Physics Questions People Ask Fermilab
Question on Antimatter
I am an undergraduate student at the University of Minnesota at
Duluth. I am doing a research paper on the need to increase
alternative/new energy R&D funding. I would appreciate it if you could
answer a couple of questions for me.
I am an undergraduate student at the University of Minnesota at Duluth. I am doing a research paper on the need to increase alternative/new energy R&D funding. I would appreciate it if you could answer a couple of questions for me.
My name is Glenn Blanford. In addition to working with Fermilab's Public Affairs Office, I am a researcher on the Antihydrogen Production experiment, E862, a small group (8) who have started to observe antihydrogen atoms (at relativistic momenta, 3-9 GeV/c) using antiprotons and a hydrogen gas jet target.
1. What is your current yearly budget, and how does it compare with previous years funding?
The total annual budget for Fermilab this year is about $260 million; last year it was $263 million. But it should be pointed out that this sum does not go toward developing antimatter as an alternative energy source.
Fermilab uses far more energy than it could ever supply. It is true that there is a large amount of energy given off when a particle collides (annihilates) with its antiparticle. But the amount of energy needed to produce the antiparticle is far more than can be gained from the annihiilation. Let's talk some numbers:
Fermilab creates antiprotons. In order to create an antiproton you have to accelerate a proton to very high energy and slam it into a metal target. Fermilab's Main Ring (synchrotron ring) accelerates protons to 120 GeV of energy. An eV (electron volt) = 1.6 x 10-19 Joules of energy, a very small amount. A (Giga-)ev or GeV is 109 or a billion eV. A (Mega-)ev or MeV is 106 eV.
In order to accelerate the proton, hundreds of magnets for bending and focusing the beam as well as radio-frequency cavities have to powered. 10's of MegaWatts are needed for this in addition to similar beamline elements in the proton production stage. Once at the right energy, the protons are diverted onto a metal target. The results of the nuclear reaction (not a fission type) is that for each 200,000 protons hitting, one antiproton is produced. This factor includes the fact that the antiprotons are produced within a large angle cone and only those whose direction is close to the original proton direction can be accepted.
Then the antiprotons enter the Antiproton Debuncher and Accumulator rings which make the beam profiles and otehr distributions smaller and more manageable. They actually stack antiprotons until up to about 1012 of them are kept in this storage ring (the Accumulator).
Consider that one proton-antiproton annihilation both at rest will yield 2 photons (X-rays) with a combined energy of only 1.88 GeV. On the other hand, the maximum antiproton energy after reaccelerating it in the Tevatron is 1.0 TeV, a factor of 1 million greater. So 2.0 TeV = 2x102 eV = 3.2 x 107 Joule can be produced from one collision. Unfortunately, the Tevatron has a maximum energy of 1.0 TeV per particle. It is the second-highest-energy proton accelerator in the world. To make one larger you either have to make a ring larger than 4 miles around or make magnets with larger magnetic field. The state of the art for magnet design still does not allow for generation of consistent fields larger by more than a factor of ten.
It takes about 2 days to get 1012 antiprotons and consider a watt = Joule/sec so with a beam of 1012 protons and the same of antiprotons colliding given they all collide when you want them to which never happens, you get:
1012 x 3.2 x 10-7 / 2 x 24 x 3600 ~ 2 Watt
Compare this with the 107 Watts you are burning up doing all the accelerating. A factor of 10 million is not just inefficient, it does not even come close.
These are ultimately collided with protons, etc. to do particle physics experiments. Fermilab after all is a federal government mission laboratory and is devoted to doing particle physics experiments whose consequences are considered far more reaching. It is devoted to figuring out the basic physics though. For example, now that antimatter has been found to exist (not by Fermilab but years ago in a similar research environment), it may be conceivable that a reaction in a distant star would provide the high acceleration and intensities needed to create antimatter in large quantities. Without the research at places like Fermilab, we would not even understand the potential for it to be there much less what it uses it could serve.
Now all this does not include any efficiencies when converting your annihilation X-rays into something useful for power generation. Cars don't run on X-rays. These are powers of ten that you lose not just 5% or so. There are other schemes that are a little better but none come near breaking even. Another way of thinking about it is to collect the antiprotons in traps and collide them later. From the discussion above, you can see that the net energy output is even smaller since the particle energies are smaller. This is because they cannot be collected unless their energy is very low since they have to almost stop inside the trap. Compare the energy output for annihilation at rest versus that at high energy.
On the other hand, researchers have looked at it not from a large scale power plant approach (100 MW to GW capacity such as nuclear power plants) but as an alternative to space probe power. In other words powering missions to Mars, for example. It would not be that cost effective overall but neither are other methods currently used. It could be at some stage easier to handle and not present hazards. In addition, the space and weight requirements for the primary plant are reduced drastically although secondary conversion would still be needed. This is probably the most compelling practical benefit it could get.
I will give you the URL here of some research which considers this approach although keep in mind, their numbers for antiproton production is way too liberal and depend on using 100% of antiprotons. Fermilab is committed by the federal government and physics community to use most of those in its collider and fixed target experiments and would never allow more than a smaller fraction to be collected for this purpose. But perhaps you can gain some insight on what some scientists (as opposed to total kooks) think.
If there were seriously any chance of having an antiproton energy source here in the near future, the federal government would probably devote enormous research towards it such as converting Fermilab into a power plant and perhaps make it classified quickly. Obviously this has not happened. I think you would make a better point by discussing the very long time scale if not impossibility of the claims for antimatter energy solving the world's energy crisis and UFO propulsion etc. But that is just my opinion.
Actually one energy idea I saw recently seemed to have merit. It is called the energy amplifier. It is an accelerator-driven fission reactor which would have 10000 tons of molten lead used for a cooling scheme. It was designed in part by Carlo Rubbia (former director-general of CERN).
2. How could antimatter be used as a power source, and what major technological problems must be solved before such a source could be developed?
As far as using it as a (large scale) power source, I think at least for now, that is many years off. Fusion is a much more viable alternative but it is only recently reaching breakeven (where energy in = out). I tend to believe the excitement over antimatter as an energy source is in part because fusion has taken so long. I would put my money there much faster though (or in solar).
Antimatter is important for understanding the way particles interact. and the way the universe works.
In any case, let me know if you have any questions.
Thanks for the quick response, it was exactly what I needed. Your explanation was easy to follow, and will alter the direction of part of my paper.
I am curious though. Want is your view on the cancellation of the SSC? Would it have been worth its $11 billion price tag, and can anything be salvaged from the $2 billion already invested?
Again thanks, Steve Pullar
- Last modified
- email Fermilab