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An interesting development that could have applications for inertial confinement fusion. Reading the articles produced on this development, leads me to believe that the enormous significance of it has not yet been understood.
http://www.sciencemag.org/news/2018/01/ … mpty-space
If this works, mankind will have developed a device capable of efficiently converting electric power into high energy gamma rays at extremely high power density. This would appear to provide exactly what is needed to pump a plasma to very high temperatures in a very short time scale - i.e. so short that significant expansion does not occur over the course of heating.
If this does indeed work as quantum mechanics predicts that it should, then it should allow compact inertial confinement fusion, capable of solving both the energy crisis here on Earth and providing a clean means of nuclear propulsion, with enough thrust-weight ratio to achieve lift-off from the Earth's surface.
In short, high energy lasers like this could be the key enabling technology allowing human beings to escape the Earth and colonise the solar system.
Time will tell whether Louis' export figures are realistic. I have my doubts. Figures like $3 billion Coca-cola advertising budget are mentioned. Why would anyone sitting in a dome on Mars, expect that money to come their way? The idea of Olympics on Mars is a bad one. It would mean all of the players enduring 6 months of travel, with long periods of low-g and high background radiation. Netflix revenue is $6.8 billion. So what? How much of that money are they going to give you for the privilege of filming people trot around an airless desert? The global art market is worth a lot, granted. But why would we expect a small colony of a few tens of thousands to produce even 1% of what the many nations of Earth can produce with their nearly 8 billion people?
Too much hopium here I think. None the less, per capita earnings will need to be high, because per capita costs are clearly very high.
I have been reading a book on the history of the Netherlands and it occurred to me that a future Martian nation would have one thing very much in common with the Netherlands. Land in a habitable form will not be something that can simply be taken from nature, it is something that will need to be made at enormous cost.
Take a look at this brochure selling geodesic dome greenhouses:
https://fdomes.com/wp-content/uploads/2 … rchase.pdf
A 30m diameter dome costs €120,000 - that's about $150,000. And this dome is not pressurised and doesn't really require a lot of groundwork to install. If we were to build a pressure dome on Mars, it would probably cost at least twice as much. So that's $300,000 for 706 square metres of land - just a tad over a sixth of an acre, $425/m2. That puts the cost of Martian land on a par with expensive urban building land in European cities.
This suggests to me that Martian settlements are likely to be very compact. Within a pressure dome for example, there will be a strong drive to make the most of each cubic metre of pressurised volume. This suggests to me a likely pattern of living in a Martian city. People will attempt to share space wherever they can. A family of four will probably share a single room, with bunk beds extending up to the ceiling. Toilet, bathroom, kitchen, dining and sitting areas, will all be shared with many other people. Social spaces will serve multiple functions, with a dining area also serving as a meeting place, a sports room, etc. Sitting rooms will be places where people read and study as well as socialising. Sleeping areas will be where people go for privacy. It will be expensive to manufacture objects on Mars for a long time to come. There will be a strong incentive to maximize the utility provided by each manufactured item. This too suggests a pattern of collective ownership of many items. On Mars, power will be relatively expensive. Without fossil fuels, all energy must be generated by solar power or nuclear reactors. The need to minimize energy consumption per capita, will also tend to drive a highly collective way of living. In the UK, studies show that houses tend to maintain fairly constant energy consumption regardless of the number of occupants. Hence, cohousing is a very effective way on reducing energy consumption per capita, without necessarily forcing people into hardship.
This suggests something important about future Martian society. There will be close-knit social structures and social taboos. It will be very much a small village / tribal mentality, in which everybody attempts to fit in and does their best to avoid any activities that might provoke gossip and lead to being outcast. People will be social minded and will keep track of favours that they owe or are owed. Sexual relationships will take place in marriage and few people would risk extramarital affairs. Xenophobia will be an issue, as tribal groups only tend to work when there is a common ethnicity binding it's members.
Food will be a precious resource and in the environment of a tribe, will need to be shared very equitably. There will be communal dining rooms where people eat and there will be taboos against taking too much or wasting anything edible. No one will likely have too much to eat, as every calorie must be grown within an expensive pressurised space. Agriculture will be biointensive, requiring careful planning and maintenance to ensure that each square foot of land produces the most food possible. The Martians will be a thin race of people and any other body shape will be associated with gluttony.
Each dome will be filled by a single extended building right up to the limits of its fabric. The settlement will contain mixed areas of habitation, manufacturing and agriculture, so far as safety will allow. Such an arrangement not only makes the best use of pressurised volume, but also conserves heat. The outer terraces of the building will be covered with edible plants, growing right up to the limits of the dome. Many of the outer rooms will get too cold to work in at night. Social and sleeping areas will be located at the core of the structure, which will remain warm as the outer reaches of the dome drop to temperatures only slightly above zero.
The social ideal for each tribe, will be one of self-sufficient living, rather like a Greek city-state. Anything that is bought from outside, will cost money, whereas the same thing made internally will cost only the time and innovation of members of the tribe. There will be a lot of social kudos in making something that the tribe can use. There will be little private space and this will tend to constrain private time. Most of the individual's time will be spent working for the community in one way or another. Games will tend to be communal activities, but will focus on things that can be carried out in relatively small spaces. Table tennis, boxing, squash, etc.
The other option would involve using a gas gun, rail gun or coil gun to provide an initial velocity increment for your SSTO. If it can shave 1.5 km/s off of your dV, i.e. a muzzle velocity of 1.4km/s (high end rifle speeds) at a height of several km, then an SSTO with exhaust velocity 4500m/s will reach orbit with a mass ratio of 5.92.
The catch is that the capital cost of the gun would be quite high - it would be cheaper than a lower stage only above a specific launch rate.
What is remarkable about exoplanet discovery so far is how few star systems resemble our own. Most planets appear to be more massive than our own, in more eccentric orbits and with fewer planets in each star system.
The more complex life becomes the more specific the range of conditions needs to be in order for it to evolve. Bacterial life can evolve in a wide range of environments. As soon as life moves beyond the single cell, the range of conditions it can tolerate plummets. Suddenly, it needs an oxygen atmosphere, a narrower range of temperatures, etc. It is difficult to imagine a technological civilisation evolving under very different conditions to our own. It would need dry land, with stable climate, oxygen atmosphere, a sufficient abundance of ores, etc. Its physiology must include an opposable thumb and a reasoning brain, capable of complex social interaction, 3-dimensional visualisation and long-term planning. The more advanced life is, the rarer it is and the more like us it must be.
It is possible, though it is probably impossible for the ore body to go super prompt critical.
If water flowed into an enriched ore body and the ore went critical (i.e. achieved self-sustaining fission) the result would be steam generation. This could accumulate under a layer of impermeable rock (or an ice barrier?) until pressure rises enough to cause the impermeable layer to fail catastrophically. If the ice layer and ore body underneath extended for several kilometres in either direction, a blast equivalent to megatons of TNT is possible.
Today, uranium enrichment is down to 0.7% and this sort of thing would be impossible. But on young Mars, enrichment could have been 3% - which is close to the enrichment level for light water reactors. It could not have happened 180million years ago. Though it might have happened 4billion years ago.
The microwave concept we were discussing earlier, was a gun some 5km long, that would accelerate a rocket to 1.0-1.5km/s. This is nowhere near enough to reach orbit, but it is enough to eliminate the need for a lower stage. The rocket does not need to waste propellant in the dense lower atmosphere and can function as an SSTO using lox/CH4.
We settled on this because it appeared to be technically achievable with off the shelf technology and there are few if any technological stretches required.
The concept could cut the cost of launching to LEO dramatically, as total launch mass would be reduced by half and would be a single reusable vehicle. But it could only do so if traffic volumes were high enough. The build cost of the gun would be considerable.
Unfortunately, the Martian atmosphere began heavily eroding some 4.2 to 3.7 billion years ago. Had the magnetic field lasted a few hundred million years longer, the sun would have had time to stabilise. But the atmosphere probably got stripped down to its present sparse state within a few hundred million years of the field collapsing. The late heavy bombardment took place 4.1 to 3.8 billion years ago, about the same time, and would have substantially aggravated solar atmospheric loss mechanisms, as well as killing any advanced life on the planet. So unless advanced life managed to evolve in the narrow window between 4.7billion and 4.1 billion years ago, it is difficult to see how it could have developed any later. Bacterial and other single cell organisms are a different matter. There is an outside possibility that they could still be around today.
Sounds like we're getting closer now to a railgun-type design
Yes. But I think capital cost will likely dominate the total cost of launch from a device like this. One problem I can see with a space launch rail gun is the capital cost of several thousand large electromagnets and the power switching mechanism needed to activate them at sufficient speed. The only reason we are considering a gun type launch system is the potential to do away with the capital and operating costs of the lower stage. The lower the amortization cost of the gun, the greater cost reduction you achieve. I think a sled equipped with a single magnetron will probably be cheaper than a long line of electromagnets. As the muzzle velocity is only 1000m/s or so, there are a number of options that could be made to work. It is all about finding the one that is cheapest to build.
I like the microwave idea. It would be especially elegant if you could mount the magnetron into the sled and feed it with power through rails mounted in the barrel. The barrel can then be technologically simple - two long pipes containing compressed hydrogen with solenoid valves every several metres and perpendicular conductor rails.
Perhaps an all-round better option would be a rail gun, using a sled that can be recovered and reused.
https://en.wikipedia.org/wiki/Railgun
The limiting factor with a rail gun is friction with the conductor rails. This limits top speed, as the rails suffer progressively greater erosion as speed increases. The wiki article notes that railguns readily achieve muzzle velocity of 3km/s. Achieving a muzzle velocity of 1km/s or even 1.5km/s would appear to be technically well beneath state of the art, as this is high end rifle bullet speed and should therefore be achievable using ordinary materials like steel and aluminium alloy.
A clear disadvantage over the gas gun is the additional complexity and capital cost added by so many thousands of electromagnets along the track.
As with any static launcher concept, the economics depend upon frequency of use. The more traffic it sees, the cheaper it becomes.
Notionally, the idea with using water was to leverage its higher speed of sound to keep the flows purely liquid, mechanical, low-temp, and laminar, but I think we've shown between our analyses that this isn't a realistic proposal and we've ended up back at the light gas gun. The light gas gun is a perfectly reasonable idea, but it's a little disappointing the water gun probably wouldn't work.
It is uncertain whether a water ram would work at speeds that would be useful. I wouldn't dismiss the idea completely, but can certainly see problems.
I think one potential problem with the gas gun idea at the scale we are talking about is that over a length of 5km, it would take a steam molecule ~ 2.5 seconds to travel from one end of the barrel to the other (even at 3000K), whilst the total acceleration time of the projectile takes only 10 seconds. This suggests to me that there could be stratification effects within the barrel, with the gas close to the bottom remaining quite hot and the gas at the top being cooler, having done work on the projectile. This could result in a less than expected muzzle velocity and lower energy efficiency. In a gun, we are generally relying upon the fact that gas temperatures are homogenised by conduction and diffusion, so we exploit the full thermodynamic expansion energy of the gas. That is reasonable on the small scales of a normal gun barrel, but it becomes a bit of a stretch when the gun barrel is kilometres long. Again, it is difficult to say exactly how much of a problem this would be without some really impressive CFD analysis. It may be no problem at all, or it could introduce significant inefficiencies.
One way around this would be to mount multiple steam generators along the length of the tube, each discharging as the projectile passes. The problem with this idea is that we are then building complexity and cost into a concept whose main advantage is simplicity and low cost.
One concept that does interest me is the plasma gun. This works in much the same way as the gas gun, but is pumped by a plasma arc generator instead of a chemical explosion. One advantage is that the much high rms speed allows much greater muzzle velocity. Significant disadvantages are high electric power consumption, electrode erosion and barrel erosion in the superheated plasma. But theoretically, such a gun could launch dumb payloads to escape velocity.
It seems to me that if you're using a gun like this it would be tricky to modulate the acceleration well. What you might do would be to put your payload inside some kind of mostly-empty capsule that would act as a sail and jettison the capsule once you've freed yourself of the water stream. You might also be able to gain additional velocity after leaving the gun itself by riding in the stream of water.
We definitely want laminar flow for this, so let's say we want a Reynolds number of 2000. If the water speed exiting the cannon is 1,000 m/s, density is 1,000 kg/m^3, and viscosity is 8.9e-4, the diameter of the pipe would need to be less than 2 micrometers for laminar flow. (This is a non-physical scenario; practically speaking we're dealing with highly turbulent transonic flow with Re>1,000,000,000).
You would definitely need a capsule and would need a closely fitting seal between the capsule and barrel of your gun. At the sort of acceleration we are talking about, the forces acting on the rocket would be much greater than buoyant forces and the water column would overtake the rocket exerting horrible shear stresses unless a closely fitting seal is provided.
I do not know how an incompressible liquid like water would actually behave if accelerated close to its sonic velocity. At relatively low velocity, the static pressure of the liquid would drop to the point where any diffused gas would come out of solution. That happens at much less than sonic velocity. Centrifugal pump speeds need to be carefully controlled to avoid cavitation, as bubble surface tension shock blasts the interior of the pump. Would these sorts of effects place limitations on the maximum velocity of a hydraulic ram? I do not know. But the forces acting on individual components at a flow speed of 1500m/s would be huge. The Bernoulli equation indicates that dynamic pressure would be ~1GPa, but it is questionable that this applies at these flow speeds, as the water would be subject to significant density change.
Maybe some sort of chemically propelled canon or gas gun would be more practicable. Using cordite, there is an approximate limit of 5000fps (1540m/s) on the muzzle velocity of a gun. This is imposed by the rms speed of the expanding gas, which is mostly CO2, SO2 with some steam. To accelerate bullets to much more than 1km/s starts to get increasingly inefficient, and for muzzle velocity of 4500fps, the cordite charge has about 50 times the volume of the projectile. One way of improving upon this would be to use superheated steam as the propellant gas. At 3000K, this has rms speed of 2000m/s. One could generate steam at this temperature by igniting a hydrogen-oxygen mix within the gun chamber.
For muzzle velocity of 1km/s, it is easy to chemically propel a projectile – many rifles have muzzle velocity in this range. Using H2/O2 mix, that speed could be increased to 2km/s, with declining energy efficiency as that limit is approached.
With a 20% energy loss from atmospheric drag, a 1km/s muzzle velocity would propel your spacecraft to 130,000feet. That is outside of the sensible atmosphere as far as rocket engines are concerned.
Here's an unconventional way to LEO: Initial launch with a water gun.
The basic idea is that the speed of sound in water is much faster than the speed of sound in air, at roughly 1500 m/s (vs 340 m/s for air and 1240 for H2).
I would put this into motion by having a giant tank of water with a piston at one end (or alternatively maybe just an inflatable balloon, perhaps inflated by vaporizing dry ice using heat exchange with seawater). The top of the tank would be a converging nozzle that accelerates the water to its speed of sound. A rocket would get caught up in this flow and come out moving at 1500 m/s, which will have the effect of substantially reducing the required delta-V of the rocket.
That's an excellent idea. An ocean launch gun would eliminate the need for digging a tunnel or maintaining a high tower, although an excavated barrel could take advantage of the compressive strength of rock. It all comes down to economics.
For ocean launch: One could use a long steel or concrete tube that is floated into position and then tilted vertical by flooding a ballast tank at the base. The hydrostatic pressure at depth would partially compensate internal pressure during launch. Maybe reinforced concrete could be used for the lower parts of the barrel, with steel liners, with either carbon steel or pre-stressed concrete used for the upper parts close to or above the surface.
In terms of propulsive power, a simple gas-driven hydraulic ram would appear to be the cheapest option. Compressed air would be the technically easiest way of powering this, but would require quite a lot of electrical energy to charge before launch, so maybe not the cheapest. Why not simply ignite a natural gas air mixture above a sea water hydraulic piston? That way you achieve a very rapid transient to a pressure of ~10bar (if starting at atmospheric) and the energy cost of natural gas is <1US¢/MJ.
A 5km long ram, with acceleration of 10g, would give a barrel velocity of 1km/s. That's enough to push the rocket to edge of the stratosphere. At this point, the engines are firing in true vacuum, so a ram launch like this should allow the use of a Lox/methane SSTO with an acceptable mass ratio.
Interesting idea here from nearly 40 years ago: An Earth-launch mass driver.
http://www.nss.org/settlement/L5news/19 … driver.htm
The mass driver would accelerate 12' diameter 'telegraph pole' projectiles to Earth escape velocity from a surface launch. Atmospheric drag would have resulted in 3% mass abrasion and 20% energy loss. The mass driver itself would be vertical and some 7.8km long.
The idea never came to anything, presumably because of the high capital cost of the launcher and power supply and its inflexibility - the 1000g acceleration limits it to dumb payloads launched on escape trajectories.
Still, a high volume low cost option like this could still be useful provided the payloads could somehow be intercepted in high orbit and used as feedstock for space manufacturing. Back in 1980, the energy and amortisation cost were reckoned to be $20-40/lb - about $40-80/kg. One would need a large power plant to power such a device. A 1GW powerplant would limit launch rate to once every 90 seconds. Since the launch rate is limited by power supply, ideally one would want half a dozen PWRs powering this thing. That would bring amortisation costs down to a few dollars per kg (1980$, presumably).
Is there some way to use CO2 as both a coolant for the reactor and hot feed stock for SOXE in order to get rid of the heavy radiator panels? For example, could a small CO2 compressor cool the reactor by driving the compressor with a working fluid or gas. I'm not talking about collecting CO2 in a tank, I just want to know if it's possible to actively cool the unit, simultaneously compressing and heating CO2, and then feeding the hot CO2 to a SOXE cell heated by the reactor. Think of it as a miniature turbofan / generator running atop the unit on magnetic bearings. Instead of something 3.3m in diameter, we now have a package closer to 1.5m tall and .75m in diameter.
Everyone has seen the Vortex Powerfan, right? Imagine that sitting on top of the reactor. The heat pipe system from the reactor drives an internal turbine connected to the compressor. The fan compresses the incoming CO2, heats it a bit in the process, and then feeds it to a SOXE cell that also uses heat from the reactor to keep the cell hot. A smaller electric generator rotating on a common shaft provides electrical power for the cell. The compressor forces most of the CO2 over a radiator to cool the reactor and bleeds the rest through the SOXE cell to produce CH4. The reactor is 40kWt, so there is plenty of thermal power for heating.
We're making rocket propellant, not baby food, so if there's a little contamination from its brief pass through the reactor it should still be fine. The reactor happens to be running at about the right temperature for the SOXE cell to use, and so presumably less electrical power would be required to keep the cell at the correct temperature.
Anyway, it's just a thought for getting us above 25% output efficiency for this particular use case. Even if the cooling system fails entirely, the reactor won't melt down as a function of its surface area to volume ratio and the materials used.
A direct cycle nuclear gas turbine is an interesting idea. The problem with using Martian atmospheric CO2 as a direct cycle reactor coolant is its low density – about 0.02kg/m3. The specific heat (Cp)of CO2 at 250K is 791J/KgK; @300K it is 846J/KgK, which increases to 1075J/KgK at 600K. Let's say about 0.9KJ/KgK on average, between 250-600K. To remove 30kW of waste heat would require 0.095kg/s flowrate. That means compressing 4.76m3 of atmosphere and blowing it through the reactor or heat exchanger every second. Assume that we compress the CO2 to roughly 10bar. Lets use the idea gas law to work out the power requirement:
PV=nRT
W = PdV
Rearranging and integrating gives:
W=P1V1 x (ln[V1]-ln[V2])
P1 = 0.6KPa, V1 = 4.76, V2 = 4.76 x (P1/P2) = 0.0029m3.
W=600x4.76 x (1.56--5.86) = 21.2kW
That's the amount of energy needed to compress an ideal gas. The critical temperature of CO2 is 304K. The inlet temperature is taken here to be 250K. My compressibility chart only goes down to a TR of 1, for which compressibility factor is 0.2 at critical pressure. So the actual compressor work could be reduced by a factor of 5 or more if intercooling is used – so compressor power ~4kW. At night, the compressor would be even more efficient – in fact there may be a problem with dry ice deposits at low temperatures and high pressure.
Let's say the back-end of the turbine converts 60% of thermal power into mechanical work (24kW). The compressor power is ~4kW. So, a Martian direct cycle nuclear gas turbine could be up to 50% efficient from a mechanical power viewpoint and perhaps 48% efficient from an electrical power viewpoint.
I initially assumed a 40kW heat source producing 30kW of waste heat at 600K. It would need to compress 4.76m3 of Martian air per second. Let's assume we take advantage of Martian winds to deliver the required gas to the front of the compressor. Since average Martian wind speed is about 5m/s, the frontal area of a 19kWe nuclear gas turbine would need to be about 1m2. So a direct cycle nuclear gas turbine may be a more mass optimum idea than a closed cycle sodium cooled reactor with a radiator. But there are a few obvious downsides:
1) The bombardment of oxygen with neutrons generates N-16. This has a half-life of 7 seconds, but is a powerful gamma emitter. The gas turbine must be located some distance away from the settlement and preferably downwind;
2) In the event of fuel damage, there is no containment. Less of an issue on Mars than it would be on Earth, but could be a hazard to the crew or any future explorers visiting the site;
3) The reactor would only be useful for surface missions on Mars, whereas the Kilopower concept is useful for a huge range of missions to solar system bodies.
Future nuclear reactors built on Mars could use a direct cycle CO2 coolant. As CO2 absorbs very few neutrons, the fuel used could be natural uranium, probably canned in zircalloy cladding. The moderator would either be graphite or heavy water and the fuel would be housed in pressure tubes, rather like a CANDU.
Integrating the reactor into the propellant plant makes sense from an energetic efficiency viewpoint, but may not be the cost optimum thing to do. This is because (1) It is a very bespoke solution that requires a separate development programme; (2) Safety analysis for the reactor must concern itself with interactions between the reactor and propellant plant. It may turn out to be cheaper to develop a nuclear electric plant and simply feed the ISRU plant with electric power remotely, rather than building the reactor into it.
The 4+1 kilopower concept weighs about 9 tonnes. That's half as much as the competing solar concept even at a good location for solar.
However, this is still a far cry from Zubrin's proposed 4te 100kwe reactor concept in Case for Mars. NASA research from the early 90s suggested a mass of 6te for a 100kwe SP-100 reactor.
It would appear that these systems scale up much better than they down.
Interesting paper on kinetic impact driven fusion.
https://www.jstage.jst.go.jp/article/ls … 3/_article
To achieve sufficient compression on impact, a macro projectile must be accelerated to ~200km/s into a solid target.
A typical bullet achieves acceleration between 50,000 - 100,000g. To achieve a final velocity of 200km/s with acceleration of 100,000g, an accelerator would need to be 20km long. A coil gun concept would appear to be most practical, firing two converging projectiles at individual velocities of 100km/s. This would require two opposing accelerators, each 5km long, exiting into a reaction vessel.
This would appear to be an achievable power plant, especially if the accelerators could be buried in trenches beneath the ground.
Sodium/CO2 reaction was a concern in the development of heat exchangers for fast reactors using an S-CO2 secondary coolant. But that was CO2 at high pressure and density.
Combustion isn't just about theoretical ability of two chemicals to react. The combusting surface must release heat at sufficient rate to keep temperature high enough to maintain sufficient reaction rates, when radiated heat release is accounted for. A CO2 atmosphere will have lower heat of combustion than oxygen, because two strong double bonds must be broken rather than just one. Now account for the fact that the Martian atmosphere is 100 times thinner and it becomes highly unlikely that sodium could sustain combustion in the Martian atmosphere.
One of the biggest issues with sodium fast reactors is keeping air away from the primary circuit. Not so much for fire, but for contamination. Sodium oxide is highly abrasive and will rapidly scour the inside of the primary circuit of the reactor.
A physical vessel could, but not at 100 million K. The extreme temperature gradient required to sustain that temperature anywhere within a solid vessel (even if it's tens of kilometers big) will rapidly equilibrate and cause fusion processes to stop, and might also vaporize the fusion vessel (depending on the total energy content of the system, of course).
It probably won't work for exactly this reason. This is an inertial confinement concept and is essentially an artificial star. Red dwarf stars have surface temperatures as low as 2000K despite core temperatures being several million K. This is the case because the surface area of the chronosphere is large compared to the surface area of the core, so heat spreads out as it convects through the star. However, red dwarf stars are the size of Jupiter and are as dense as platinum. So it is very likely that the minimum critical size of the reactor would be huge, even using tritium and deuterium it would probably need to be many kilometres in diameter. It would also be dangerous in a way that would make nuclear meltdowns appear tame. Who wants to be anywhere near a tank of superheated hydrogen with as much stored energy as a thermonuclear weapon? Also, if the minimum critical size is measured in kilometres, where would we find that much tritium and deuterium? Start-up costs would be excessive.
I think it could be made to work at very high pressures, because the reaction rate within the core at a pressure of 1000atm, would be huge - maybe enough to balance the rate of heat loss by conduction and convection. I don't think melting the walls would be the biggest problem, because the heat capacity of the non-plasma outer regions of the gas would be much greater than the plasma due to their greater density. The problem would be quenching the plasma due to conduction and heat loss into the colder gas. The plasma would need to generate heat at a rate that is greater than the conduction heat loss rate.
Ah...the religion of peace. We are all supposed to be soul searching at this point. They were extremists. They weren't proper Muslims. They were 'radicalised'. I don't think it is irrational to want to keep these people out of your country, although Trumps wall won't be much use in this situation.
Also, if you're looking for isotopes to bombard with neutrons, can I recommend Ca-48?
Ca-48+n->Ca-49->Sc-49->Ti-49
Ca-49 has a half-life of 9 minutes and Sc-49 of 57 minutes, so the energy will be released pretty quickly although not immediately.
Neutron absorption results in an energy of 5.14 MeV (most likely in the form of a gamma). The first decay releases 5.26 MeV (by beta emission) and the second releases 2.00 MeV (also by beta emission), for a total of 12.4 MeV per neutron.
Still probably a net loss relative to any known neutron production but it's pretty good all things considered.
Interesting idea. I think the problem is that abundant neutrons need to be generated by a fission or fusion reactor. They aren't really cheap and most of them are needed to keep the reaction going in one way or another. If you have spare neutrons, you could absorb them in Ca-48 generating 12.4MeV or into U-238 generating Pu-239, the fission of which would release 200MeV. That's 8 times the energy per neutron, since 2 are needed to breed and fission a Pu atom.
Interesting. I will give it full scrutiny later.
The explanations behind LENR generally revolve around the production of cold neutrons that are subsequently absorbed into metal atomic nuclei. But this doesn't really correspond well with how these devices are claimed to work. Neutron absorption would result in substantial gamma emissions as well as production of radioisotopes. The LENR experiments carried out so far do not appear to generate gamma and there are no reports of induced radioactivity. So either the LENR claims are bogus or something more complex is going on.
It would be great if it works. A fuel that generates just 10 times the energy per unit mass of lox/methane at high power densities, would revolutionise space launch capabilities, provided the fuel were relatively cheap. So this doesn't necessarily need to be as energy dense as fission or fusion to be very useful to us. But scepticism is certainly understandable, as what the advocates claim does not fit well with existing nuclear physics.
It's definitely possible to overstate how easy it is. We have inertial confinement systems already, after all, and they're not really good enough. The size of the ICF vessel isn't really the limiting factor either.
It's my understanding that Q is defined as "The energy produced by fusion reactions divided by the initial heating energy required to heat the plasma", with breakeven being Q>1. Containment energy is excluded from the breakeven calculations.
The vacuum would probably help as far as fusion is concerned because it seems like something that would benefit from economies of scale, but it's not enough to make it get to breakeven. Gases that are rapidly expanding into the vacuum tend not to collide at all which sort of puts a damper on the rate of fusion.
Pressure is another variable. At 100million K, hydrogen gas is ridiculously diffuse, about 1milligram per cubic metre at 1atm. At 1000atm, density increases 1000 fold. A magnetic field cannot sustain those sorts of pressures. A physical vessel could. But the plasma would need to sustain a temperature gradient to prevent the vessel walls from eroding.
https://www.businessgreen.com/bg/news/3 … n-a-decade
An interesting report from Bloomberg on how the energy environment is changing rapidly.
With all these improvements in green energy price and technology, I wonder whether there would now be scope for the following approach:
Build a giant oil tanker-style floating craft with 500,000 tonnes of batteries on board. So that's 500,000,000 Kgs. At 12 kwHs per kg, fully charged this floating battery could produce 6,000,000,000 KwHs or about 6,000 GwHs of electric power. UK average electric power output is 11GwHs. So that would be enough to power the UK for something like 545 hours or 22 days.
The battery tanker heads south from the UK to the sunlit waters of the central Atlantic (3 to 4 day journey). There, it unrolls huge arrays of flexible PV panelling stretching for hundreds of metres all around the vessel and maybe also tethered arial solar barrage balloons. It then recharges its batteries. You would need 1200 million sq metres of PV panelling to recharge the batteries in one day (averaged out). To recharge them over a year you would need 3.3 million sq. metres of PV panel or about 1800 metres by 1800 metres. Some trawler nets cover much bigger areas.
If it was one year recharging you would need something like 17 vessels working on a rota to generate enough electricity to serve the whole of the UK, with not a single wind turbine or other UK based facility involved.
That sort of solution is looking more and more doable though no doubt in reality it would be unlikely that we would ever rely 100% on such a solution to the UK's electricity needs.
Another similar solution would be a floating barge-tank full of salt phase-change material that could be melted using direct solar thermal power at a low latitude facility. This could then be towed back to the UK and plugged into a shore mounted heat engine. This would have lower energy density than state of the art Li-ion batteries, but would be much cheaper, as it would be a simple steel tank containing salt and a heat exchanger.
12kWh/kg (43MJ/kg) would be difficult to achieve using a battery system. The energy density of petrol is about the same when burned in air, which is 95% of the mass of the reactants. With a battery, you have two reactants contained and you are altering their oxidation states in a way that needs to be reversible. You also have electrodes and containment vessels that need to remain intact and conductive. This is why is very difficult to build a battery that achieves energy density much greater than 1MJ/kg. They are feeble things. A synthetic fuel is a possibility that would offer better energy storage density, but whole system energy efficiency tends to be poor, which is why we don't use synthetic hydrogen as a fuel on any practical scale.
Arguably, better than either of these options would be long-distance high-voltage DC cables under the ocean. Intermittency could be managed on the UK side using a static storage facility of some kind. Of course, that involves a lot more infrastructure and capital cost than having just one natural gas or nuclear power plant in the UK. But the system could be made to work in principle at least.