Abstract
In this paper, a detailed discussion of the rf-related beam dynamics in rf guns and accelerating cavities is presented. Other rf-gun-related aspects such as space charge and cathode physics are not treated. An effective start phase is introduced in order to yield a better description for the synchronous phase, the energy gain, and the bunch compression factor in gun cavities. Energy spread and longitudinal emittance are treated in a form applicable to guns as well as to accelerating cavities. Discussions on the transverse emittance include the chromatic emittance variation at high emission phases and effects of field asymmetries and combined solenoid-cavity sections.
Highlights
Photocathode rf guns are the electron sources of choice for many modern accelerators requiring high brightness beams, such as, for example, free electron lasers
The beam dynamics in rf guns is characterized by two unique characteristics: the particles start inside an rf cavity, and the phase changes rapidly at the very beginning of the acceleration process
Since we have described the total energy gain of the rf gun as the sum of the energy gained in the individual cells, the field flatness can be included in our considerations if we allow for different values of α in the equations describing the energy gain
Summary
Photocathode rf guns are the electron sources of choice for many modern accelerators requiring high brightness beams, such as, for example, free electron lasers. There are two key aspects to these sources: electron generation by means of photoemission and direct acceleration in an rf cavity. Generation inside an rf cavity [2] provides higher fields at the cathode and a higher total accelerating voltage than a dc gun, both important aspects to control space-charge-induced emittance growth. This report concentrates on rf-related dynamics; other aspects such as space charge and cathode physics are not discussed. The beam dynamics in rf guns is characterized by two unique characteristics: the particles start inside an rf cavity, and the phase changes rapidly at the very beginning of the acceleration process.
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