Toward Asymptopia

Except for the space program, there is hardly a costlier quest in all of science than exploration of the inner universe of the atom. To peer more deeply into that hidden world--in which more than 100 strange subnuclear particles have already been discovered --scientists have been forced to build ever more powerful atom smashers. Trouble is, the cost of such monsters is now so high--$250 million, for example, for the 500-billion-electron-volt (BeV) accelerator now nearing completion at Batavia, Ill.--that high-energy physicists are anxiously looking for alternate ways of getting a bigger bang for increasingly scarce bucks.

One economizing technique has now been put to work by imaginative scientists of the 12-nation European nuclear research center (CERN) outside Geneva. It is incorporated in a remarkable, new and relatively low cost ($80 million) atom smasher called ISR (for Intersecting Storage Rings) that has broken all existing energy records.

Apart from ISR, all atom smashers rely on the same basic principle: subatomic particles--usually protons--are accelerated to high velocities and slammed at stationary targets. Upon impact, the nuclei in the target atoms break apart, scattering the fragments for physicists to observe. This "bash-and-see approach" has drawbacks. As an accelerator's bullets approach the speed of light, the strange effects predicated by the relativity theory begin to take a toll: the proton's mass becomes much larger than that of the stationary targets. Much of the proton's energy is spent simply in pushing the target particle. The Soviet Union's giant Serpukhov atom smasher, for example, accelerates protons to 70 billion electron volts, but the actual useful energy on impact is only 12BeV.

Energy Bonus. For their new machine, CERN's planners adopted an ingenious strategy. After being accelerated in the usual way in CERN's 28-BeV synchrotron, protons are deflected with powerful magnets into two large concentric rings. Particles are sent alternately in clockwise and counterclockwise directions in the interlaced vacuum tunnels (see diagram, previous page). The result is two opposing beams of protons, each packing a wallop of 28 BeV, which can meet nearly head-on at eight different points where the rings intersect. In those collisions between protons, both particles can be made to come virtually to a dead stop, making use of most of the energy of impact to shatter the particles. In addition, there is a spectacular energy bonus caused by the effects of relativity. Because the velocity of the particles nears the speed of light, their mass increases dramatically. As a result, the 28-BeV protons collide with an energy equivalent to that produced by a conventional accelerator of nearly 1,500 billion electron volts.

Why didn't physicists try to achieve such high-powered collisions much earlier? For one thing, protons are so small (less than 0.00000000000025 of an inch in diameter) that many accelerator designers despaired of ever getting two of them to hit each other. In fact, Soviet Physicist Hersh Budker recently compared the marksmanship involved to "a collision of two arrows, one sent by Robin Hood on earth, the other by William Tell on one of the planets of Sirius." Yet the ISR team, led by Norwegian Physicist Kjell Johnsen, managed to increase the odds in favor of collisions. Using their powerful magnets to bundle hundreds of beams together, they created, in effect, two "showers" of protons about half an inch high and three inches across. They contain so many particles that some are bound to collide.

Since ISR went into operation, CERN's colliding beams have been a smashing success. Among other achievements, they have yielded important new information on the proton itself. In the months ahead, they will be used to hunt more elusive quarry: short-lived fragments of matter which are believed to be the "carrier" of the so-called "weak" force in atomic nuclei that leads to their radioactive decay, and the even more mysterious quarks, tiny particles that so far exist only in theory but may be the building blocks of all the other myriad parts of the atom.

CERN's new machine has created worldwide excitement among physicists. Russia's Budker is already working on a colliding beam accelerator that will bring together protons and their antimatter opposites, antiprotons. Such experiments may provide answers to theorists who believe that there are whole galaxies in the universe composed of antimatter. In the U.S., physicists at Long Island's Brookhaven National Laboratory are planning an even more awesome atom smasher. Employing the colliding-beam technique, they hope to achieve energies equivalent to 100,000 billion electron volts. Such fantastic power could finally bring experimenters to that wonderland of high-energy physics that Brookhaven's S.J. Lindenbaum calls "asymptopia"* :the far-out region on the energy scale where all the complex events inside the atom--and hence the very nature of matter--comes within reach of man's understanding.

* Derived from the mathematical concept of an asymptotic formula which, simply stated, is an approximation that becomes increasingly more accurate as one of the variables becomes larger and larger.

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