C. Y. Gung’s scientific contributions

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Publications (1)

Fig. 3. Spatial and temporal variation of left leg to right leg joint voltages during a zero-field, 45s, SOkA flat-top current waveform. current upramp, the subcable potentials are determined largely by inductive effects, with current transfer concentrated near the top of the joint. At the start of the current flattop, the induced potentials decay as the current transfer redistributes along the joint to an asymptotic distribution determined by the individual subcable to termination resistances. This ·variation in subcable potentials influences the asymptotic values of the externally measured termination voltage readings (Fig. 3) which vary from a low of 160µV near the bottom of the joint (L V13-RV13) to a maximum value of 265µV near the joint's midpoint (L V9-RV9). Simple estimates of joint resistance may be obtained by dividing each asymptotic voltage in Fig. 3 by the total transport current. These simple estimates yield resistance values ranging from 3.2nn near the bottom of the joint to 5.3nn near the joint's midpoint. Fig. 4 presents a more advanced evaluation of the voltage data collected during PTF shot 960814006 [6]. To create the electrical potential diagram in Fig. 4, a single point, in this case MV13, is arbitrarily selected as the ground potential. Then, working backwards, all interconnected voltage tap pairs are evaluated to determine the electrical potential at each tap location. The intent of this diagram is to use measurements taken from the outer surface of the termination to estimate a representative value of the voltage drop; across the copper saddle piece, for the underlying right leg to left leg superconductor cables. The voltage tap locations LVl, LV2, RVl, and RV2 were intentionally omitted from the evaluation of the lower joint resistance. The tap locations LVl and RVr are invalid because they explicitly include contributions from terminal connections to the· facility bus bars. Similarly, because of their poor coupling to the superconducting cables, the taps on ~e loosely fitting upper Monel blocks, L V2 and RV2, are . too heavily influenced by current transfer to accurately depict the underlying superconductor voltages. Of the remaining taps, a maximum right leg to left leg potential difference of 295uV is observed from LV7-RV9; this yields an upper bound estimate for the zero field joint resistance of 5.~ nn. Elec~cal potential diagrams have . similarly been constructed for data collected at· 20, 40, and 45kA current; these diagrams show roughly linear scaling of the potential at each tap location with current, that is, the joint resistance is independent of current. Potential diagrams constructed for data taken in the presence of 4T background induction indicate joint resistances of roughly 6.1 nn in parallel background field and 6.4 ·nn in a transverse field orientation.
Fig. 5. Distribution of lateral current transfer along the length of the joint, deduced for PTF shot 9608 14006 using a 72 element curre nt stick model of the sample. Current at each position along the sa?dle h~ been . normalized with respect to the current flow expected for a uniform dtstnbutton.
US Preprototype Joint dc Performance
  • Conference Paper
  • Full-text available

October 1997

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11 Reads

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5 Citations

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C. Y. Gung

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Citations (1)

... H ELIUM flow calorimetry is widely used to characterize the performance of large-scale, forced-flow superconductor cables and coils. Flow calorimetry can be used to verify DC dissipation in superconductor joints [1], particularly when voltage measurements yield ambiguous results due to significant maldistribution of current in neighboring multi-stage cables [2]. Calorimetry has been used to monitor the onset and extent of the superconducting transition in cable samples [3], and to characterize the heat transfer to and among conductor and coil elements [4], [5]. ...

Reference:

Supercritical Helium Flow Calorimetry at the MIT Superconducting Magnet Test Facility
US Preprototype Joint dc Performance

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C. Y. Gung

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