A quadrupole coil that produces an inwardly convex curvature of the induced electric field lines and low induced magnetic fields in the plasma zone has been constructed. Hydrogen and boron plasmas were produced by the use of such a coil. Faraday cup measurements showed that the maximum proton energy in the loss cone of a magnetic bottle was 630 eV. Two such quadrupole coils were oriented to have nearly zero mutual inductance. Energy was imparted independently by ion cyclotron resonance to two different species in a plasma in a common dc magnetic field. A diborane plasma was produced by simultaneous operation of the two coils and the 2497-Å boron I line identified. The energy was supplied directly to protons and to boron ions. The quadrupole coil appears to be promising as a primary or supplementary heating source for certain fusion devices of the magnetic bottle type.