Using E-beam Mapping to Detect Coil Misalignment in NCSX Page: 3 of 10
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Using c-beam mapping to detect coil misalignment in NCSX
E. Fredrickson', A. Georgiyevskiyl, V. Rudakov2, M.C. Zarnstorffl
'Princeton Plasma Physics Laboratory, Princeton, NJ,
2 Institute of Plasma Physics, National Science Center
"Kharkov Institute of Physics and Technology", Kharkov, Ukraine.
Following assembly of the NCSX device, a program of e-beam mapping experiments is
planned to validate the accuracy of the construction and assembly of the NCSX coil systems.
To aid in the development of requirements for the e-beam mapping hardware and machine
requirements, simulations of the e-beam mapping experiments, including various coil
misalignments, have been done. The magnetic flux surface configuration was constructed using
a numerical code, based on the Biot-Savart law, to calculate the magnetic field components and
trace the field line trajectory many times around the torus. Magnetic surfaces are then mapped
by recording the field line intersections with toroidal cross-sections of the magnetic system,
much as in an actual e-beam mapping experiment.
The NCSX coils were designed to provide good magnetic surfaces at high beta with
significant bootstrap current. The coil set includes separately powered modular, toroidal, and
poloidal field coils, and can produce a wide range of magnetic configurations. Many of the
vacuum field configurations with low order rational surfaces have stellarator-symmetric islands
present. In particular, configurations with an t = 0.5 surface are found to be most sensitive to
coil alignment errors and typically have a stellarator symmetric 3/6 island chain (the t = 1/3
surface has been found to be much less sensitive to coil alignment errors). Nevertheless, despitei
nr~
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A-0.3L-
1.31.5
1.7
R(m)Fig. 1. K =1.05, BZ=6.47% (
PFC currents) Bo=1.7 T, to =
i,.=0.508, 1-st module displathe presence of these islands, configurations have
been found which will allow, we believe, the
. identification of modular and poloidal field coil
; - displacements of < 0.5 mm. In the course of
these calculations, a catalogue of many hundreds
; of vacuum magnetic configurations was
compiled, each with varying sensitivity to the coil
displacements.
1.9 2.1 With three coil sets, connecting a measured
field error to a specific coil misalignment is a
without challenge. Some progress in this regard has
0.448, been made through the recognition that many
ced 1 mm. useful vacuum configurations may be created byenergizing only a subset of the field coils, e.g., many configurations with good surfaces may be
Z(m)
0.a .
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Fredrickson E, Georgiyevskiy A, Rudakov V, Zarnstorff MC. Using E-beam Mapping to Detect Coil Misalignment in NCSX, report, October 18, 2005; Princeton, New Jersey. (https://digital.library.unt.edu/ark:/67531/metadc886332/m1/3/: accessed April 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.