# A comprehensive reference for RF linear accelerator's operation

I'm doing a research on RF linear accelerators (RF Linac), but while studying the material I encountered many problems. I cannot understand the basics of the RF linear accelerators in many ways, for instance

• Why the particles are accelerated in the gaps and not in the drift tubes?

• How they become in phase with the bunches of particles?

• What does bunching particles mean?

Etc.

I am reading some books but none of them has explained the principles of working in detail or with some illustrations and comprehensive figures.

• So where can I find a comprehensive resource describing the structure and operation of Rf linacs?
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## 1 Answer

I am not sure what your level is, but I think you will find that material on accelerator structures generally requires upper division E&M. However in terms of concepts, this overview and these pictures (from Illinois Tech) will go a long way toward answering the questions you have lined out.

• In a drift-tube linac, the drift tubes sit inside a larger RF cavity and act as shields. Thus, the electric field inside a drift-tube can be approximated as zero. The gaps between drift tubes will still have an E-field, however, which varies sinusoidally in the direction of travel. When the particle is in the gap between drift tubes, it will experience an E-field and undergo acceleration.
• Let's say we are accelerating protons. We want to accelerate them in a particular direction, but half the time, the E-field in the gap is pointing in the wrong direction. Hence we can't make a continuous beam with this particular technology; we have to break the beam up into "bunches". This is by-and-large a limitation of all RF accelerating structures.

A truly comprehensive reference for Linacs is the SLAC "Blue Book", which is now freely available from SLAC. It is somewhat dated, but covers all aspects of building a linear accelerator in great detail. There are also a good number of SLAC publications that deal with Linacs, such as SLAC-PUB-7802. You may also consult material presented by the US Particle Accelerator School. Finally, there is the RF Linac textbook by Wangler.

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