Wikipedia
The polywell is a type of nuclear fusion reactor that uses an electric field to heat ions to fusion conditions. It is closely related to the magnetic mirror, the fusor, the biconic cusp and the high beta fusion reactor. A set of electromagnets generates a magnetic field that traps electrons. This creates a negative voltage, which attracts positive ions. As the ions accelerate towards the negative center, their kinetic energy rises. Ions that collide at high enough energies can fuse.
The polywell is one of many devices that use an electric field to heat ions to fusion conditions. This branch of fusion research is known as inertial electrostatic confinement. The polywell was developed by physicist Robert Bussard, as an improvement over the fusor. His company, EMC2, Inc., developed prototypical devices for the U.S. Navy.