The Russian-American high magnetic field collaboration Page: 5 of 8
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cade, these too become flux trappers. The highest fields are obtained when all three cascades are
used. As noted later, some of our experiments were done with only two cascades to permit a
larger initial experimental volume.
Owing to obvious shipping restrictions, all components made of or requiring explosives
were made at Los Alamos. Besides the main cylindrical charges, small amounts of explosives
were also required for the initiation blocks. There were enough new features in the explosive
systems that we decided to make a general compatibility test. Figure 2 shows the test setup. Only
three initiation blocks were used instead of ten that are required for the complete assembly.
These were symmetrically placed over a Composition B hemicylinder. An aluminum liner served
as a crude mockup of the first cascade. The test results: confirmed that the implosion was
smooth, as determined from a framing camera picture sequence of the liner surface; confirmed
that firing the initiation block detonators in parallel at 2500 volts was satisfactory ; and supplied
the crucial timing from load ring to inner charge diameter, through use of judiciously located
Two complete system tests were made before embarking on the rather complicated super-
conductivity studies. The tests had a dual purpose: to check out the entire system and to obtain
some code benchmarking data.
In both shots, all three cascades were used to get maximum fields. The first (solenoid)
cascades were powered by two modules (3000 pF each) of the Ancho Canyon Site capacitor
bank. A bank charging voltage of about 18 kV was sufficient to generate the 2.0 MA normally
used. This current generated an initial field of about 16T in the center of the system.
The Russians use a 50/50 mix of RDX/TNT explosive for the main charge. For the
benchmarking tests we used two different explosives: Composition B (60/40 RDX/TNT) and
PBX 9501. Composition B was used for the remaining three shots in the series.
Magnetic fields were determined in two ways: integration of voltages obtained from
calibrated B-dot inductive probes, and the measurement of Faraday rotation of plane, polarized
light through a standard material
The first method has been used at Los Alamos for decades. Probe calibrations are ob-
tained from a special capacitor bank-coil system set up for this purpose. Both the probe of un-
known area and a standard probe, whose area is accurately known, are placed inside the coil.
Comparison of the signals obtained when the capacitor bank is fired gives the area of the probe
under calibration in terms of the standard probe area.
On the other hand, the Russian team generally uses the Faraday rotation method.' This
measurement is often supplemented with B-dot probe measurements, but the Faraday
measurement is the primary one. Their standard arrangement employs He-Ne laser light (0.6328-
pm) and a standard, heavy flint glass as the optically active medium. We used both methods
here. Figure 3 gives an enlarged view of the third cascade. The first shots were heavily
diagnosed. Three different Faraday sensors were used. They were placed in 1- mm wall ceramic
tubes (2- nmm. ID). Two B-dot probes, encased in shrink tubing, were nested between the ceramic
tubes. Finally, a single-mode optical fiber was nested between two of the ceramic tubes, and the
Faraday rotation of light in the fiber measured the current flowing through the cascades
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Fowler, C.M.; Christian, J.M. & Freeman, B.L. The Russian-American high magnetic field collaboration, article, July 1, 1995; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc791648/m1/5/: accessed March 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.