Preliminary results of the partial array LCT coil tests Page: 2 of 5
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system, and quench detection circuits. The coils were
then run extensively (Fig. 3) to shakedown the facility
and test the GD and JA coils. One test remains, sub-
atmospheric operation of the refrigerator, before
warmup begins on Sept 15.
J 2 3 4 5 6
Fig. 2. Winding temperature and resistance of one coil
(JA) in the final stages of cooldown. Typical of all
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Fig. 3. History of coil currents during the partial-
array tests. Downward arrows represent dumps. Hold
points and energizations below 5% (500 A) are omitted.
Quench Detection. In the LC'TF, an asynnetric multi-
coi array, a conventional single-bridge detection
circuit would be ineffective due to mutual coupling
effects. Thus a unique pickup coil compensation
scheme- was used to cancel the inductive signals
caused by the coil and its neighbors so that a resis-
tive (normal zone) voltage could be detected. The
pickup coils, each consisting of 64-turn shielded
cable distributed around the outside surface of the
coil case, provide inductive signals for compensation
modules of self coil and neighboring coils. For each
coil, eight quench detection modules were provided to
cover different portions of the coil redundantly.
Appropriate gains in the compensation modules were set
manually for both coils just before they went into
superconducting state (T 't 15-20 KC). It was not
necessary to change the gain settings during the test
Each module provided high-level quench signal
(0.5-V threshold with 0.2-s delay) and low-level
quench signal (0.25-V threshold with 8-s delay) to the
PLC for coil protection. Hote in Fig. 4 that while
two coils were simultaneously charged with about 4 V,
the residual compensated voltages stayed well below
the 100-mV level.
Coil Dumns. Several coil dumps were performed from
appreciable current levels (Fig. 3) showing that the
associated facility systems worked well to 10.2 kA.
The GD terminal voltage was balanced with respect to
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Fig. 5. Single-coil dump with both coils energized.
JA coil in persistent mode.
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Fig. 4. Total voltage, current, and compensated
voltage while two coils are simultaneously charged.
ground within +1.71, and a 100-kf, center-tap ground
resistor was added to help insure this balance. Also,
a series of single-coil .dumps were attempted while
the other coil was held at constant current to demon-
strate that the quench detectors would not dump the
adjacent coil. This was successful, giving promise of
great savings of time and helium in the six-coil
testing by using selective rather than simultaneous
dumping. In one test (Fig. 5), the JA coil was first
set into a persistent mode with coil current at 7010 A
and then the GD coil was dumped from 4100 A. Figure 5
also shows an increase in the JA current of about
490 A, due to the magnetic coupling of the coils.
Refrigerator Operations. After the successful cooldown
of the coils and facility the refrigerator was operated
continuously to maintain system temperatures and
liquid helium levels. Pressure on the pool-boiling
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Luton, J.N.; Cogswell, F.D.; Dresner, L.; Friesinger, G.M.; Gray, W.H.; Iwasa, Y. et al. Preliminary results of the partial array LCT coil tests, article, September 10, 1984; United States. (digital.library.unt.edu/ark:/67531/metadc1205208/m1/2/: accessed December 11, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.