NSTX TF Flag Joint Review ANALYSIS & DESIGN C Neumeyer 9/3/3

Topics Backround Requirements Forces and Load Paths Thermal Effects Contact Resistance Features of New Design Performance of New Design

BACKGROUND TF joint failed on February 14, 2003 due to structural weaknesses Project has developed a more robust design –factor in lessons learned from failure –all engineering aspects analyzed at appropriate level of detail –testing as necessary for engineering input and design verification –reduced dependence on precision manufacturing/assembly –easier maintenance

RECOVERY ACTIVITIES

DESIGN 3D modeling complete, including… integrated TF inner leg bundle coolant tube routing and bulkhead outer leg connections Fabrication drawings complete, including… conductors flags flag boxes shear shoes hub assembly torque collar* * Under revision

ANALYSIS Structural FEA complete, including… both tiers of conductors out-of-plane load path through spline collar and wet lay-up representation in-plane, out-of-plane, thermal loads SOFT, EOFT, EOP cases Various off-normal cases Other analysis complete, including… force calculations temperatures, including joint temperature rise fastener sizing calculations miscellaneous calculations Torque Collar analysis continuing

TESTING Component testing (design input data) consists of: Pull-out tests on threaded inserts - one time and cyclic at 100 o C Pull-out tests on bolts threaded in copper - one time and cyclic Friction coefficient and electrical resistance tests Shear tests on torque collar attachment Status: Complete except more data to be generated for torque collar shear at high compression Prototype testing (design verification) consists of: Mechanical mock-up of single joint for cyclic fatigue testing Electrical mock-up of single joint tested at full current and I 2 T Status: In Preparation

CURRENT WAVEFORMS Engineering design accounts for PS response, inc’l L/R decay in case of fault from I max ∫I 2 T = 6.0 x 10 9 A 2 -s for 3kG-4.5s ∫I 2 T = 6.15 x 10 9 A 2 -s for 6kG-0.6s Design basis ∫I 2 T = 6.5 x 10 9 A 2 -s which causes adiabatic  T of 80 o C in Cu 6kG pulse is most critical for joint since forces are maximum and time for heat diffusion is minimum Short Pulse Long Pulse

NUMBER OF PULSES & THERMAL CYCLES Assume 50,000 pulse requirement at 6kG - 10 yr*20 week*5day*8hr*6pulse/hr = 48,000 - Highly conservative - NSTX 5yr plan calls for … 3kG (25% EM load) 4kG (44% EM load) 5kG (69% EM load) 6kG (100% EM load) 100% Assume 1,000 thermal ratcheting cycles (= number of days) - 10 yr*20 week*5day = drives flag fastener fatigue cycle requirement - assuming 12 pulse/hr rate to set thermal ratcheting (conservative)

EM FORCES In-Plane -vertical load and moment due to magnetic pressure from self-field Out-of-Plane -lateral due to I tf xB z(oh&pf) -torsional due to I tf xB r(oh&pf) 9.3klb 2.3klb 4.7klb 3klb 148kft-lb 40.8kft-lb Notes: 1)All coils assumed at full current, worst case polarity (conservative) 2)Forces equal and opposite on two ends of bundle

FUNCTIONS OF JOINT Mechanical Function Preload for High Contact Pressure Structural Support Against EM & Thermal Loads Maintain High Contact Pressure Low Electrical Resistance and Dissipation Peak Temperature within Limit Electrical Function

LOAD PATHS 1)Friction 2)Shear Shoe 3)Torque Collar 4)Hub/Spline/VV

THERMAL EFFECTS Vertical length of inner leg bundle from bottom to top increases by up to 0.35” during a pulse Vertical length of inner leg from torque collar to top of bundle increases due to inner leg temperature rise, whereas flag and hub remain relatively cool Radius of inner leg bundle increases bundle increases by approximately 0.006” during a pulse Flag heats modestly during pulse (  T ≈ 5 o C) but can ratchet to  T ≤25 o C at rated duty cycle (conservative),  r ≈ 0.005” in length

CONTACT RESISTANCE Req’d Flat Top Time =0.6 sec Tolerable Resistivity ≈ 2.5µΩ-in 2 (700psi) Note: assuming constant resistivity along joint

CONTACT PRESSURE & RESISTANCE R max P avg

KEY DESIGN FEATURES Flag Flag bolts (studs) Shear Shoe Flag Box Box Bolts (stud) Torque Collar Hub Disks

TORQUE COLLAR Prior Design (August 7) -not vertically symmetric -Torque reacted through moment arm New Design -vertically symmetric -torque reacted tangentially

VOLTAGE PROBES FOR IN-SITU JOINT RESISTANCE MEASUREMENT IDI Coaxial Probe - commercial spring-loaded probe used in semiconductor test industry -2 probes per flag, 1 connected to instrumentation, 1 redundant spare -All 72 joints monitored 200A, real time at full current)

DESIGN HIGHLIGHTS Solid (not split) flags insulated with 4 layers Kapton, glass wrapped, potted in 304SS boxes Boxes attached to hub disks using 1/2” studs Flags attached via 3/8” Inconel studs preloaded to 5000lbf Shear shoe on outer edge of flags is bolted to ends of inner leg conductor using Inconel bolts, one vertical and one angled for moment reaction 3-segment torque collar w/two 1/2” 10000lbf per joint, 0.180” wet lay-up with better type of epoxy (Hysol E-120HP) Collar transmits torque only to hub structure at 3 anchor points Redundant voltage probes are located on each side of the flag

FEATURES OF OVERALL FEA MODEL Includes All Essential Structural Components Contributing To Flag Joint Performance –FLAGS- BOXES –COLLAR- HUBS –CENTER STACK- BOLTS –SPLINES- UMBRELLA –etc. Models non-linear behavior (friction) 24 fold symmetry (collar gaps, etc. not modeled)

LOAD CASES EXAMINED Time Points –START OF FLAT TOP (SOFT) –END OF FLAT TOP (EOFT) –END OF PULSE (EOP) Conditions –Normal –Off Normal Low Preload (60%) High Friction Coefficient Low Friction Coefficient

FEA USED TO ASSESS STRESSES, DISPLACEMENTS, CONTACT PRESSURES

SUMMARY OF RESULTS

Temperatures Well Below Limit of 120 o C Contact Region Max Temperature of 94 o C Occurs Just After EOFT Tflat = 0.7sec (vs. 0.6 req’t) Bolt Holes not exactly modeled (+10 o C) OH constant at max current (-TBD o C) Insignificant change from constant resistivity simulation

OFF-NORMAL CASE: 60% PRELOAD Normal Peak Temperature ≈ 3 o C Higher Temperature Distribution Different Current Redistribution Beneficial Notes: 1)Held SOFT pressure conditions after SOFT due to lack of EOFT data 2)Color scales different Off-Normal

TORQUE COLLAR FEA Detailed analysis of prior design revealed high stress concentrations in wet lay-up due to lack of vertical symmetry

NEW TORQUE COLLAR FEA -preliminary results indicate adequate safety margins -work still in progress

DESIGN MARGINS

DESIGN IMPROVEMENTS FeatureOld DesignNew Design Hub StiffnessNot adequate; lacking stiff linkages between disks because flags could slide w.r.t. disks Very stiff. Boxes form webs with disks like I-beams Flag Bolts/Studs Shoulder engagement was too smallShear Shoe using two 3/8” dia bolts 5/16” Bolt thread necked down too far, shank not necked down, not compliant for thermal cycling 3/8” Studs necked down to root diameter, belleville washers Torsion in long bolts during tightening, inaccurate tensioning Studs with nuts used in place of long bolts, stud tensioner Dual purpose bolts, combined tension and shear functions, tolerance issues Loose fitting clearance holes for studs, separate shear shoes Four 5/16" 2500#, marginal friction to carry shear Four 3/8" 5000#, doubling of preload Thin washers under bolt heads1/4" thick washer plate over Belleville washers

All defects contributing to original failure have been addressed FeatureOld DesignNew Design InsertsKeensert type, marginal thread engagementTaplok type, thread engagement > 0.5" ShimmingManually selected and inserted G10 shim stockHysol/glass tape potting in boxes, mold released to permit thermal growth Out-of-Plane Load Path Wedged G10 blocks with pusher boltsFlags potted in boxes, boxes bolted to hub disks Torque CollarTwo piece collar bolted directly to hub. Wet lay- up 0.25” thick Hysol RE2039 & HD3561. Holes in collar for epoxy outflow to enhance adhesion. Three piece collar with sliding contact with hub for torsion-only connection. Wet lay-up 0.180” thick Hysol E-120HP (improved adhesive strength). Serrations in collar to enhance adhesion. Joint Resistance Measurement 10A Biddle measurement via connection to two half flags on disassembled joint, 1µΩ resolution 200A precision measurement using voltage taps in situ, ≈ 20x enhanced resolution, plus real time measurement every pulse

CONCLUSIONS New Design Corrects All Defects Associated with Original Design New Design Has Sufficient Margins at 6kG (pending torque collar resolution) Follow-on Activities Will Increase Confidence Mechanical Prototype Testing Electrical Prototype Testing Instrumentation During Commissioning and Operations - resistance measurement (200A maintenance and real-time) system - temperature, strain, displacement)