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 2 Elliptical Cell Geometry Non-reentrant (πΌ > 90°) Reentrant(πΌ < 90°) Geometric Constraints Free Parameters β’ β’ β’ β’ 7/17/2015 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 3 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 7/17/2015 Joel Newbolt, Valery Shemelin 4 Geometric Constraints (cont.) Aperture Radius, πΉπ Equatorial Radius, πΉππ ο§ Propagation of higher-order modes (HOMs) 1 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 1 πβ 3 π π ο§ Cell-to-cell coupling in multicell cavities 7/17/2015 Joel Newbolt, Valery Shemelin 5 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 7/17/2015 Joel Newbolt, Valery Shemelin 6 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 7/17/2015 Joel Newbolt, Valery Shemelin 7 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) 7/17/2015 Joel Newbolt, Valery Shemelin 8 Multi-Cell Cavity Optimization Optimization by V. Shemelin ο§ Reducing wall angle reduces minimum π»ππ πΈπππ 7/17/2015 Optimization when π· = π π <π ο§ Same trend for π½ < 1 ο§ Increasing π½ increases minimum π»ππ πΈπππ Joel Newbolt, Valery Shemelin 9 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 7/17/2015 π΅ π΄ ο§ Produces a minimum πΈππ πΈπππ for a given π , π and πππβπ Joel Newbolt, Valery Shemelin 10 INFN Extension ο§ Increasing wall angle increases optimal iris ellipse ratio 7/17/2015 ο§ Increasing wall distance increases optimal iris ellipse ratio Joel Newbolt, Valery Shemelin 11 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’ 7/17/2015 Different levels of free parameter accuracy Different simulation codes (SUPERLANS vs. SUPERFISH) Joel Newbolt, Valery Shemelin 12 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 7/17/2015 Joel Newbolt, Valery Shemelin 13 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 7/17/2015 Joel Newbolt, Valery Shemelin 14 Single-Cell Cavity Length Half-Cell Length Beam Pipe Fields E-field lines Beam pipe Half-wavelength cell π£ πΏ= 4π 7/17/2015 π½π π πΏ= 4π ο§ Electric field decays exponentially into the beam pipe Joel Newbolt, Valery Shemelin 15 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% 7/17/2015 Joel Newbolt, Valery Shemelin 16 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 7/17/2015 Joel Newbolt, Valery Shemelin 17 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 Joel Newbolt, Valery Shemelin 18