EEVblog #836 - Tour Of The Australian Synchrotron

[Z80]

Hi, I used to work at a large synchrotron here in the UK some years ago so can give you a bit of info although I'm no physicist.

1) Essentially yes, the luminosity, spectral purity and energy level are the reasons why they are generated this way.  X-ray crystallography for instance needs very bright hard X-rays which couldn't be made practically with a conventional tube.  The higher the energy, the shorter the wavelength, the better the resolution.

2) The energy is attenuated by bending the beam, but in the case of a synchrotron this is what you want.  As the electron beam is bent, photons are emitted (synchrotron light) and this is what is sent off down the beam lines.  In fact to increase the energy the beam is intentionally bent in devices called wigglers which are just an array of very powerful magnets which pull the beam back and forth to shake out the photons.  Increasing the size of the ring allows you to store a more powerful beam, the energy is limited by how much the magnets can bend it in one go.

3) I don't remember the timings off hand, but the electrons travel round in bunches yes.  This is due to the way they are accelerated.  Energy is pumped in by an RF field, the electrons being charged are pushed along by it and all end up collecting on the wave peaks (like surfers in the ocean).

4) It's not the electrons that are used, they just go round and round the ring.  Whenever they are deflected, physics happens and synchrotron radiation is given off.  Think of the electrons like a wet sponge being swung round on a piece of string, the water flying off is the radiation.

Regarding extracting energy from the beam mentioned earlier, yes you can.  A moving charged field can be coupled to and energy extracted, this is exactly how microwaves are generated in a magnetron.  I saw a research experiment when I last visited the lab where an RF cavity was used to extract the energy out of the end of a linear accelerator beam (the beam is usually just dumped).  This energy was fed back to the other end which significantly reduced the power required to keep the beam flowing, interesting stuff indeed.

[tpw_rules]

It seems they're a bit lax on radiation safety, actually. Do you know the numbers that people are actually exposed to? I visited a cyclotron used to produce nuclear medical imaging chemicals (tracers and stuff). In addition to having a 7 foot thick concrete door to the machine, I was required to wear an electronic dosimeter to record my exposure during my visit. They had Geiger counters for your feet and hands to make sure you didn't track anything out. Does the concrete do a good enough job to not need any of this? Are Australian regulations different? Certifying that you're meeting maximum exposure limits is pretty easy if you don't know what it is...

[michelinux]

Elettra Synchrotron in Italy:

https://www.elettra.trieste.it/lightsources/elettra/beamlines.html