REQUIREMENTS & ASSUMPTIONS C Neumeyer 4/10/3

FIELD AND CURRENT Base GRD requirement: 3kG at R 0 =0.854m with 4.5 sec flat top, once every 300s Amp with 36 turn coil High field GRD requirement: 6kG at R 0 =0.854m with 0.6 sec flat top, once every 300s Amp with 36 turn coil

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 Current (kA) Time (sec)

VOLTAGES TF PS is 1kV DC no-load – volts DC avg –750*sqrt(2)=1060 volts peak High resistance grounded, V line-ground =500V nominal, 1kV max CHI can elevate hub assembly and OH tension tube to 1kV Max design voltages: –turn-to-turn = 1000/36 ~ 30V for adjacent conductors, 1kV max –turn-to-ground (hub and OH tension tube) = 2kV –base hipot = 2E+1= 5kV –routine hipot ~ 3kV

CONTACT PRESSURE & RESISTANCE ASSUMPTIONS Contact Resistance vs. Pressure behavior is key design driver –contact pressure requirement drives structural design –contact resistance determines heating and potentially limit flat top time Achievable resistance range is bracketed by two cases... –virgin silver plated joints as tested during NSTX R&D –actual installed silver plated joints after operational cycling Prior in-situ measurements hint at what is achievable –QC will be enhanced to improve results and lessen variability Future measurements will establish actual values and be used to set operating envelope

THEORETICAL Cu-Cu JOINT Ref. Copper Development Association (CDA) pub. “Copper for Busbars”, ch. 5, p. 82 R=10000/P 1.04

NSTX R&D MEASUREMENTS

IN-SITU MEASUREMENTS 10/6/98: Prior to 1st Plasma 5/25/00: After 1st Ops Campaign ILL=Inner Layer Lower ILU= Inner Layer Upper OLL=Outer Layer Lower OLU= Outer Layer Upper

FIELD DATA INTERPRETATION ANSYS Finite Element Model Used to Extract Contact Resistance Field Values:0.8 min, 1.8 avg, 3.0 max  /in 2 Min Avg Max

COMPARISON OF DATA Goal

CONTACT RESISTANCE IMPACT Contact resistance and temperature allowable will essentially dictate the realizable system performance Req’t = 0.6 sec

DESIGN REQ’TS & ASSUMPTIONS Maintain 1ksi minimum contact pressure across joint Goal contact resistance of 1       P ≥ 1ksi –evaluate impact of higher resistance on flat top time –perform measurements during prototype testing and on installed system to track actual range of values –Improved procedures (surface prep, silver plating) and QC can improve situation compared to original installation, reduce variation joint-to-joint Peak local temperatures to be limited to 120 o C

OTHER ASSUMPTIONS & CONSTRAINTS TF flag  T - 5 o C per pulse - 25 o C including ratcheting - impacts fastener requirements OH Coil must slide over TF Inner Leg Assembly - joints must be demountable at least on one end