Defining terms

I’ve had this blog running around in my head for quite a while now so I figured it was about time I got it written. Now anyone who follows my Facebook statuses (you know who you are) will probably have noticed certain terms featuring time and time again and maybe, just maybe, you might be a little curious as to what I’m gibbering on about. If that’s the case then this post is for you.

1. Synchrotron/Spring8

In short this is where I work and essentially where I live. A synchrotron is a kind of particle accelerator, the name coming from the synchronous tuning of a guiding and accelerating magnetic field that ensure particles in the accelerator ensure both a circular path around the synchrotron and also keeps there speed constant at just below the speed of light.

Now note I said accelerator, not collider. I do not smash atoms together. I do not create black holes. I am not looking for hitherto undiscovered particles (godly or otherwise). Right now that that’s off my chest I’ll tell you what I am doing which involves exploiting a handy little oddity of electrons.

As these electrons whizz around the ring at breakneck speeds they are constantly being deflected, to maintain that all-important circular path. At the deflection points they will slow down a bit losing energy. But that energy has to go somewhere and so it is radiated in the form of photons of light, x-rays to be precise. Originally this was an accidental side effect but these days’ synchrotrons are built with this phenomenon in mind and with that we come nicely to term number 2.

2. Beamline

These are the positions around the synchrotron at which the x-rays are actually emitted. X-rays act just like any other rays of light so they can be diffracted reflected and focussed in the same ways. The beamline contains the apertures; lens and mirrors used for this purpose as well as big end-station hutches that house the equipment needed for the particular experiment you want to perform. They are essentially a synchrotron scientist’s lab.

 

3. Beamtime

As you can imagine synchrotrons are not infinitely large, such a shame I know. As such the number of simultaneous experiments is limited. Unfortunately the number of scientists wanting to perform experiments is much greater than the number of beamlines. The usage period is therefore allocated in time slots that users refer to as “Beamtime”. This time is always fairly limited and precious so we try ti make as much use of it as possible, hence all the sleepless nights . In fact nothing causes more sleepless nights than the next term.

4. Beam dump

The original term comes from the piece of equipment used to absorb the energy of particles in a particle accelerator to safely stop them. For me and anyone working in a synchrotron however the term is synonymous with “Oh no not again”. Without circulating no x-rays will be emitted and therefore no experiments can be performed. They can happen for a number of reasons. Sometimes it can be down to hutch interlock problems meaning there is a chance a worker could be irradiated by escaping X-rays and so they need to be shut off as quickly as possible. Other times it is down to the electron source (wonderfully known as an electron gun) or the accelerator itself, which leads to instabilities. What it always is though is damned inconvenient. Sometimes a dump is a matter of moments, other times it can last for hours and when the beam comes back all it’s parameters may have changed, meaning the experimental set up has to be re-optimised and more time is lost.

5. Beamline staff

Golden rule, make these guys your friends. They are the people who run the beamline with expertise generally in construction engineering. They develop and maintain most of the equipment and software for performing experiments and will help your experiment run as smoothly as possible. Treat them nicely and you’ll have a nicer time during experiments, especially if there are problems – there are always problems.

 

6.Speckle patterns

These are the stuff that dreams are made of, provided you dream about coherent diffractive imaging (CDI). The experiments I perform involve illuminating samples with very bright X-rays and measuring their reflections from atoms within the sample using a detector similar to those found in digital cameras (though quite a fair bit more expensive). Speckles occur when photons of light with the same wave length, the distance between the humps of the lights wave form, interact with different regions in the sample and are reflected to the same degree. The photons interact additively or destructively and so we see spots of very intense signal or patches of no signal on the detector.

Each speckle contains contributions of reflection from the whole sample so it is the variation in intensity and the periodicity of the samples that hold the important structural information. If that is a little confusing don’t worry, I’m still not fully on top of it myself. What I do know though is that they can be very pretty. Whilst getting the hard structural information requires a fair amount of computation we can still draw some interesting conclusions about overall structural changes within a sample from changes in speckle position and intensity alone. It is quite nice that the data we collect is something you can physically see straight away.

Right science waffle over, hope you feel a little bit more enlightened in regards to my research and hopefully next time I post won’t be so far away.