Transcript Slide 1
Optimization of Elliptical SRF
Cavities where π£ < π
Joel Newbolt
Mentor: Dr. Valery Shemelin
Why π£ < π?
ο§ Acceleration of large subatomic particles
ο§ Accelerator driven systems (ADS)
β’ Neutron Spallation
β’ Tritium production
β’ Nuclear waste transmutation
π£
INFN Milano Cavity, π = 0.5
7/17/2015
Joel Newbolt, Valery Shemelin
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Elliptical Cell Geometry
Non-reentrant (πΌ > 90°)
Reentrant(πΌ < 90°)
Geometric Constraints
Free Parameters
β’
β’
β’
β’
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Half-Cell Length, πΏ
Wall Angle, πΌ
Equatorial Radius, π
ππ
Aperture Radius, π
π
ο§ Equator Ellipse Axes
β’ π΄ and π΅
ο§ Iris Ellipse Axes
β’ π and π
Joel Newbolt, Valery Shemelin
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Geometric Constraints
Half-Cell Length, πΏ
Wall Angle, πΆ
Constrained by mode of operation
Constrained by chemical treatment method
ο§ In-phase mode
Non-reentrant
Reentrant
ο§ π mode
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Joel Newbolt, Valery Shemelin
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Geometric Constraints (cont.)
Aperture Radius, πΉπ
Equatorial Radius, πΉππ
ο§ Propagation of higher-order
modes (HOMs)
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πππ’π‘πππ β
π
π
ο§ Tuned to make the
frequency of TM01 equal to
the driving frequency
β’ Removed by resistive loads
ο§ Power left in cavity by
wakefields
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πβ 3
π
π
ο§ Cell-to-cell coupling in multicell cavities
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Peak Fields
Magnetic Quenching
Field Emission
ο§ Superconductor
enters a normal
conducting state
ο§ Electrons are
emitted from the
superconductor
β’ Magnetic field
changes too rapidly
β’ Magnetic field is too
strong
β’ Electric field is too
large
ο§ Threshold raised
by heat treatment
ο§ Causes heating of the
material
β’ Spreads the region
of normal
conductivity
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Numerical Simulation
SUPERLANS
ο§ Simulation for axially
symmetric cavities
TunedCell
ο§ Wrapper code for
SUPERLANS
β’ Adjusts π
ππ to make the
frequency of TM01 equal to
the driving frequency
β’ Creates geometry file for
SUPERLANS
β’ Linearly varies free
parameters
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Cavity Optimization
Goal of Optimization
ο§ Minimize π΅ππ πΈπππ (and
equivalently π»ππ πΈπππ )
ο§ Optimization constraints
β’ Minimum wall angle, πΌ
β’ Maximum πΈππ πΈπππ
Cavity Optimizer
ο§ Matlab wrapper code for
TunedCell
ο§ Minimizes π΅ππ πΈπππ
ο§ Enforces geometric and
electromagnetic constraints
β’ Minimum radius of curvature
of the cell (two times the
Niobium sheet thickness β 6
mm)
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Multi-Cell Cavity Optimization
Optimization by V. Shemelin
ο§ Reducing wall angle reduces
minimum π»ππ πΈπππ
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Optimization when π· = π
π
<π
ο§ Same trend for π½ < 1
ο§ Increasing π½ increases
minimum π»ππ πΈπππ
Joel Newbolt, Valery Shemelin
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Istituto Nazionale di Fisica Nucleare (INFN)
Varying Iris Ellipse Ratio
Free Parameters
ο§ Equator Ellipse Ratio, π
=
π
ο§ Iris Ellipse Ratio, π = π
ο§ Wall Distance, π
ο§ Wall Angle, πππβπ
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π΅
π΄
ο§ Produces a minimum
πΈππ πΈπππ for a given π
, π
and πππβπ
Joel Newbolt, Valery Shemelin
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INFN Extension
ο§ Increasing wall angle
increases optimal iris ellipse
ratio
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ο§ Increasing wall distance
increases optimal iris ellipse
ratio
Joel Newbolt, Valery Shemelin
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Bhabha Atomic Research Center (BARC)
BARC Optimization
ο§ Single-cell cavity
Multi-Cell Boundary Conditions
β’ π½ = 0.49
β’ π΄ = π΅ = 20 mm
β’ π π = 0.7
β’ π
π = 39 mm
ο§
ο§
Qualitatively similar
Differences attributed to
β’
β’
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Different levels of free parameter accuracy
Different simulation codes (SUPERLANS vs.
SUPERFISH)
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BARC Verification
Single-Cell Boundary Conditions
Multi-Cell Boundary Conditions
ο§ Clear minimum in πΈππ πΈπππ
ο§ Lower values of πΈππ πΈπππ
and π΅ππ πΈπππ
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BARC Improvement
BARC Optimization Results
Free Parameters
Electromagnetic
Parameters
π΄ = 20 mm
πΈππ
π΅ = 20 mm
πΈπππ = 4.26
π π = 0.7
π΅ππ
πΈπππ
πΌ = 96.5°
= 8.02 mT/(MV/m)
Single-Cell Cavity Optimization
Free Parameters
Electromagnetic
Parameters
π΄ = 20.81 mm
πΈππ
πΈπππ
π΅ = 51.3 mm
= 3.50
π = 10.51 mm π = 18.41 mm
π΅ππ
πΈπππ
= 8.15 mT/(MV/m)
ο§ Optimized under BARC constraints (π½ = 0.49 and π
π = 39 mm)
ο§ Result for minimum π΅ππ πΈπππ
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Single-Cell Cavity Length
Half-Cell Length
Beam Pipe Fields
E-field lines
Beam pipe
Half-wavelength
cell
π£
πΏ=
4π
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π½π π
πΏ=
4π
ο§ Electric field decays
exponentially into the beam
pipe
Joel Newbolt, Valery Shemelin
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Scaled Cavity Length
ο§ Reducing cavity length decreases π΅ππ πΈπππ
ο§ Reduction from BARC design
β’ π΅ππ πΈπππ by 8%
β’ πΈππ πΈπππ by 17.8%
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Future Work
ο§ Continue optimization of cavities with π½ < 1
β’ Prove reentrant shape is ineffective
ο§ Optimize the shape and length of single-cell
cavity with record setting accelerating
gradient
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Acknowledgements
Special thanks to
ο§ Dr. Valery Shemelin
ο§ Dr. Ivan Bazarov and Dr.
Georg Hoffstaetter
ο§ CLASSE Student Researchers
7/17/2015
Funding Agency
ο§ National Science
Foundation
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