Talking about antimatter, as we’ve done in the past two posts, leads to the question of why the stuff is so hard to find. When we make it on Earth, we do so by smashing protons into targets inside particle accelerators of the kind found at the Fermi National Accelerator Laboratory in Batavia, IL and CERN (the European Organization for Nuclear Research). It’s not exactly an efficient process from the antimatter production standpoint, as it produces a zoo of particles, anti-particles, x-rays and gamma rays, but it does give us enough antimatter to study.
But there is another way to find antimatter, for it occurs naturally in the outer Solar System and even closer to home. James Bickford (Draper Laboratory, Cambridge MA) has looked at how we might trap antimatter that occurs in the Earth’s radiation belts. In a report for NIAC back in 2006 (available here), Bickford laid out a strategy for using high temperature superconductors to form two pairs of RF coils with a radius of 100 meters, to be powered by nuclear or solar power. The idea is that the magnetic field created through the RF coils will concentrate and trap the incoming antiproton stream.
Now the model changes from production on Earth to harvesting natural antimatter in space. We get antimatter in the Solar System because high-energy galactic cosmic rays (GCR) bombard the upper atmosphere of the planets, causing ‘pair production,’ which is the creation of an elementary particle and its antiparticle. The kinetic energy of the cosmic ray particle is converted into mass when it collides with another particle. According to Bickford’s calculations, about a kilogram of antiprotons enter our Solar System every second, and any planet with a strong magnetic field is fair game for collection.
As the planet’s magnetic field holds the antimatter particles, they spiral along the magnetic field lines. This is a process that continually replenishes itself both for matter and antimatter. Jupiter is a source, but Saturn is even better, for a larger flux enters its atmosphere. Saturn is, in fact, the place where the largest total supply of antiprotons appears, with reactions in its rings injecting 250 micrograms per year into the planet’s magnetosphere. But we can start with the Earth, for the antimatter production process was confirmed here in 2011.
These results came from the PAMELA (Payload for Antimatter/Matter Exploration and Light-nuclei Astrophysics) satellite, a joint mission among scientists from Italy, Germany, Russia, and Sweden (see Antimatter Source Near the Earth). The most abundant source of antiprotons near us is found to be in a thin belt that extends from a few hundred to about 2000 kilometers above Earth, moving along Earth’s magnetic field lines and bouncing between the north and south magnetic poles.
Image: An antimatter reservoir near our planet in the form of a belt of antiprotons that lies within the innermost portion (pink) of Earth’s magnetosphere, the large bubble-like region interior to the blue arc that is controlled by the planet’s magnetic field. Credit: Aaron Kaase/NASA GSFC.
Compared to harvesting antimatter on Earth, space harvesting is five orders of magnitude more cost effective, and Bickford’s report suggests we could be collecting 25 nanograms of antimatter per day near our planet. And here’s a spectacular mission concept that can grow out of this, also drawn from the Bickford report:
The baseline concept of operations calls for a magnetic scoop to be placed in a low-inclination orbit, which cuts through the heart of the inner radiation belt where most antiprotons are trapped. Placing the vehicle in an orbit with an apogee of 3500 km and a perigee of 1500 km will enable it to intersect nearly the entire flux of the Earth’s antiproton belt. The baseline mission calls for a fraction of the total supply to be trapped over a period of days to weeks and then used to propel the vehicle to Saturn or other solar system body where there is a more plentiful supply. The vehicle then fully fills its antiproton trap and propels itself on a mission outside of our solar system.
We can imagine fuel depots in the Solar System that could support our growing infrastructure with missions to Mars and the asteroids. There is even the possibility, tantalizingly referenced in the report, of using the galactic cosmic ray flux enroute to a destination to further bulk up the fuel supply. It’s bracing stuff, and a reminder that when we talk about gathering antimatter for a mission, we aren’t necessarily limited to the sparse production from today’s colliders.
Symmetry Violations
But back to the original question. Why is antimatter so hard to find? If it is truly ‘mirror matter,’ as the title of Robert Forward’s book suggests, shouldn’t there be equal amounts of it, and shouldn’t that equality have prevailed from the beginning of the universe? It seems logical to think so, but of course if that had occurred, we would not be here to contemplate the problem.
Now we’re entering the realm of charge-parity (CP) symmetry, which asserts that physics should be unchanged if we plug in antiparticles where particles currently are. Most particle interactions show this charge-parity symmetry to hold, and it carries the implication that the universe should have begun with equal amounts of matter and antimatter. Why and where CP symmetry does fail is a serious question, one that has us looking for any observable violation of the principle.
We have no definitive answer, but we do have interesting results from the T2K experiment in Japan, as reported in New Scientist following their discussion at Neutrino 2016 (the XXVII International Conference on Neutrino Physics and Astrophysics), held in London in early July. The researchers at T2K have been monitoring the oscillations that occur when neutrinos spontaneously change ‘flavors’, from electron to muon to tau. Neutrinos as well as antineutrinos each come in these three types, and all three types can undergo such oscillations.
Image: The inside of the Super-Kamiokande detector in Japan. Credit: T2K.
Observing that 32 muon neutrinos that traveled between the J-PARC accelerator in Tokai to the Super-Kamiokande neutrino detector in Kamioka had turned into electron neutrinos, the team ran the same experiment with muon antineutrinos. Charge-parity symmetry says that the rates of change should be the same, but the researchers report just four muon antineutrinos have changed into the anti-electron neutrino. The numbers are small but the possible violation of CP symmetry is provocative. Results from NoVA, a similar experiment sending neutrinos between Illinois and Minnesota, are showing roughly similar values for apparent CP violation.
More data are needed to reach any firm conclusions, but these results point to the direction of future work at both installations. Some process that violates CP symmetry has to be in place to explain the overwhelming difference between the amount of matter and antimatter in the universe. Thus we can expect any results showing deviations from this symmetry will make news. Meanwhile, from a propulsion standpoint, we have to reckon with the paucity of antimatter by imagining creative ways of creating or finding enough to use in our future experiments. Space-based antimatter harvesting may prove to be the most cost effective way to proceed.
I’ll close by quoting James Bickford in a 2014 interview, where I think he strikes just the right note about the need for small scale experiments as well as avoiding antimatter hype:
For the most part, propelling spacecraft to near the speed of light with antimatter lives in the realm of Star Trek. The technical obstacles are non-trivial and probably won’t be solved in the near future, if ever. From this perspective, the potential for antimatter probably has been overhyped. However, the small scale experiments are just the first baby steps that could help us down the long path. More importantly, research and development in this area is part of a broader framework that could help fundamental science and our understanding of the universe. Antimatter plays a central role in some of the Holy Grail problems of physics, such as the nature of dark matter and why matter dominates over antimatter.
One day we will create our own huge magnetic fields beyond even that of Jupiter. Once we can do that we can with use if a feed material create AM on a huge scale. I see us as storing the AM in magnetic field containments on the ends of rotating cables or supports so if something goes wrong the AM store is ejected into space by centrifugal action protecting most of the ship or station.
Well, it looks the Saturn system will be the most important player in
the deep future of human space development. A C Clark was prescient
again with his Titan novel “Imperial Earth”.
The abundance of Energy for power generation brings Titan into play
as a strong candidate for colonization. It will probably also serve the resupply needs of ships needing C,H,O,N as stock materials in concentrated form rather than trying to mine it piecemeal from Asteroid/comets.
The big unknown is human physiological effects of a lunar like gravity
in utero and for maturing beings. That goes double for plant and auxilliary
animals humans will certainly need. Fortunately this can be tested on
Luna. In addition to physiology we will have to create ice mountains on permanently shadowed craters on Luna . We need to test the viability of large Ice Caverns, as spaces for colonial development
I have read how a warn hydrogen structure could support an Aerostat
at reasonable temperature and 1 atm in the upper Saturn atmosphere. I guess this is a back stop, if humans cannot live a full life span on Titan. (but this would turn it back into a large outpost instead of a 2nd home)
Of course this also an open question for Mars Colonization attempts.
While the emphasis in the previous threads was to create high Isp photon rockets, this isn’t needed for travel in the solar system. Robert Forward’s book “Future Magic” has a chapter on using antimatter (Magic Matter) to heat water in “conventional” rockets. [A less technical version from a similar chapter in “Mirror matter”?] The technology seems simpler and if doable, would completely change the economics of space travel. This approach would seem to fit well with the concept of anti-matter harvesting. The beauty is that reaction mass, water or hydrogen is very abundant in the solar system, and transporting anti-matter power sources to where they might be needed would be very economic as they would be little more than the mass of the containment system.
Harvesting anti-matter and the developing the technologies to contain and use it are ideally done in space, preferably isolated. Possibly a good industry to start R&D on by a visionary.
Your comments are a nice précis of the last few day’s discussions. I have a New Scientist article by @JoelDavisWriter from 24 June 1989 that discusses options including photon rockets and those using a working fluid, if anyone is interested (also here: https://books.google.com.au/books?id=t6k3RHx52_cC&pg=PA68&lpg=PA68&dq=bruno+augenstein+antimatter+engine&source=bl&ots=ksCG-mHshQ&sig=BcL83IJ2aKAxkAQr7QeYMfTKvjM&hl=en&sa=X&ved=0ahUKEwiWuLWwm6fOAhVJipQKHQplDQkQ6AEIMDAD#v=onepage&q=bruno%20augenstein%20antimatter%20engine&f=false).
What is the energy density of the best anti-proton traps ? How long can they hold anti-protons ?
Good question. I am not sure, but I have heard about the possibility of using nanotechnology to fabricate sub-millimeter sized tiny traps for anti-protons in the context of the development of the next generation of “pure fusion” nuclear weapons. The small anti-proton trap would trigger fusion in a lithium deuteride capsule without the need for a fission device. How close we are the actually making one of these tiny traps is another question.
Very interesting. I guess the fact that the military is interested gives the best chances for them to be actually developed. In time they will be available civilian use albeit in a controlled way (like space missions).
Saturn does seem to be a much better candidate for colonization than most of the usual candidates, and being able to harvest a rich supply of antimatter is icing on the cake.
Titan has been mentioned because it is a source of hydrocarbons and nitrogen, all important for life support and industry. Multiple other moons and the rings provide opportunities to harvest water and mineral resources, and it is an overall lower radiation environment, so even without antimatter, Saturn should be considered as perhaps the centre of some future civilization in the solar system.
Other candidates like Mercury (abundant solar energy and iron), Jupiter (harvesting the incredible energy of the magnetosphere and colonizing 67 moons), or Uranus (3He mining of the atmosphere) are attractive, but don’t have the breadth of resources Saturn can offer.
while the problem with obtaining antimatter is daunting, it can always be solved by production scaling and brute-force. The real problem lies in storing it safely at sufficiently high ratios of fuel-to-storage mass. If the magnets required to induce enough diamagnetic repulsion are too bulky, more of the fuel is spent accelerating more storage mass, according to the rocket equation. As always, any good and fast method of interstellar propulsion will also double as an extinction-event weapon.
Perhaps someday we will learn to harvest the suns energy to make antimatter
The power that can be generated from the 250 micrograms/year at Saturn, if harvested and converted with 100% efficiency, is about 1,200 Watt. Just enough to operate one toaster.
You get this quite easily by multiplying the mass rate by the square of the speed of light. 250 micrograms/year is 7*10^-15 kg/s, times c^2 makes approximately 600 W, times two (equal amounts of protons and antiprotons) makes 1,200 W.
Not much good as an energy source in general, or a starship in particular. It would take a very long time to collect enough for an interstellar voyage.
Or, perhaps I have made a mistake?
First, we need to standardize on units. Let’s use MKS since that’s how you’ve started.
E = kg (m^2 / s^2) J
E = 250*10^-9 (3*10^8)^2 J
E = 2.25*10^10 J
But since there is an equal amount of matter in the reaction we must double this energy.
E = 4.5*10^10 J
If we assume we are gathering the anti-matter for free and “burning” it continuously at 100% efficiency, and since this is an annual harvest of anti-matter we get:
P = (4.5*10^10 J) / (3*10^7 s) W
P = 1,500 W
Not much thrust but lots of toast. Or tea.
More than enough to make a “really hot cup of tea” to power the “infinite improbability drive”.
Looks correct to me. Nice calc putting this in context.
Yes, a hot cup of tea and a toasted raisin bun….watching Titan rise over Saturn, can’t think of anything more heart warming.
The actual energy content is very low but anti-protons are very good at catalyzing nuclear reactions which is where most of the energy for propulsion comes from. This allows you to leverage the intrinsic nuclear energy without the usual overhead of a nuclear reactor. Page 7 of the report (link below) summarizes several prior systems in the literature which leverage this approach.
https://centauri-dreams.org/wp-content/Bickford_Phase_II.pdf
I wonder if They used antimatter to get there? Tabby’s Star is only ~0.2 aeons old.
KIC 8462852 Faded Throughout the Kepler Mission
http://arxiv.org/abs/1608.01316
Existence Proof of interstellar travel.
I am looking at article here about an antimatter rocket to Mars.
http://science.nasa.gov/science-news/science-at nasa/1997/msad12nov97_1/
It says 1 gram of anti-matter has as much potential energy as 1,000 shuttle external tanks. Which would make for a one month duration trip to Mars
Saturn yields 250 micro gram or, 250 x 10^-6 of a gram per year. You would need 4,000 years worth of 100% efficient harvest to aquire 1 gram of anti-matter.
It was not clear from the article, since 250 micrograms of anti-matter is
made per year, does that mean this accumulates over time and is not all
destroyed.? If it is not all destroyed would there be a reservoir of anti-matter far beyond 250mg?
Because if we talking about 250 mg and 1,500 watts per year only, there are better ways of getting much more Energy from the Saturn system than that.
Your last sentence should be “250 micrograms” and either 1500 watts (no “per year”), or 13,140 KW hrs per year , or 4.7E10 Joules per year.
In any case, as Eniac has shown, harvesting antimatter at Saturn is not much use unless it accumulates. I don’t see how that can happen, as the probability of annihilation increases as the anti-matter accumulates.
It might seem worth looking for chunks of anti-matter in space, but as we’ve shown with impacts from the ISM, the likelihood of a chunk surviving for any period of time must be quite low. That doesn’t rule out a possible existence, but that it is going to be very expensive to search for assuming some exists.
If I type “cost of antimatter” in Google, it gives me $25B/g for positrons. This, I presume, with current technologies. 250 micrograms would then be a puny $ 6.25 M, certainly not a reason to go to Saturn. It does give $62.5 T/g for anti-hydrogen which would give a more respectable cost of $15.625 B for the same 250 micrograms.
This would make the mission more viable, especially considering that it would collect that amount every year (without considering efficiency in capturing and storage) .
However before going there, it would be necessary exploring what it can be done here to improve the production. I think I read that it could be improved by at least a couple of order of magnitude, making Saturn not very appealing.
It seems to me that mass for mass, proton/anti-proton annihilation produces the same amount of energy as an electron/positron one.
While it is extremely hard to store charged particles in a small space, why not store them in a large volume of magnetic fields in space? If micrograms can be contained in Saturn’s magnetic fields, perhaps we can repurpose magsails to store “cheap” positrons with relatively slow losses to escapes and annihilations?
“It seems to me that mass for mass, proton/anti-proton annihilation produces the same amount of energy as an electron/positron one. ”
True, but antiprotons are more useful to induce fission (see my post below) as they fall into the nucleus. Fission can then induce fusion. I’m guessing here, but they can be seen as “critical mass reducers” for mini or micro fusion bombs (pellets for propulsion ?).
But maybe it is possible to produce enough heat/pressure with positrons alone to induce fusion. I really don’t know.
About 8-10 years ago I remember reading about using positrons to heat a gas for propulsion as a realistic, relatively near term thing.
Also, at least with current technology, I see the value of antimatter not as pure fuel but as an ignition facilitator for fission/fusion. In other words, I see it as a match, not as fuel.
According to this :
https://en.wikipedia.org/wiki/Antimatter_weapon#Antimatter_catalyzed_weapons
A tiny amount of antiprotons can be used to trigger 1 kiloton explosions.
In that context, even small amounts are very valuable.
Hmm – there are magnetic cages being developed as part of the fusion program as we speak. ITER uses niobium-tin magnets. Or maybe the way to go is using something electrostatic. I have a sensation it would help us storing it with a smaller decay rate if we make the bottle really big, wich shouldn’t be too much of a problem technically, in space (Saturn orbit?). The economical part is another question.
An antimatter question. Would antimatter pass through matter ?
I’m talking about neutral atomic matter and antimatter, not just proton, electrons, positrons etc.
One of the reasons that matter doesn’t pass through matter is electromagnetic repulsion of the electrons. That would not be the case for matter antimatter. They should actually slightly attract each other at short range and start to pass through each other (plenty of room between nuclei). At some point annihilations would start with subsequent explosion etc.
Is the scenario above realistic ? I never thought about it before, if so, it would add to the quirkiness of antimatter.
If they’re solids the interaction would be immediate though not necessarily highly destructive. In a solid adjacent molecules’ electron clouds interact so there is really no space for a solid to pass through. This is well outside my expertise but I have read some informed speculation from physicists that a matter object striking an anti-matter object would cause a very big bang when they contact (electron-positron), partially or totally shattering the masses, but the explosion would also drive them apart. You still wouldn’t want to be nearby.
Getting a complete reaction with conventional explosives is similarly difficult. Two lumps of stuff brought together don’t do much. They must be thoroughly mixed so the reaction surface is maximal. Matter and anti-matter are the same. Even if we had lots of anti-matter it is a large technical challenge to achieve even moderately efficient mutual annihilation with matter. Nuclear fission is different since the freed neutrons traverse the material very well, enabling a chain reaction without a reaction surface.
“In a solid adjacent molecules’ electron clouds interact so there is really no space for a solid to pass through.”
Exactly, but in this case the other solid is antimatter, with positronic clouds. They would actually attract electronic clouds and annihilate. So, some level of compeneatration should be possible. Eventually, as annihilation starts at the point of contact, the heat generated would cause a repulsive force in the form of gas/plasma expanding. That might separate the objects enough to stop annihilation. That probably would make difficult a complete annihilation. Not sure.
Leaving annihilation aside for a moment, I’m not sure that there is anything that would stop the two objects from passing through each other. At short range the electronic and positronic clouds would attract each other with some compenetration. As the solids pass through each other, an even stronger Coulomb force would then be felt from the nuclei.
It seems to me that, once the contact has been initiated, only the annihilation itself could stop the objects passing through each other,
I feel charge parity will hold for all tests, I suspect that when the universe came into existence it was like a crystallisation event, remember S-T has properties much like a ‘liquid’. In the crystallising event our matter ‘spin direction’ just happened to be chosen but it was equally likely to have been AM but not both at the same time. I am wondering if in black holes the crushing singularity or an effect before it has the effect of forcing all matter to have their nuclear spin atomically in one or the other direction, either matter or AM.
Paul, thank you VERY much for putting up Bickford’s Phase II report. Wanted to link to it in an end note, but couldn’t find it anymore.
Are there any studies being conducted regarding the design of an antimatter harvester? A brief search ended up with this one, http://www.hbartech.com/, but generally I don’t see many.
What could you do with the 250 micrograms of antimatter?
If you could use the energy of annihilation of that much antimatter with 100% efficiency it would put 1.4 tonnes of material into LEO. Not enough for a substantial space program.
Is there any prospect of collecting much larger quantities of antimatter to make useful antimatter rockets?
Jim, at the levels we could accumulate naturally from space harvesting, the antimatter would have to be used to hybrid fusion or sail missions like Steve Howe’s antimatter sail. If we’re talking the amounts we’d need for a true antimatter rocket, then we have to develop a whole new antimatter production strategy.