Compact linac

A linear accelerator comprising:

• an electron source region in which is located an electron source;
• a cavity comprising a plurality of cells with each cell linked to an adjacent cell by a side chamber, wherein the cavity is configured to accelerate electrons received from the electron source region through the series of cells with a radio frequency field having an accelerating field amplitude in each of the cells;
• and
• a radio frequency source configured to generate and inject the radio frequency field into the cells, wherein the side chambers are configured to couple the radio frequency field between the connected pairs of linked cells;
• wherein
• the plurality of cells comprises a succession of cells extending from a first cell of the plurality of cells that receives electrons generated by the electron source to a final cell of the plurality of cells;
• the plurality of cells comprises a capture section, comprising the first cell and a second cell, and an acceleration section, comprising the final cell and a plurality of cells immediately preceding the final cell, and the length of each cell in the capture section is shorter than the length of each cell in the acceleration section;
• the cavity is configured such that, when the radio frequency source injects the radio frequency field into the cells, the field amplitude in the capture section is a lower field amplitude and such that the field amplitude in the acceleration section is a higher field amplitude relative to the lower field amplitude in the capture section.