In this module, we will focus on how we acquire data. To help us in this, we will have Henning Friis Poulsen who is professor at the Physics Department of the Technical University of Denmark, and he will show us that, to do experiments, we need an X-ray source and we will start by looking at the large scale, the synchrotron facilities, and Henning will take us to one of them, they are available all over the world. He will take us to the one which is situated in Southern Sweden in Lund. The MAX IV laboratory. Hello, my name is Henning Friis Poulsen, I'm a professor at DTU physics and I'm here to give you a brief introduction to X-ray tomography. In order to do so, on this wonderful day, we've gone to the Southern part of Sweden to Max IV. This is a synchrotron facility, it's a landscape facility as you probably can see, inaugurated in the end of 2016. This facility is one out of approximately 50 that you find around the globe and they've been built within the last 10, 20, 30 years as a consequence of that the particle physics people. The accelerated physics have been able to produce accelerated rings which are just more and more powerful. What we obtained from the synchrotron is very high power of X-rays. This allow us to measure faster and also with better resolution of sizes, but it also gives us access to other modalities that give us, for example, specificity to what kind of elements are in the sample and also sensitivity to, for example, magnetic structures. So, what does a singleton look like in terms of geometry and scale and how are X-rays generated in such a facility? Henry will tell us more in a moment and he will use a term called keV, it's an abbreviation for kiloelectron volt which is a measure of the energy of the X-rays generated in the synchrotron. It tells us something about the, it is directly related to the wavelength of the X-rays and also in turn then defines the resolution that we can access, but also the amount of material we can penetrate. Let's hear Henry. So, we now are at the top of the atmosphere two building and the reason that we're here is because I wanted to show you the synchrotron. The synchrotron as you can see, is a ring and actually we have electrons over there which is being injected into the ring and they're being accelerated and as times goes by, the speed of these electrons will be higher and higher and eventually they will be very close to the speed of light. Now, if you take a charged particle like an electron and you accelerate it, it will radiate electromagnetic radiation and as we get closer and closer to the speed of light, this becomes more and more energetic. In fact for a ring of this size, it means that the radiation that we're going to see is going to be X-rays in the range between 15 to 35 keV. You will also find other rings around the world which is somewhat smaller and which therefore produces X-rays specifically in the one to five to 10 keV. Finally, you will also find some synchrotrons, which is even larger with the circumference about a kilometer or so, which produces really hard X-rays up to several 100 keV. As you can see, synchrotrons are large structures and as Henning pointed out, their size is actually related to the range of energies they can provide. Now, let us go inside the synchroton and see what happens inside. Now, we're in the experimental hall and I brought you here in order to do that you should see that, the ring is actually not really a ring. What you can see is that it's a polygon. In this case, it has 20 different straight sections and its in these straight sections that the accelerated people have put so-called undulators and it's the undulators that actually produce the X-rays. So, from the undulator, the X-rays that emanate come out in a very narrow cone and the beam is let down its beam lights to the sample and the sample can be positioned somewhere between 15 and 100 meters away from the source. The word undulator that Henning used designates a certain magnetic structure which is used in the storage ring, the synchrotron ring, to as he mentioned create X-ray radiation. It's not so important what type of magnetic structures are used. There are various forms that are used in various places in the synchrotron, but this is just to tell you that there are different ways of accelerating the electrons in the synchrotron and they create X-rays in various different manners. Around the ring as Henning also mentioned where these oscillators are placed, the experimental stations are located where the X-rays are emitted from the undulators. Let's go inside one of them and take a look. Now in the nano marks experimental hatch, this is where the actual experiment takes place. The X-rays that comes in here are nearly parallel and typically before they actually enter here, they have been conditioned in one way or another. It can be that we have found ways in which we can make the beam smaller or larger in order to fit with the size of the sample and typically also, instead of using the white beam that comes from the source itself, we would monochrome isosceles in one way or another and that can be that the energy band of that of the X-rays that comes here could be one percent, that's known as a pink beam or even more typical that one uses a monochromator in order to get something like 10 to the minus four in Delta E over E. So, having now seen what it looks like inside the experimental hatch, you may wonder how do you actually get to do experiments in such a place. After all, the synchrotron has on the order of 20 experimental stations around the ring and measurement time is in very high demand. Henning explains. It's also typical for the work of using a synchrotron that people come from all over the world. The way that you get access is via that you apply for beam time, this goes to a review panel and if the science case is considered strong enough, you would be granted beam time and that would be free of charge. In order to use this, you have to be well-prepared and you often see that the groups that come here would be teams with two or four or six people and they work 7/24 for a day or for a week of beam time. That was a brief introduction to large scale facilities like synchrotrons and how you do experiments there. In the next video, Henning will explain the basics of the tomography experiment and how it is applied both synchrotrons and also at laboratory facilities.
