  Due to its simplicity the classical cyclotron has been used very early for
applications in sciency, medicine and industry. Higher energies and intensities
were achieved through the concepts of the sector focused isochronous cyclotron
and the synchro-cyclotron. Besides those the fixed field alternating gradient
accelerator (FFA) represents the most general concept among these types of
fixed field accelerators, and the latter one is actively studied and developed
for future applications.
