 on the world to study turbulent mixing. So this is the second talk on work we're doing on the NIF laser to study turbulent hydrodynamics in the presence of high temperatures and high radiation temperatures. This we all know, but this is just showing instability on the left hand, on your right hand side, in a classical sense, in the absence of magnetic fields and radiation and the basic equations are being written down on your left hand side. And so this is the starting point. That's the phenomenon we're going to study, but we're going to do it in an environment that's very unique in its own right. And then try and see if we can push forward in some new areas of science combining these two effects. The turbulent mixing hydrodynamics combine with the high energy density setting with lots of high temperature plasma and radiation. That's just stopping it so you can take a look at it. And you can see lots of structures and ripples and perturbations growing, and they evolve with time. And so these are the different types of HED facilities that are widely used around the world. There's several to many. The NIF laser is only one of many of these. And so you can see up here the GECO laser, the Shangguan laser, GECO in Japan, Shangguan in China, the Orion laser in the UK, the LMJ laser in France, NIF in the United States, and the Vulcan in the UK again. And so the field is evolving along with the facilities. So this is a capsule implosion simulation for NIF experiments. And so in the NIF setting, a radiation drive is what forces the capsule to implode inwards. And so the capsule implosion is sort of the simple part of this. The part that the eye catches is all the structures and perturbations that are growing that make the sphere what's supposed to be a spherical implosion very complicated. And so a lot of this leads to hydrodynamic instabilities growing that drive material from the outside down into the very center. And what's supposed to be in the center is a hotspot, which is just something like the center of the sun. But when you inject this outside material of plastic or doped plastic down into the hotspot, it radiates the heat away. And the hotspot doesn't stay hot. And so the nuclear yield is what goes down because the temperature drops. So we have in the ICF program in inertial confinement fusion program, we have a very strong interest in understanding it at the fundamental level how these instabilities grow, how large they get, and how much material they inject down into the hotspot that lowers the temperature when we're trying to make the temperature high and keep it high for as long as we can. I mean, you want high temperature and you want to hold it there for as long as you can to get the most nuclear reactions to happen, the nuclear yield. Okay, so let's see. Just grabbing a couple of snapshots from experiments that examine this, this is an implosion experiment. Notice the time scales are varying by 100 picosecond steps. So 22.3, 22.4, 22.5, and 22.6. You can see the hotspot is changing in time as material from the outside is being injected in. And so these hotspots are plastic material from the outer shell that has been injected into the hotspot, which is supposed to be just plasma, DT plasma, deuterium and tritium. And so when you inject CH dope with silicon or CH dope with germanium down into that hot central region, it cools the hotspot because it radiates. And when you cool the hotspot, the D and T, the deuterium and tritium stop fusing. And so we would like these hotspots and the mixing of the plastic down into the hotspot, we'd like to minimize that because then the nuclear yield would go up and the burn duration would increase. So that's what we're working on. Now let's see, I think I want to back up a couple. That's the, and so here that is the consequence. And so this is, these first few paragraphs are sort of the summary of the talk. The consequence of inserting shell material down into the hotspot, which is quantified in terms of nanograms of plastic. The plastic is the outer shell, plastic dope with silicon. So the amount of plastic dope, silicon dope plastic that makes it into the hotspot in nanograms, when that increases to the right, you can see that the nuclear yield is dropping and this is a long plot. And so when you put plastic down into the hotspot, it radiates the heat away, the DT plasma that's supposed to be hot cools and the nuclear yield drops. And so we're studying this effect carefully and quantifying it so that we can control how much mixing happens into the hotspot so we can not lower the nuclear yield. And we measure the amount, or we infer the amount of mass mixed into the hotspot in terms of the x-rays they emit. The hotspot is supposed to be just deuterium and tritium, so hydrogen isotopes. When you put plastic down in, or especially plastic dope with silicon, suddenly the amount of electrons that can radiate goes up and so the x-rays coming out of the hotspot increase. And so we go from a measured enhancement in the x-ray output to inferring the mixed mass and once we know the mixed mass, we then know how the implosion is being affected by that mixing into the hotspot. And so again, we measure the hotspots there, the x-ray enhancement factor are these bright spots, that's the added radiation coming out of the hotspot because plastic has been injected into it. Okay, so now going back, and so that's the summary of the talk, going back a few years back, how do we make the measurements? The measurements have been under development for several decades now. And so this is going back to the NOVA laser where we were measuring perturbations growing on planar samples as a function of wavelength in an x-ray environment. And so in this case at the Livermore, we use the indirect drive approach which takes the laser, the large lasers, they go inside a cylindrical gold hole rub, it's just a cavity, they convert the x-rays, the soft x-rays then are what drive the physics experiment. And so then we plot the growth factor versus wavelength for pre-imposed ripples on a planar sample on the NOVA laser, that methodology was worked out back in the late 1980s and early 1990s. On the omega laser, we then have the opportunity to explore direct illumination of the lasers on the physics package as opposed to first converting to x-rays if you just directly illuminate the package with the lasers directly, you get more energy onto the sample, but you then have to contend with the fact that lasers are not perfectly uniform, they have hotspots. And so these hotspots imprint upon the sample where you start out, let's say with a flat sample, now you have perturbations formed and those perturbations grow and we try and diagnose them to see how large did they grow and can we find means to understand that growth and control it. Another example of just direct laser illumination driving a physics sample and what the radiographs show that the perturbations that they impart are getting larger with time and larger in amplitude and larger in wavelength. You can see they're evolving to larger characteristic wavelengths and the ripple amplitudes are getting larger and it eventually will shred or break a target into pieces. So that's the effect that we're trying to quantify and then ultimately control. Okay, going to NIF now. So using the NIF laser, we're switching back to indirect drive. So the lasers come into a radiation cavity, a gold, hollow gold cylinder. They convert to x-rays and the x-rays in this case drive a planar rippled foil, the physics package, and then we shine lasers onto a backlighter and take radiographs from an external x-ray source through the physics package and so these time-resolved in-flight radiographs are how we infer or deduce what's happening as a function of time and then we analyze these in Fourier space and you can see that the ripples are growing with and the ripples are growing in amplitude and their characteristic wavelength is getting larger with time. And so those are the kinds of measurements we're making. Here is a capsule and the way it's mounted up in the radiation cavity for NIF and so the outer part is the cylinder that's gold. The lasers come to the inside of the cylinder and convert to x-rays. A spherical capsule that's going to implode is held in the center but you have to hold the capsule somehow the capsule is held with a thin form var plastic web that's about 70 nanometers thick and so we hold the capsule in place with the thinnest foil that we can manufacture so that it's just barely being held there and you'd like the web, the tent, to be very thin so that it doesn't leave large imprint on the capsule because when the x-rays fill up the whole room they blow up the tent the tent creates a pressure perturbation that imparts a scar on the capsule implosion and then as the capsule implodes that perturbation gets larger and it's a large source of material of plastic that gets inserted down into the hot spot cooling the implosion hot spot. So this is some of the other things that can happen in such a setting and so there's two things to look at here one on the right hand side since it's a movie is what we call meteors it's a fill tube or other discreet perturbation on the capsule shell when you implode the shell you can see this is in action this is a, these are experimental x-ray radiographs I'm not sorry, x-ray emission so we're measuring the hot spot in x-ray emission with pinhole cameras and you can see a perturbation that existed likely from the fill tube is launched as it enters the hot spot you can see as the x-ray yield is coming up when the perturbation gets to the center it radiates the heat away and the temperature drops and the burn stops so it's a very good demonstration of a large perturbation once it gets to the hot spot that's supposed to be very hot it starts to radiate the heat away and the temperature drops and the yield stops and the kinds of perturbation patterns that evolve from a tube a fill tube for example are a little bit surprising the fill tube is a tiny little sort of 15 micro, 15 millimeter diameter tube but then the pattern that is imprinted on the capsule has got this funny structure to it and what you're seeing is that that's those are shadows formed by x-rays so the fill tube is sitting here and when the laser beams first enter this cavity the x-ray spots are localized and the fill tube then casts an x-ray shadow onto the capsule and that's what creates this rather large perturbation from a very small fill tube and then it grows and becomes a source of shell material mixed down into the hot spot and I would also point out that in retrospect of course these things are obvious both the effects of shadowing by the fill tube and if I can back up the effects of the tent creating the scar in after the fact after we've seen an experimental piece of data that shows it suddenly it becomes obvious but neither of these two effects as large as they are in the capsule implosions neither were predicted they were quickly understood after a piece of data came in because I was standing there in the hallways when the experimentalist came in and said we look at this this is what I think is happening so it's a nice demonstration of even in the complicated setting like a large laser the experiments still have a very serious role to play and the same thing with this perturbation caused by the fill tube with the spoke patterns coming out they're caused by shadowing and it was only with the experiments then it's obvious you're thinking oh I see that we should have thought of that which we should have but we didn't okay so what we do to try and quantify these effects this is a capsule that has a pre-imposed perturbation machined into it so as it implodes you have a single mold you can study versus just imploding a capsule without any pre-imposed perturbation and you can see depending on whether the capsule was rough or smooth you get more or less growth and also these are the the perturbations caused by those tents and we also try and adjust the x-ray drive to be more forgiving so these initial imperfections don't grow so large so that's the basis of our research and then how we do it there's one there's a technique that's very nice and what it does is that we put some dope gas into the capsule and so when the capsule starts to implode and the shock reaches the center the source of x-rays that we use for radiography are coming from the center of the implosion and so the center of this implosion has a hot spot that radiates and that becomes the source of the x-rays that are going through the capsule and allows us to measure modulations versus radius and so that's called self-backlining with the hot spot x-rays and so this is the type of perturbation we can measure it allows us to measure perturbation growth at the inner surface the inner shell gas interface which is otherwise hard to access and so the way we do it is we use the x-ray source from the hot spot gas itself and this shows a technique where you can imagine in a large program when we were carrying out these measurements what finally gets sorted out is very obvious after the fact it's always not so clear when you're doing the experiments and so for several years there was a big debate amongst all of us the theory, the simulation people and the experimentalists whether or not we were getting capsule shell material mixed down into the hot spot we had a national location campaign we had milestones to meet and so there was a lot of tension about whether to stop and do more careful science experiments or just keep doing performance experiments and so one of the experiments we did that showed conclusively and beyond any argument that there was shell material being mixed down into the hot spot which is supposed to be just D and T but in fact we were getting CH and germanium is that we put a germanium-dope layer in the plastic shell offset from the hot spot by 70 microns of the DT fuel I think is what we have here and so absent strong mixing you would not get germanium down into the hot spot because it was offset by 70 microns albeit prior to compression and so then we did the experiments when the germanium goes down into the hot spot it gets hot and we see germanium spectra x-ray spectra in emission so helium alpha, germanium emission in the hot spot is conclusive proof that shell material that was offset got down in deep enough to get hot and radiate so at that point five years ago or maybe six years ago we said we have a mixed problem we actually are getting shell deep down in the hot spot radiating the heat away and dudding or decreasing the performance so from a science point of view it's beautiful we get spectra, we can analyze it to back out how much material got down into the hot spot and how hot did it get we can also back out what was the effects of the mixing so if you plot up neutron yield for the front against with the sit plotted versus silicon mix carbon plastic carbon silicon mix mass you see that is when the mix mass gets up over up around several hundred nanometers the nuclear yield just drops and plummets and so we call that the mixed cliff and this was a big step forward when we realized in fact we have a mixed problem it's killing us and so we have to slow down and do careful science experiments to quantify it, see how big it is and more importantly, or most importantly learn how to control it in a way that still allows us to get the ignition criteria met more experiments on this so let's see we also can measure the amount of atomic mix in this case we put an inner layer of CD instead of CH just replace the the H with deuterium put it right at the inner layer but then we fill the hot spot gas with tritium so the fill is tritium gas the innermost layer is CD if the D gets down into the T it gets hot then you have DT fusion and you'll get 14 MAV neutrons coming out so this was a nuclear diagnostic and of course indeed we did get DT yield and we also measured that as a function of how far back we offset that deuterated layer so this is the DT nuclear yield that's the mixed signal as a function of the distance that CD layers recessed back away from the hot spot and of course you see the farther back the CD layer is the less of DT it is it's a way to map out very carefully what the actual mix width is because once you've moved far enough away that the mixing stops you know how much distance there was at that direct measure of the mix width or mix extent in such an implosion and so this is getting to the end so if we plot up so here's the plot of perturbation growth as a function of mode number in a capsule implosion where the modes are machined on single mode onto the capsule and imploded convergences of few and what we plot up is the ripple amplitude versus mode number we know what the initial amplitude is so you can turn that into growth factor and this allows you to back up what we would call a dispersion curve where now we can test out various kinds of drives so one kind of drive is very prone to hydrodynamic instability growth that's called what we call it the low foot the leading shock strength was recently small whereas if the leading shock in the drive is much larger it imparts more heat early on it makes the capsule less compressive and it reduces the level of instability growth and so by raising the strength of the leading shock you could lower the amount of rarity of growth but you also lower the compression and so this is the balance we have if we want high compression you risk having high hydrodynamic instability growth and mix if you want to turn down the instability growth and mix you can do so by increasing the adiabat but then the compression drops and of course we need both high compression and high temperature and so that's the sort of the balancing game we have and we have drives that go in between these they're called adiabat shaped that's just playing with the strength of the leading shock and so by varying those leading shock strength we can try and put ourselves in a parameter space more favorable for getting out the nuclear yield that is our goal that's a plot of all that taken together so the one point I would like to raise before I finish is that we have what's called discovery science program and if we allocate about 10% of the laser time to outside users it's an annual call for proposals and it's an issue, it's a call that's issued to the world it's an international call and so if you are interested in or want to think about the possibility of NIF experiments then you should talk to a supremeeer while we're here we can explain how it works what you have to start what kinds of things you need to do to prepare but this is the 10% of the facilities allocated separately for just basic science both internally and outside I mean our inside people compete as well so it's just open, there's no criteria that way and so just talk with us if you have any interest in being involved with your own NIF experiment either anybody's an experiment but in particular you could propose your own okay so these are some of the experiments that are done through that discovery science program we usually call every year so every year there's another team of eight to 10 people that we try and start so this is the latest round and you can see that the types of science that people propose most of these are outside people nuclear science proton beam generation by the TNSA process studying materials at high compression in this case this is carbon as it relates to white dwarfs planar hydromic instabilities, planar direct drive particle acceleration, collision of shock formation which I think Hayesu touched upon in just a bit the properties of brown dwarfs put charged particle stopping powers the equations of state of matter at gigabit pressures and studying the properties of dense hydrogen as you force it to turn liquid or even possibly freeze and so in this 10% that we issue an open call for the types of science really cover a wide space because we basically ask everybody outside if you had access to NIF what would you like to do it's not programmatically driven that's why the types of things we're doing span quite a range okay I think at that point I'm done so I talked about capsule implosions both Hayesu and I have quite an interest in laboratory astrophysics and there's some of this going on through the discovery science program and of course there's a very strong equation of state team as well the studies planetary interiors and planetary formation dynamics as well as the programmatic ICF capsule implosions and so if you're interested in any of this we're here all week and we'd be happy to talk with you thank you