Saturday, June 20, 2009

map analysis

In a circular accelerator, if you look at a single beam position monitor (BPM), or say, a couple of them, to give you phase space, you essentially looking at the properties of the one and many turn behavior of electrons. The value of the Hamiltonian -free description, the map description, is that it treats the machine as a whole, without necessarily thinking of how that map comes about.
This is analogous to solid state physics and scattering analysis. You define various quantities of the material that can be probed via scattering stuff off it. You don't need to know the position of every atom in the material in order to define these quantities.

Why has this approach not developed further in accelerator physics? Because there aren't enough accelerators. Each one has its own peculiarities, and so people think more about how to change those peculiarities and effect certain global behaviors rather than be more creative in defining the global behaviors. It would be like analyzing ten space ships, each of which was rather different from the other. One would probably not extract a general theory of space ships out of this.

Tower of Babel

At some time, I'd like to try to lay out the genealogy of particle tracking codes in accelerator physics. Looking about the CERN site for MADX, we find a presentation on the Universal Accelerator Parser for the Accelerator Markup Language. Here, we see the status of accelerator codes described by Sagan as a "Tower of Babel". But, to be honest, at this point, I would not say that this accelerator markup language has caught on that widely.

I don't know why, but I keep trying to construct some kind of epic narrative about this topic. If the field of particle tracking codes is the tower of Babel, then we might refer to the shutdown of the SSC as the "hand of God" coming in and crushing the unified human effort to pierce Heaven for the glorification of Man.

Yes... dangerous waters. There is already far too much implicit religious metaphor pervading this field.

In any case, let us hope that something like the UAP/AML can help put the pieces back together again.

I should also mention another effort in this direction, the UAL, Unified Accelerator Library. I don't know the best link for this, since the BNL site seems to not be online anymore. Here's a paper, or here for a SPIRES search.

Friday, June 19, 2009

mathematical methods of accelerator physics?

There is a post by Mark at Cosmic Variance requesting ideas for topics for a course on mathematical physics. I added a comment suggesting non-linear dynamics for storage rings could make a good topic.
Thinking it through a bit more, perhaps this would be tough. I myself am in the process of trying to understand this field better and pick out what is and isn't essential. So maybe its not ready for someone to pick up outside the field.
The references I mentioned were to Dragt's online book and to the book by L. Michelotti called “Intermediate Classical Dynamics with Applications to Beam Physics”. The wikibook might still be a good place to sort this out.
Perhaps if one is talking about Lie Algebras or Lie Groups, this is nice to know that they are not just used in particle physics, but in classical mechanics as well. And classical mechanics is such a broad subject. It is almost the same as mathematical methods of classical systems.

I also mentioned that the maps with their resonance islands and separatrices and chaotic and non-chaotic regions had made their way into atomic and molecular physics through the quantum accelerator modes. Here is a link, first from google, but I haven't looked into the field enough to judge it yet... A topic for more investigation. I do know that the name of Shmuel Fishman comes up a lot with respect to this research area.

(Added comment: This topic did make it into several articles in Journal of Mathematical Physics. For example, see an article by Forest here.)

Monday, June 08, 2009


We accelerator physicists are the builders and caretakers of machines. We build machines that bring charged particles to very high energies, small sizes, strong currents. These flows of charge smash into each other, produce light, smash into targets and produce neutrons, are guided with great precision to be measured with great precision. We seek to control the flow, the identity, the environment of our charged armies. We build electronic systems, and software control, we protect, clean, and raise money for, and mourn the death of our machines. We are machine physicists. We create families of quadrupoles and sextupoles. We analyze power consumption, and ground vibrations. We deliver our beams shining and controlled, coherent and stable. We talk to the users of these beams- the scientists, the doctors, the patients, the companies. They want our beams- bright, stable, and on time. But we know that we need our machines to accomplish this.

Thursday, June 04, 2009

bottom up/top down organization

I recently read "Here Comes Everybody: The Power of Organizing Without Organizations " by Clay Shirky. It was a very refreshing book that made me feel like I got a bit of perspective on the changes we're encountering as we become more used to internet communications. He gave several examples of ways in which new things are possible in self organization with internet tools- basically, group forming and communication becomes easier, and because the technology to form these groups is essentially part of the web infrastructure, there is minimal cost associated with their formation.

As I've been thinking about jobs and where to go with my career, I've been seeing that there is a tension between the organizations that may want to hire me, and the connections I have and projects I can see to work on that cross organizational boundaries. I see the field of accelerator physics and how fragmented it is, and think that the internet could really facilitate some formation of commonality. At the same time, the reason the field exists is to build and operate accelerators that serve specific purposes or user communities. The building and running of such a facility is a rather expensive operation, and though there are new challenges for any project, many of the methods and technologies are already developed. So, from the facility perspective, a large amount of rather well-defined work needs to be done. This perhaps can only be done with the help of a more traditional top-down organization.

So I'm trying to understand how these two types of organization can work together- bottom up, spontaneous, informal, and multifacility on the one hand, and top-down single purpose, long term planned on the other hand.