  The magnetic field control subsystem of the Nuclotron - a superferric ion
synchrotron - is described. The bending (BM), focusing (QF) and defocusing (QD)
magnets are powered by three supplies. The BMs are driven by the supply of a
6.3 kA nominal current. The QFs and QDs are connected in series and powered by
the 6 kA supply. An additional supply of 200 A for the QFs is used to keep the
reqired ratio I(QF)/I(QD). The BM magnetic field shape is set by a pulse
function generator which produceds a reference burst (Bo-train) with a 0.1 Gs
resolution. A real B-train of the bending magnet field with the same (0.1 Gs)
resolution is used for feedback loop and as reference function for QD and QF
supplies. The QD and QF trains are utilized for feedback loop in the QD and QF
supplies. The control of slow extraction system suppllies is described as well.
