Preliminary results of the partial array LCT coil tests Page: 3 of 5
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coils was maintained at 14.5-15.0 psia corresponding
to a bath temperature of 4.2-4.3 K. The flow through
the CH coil was maintained at '4.4 K by flow through a
bath-cooled heat exchanger.
Operational disturbances were few. The large
compressors were inadvertently tripped off several
times, resulting in time loss of 1-2 h per event. The
most serious event was the loss of vacuum in the
19,000-L storage dewar, costing about one week's time
and several thousand liters of LHe.
Heat Losses. After cooldown was completed and the
system thermally stabilized (1.22 days after the coils
were first filled), 4.2-K refrigeration heat loss
measurements were performed on isolated sections of
the system by observing liquid depletion rates in each
component while the rest of the system was held at a
nearly constant helium level. The major components of
the system at 4.2 K are the three coils (45-50 W per
pool-boiling coil, nearly independent of current), the
bucking post and associated structure (low), the four
vapor-cooled lead dewars and bus ducts (at I . 0,
1*0 N cold gas plus six SCFM warm gas), the two exter-
nal LHe storage dewars (1 W for the 2,000-L dewar,
2 SCFM warm gas for the 19,000-L dewar), and the
vacuum jacketed liquid and vapor lines connecting
Magnetic Field Surveys. During the coil tests, peri-
odic stray-field surveys were made to confirm that
personnel and equipment in the building were not being
exposed to excessive magnetic fields. The results
confirmed earlier calculations. With 10.2kA in the GD
coil and 4.1 kA in the JA coil, the highest field out-
side the fenced area was 227 Gauss; the highest field
in an occupied office was 65 Gauss. Computer monitors
were upset, personnel were not.
Coil Power Supplies. The power supplies used during
the coil tests were 12 V, +16 kA, 12-phase, SCR units
manufactured by PWR Inc. The negative voltage gives
an adjustable, convenient way to slowly ramp down the
coil current. The usual problems in commissioning
large feedback type power supplies were aggravated by
the fact that they had not been previously tested with
a 2-H. 10-kA inductive load. As debugging progressed,
the supplies ran smoothly in the voltage control mode
at currents to 10 kA with 4 kA in the adjacent coil.
Single-Coil Heater Tests. Several of the JA heaters
were energized successfully reproducing the earlier
tests in Japan. Two of the GD heaters were energized
using several combinations of heater power, pulse
duration, and coil current. Figure 6 shows voltage
traces taken when a half-turn heater adjacent to the
coil case sidewall and spanning the outer leg of the D
was energized at full coil current (10.2 kA). The
flat tops of the voltage traces show that the heater
drove the conductor fully normal. This conclusion is
confirmed by the agreement of the measured flat-top
voltage with that inferred from the measured normal-
state resistance at zero field corrected for the
Recovery is rapid (a few hundred ms) and occurs
simultaneously over the length of the heated half-
turn, indicating that recovery was from the sides
rather than from the ends. The normal-state heat flux
at 10 kA in the self-field of 5.3 T near the heater is
0.12 N/cm2. To this must be added an uncertain con-
tribution from the outflow of heat deposited by the
hot heater; we estimate this to be not more than
,).1 W/cm2. Being in the Stekly regime means that
this heat flux is smaller than the minimum film boiling
heat flux, the measurement of which ChristensenE in-
dicated to be about 0.18 W/cm2 for a similar heat
Rapid as recovery is, it is still much slower
than expected for this conductor with no heater embedd-
> 41 I 1
0 500 4000 1500 2000 2500
Fig. 6. Results of pulsing half-turn heater on outer
vertical leg with GD coil at full current. (a) Voltage
across upper one-sixth turn. (b) Temperature at center
of lower one-sixth turn, on the narrow side of the con-
ductor opposite to the heater. (c) Heater current.
ed in it (recovery time 1L10 ms). The resolution of
this discrepancy lies in the fact that the nichrome
heater wires are driven to high temperat .es (100 K or
more) and leak heat slowly into the conductor. This
is borne out by the comparison (Fig. 7) . the measured
response timing of the heated half-turn with the pre-
dicted response times made for a conductor with a
heater embedded in it, times are based on GD Conductor
Cooling and Heater Verification Test (CCHVT) data
analysis.7 Agreement is good except for one pulse
which was just enough to drive the conductor into the
current sharing regime. There is no reason to think
that a normal zone accidentally created, would not
recover in milliseconds.
Acoustic Emission (AE). The GD coil with its adjacent
structures was fitted with 30 low-noise AE sensors.E
The JA coil had four such sensors and four of another
kind. Data for off-line analysis, now underway, were
----GENERAL DYNAMICS PREDCTED vAUES
a .C' MEASURES RECOVERY TME
a TIME TO PEA- TEMPERATURE
(INFERRED FROM MEASUREMENTS'
5 .CT MEASE-D SRE-A.A- T~M
- 'COMPLETE --
SPE A C L -
----r Y a -- - -
0 400 200 300 400 500
PULSE ENERGY DEPOSE TION (mi/cn" of c-'duco
Fig. 7. Comparison of GD prediction with measured
response timing of heated half-turn.
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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/m1/3/: accessed February 22, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.