Final answer:
The particle accelerator that uses oscillating electric fields to accelerate particles along a fixed radius track is the cyclotron, which employs fixed-frequency alternating electric fields for particle acceleration.
Step-by-step explanation:
The type of particle accelerator that uses oscillating electric fields to accelerate particles around a fixed radius track is known as a cyclotron. In a cyclotron, particles are accelerated using fixed-frequency alternating electric fields while they spiral outward along a magnetic field, making increasingly larger radius orbits on each pass. As opposed to a cyclotron, the synchrotron uses varying frequencies of accelerating voltages and an increasing magnetic field strength to keep the particles travelling in a fixed-radius path as their energy increases.