The surface resistance of a
  superconductor is 5 orders of magnitude less than
  that of copper. After discounting for the
  electric power of the helium refrigerator a
  factor of hundreds still remains. Again a no
  brainer

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SRF to Copper Cavity Comparison

• We compare two photocathode electron sources
  one SRF, the other copper. Both are powered by
  two one CW megawatt RF power systems. Each
  provides a ½ ampere current. The SRF source
  yields a 4 megavolt electron beam while the
  copper source yields 2.6 megavolts.
• The SRF source needs a 10 kilowatt electric
  refrigerator to cool it while the electrical
  losses in the copper source are around 700
  kilowatts.

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Photocathode Electron Guns
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SRF Cavity RD

• The prime goal of SRF cavity RD today is to
  increase the accelerating voltage gradient, E.
  The units of E are MV/m.
• The ILC goal for E is 35MV/m, to date only 40 of
  the ILC RD cavities have reached this goal.
• The maximum value of E is determined by the value
  of the resulting magnetic field, B, at the
  cavitys maximum radius. If B exceeds a certain
  value the cavity will quench, i. e. it will go
  normal.
• The Maximum value of E achieved to date in a
  single cell ILC RD cavity is 59MV/m.

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The Bright Future of SRF Accelerators

• New SRF Accelerator Projects
  In Europe
• CEBAF Upgrade, JLAB
  XFEL, DESY
  
• ERL, BNL
  SPL, CERN
• RHIC Upgrade, BNL
  CRAB, CERN
• FRIB, MSU,
  ESS, Sweden
• Atlas Upgrade, ANL
• Mo99 Production, Triumf
• ILC RD, Fermilab
• Project X, Fermilab
• ERL, Cornell, ANL, LBL
• Navy FEL Ship Self Defense, ONR
• e-RHIC, BNL
• ILC
• Accelerator Transmutation of Waste, ATW