Adjusting energy of a particle beam

A particle accelerator comprising:

• a coil to provide a magnetic field to a cavity;
• a particle source to provide a plasma column to the cavity;
• a voltage source to provide a radio frequency (RF) voltage to the cavity to accelerate particles from the plasma column, the magnetic field causing particles accelerated from the plasma column to move orbitally within the cavity;
• an enclosure containing an extraction channel to receive the particles accelerated from the plasma column and to output the particles from the cavity;
• and
• a regenerator to adjust the magnetic field within the cavity to thereby change successive orbits of the particles accelerated from the plasma column so that, eventually, the particles output to the extraction channel;
• wherein the enclosure comprises magnetic structures, at least one of the magnetic structures having a slot therein, the slot containing a magnetic shim that is ferromagnetic and movable within the slot, the magnetic shim being movable relative to the regenerator to affect an amount by which the regenerator adjusts the magnetic field.

A particle accelerator comprising:

• a cryostat comprising a superconducting coil, the superconducting coil conducting a current that generates a magnetic field;
• magnetic structures adjacent to the cryostat, the cryostat being attached to the magnetic structures, the magnetic structures containing a cavity;
• a particle source to provide a plasma column to the cavity;
• a voltage source to provide a radio frequency (RF) voltage to the cavity to accelerate particles from the plasma column, the magnetic field causing particles accelerated from the plasma column to move orbitally within the cavity;
• an extraction channel to receive the particles accelerated from the plasma column and to output the particles from the cavity;
• and
• an actuator that is controllable to move the cryostat relative to the magnetic structures.

A variable-energy synchrocyclotron comprising:

• magnetic structures defining a cavity in which particles are accelerated for output as a particle beam that has a selected energy from among a range of energies;
• an extraction channel to receive the particle beam;
• and
• a structure proximate to an entry of the extraction channel to intercept the particle beam prior to the particle beam entering the extraction channel, the structure being movable based on the selected energy, the structure to absorb at least some energy of the particle beam prior to the particle beam entering the extraction channel.