Radio Frequency Quadrupole Linac Question

[Strat-O]

(Sorry if this is off-topic for this group. There's really no group that addresses accelerators in the Physics Forums)

I've looked at many examples of RFQ linear accelerators. Most of them share the same characteristics:
1. So-called vane electrodes
2. Opposite-facing electrodes are energized with a common RF signal
3. Adjacent pair of opposite-facing electrodes are energized with RF + pi or 180 degree out of phase RF signal

However, from all the images and diagrams I've seen, it looks like all four electrodes have continuity with each other. That's the way it appears but it doesn't make sense. What reinforces this idea is often the electrodes are machined from solid pieces of copper then brazed together apparently forming a monolithic unit.

Can anyone shed light on what's going on here? If so I would appreciate it! Thanks--Marlin

 

[marcusl]

Linacs accelerate particles through "slow wave" structures consisting of RF/microwave waveguides. The RFQ modulates the RF field alternately in two planes to achieve both acceleration and focusing at the same time. These are analogs of ordinary transmission lines, but at high frequencies it is possible to propagate along structures that defy simple intuition.

To understand the complex RFQ structures, you should first learn something about how microwaves propagate down basic waveguides. This is a topic covered by hundreds of texts on E&M, microwaves and microwave electronics. You'll need to understand Maxwell's equations at a sophomore/junior level for it to make much sense. There are non-mathematical websites that will give you a flavor, though probably not much understanding:

http://www.microwaves101.com/encyclopedia/waveguide.cfm"
http://en.wikipedia.org/wiki/Waveguide"

 

[Strat-O]

Thanks marcusl. I'll check out that first link which sort of looks like a pretty good waveguide primer and then see what I can learn about Maxwell's equations.

Marlin

 

[Strat-O]

I had another question regarding this type of linear accelerator. Virtually all of the existing designs are made of nearly solid copper. I did an estimate on one design based on the volume of material and the 5 meter long machine would probably require around 2 tons of copper. And this is for a machine that could benefit from being mobile (contraband detector)

Why solid OFHC Copper? Why not a fairly thin shell of copper and use the open interior spaces for coolant. Or perhaps better yet build the electrodes out of a plastic such as fiberglass and use copper plating on the fiberglass and again use the interior spaces for channeling coolant. With a high frequency RF generator you will have a certain fairly shallow skin depth that even when multiplied by 5 is easily within the realm of some form or another of copper plating/coating technology.

TIA,

Marlin

 

[alphy]

I can provide some insight into the design and operation of RFQ linear accelerators. The Radio Frequency Quadrupole (RFQ) is a type of linear accelerator that is used to accelerate charged particles, such as protons or electrons, to high energies. It is an important component in many particle accelerators, including those used in research and medical applications.

The design of the RFQ is based on the principles of radio frequency (RF) acceleration, which uses alternating electric fields to accelerate particles. The vane electrodes, or vanes, are the key components of the RFQ. They are typically made of copper or other conductive materials and are arranged in a four-sided structure, with opposite pairs of vanes facing each other.

The RFQ works by applying an RF signal to the opposite-facing vanes, creating an electric field between them. This field alternates in direction at a high frequency, causing the charged particles to accelerate as they pass through it. The adjacent pair of vanes are energized with an RF signal that is 180 degrees out of phase, which helps to focus the particles as they travel through the RFQ.

Now, to address your question about the continuity of the vanes. While it may appear that all four vanes are connected, they are actually electrically isolated from each other. This is achieved through careful design and construction of the vanes, which are often machined from a single piece of copper and then brazed together. This ensures that the electric fields between the vanes are well-defined and controlled, allowing for precise acceleration of the particles.

In summary, the vane electrodes in an RFQ linear accelerator are carefully designed and constructed to create and control the electric fields necessary for particle acceleration. The apparent continuity between the vanes is a result of the construction process and does not affect the overall operation of the RFQ. I hope this helps to shed some light on the design and function of the RFQ.