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SNS DTL Faraday CupEngineering ReviewMarch 12, 2002: 

SNS DTL Faraday Cup Engineering Review March 12, 2002 Steve Ellis SNS-03

General Requirements: 

General Requirements Six designs required, one for each DTL tank Assemblies #1 through #5 mount in beam box after DTL tank Assembly #6 mount after CCL segment #4 Large aperture variant of tank #1 design also required for D-plate 1.25-in aperture, limited axial beam box space Energy degrader & bias ring 26-mA beam, 50-ms pulse, 10Hz

Faraday Cup Section View: 

Faraday Cup Section View Faraday Cup #3

Absorbers: 

Absorbers Sized to stop all ions below specified energy levels Simple, disc shaped, fastened to FC face Very accurate thickness tolerance Absorb approximately 70% of beam power Cooled via conduction through FC body to heat exchanger Graphite utilized for first three assemblies Low energy graphite absorbers are quite thin, fragile Glidcop AL-60 utilized for subsequent assemblies due to axial space limitations FC #3 graphite absorber Absorber Material & Thickness

Collectors: 

Collectors Graphite for all designs 0.25-inch thick, 1.75-inch diameter Grooved design necessary for three low energy designs dE/dx significantly higher at lower energies Simple disc geometry utilized for three high energy designs Absorb approximately 30% of total beam power Vespel & Macor insulators for electrical isolation Cooled via conduction over entire back surface through Macor insulator to heat exchanger Kapton insulated signal wire attached with threaded fastener to radius FC #1 - #3 graphite collector

UCAR ATJ Graphite: 

UCAR ATJ Graphite Isostatically molded graphite Superior thermal conductivity Low density, high specific heat Low CTE, low modulus Nominal room temperature thermal properties: Nominal room temperature mechanical properties: Conventional machining techniques Vacuum compatible

Cooling Scheme: 

Cooling Scheme Heat exchanger fastened to back of each FC OFE copper body Simple coaxial tube flow scheme Nominal flow parameters: 1/2-gpm ~ 6-psi drop Adequate thermal performance

Fabrication: 

Fabrication Common materials Low carbon steel, OFE copper, 304L stainless, & isomolded graphite Ordinary concerning machining difficulty Conventional fabrication techniques Primarily mill & lathe work One braze operation No unusual surface finish requirements Reasonable tolerances No heat treatment FC #1 - #6 steel body

Supporting Engineering Analysis: 

Supporting Engineering Analysis Cooling scheme Required flow, convective film coefficients, pressure drop, etc. Beam heating Absorber geometry & material selection Thermal response & thermally induced structural loading Calculation of temperature distribution due to beam impingement Calculation of corresponding thermally induced stress Transient (single pulse) as well as steady state solutions

Beam Heating: 

Beam Heating Energy deposition due to proton kinetic energy loss 7.5-MeV to 86.8-MeV H- ions, 26-mA 50-ms pulse durations 10-Hz repetition rates 3-D spatial energy deposition Bi-Gaussian transverse beam distribution Depth dependant energy loss Bi-Gaussian beam density plot Proton energy loss per depth increment

Thermal & Structural Analysis: 

Thermal & Structural Analysis Finite element code ABAQUS utilized for numerical solution Problem symmetry allowed the use of axisymmetric mesh & ¼ symmetry 3-D mesh Temperature dependant material properties necessary Maximum temperature excursion ~1000 K Isotropic material behavior utilized with respect to thermal & mechanical properties Accurate spatial body heating due to beam impingement applied to mesh with FORTRAN subroutine Function of x, y, z, sx, sy, penetration depth, beam current, energy Requires very fine mesh to accurately capture behavior near Bragg peak

7.5-MeV Faraday Cup CollectorTransient Thermal Response: 

7.5-MeV Faraday Cup Collector Transient Thermal Response Collector axisymmetric model Small section of collector modeled 26-mA beam current 50.0-ms pulse 1.31-mm RMS beam size Spatial body heating Calculated temperature rise, Kelvins BEAM

7.5-MeV Faraday Cup CollectorTransient Thermally Induced Stress: 

7.5-MeV Faraday Cup Collector Transient Thermally Induced Stress Collector axisymmetric model Small section of collector modeled 26-mA beam current 50.0-ms pulse 1.31-mm RMS beam size Spatial body heating Calculated thermally induced max principal stress, psi BEAM

7.5-MeV Faraday Cup CollectorSteady State Thermal Response: 

7.5-MeV Faraday Cup Collector Steady State Thermal Response Collector axisymmetric model 26-mA beam current 1.31-mm RMS beam size 10-Hz operation Heating applied as steady surface flux ~ 30-Watts Calculated temperature rise, Kelvins BEAM

7.5-MeV Faraday Cup CollectorSteady State Thermally induced Structural Response: 

7.5-MeV Faraday Cup Collector Steady State Thermally induced Structural Response Collector axisymmetric model 26-mA beam current 1.31-mm RMS beam size 10-Hz operation Heating applied as steady surface flux ~ 30-Watts Calculated thermally induced max principal stress, psi BEAM

86.8-MeV Faraday Cup AbsorberTransient Thermal Response: 

86.8-MeV Faraday Cup Absorber Transient Thermal Response Absorber 1/4 symmetry 3-D model 26-mA beam current 50.0-ms pulse 1.44-mm by 0.79-mm RMS beam size Spatial body heating Calculated temperature rise, Kelvins BEAM

86.8-MeV Faraday Cup AbsorberTransient Thermally Induced Stress Levels: 

86.8-MeV Faraday Cup Absorber Transient Thermally Induced Stress Levels Absorber 1/4 symmetry 3-D model 26-mA beam current 50.0-ms pulse 1.44-mm by 0.79-mm RMS beam size Spatial body heating Calculated thermally induced von Mises stress, psi BEAM

Analysis Summary: 

Analysis Summary Pulse length ability >50mS strongly desired Want to operate very close to material structural limits Maximum pulse length limits calculated for each device (10-Hz operation) Absorbers for FC #4 - #6 at structural material limits on aft face May generate small surface cracks on aft surface, will relieve stress Recommend inspection & possible absorber change out during routine maintenance

Current Status: 

Current Status Engineering analysis complete Design & engineering report near completion Drawing package complete Need final modifications if any to degrader thickness Prototype fabrication of FC #1 underway