Antimatter is by far the most expensive and difficult stuff to get. The efficiency of antimatter production and storage is extremely low. Just to for context reference, about 1 billion times more energy is required to make antimatter than is finally contained in its mass.
Using E = mc2, it was found that 1 gram of antimatter contains:
0.001 kg x (300,000,000 m/s)2 = 90,000 GJ = 25 million kWh.
Taking into account the low production efficiency, it would need 25 million billion kWh to make one single gram! Even at a discount price for electric power, this would cost more than a million billion Euros!
However experiments to produce antimatter particles have been already successfully done and the research on this topic is on going. Despite the discouraging huge numbers in terms of energy needs and costs, we can indeed make antimatter. But to create antimatter is important to understand how matter occurs. For this let’s go back in time and reply the Big Bang event.
REPLAYING THE BIG BANG
Not only is matter on Earth, not typical of the universe at large, but matter in the universe has also evolved through the eons. On Earth matter is made from atoms: electrons trapped in the cold by the electric force of the atomic nucleus which in turn is made of protons and neutrons, the electrons orbiting around the atomic nucleus. As temperature rises, atoms bump into one another ever more violently and their electrons become dislodged. At temperatures above 10.000 °C atoms can no longer stay in one piece. Their electrons are liberated and flow freely in a gas of electrically charged particles known as ‘plasma‘. This is how it is in the center of the Sun where the temperature exceeds 1 million °C and its hydrogen is utterly disrupted into independent gases of electrons and protons.
We can do experiments with beams of electrons and protons and see how they behave when bumping into one another at the energies typical of such a temperature. These confirm that the Sun is indeed a huge nuclear fusion machine, working its way through the first stage of chemical cookery. Experiments show that at temperatures even higher than 1 million °C matter takes on yet more novel forms. As far as we can tell electrons stay the same at all temperatures, but protons and neutrons do not. In the cold conditions on Earth, and even in the hot center of the Sun, protons and neutrons are clumps of quarks, held together by gluons. At much higher temperatures, at the limit of what can be studied in the most powerful accelerators currently available, nuclear matter seems to melt away: as atoms turn into an electrical plasma above 10.000°C, so do protons and neutrons turn into ‘quark gluon plasma’ at temperatures above about 1 million billion °C. Nowhere in the universe is that hot today, except transiently in the collisions between particles in high-energy accelerators.
Even 60 years ago the BeVatron (a former particle accelerator at Berkeley Lab that operated from 1954 to 1993) was able to create conditions far hotter than the Sun. Today we can simulate the conditions that prevailed in the immediate aftermath of the Big Bang. This is where antimatter, in the form of antiprotons and positrons, has proved the perfect tool. When protons smash into targets of matter, such as other protons, much of their energy is wasted in scattering off the material and only a fraction is available for creating new particles. However, speed antiparticles to near the speed of light, and then have them collide head on with a similar high speed beam of their material nemesis and there is total annihilation: all of the energy previously locked within their individual E = mc² is set free.
The experiments at LEP (Large Electron Positron) collider at CERN, confirmed that the Big Bang spawned electrons and positrons, quarks, and antiquarks, and lots of photons and gluons. That is how it was in the long ago dawn when the temperature was billions of degrees hotter than even the Sun is today. As the universe aged and cooled, these basic pieces clumped together building ever more complicated structures. Trios of quarks became glued together making the permanent structures that we call protons and neutrons, and the balls of plasma that these formed, the stars, began baking the seeds of the elements. As the temperature fell further, towards what we today call room temperature, these nuclear seeds were able to hold on to passing electrons and form atoms, chemistry, biology, and life.
So, we have a good understanding of how matter as we know it has formed and evolved during the 14 billion years since the Big Bang. It is ironic that we have learned much of this by using antiprotons and positrons as tools to take us back in time and see how matter was made. Had there been antiprotons and positrons in abundance in the cosmos, they could as easily have gravitated into anti-stars, whose cosmic kitchens would have cooked these ingredients to form anti-elements. But none of these have been ever found, there is no evidence of any important antimatter amount anywhere in space, at least not in our solar system.
The message is that matter and antimatter formed in matching pairs immediately after the Big Bang; yet only matter has managed to survive. Somewhere in the first moments of the universe, earlier than the billionth of a second that was studied by experiments at LEP collider, an imbalance between matter and antimatter must have emerged.
HOW CAN WE CREATE ANTIMATTER
Now to put antimatter in context, let’s make the analogy with the simplest atom in existence: Hydrogen. The Sun is mostly made of Hydrogen. A hydrogen atom is made up of a nucleus made of a positively charged proton and negatively charged electron orbiting it. With antimatter, the electric charges are the other way round. Therefore to understand what’s going on, let’s take antihydrogen, which is the antimatter version of hydrogen. A antihydrogen atom has nucleus made of a negatively charged proton (antiproton) also with different quantum numbers and a positive version of the electron (positron) orbiting it.
Actually, if you were to see a lump of antimatter, you wouldn’t know it; to all outward appearances it looks no different to ordinary stuff. So perfectly disguised that it is seemingly one of the family, its ability to destroy whatever it touches would make it the perfect “enemy within”.
The recipe for antihydrogen is hence theoretically very simple: take one antiproton, bring up one positron and put the latter into orbit around the former. Yet practically this is extremely difficult to carry out as such antiparticles have never been found naturally on Earth, so they can only be created artificially in the lab.
Antihydrogen atoms were first created at CERN in September 1995. 9 such atoms were produced in collisions between antiprotons and xenon (Xe) atoms over a period of 3 weeks. Yet unfortunately, each one remained in existence for only about 40 *10-9 s (40 billionths of a second, travelled at nearly the speed of light over a path of 10 meters and then annihilated with ordinary matter. However, the annihilation produced the signal which showed that the anti-atoms had been created. It wasn’t until 2010 that scientists managed to trap and study them properly – even if only for fractions of a second. In 2011, researchers managed to hold onto the antimatter atoms for a solid 16 minutes, allowing them to eventually study their spectra to see how they compare to regular old hydrogen.
Antimatter is produced in many experiments at CERN by accelerating protons (or other particles) to energies of usually 26GeV (giga electronVolts) (about 30 times their mass at rest) such that, when they collide with nuclei inside a metal cylinder called target, a part of the energy is transformed into particle-antiparticle pairs. About 4 proton-antiproton pairs are produced in every million collisions. When they occur these particle pairs move at speeds that are close to the speed of light. But this is much too fast for them to be controlled by the researchers. So how the antimatter particles can be tamed?
The first step is to slow them down, which the researchers do by sending them around a magnetic ring. In this way the particles are guided to the Antiproton Decelerator, where they are slowed down from 96% to 10% of the speed of light. The antiprotons and positrons are then sent through beam pipes into a giant magnet, where they mix to form thousands of atoms of antihydrogen. The magnet creates a field, which then traps the antihydrogen. If it were to touch the side of the container it would instantly be destroyed, because antimatter can’t survive contact with our world.
In practice, when using a fixed target, as a function of invested energy, the maximum antiproton production yield occurs when the protons are accelerated to an energy of about 120 GeV. Since less than one collision out of thirty produces an antiproton, and since the mass of an antiproton corresponds to only 0.94 GeV, the energy efficiency is obviously very poor. In theory, an even higher yield could be obtained if conditions similar to the original “Big Bang” could be recreated in the laboratory, conditions in which proton-antiproton production becomes spontaneous. Such conditions might be found in quark-gluon plasmas, which could be produced in high-energy heavy-ion collisions, which are presently the subject of intense research. But if this can be indeed one day practically achieved remains to be seen.
Nowadays, CERN can readily produce antiprotons in a particle decelerator, slowing them down to be captured in a specially-designed trap. But to really make the most of them, it’s time for the volatile substance to leave the nest, and be put to work in other areas of research. Antiprotons and positrons are probably the only forms of antimatter that will be able to be fabricated, in substantial quantities, in the near future. Substantial quantities meaning less than few nanograms.
The equipment used to create Antimatter is at CERN is called ALPHA ( as Antihydrogen Laser Physics Apparatus) and which is working with trapped antihydrogen atoms, the antimatter counterpart of the simplest atom, hydrogen. In the ALPHA experiment the antiprotons are passed through a series of physical barriers, magnetic and electric fields, and clouds of cold electrons, to further cool them. Finally the low-energy antiprotons are introduced into ALPHA’s trapping region. Meanwhile low-energy positrons, originating from decays in a radioactive sodium source, are brought into the trap from the opposite end. Being charged particles, both positrons and antiprotons can be held in separate sections of the trap by a combination of electric and magnetic fields—a cloud of positrons in an “up well” in the center and the antiprotons in a “down well” toward the ends of the trap.
As shown in fig 3, Antiprotons and positrons are brought into the ALPHA trap from opposite ends and held there by electric and magnetic fields. Brought together, they form anti-atoms neutral in charge but with a magnetic moment. If their energy is low enough they can be held by the octupole and mirror fields of the Minimum Magnetic Field Trap.
To join the positrons in their central well, the antiprotons must be carefully nudged by an oscillating electric field, which increases their velocity in a controlled way through a phenomenon called autoresonance.
Antiprotons with their greater mass were much harder to tame than positrons, but once under control, the antiprotons packed a far bigger punch. It was this that excited the physicists. Through the annihilation of antiprotons and protons, they could reproduce in experiments conditions that had existed in the first moments of the Big Bang. For the technologists, it was the tour-de-force of the cooling, the variety of specialist race-tracks and the sophisticated electronics that amazed and illustrated that antimatter can be tamed. So Yes, it is possible to make and tame antiprotons, but it is slow, requires great patience and the price-tag corresponds to millions of euros.
Even if CERN used its accelerators only for making antimatter, it could produce no more than about 1 billionth of a gram per year. To make 1g of antimatter would therefore take about 1 billion years. The total amount of antimatter produced in CERN’s history is less than 10 nanograms – containing only enough energy to power a 60 W light bulb for 4 hours.
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