Equilibrium field coils

Also called the poloidal field coils when excluding the toroidal field (TF) and ohmic heating (OH) coils, this is the set of electromagnets used to confine, control, and shape LTX plasmas. As in any tokamak, the TF coils provide a strong guide field along which the plasma can flow freely; the OH coil drives toroidal plasma current to compensate for the grad-B and curvature drifts in the toroidal field; a Helmholtz coil (blue coil) sets up a vertical field to compensate the tire and current-loop forces pushing the plasma outward radially. The remaining coils provide vertical and radial stability, eddy current and field null compensation, and poloidal cross-section shaping.

More details of equilibrium coil design (number of windings, conductor cross section, etc.) can be found in this document.

Simple model of OH circuit: https://www.circuitlab.com/circuit/6sg6ae9zmf89/ltx-oh/

Fig. 1: Poloidal cross-section showing field coils, excluding TF coils. Coils are color-coded, except the OH which is plotted in black.

Coil Parameters

Color	Purpose	Power Supply	Waveform source	Coil radius (R)	Coil height (Z)	Inductance	Resistance
	Toroidal Field	Robicon T1+PEI	Chronos AO-06	~0.75m	U: ~0.7m L: ~-0.7m	5600μH	148mΩ
	Ohmic Heating (OH)	OH cap bank (OH cap room)	OH Controller VI	OH1 (N=74): 0.0747m OH2U(N=2): 0.513m OH2L(N=2): 0.513m OH3U(N=2): 0.154m OH3L(N=2): 0.154m	OH1 (N=74): -0.534m...0.534m OH2U(N=2): 1.02m OH2L(N=2): -1.02m OH3U(N=2): 0.511m OH3L(N=2): -0.511m	113μH	7.81mΩ
Blue	Vertical Field	Robicon IF	Chronos AO-01	U: 0.862m L: 0.862m	U: 0.406m L: -0.413m	U: 337μH L: 333μH	U: 5.2mΩ L: 5.2mΩ
Red	Shaping	Robicon DF	Chronos AO-05	U: 0.673m L: 0.673m	U: 0.494m L: -0.497m	U: 147μH L: 142μH	U: 11.8mΩ L: 11.7mΩ
Orange	Field curvature	Robicon T3	Chronos AO-03	U: 0.3923m L: 0.3923m	U: 0.8240 L: -0.8240m	U: 520μH L: 520μH	U: 20.75mΩ L: 20.75mΩ
Yellow	VF Null	Yellow cap bank (L210 N wall)	RLC Circuit	U: 0.724m L: 0.730m	U: 0.800m L: -0.787m	U: 12.8μH L: 12.28μH	U: 0.96mΩ L: 0.96mΩ
Green	OH Eddy Cancellation	Robicon T4	Chronos AO-04	U: 0.100m L: 0.094m	U: 0.486m L: -0.490m	U: 300μH L: 300μH	U: 24mΩ L: 24mΩ
Internal	Active Feedback	Robicon T2	Chronos AO-02	U: 0.632m L: 0.632m	U: 0.367m L: -0.367m	U: 35μH L: 35μH	U: 2.1mΩ L: 2.1mΩ

Related Pages

Coil current monitors - lists current monitor diagnostics and their integrator and digitizer channels.
Measurement conventions: Currents, Fields, and Flows - lists the relative directions of currents in equilibrium field coils.
Power supplies - details on the power supplies for the field coils.