Meera Senthilingam: This is the Diamond podcast with me, Meera Senthilingam. In this first edition for 2010 we probe into the synchrotron itself to find out what makes Diamond such a useful tool in scientific research, as well as discover how its X-ray beams are created with such accuracy and intensity. We'll be investigating how the design of a synchrotron like Diamond is crucial when the research it's used for operates at the micron level.
Jim Kay: We derived a specification of the floor being stable to one micron over ten metres per hour, and ten microns over ten metres per day. Now a human hair is forty microns in diameter, you can imagine that over a day we're not wanting the floor to change by more than a quarter of a human hair.
Meera: We also find out how the movement of such high speed electrons is controlled.
Mark Heron: They monitor all the parameters, they can see summary screens, they also have alarms if something goes wrong. Most of those are updated ten times a second, so people see the information in real time.
Meera: Plus we discover how electrons moving at this high speed are manipulated to make the right light.
Emily Longhi: If you can control how far the electron beam moves from left to right then you control the actual colour of X-rays that come out from that process.
Meera: All that plus the latest news and events from Diamond coming up on this month's Diamond Light Source podcast.
Voice-over: The Diamond podcast - for more information look us up online at www.diamond.ac.uk/podcast.
Meera: Previous editions of the Diamond podcast have provided an insight into the fields of research taking place at Diamond. But this month we're looking at the workings of the machine. This research that takes place works on scales as small as microns and nanometres. That's one millionth of a metre and smaller. So we're going to investigate how such precision and stability are enabled at this level. So first we meet Jim Kay, Head of Engineering at Diamond Light Source. He explained to me how producing accurate beams of light on this miniscule scale requires careful design and planning from the outset.
Jim Kay: In designing and building Diamond one of the key things is the stability of the electron beam. The electron beam is the source of the X-ray photons that are then transmitted to the beamlines for science. So if we have an unstable electron beam then we'll have unstable X-rays. Also where the X-rays are used, down where they are exposed to a sample, if the sample similarly is wobbling around and isn't stable then the data produced from the X-rays falling on the sample won't be very good either. And in designing Diamond to achieve that stability we paid a lot of attention to minimising the sources of vibration, hence all our main plants like water pumps, compressors, heating and ventilation fans are all housed well away from the accelerators and the beamlines.
Meera: A key thing you were looking at was maintaining a constant ground level essentially in the area of the synchrotron where the beamlines would be, and keep that separate from walkways and other pieces of land that essentially move more I guess and be used more by machinery and people?
Jim: Yes, one of the key features of the Diamond slab, where the accelerators and the beamlines are, we've built this slab on piles. This slab is about 650 metres in circumference and about thirty metres wide. It's a continuous ring, and the ring is built on 1500 piles, dug twelve - fifteen meters deep into the chalk that we've built Diamond on. And one of the keys things about this site is that the water table varies each year - in the wettest months the water is only about four metres under our feet, in the driest months it's about twelve metres under our feet, and with that varying water table the chalk shrinks and swells, and we couldn't afford that kind of behaviour being replicated on the surface of the slab where our experiments are. So by drilling these piles into the chalk we've achieved a very flat, reliable and stable platform.
Meera: And what other features are there that just further ensure that the ground level doesn't change as, say, the chalk beneath us swells and shrinks?
Jim: Another design feature that we've built into Diamond is that underneath this slab there is a 70 mm gap which allows the chalk as it shrinks and swells to do so into the void and not affecting the level of the slab.
Meera: How much can a change in the ground level essentially change the beamline by? And how much affect would that then have on the samples that you're trying to look at?
Jim: In our specification we were conscious that a typical beamline experiment might last a shift, a day of seven or eight hours, so we're keen to achieve a great deal of stability in that one-shift period. So hence we derived a specification of the floor being stable to one micron over ten metres per hour, and ten microns over ten metres per day. And to get those numbers in perpective a human hair is forty microns in diameter, you can imagine that over a day we're not wanting the floor to change by more than a quarter of a human hair.
Meera: So now you've distinguished between the slabs used in the main experimental part of the synchrotron and the walkway surrounding it, and we're currently standing in the experimental hall and I can see a very long rod of metal, is what it looks like to me, which is a special piece of machinery you use here in order to ensure and check that your ground is as accurately maintained as you hope?
Jim: Yes, this system is called a hydrostatic levelling system. It's a canal, a water canal that's sixty metres long. It goes from the source of the X-rays inside the storage ring tunnel and stretches out along a typical beamline route sixty metres to the edge of the experimental hall. And what this canal allows us to do, at various points we've fitted sensors, and you can see one here, it's typically about 125 mm diameter steel pot, about 200 mm tall and inside there is the open surface of the water canal and a capacitative sensor that's built into the top that's checking the height between the top of the top, the HLS sensor and the level of the water inside it. And so we've got eight of these sensors ten metres apart and if we measure the height change between adjacent sensors we can check are we actually achieving that performance with this instrument.
Meera: So essentially this is a very large and very accurate spirit level?
Jim: That's exactly right.
Meera: And in a way you're taking this a step further and ensuing greater levels of accuracy over greater distances is with your new I13 beamline, so what's happening there?
Jim: Yes, I13 is one of our later Phase II beamlines, our so-called imaging and coherence beamline, we want to build an experimental station that's 250 metres away from the source of the X-rays.
Meera: That's very far.
Jim: it's a long way, and a typical beamline that you can see here, the experimental sample will be of the order of forty metres away from the source of the X-rays, so we're looking to take the X-rays more than six times further away from the accelerator than we've done to date.
Meera: What are the benefits to having a beamline 250 metres away?
Jim: To get dimensions in perspective a micron is a millionth of a metre or a thousandth of a millimetre, a nanometre is a thousandth of a micron. And the next era of scientific beamlines will aim to achieve nano-focus beams, where at the moment with these shorter beamlines we deliver micron focus beams. You can focus to smaller sizes the further away you are from the source point.
Meera: Is progress going well, and when's it going to be ready?
Jim: Progress is going very well, we've cast the slab, we're building the building now, that's due to finish in the spring. And we're expecting the first photons delivered to that end station by the end of this year.
Meera: That was Diamond's Head of Engineering Jim Kay explaining how keeping the ground on which Diamond was built stable is crucial to ensure the accuracy of the beamlines created. Now Diamond was completed and began operation in January 2007. So now, three years on, I spoke to Diamond's technical director Richard Walker to find out the highlights and achievements that have taken place in this time and what we have to look forward to.
Richard: Well the main achievements over the last three years have been not only a significant increase in the number of operating hours, more than a 50% increase in June 2009 compared with 2007, but we've also doubled the beam current, we've doubled the reliability of the machine, and we've doubled the number of insertion devices in the ring. We've also introduced top-up operation.
Meera: What's top-up operation?
Richard: Top-up operation is a means of operating the storage ring. Instead of injecting the ring twice a day it's now injected every ten minutes, so it maintains a much higher average beam current.
Meera: And how does injecting a beam, say, every ten minutes, how does that increase the stability?
Richard: Injecting the storage ring every ten minutes means that we maintain, more or less, a constant beam current, that means there is a constant thermal load on the storage ring and on the beamlines themselves, so it maintains a much greater level of stability.
Meera: And so how many beamlines have come into operation and been used by users since Diamond began in '07?
Richard: Well since Diamond began in 2007 when we started with seven operating beamlines there's a further ten come into operation since then.
Meera: So that's quite a few, have any of these been particularly challenging in terms of creating them or getting them into operation?
Richard: Well all of the new beamlines are challenging in one degree or another, but one might mention particularly the infrared beamlines and, well, the bending magnet beamlines in general, there's been some issues there that we've had to tackle, in particular for the infrared beamline B22 we've had to make a significant modification to the storage ring and we had to modify one of the vacuum vessels in the storage ring in order to allow the highly divergent infrared radiation to come out from the storage ring and use it in the beamline and that has involved replacing a vacuum vessel, which we did by building up a separate unit and then swapping the girder unit, which was quite a major operation. In November 08 I think we did that.
Meera: Now what about upcoming challenges, so what's planned for the year ahead?
Richard: Well in 2010, again we'll increase the number of operating hours compared with previous years, which of course means there will be fewer shut-downs so of course there is quite a lot of work to be done installing new insertion devices, new front ends, but of course they have to fit into a much tighter programme.
Meera: OK, so that's essentially seventeen beamlines that have come into operation until now, and so how many are hoped then for the year ahead?
Richard: Yes, so there are seventeen operating beamlines now and Phase 2 is well underway so that will bring us to a total of twenty two beamlines and that will conclude in 2012 so we have five more beamlines to come into operation in the next couple of years.
Meera: That was Diamond's technical director Richard Walker.
Voice-over: Did you know that Diamond has vibration detectors so sensitive that they picked up 10 earthquakes in 2009, including the earthquake in Tonga 10,000 miles away?
Meera: You're listening to the Diamond Light Source podcast with me, Meera Senthilingam. This month we're probing thw working of the synchrotron itself and coming up we'll be finding out how magnets are used to manipulate electrons as they circulate around the synchrotron to create the right forms of light as well as finding out how such high speed electrons, combined with thousands of magnets, are actually controlled. But first let's join Sarah Bucknall from Diamond's Communications team, for a round-up of the news and events that took place at Diamond towards the end of 2009 including the first users on the new infrared beamline.
Sarah: That's right, it's our first infrared beamline, B22, and we've had some scientists from Keele university and the University Hospital of North Staffordshire and they're using B22 to study lung cancer cells.
Meera: And how are they using infrared to look at lung cancer cells?
Sarah: Well they're looking for the characteristic markers of cancer, essentially to work towards an easier and quicker way to classify tumour development in patients in the future and so the ultimate aim is to find and assess a method that could be used in hospitals which applies infrared light to basically detect early signs of cancer as an aid to diagnosis. They're hoping to eventually be able to pick out cancer cells from healthy cells basically before the cancer cells grow and form a tumour.
Meera: Now as well as this beamline having had its first users a new beamline has just had first light?
Meera: And what can be done with X-ray Absorption Spectroscopy?
Sarah: Well it's an established technique which provides element specific information about the atomic geometry and the chemical state of the absorbing atoms in your sample. So it can be used for solids, liquids and gases in just about any field of science, and B18 is one of our three spectroscopy beamlines and it's going to provide a complementary beamline which will basically allow for more general, less demanding experiments.
Meera: So rather than focussing in on very specific things it will provide users with a more general insight and overview on certain areas?
Sarah: That's right, it will be ideal for one-time access or for new users in spectroscopy.
Meera: Ok, now as well as all of this Diamond also got a new instrument that's going to make particular existing beamlines even better?
Sarah: That's right, this is a new instrument that will be used in the Surfaces and Interfaces research village. It's the Reflectivity and Advanced Scattering for Ordered Regimes end station but we call it RASOR for short and basically it's a soft X-ray diffractometer that enables scientists to study electron systems by probing their magnetic charge and orbital structures.
Meera: How does this actually work to enhance the activity of these beamlines?
Sarah: Well it's an end station that has been build specifically for the BeamLine for Advanced Dichroism Experiments, that's BLADE, I10, which is currently under construction. But while that's being completed it will be situated on I06, that's our Nanoscience beamline and it will be used for diffraction and reflectivity experiments.
Meera: And so what kinds of areas of research can benefit from this?
Sarah: So RASOR will be useful in fundamental research. It would form a good basis for the pursuit of a new generation of data storage equipment, for example ultrafast memory devices.
Meera: And Sarah, it is the beginning of a New Year, 2010, so what's coming up at Diamond to look forward to this year?
Sarah: Well, we're going to have some exciting features on local radio and tv as part of the BBC's year of science, and we're also going to be featuring in the Royal Society Summer Science Exhibition in July later this year. It's a ten day extended exhibition to celebrate their 350th anniversary, and as well as that we'll be in Turin in Italy at the Euro Science Open Forum delivering a symposium on the latest synchrotron science from Europe and North America.
Meera: And what about back at the fort, when can people come and have a look at the next Inside Diamond day?
Sarah: So the next public Inside Diamond day is Saturday 27 March and those who are interested in coming along can look on our website for more details.
Meera: And the website address to find out more about Inside Diamond days is www.diamond.ac.uk. That was Sarah Bucknall from Diamond's Communications team, who'll be back in the next edition with more news and events. Now this month we're investigating the workings of the Diamond synchrotron. so now we meet Mark Heron, head of the Control Systems Group, to find out how electrons moving round a storage ring are controlled.
Mark Heron: In the Control Room we operate the three accelerators that make up Diamond Light Source. These are the linear accelerator, booster synchrotron and storage ring. In this process we first accelerate electrons in the linac, these are then accelerated in the booster and then we accumulate electrons in the storage ring. It's the circulating electrons that then produce the synchrotron radiation that are used by the beamline experimental stations.
Meera: Now you mention that this is all controlled from the control room, but how is this actually managed from a remote source then?
Mark: This is controlled in the control room by an operations team consisting of two people. They control the three accelerators through a distributed control system. This enables them from the control room to operate any of the thousands of pieces of equipment that control the technical systems that make up Diamond. So if we look at the technical systems there are thousands of power supplies, hundreds of pieces of diagnostics, hundreds of interlocks that form the machine protection system, the safety system, radiation diagnostics and all of these are controlled through the distributed control system.
Meera: Now that sounds like a lot of things to control at one time, and you mentioned that two people do this, so how is this possible? How many things are just visible at one time or working at one time in order to monitor so many things at once?
Mark: This possible because we bring information from all these technical systems back, to operator displays. We present the information in detailed and in summary form. Through the summary form it's possible for operators to see thousands of devices on a simple overview page.
Meera: Now, so we're just by your computer and you've got a couple of possible screens that are visible from the control room, so what have we got here and what's this kind of telling us about the state of the synchrotron at the moment?
Mark: OK, so the first screen shows us the state of the 1200 magnets that make up the linac, booster and storage ring and all of these magnets are electromagnets and are energised through DC power supplies. What we are looking to see is that the power supplies for these magnets are on, that they are set at the correct level so that the magnet is then at the correct field. And from this summary page we can see the state of these magnets grouped by family and location and if all the magnets in a given family and location are working correctly then that's shown as green. If a page is all green, life is good and the magnets are ready to run!
Meera: Now an interesting screen you've got also is a graph, basically showing you whether the beam is going through the centre of the storage ring?
Mark: It's very important to determine the position of the electron beam because that determines the position of the photon beam that goes to the beamlines and the experimental stations. We control the position of the electron beam by measuring it in 168 locations, and we measure it vertically, whether it's high or low, or horizontally, whether it's to the left or to the right of a central orbit. And this is done by electron beam position monitors and when this is working correctly is shows the beam in the centre of the vessel, which gives you a reading of zero-X and zero-Y.
Meera: So say the beam is slightly higher and it's at say 5 on the X-axis, what would you then be able to do to get that back down to zero?
Mark: If we had an error of 5 mm on the X-axis our machine protection system would have dumped the stored beam, because that would have resulted in damage to the vessel that contains the beam. To prevent that happening we run a feedback system that automatically corrects the electron beam to bring it back down to its central orbit if it starts to drift away.
Meera: So I guess an important thing then is that from the control room you're able to see things like where the magnets are, where the beam is, the power supplies, but also then you're able to make changes, to correct any problems?
Mark: Very much so, Diamond is quite a large facility, the storage ring is over half a klilometre in circumference and it's just not possible for people to have to walk to a technical system to switch it on or off or to change a value. Diamond is operated as a facility 24 hours a day by the operators. During that time they monitor all the parameters, they can see summary screens, they also have alarms if something goes wrong. In terms of the parameters that are on the screens, most of those are updated ten times a second, so people see the information in real time.
Meera: Now it's obviously impossible to control absolutely everything though, so could something go wrong with the synchrotron, and if so what can be done about it?
Mark: A number of things can go wrong when you're operating a synchrotron. There are thousands of technical systems and in the case of many of those, that if they fail that fault will be so serious that the electron beam will be lost. If we think that the electron beam goes round 500,000 times a second, the electron beam can be lost in a few turns, it can be lost very quickly. The other possibility is that another technical system can go wrong and the electron beam stays in an orbit where it produces a photon beam that will damage the vessel. In those cases the machine protection system has to this as an invalid operating condition and protect the vessel by actually dumping the stored electron beam.
Meera: Mark Heron, head of the Controls systems group at Diamond. That's almost it for this month's Diamond podcast, but before we go we look into the use of magnets at Diamond to control the path of the electrons as they flow around the synchrotron storage ring. Emily Longhi is an insertion devices physicist and she works with insertion devices to create bright, forward flowing beams of light. I met her inside the Diamond storage ring to find out more about more about the machine.
Emily Longhi: Right now we're on the experimental hall floor where we keep our spare girders. These are the girders that hold all of the magnets that comprise the storage ring. So this is basically one twenty-fourth of what's inside the tunnel. On these girders we've got dipole magnets, quadrupole magnets and sextupole magnets and the dipoles are basically like mirrors that bend the electrons around the corner, and the rest of the magnets are like lenses that focus them into a very small spot in between the girders where we actually use them to make the X-rays.
Meera: So just next to the girder here now there's a big gap in which then soon I assume and insertion device will go?
Emily: Right so if this was actually installed in the storage ring then we would have a continuous vacuum pipe between this set of girders and the next sector. And in there we would either put magnets inside of the vacuum which would then produce the X-rays, or we have a vacuum vessel that we close magnets around.
Meera: So there's a lot of magnets being used here essentially to get the different types of beam or different types of light that you want?
Emily: That's right, synchrotrons are basically magnetic devices from one perspective. You're using magnetic fields to change the behaviour of a charged particle.
Meera: So you mentioned that after going through the girders you would then put an insertion device that would control this beam further. What is an insertion device?
Emily: So for us an insertion device is either something called a wiggler or something called an undulator and basically what it is is a series of magnets that change the direction of the electron beam. Normally sideways, so it will go left then right and then left again and it will do that many times over a couple of metres, say, and if you control how far the electron beam moves from left to right then you actually control the colour of X-rays that come out from that process. And that's the only thing that the users are interested in really, controlling the colour of X-rays that they get in their beamline!
Meera: So we're about to head out to where a wiggler type of insertion device is being made at the moment.
Emily: That's right.
Meera: So Emily, you've now brought us to a particular type of insertion device that's being built at the moment. So what are we looking at here?
Emily: We're looking at a hybrid wiggler at the moment, so what we've got here is two beams seprated by about an arms length at the moment, vertically, and we can close them down next to each other and the top and the bottom both have arrays of magnets and pole material. So the magnets are made out of neodynium iron boron, which is one of the strongest rare earth magnets in the world, and in between them we have a special kind of iron that changes the direction of magnetic fields very effectively.
Meera: So this two metre long magnet which will be placed in the path of the electron beam to do what exactly then?
Emily: So the electrons will actually pass between the two arrays of magnets and as it passes through it will experience a vertical field and if you have a charged particle moving through a magnetic field then you get a force that's basically perpendicular to the main direction of motion and to the field. So we've got vertical fields here and that means that we get a force horizontally, and that means that as the electrons pass through here they're actually going to wiggle back and forth from left to right.
Meera: What's the benefit of that happening?
Emily: The whole point of third generation light sources is to have the insertion devices which provide tunable X-rays so we can control the colour of X-rays that come out and the way that we control the colour of the X-rays here is by allowing the user to change the gap between the magnets. That changes how far the electrons move from left to right and that changes the colour of the X-rays.
Meera: Now you say colour of X-rays, what does that mean exactly, how does it differ in its properties?
Emily: Just like on the radio you can tune to different wavelengths, say 98 or 94 MHz, or in the visible part of the electromagnetic spectrum you've got red light, you've got green light, you've got blue light the X-rays are part of that continuum of electromagnetic radiation and you can change the wavelength of the X-rays that are produced.
Meera: So this is a particular type of insertion device called a wiggler and there is another type called an undulator, so how does this differ?
Emily: The easiest to explain difference between a wiggler and an undulator is that when the electrons enter into the magnetic field they either move left and right say further than the width of the electron beam or they move left or right smaller than the size of the electron beam, so the distance they travel is smaller than the total spacial extent of the electron beam. If you stay inside the electron beam its an undulator and if you don't stay inside the electron beam it's a wiggler.
Meera: This is what makes Diamond a third generation synchrotron, what does that mean exactly? Why is it third generation?
Emily: So the first generation of synchrotrons were parasitic, they had built the synchrotron for some other purpose and somebody figured out that they made X-rays and stuck an experiment in the way. Second generation expanded on that idea and was dedicated to the idea of using the light. The third generation has really optimise the design of the entire storage ring in order to provide the very best quality electron beam where we put the insertion devices in order to provide the brightest X-rays possible.
Meera: That was Emily Longhi, Insertion Device Physicist at Diamond. Now that's it for this edition of the Diamond podcast, but do join us again in March when we'll be going back to the research to bring you the latest scientific discoveries and work taking place at Diamond. In the meantime if you have any questions about Diamond or any of the research taking place there, the email address is email@example.com, or you can listen to previous editions of this podcast online at Diamond.ac.uk/podcast or nakedscientists.com/diamond. You can also subscribe to the Diamond podcast on itunes. Thanks this month to Sarah Bucknall, Jim Kay, Richard Walker, Mark Heron and Emily Longhi, I'm Meera Senthlilingam. Thank you for listening and I'll see you next time. Voice-over: The Diamond podcast is brought to you by Diamond Light Source and produced by thenakedscientists.com. There's more information on our website at diamond.ac.uk/podcast.
Diamond Light Source is the UK's national synchrotron science facility, located at the Harwell Science and Innovation Campus in Oxfordshire.
Copyright © 2018 Diamond Light Source
Diamond Light Source Ltd
Harwell Science & Innovation Campus