An actuator system for controlling the external fins on a gun-launched projectile to control the flight path of the projectile. A heat exchange catheter is provided with heat transfer fins projecting or extending outward from the catheter which may be inserted into selected blood vessels or body regions to transfer heat with blood or fluid in the selected blood vessels or body regions. Then, a shift of the electron beam, which is caused when an electric field is not in parallel with a magnetic field, is corrected and a shift of the electron beam, which is caused by a gradient of the magnetic field, is corrected, after which an increase of a beam diameter of the electron beam, which is caused by Coulomb-interaction between the electrons emitted from the emitter, is corrected.