tested it. He found that it is not effective in the same concentration as is puromycin, although the aminonucleoside fragment does inhibit protein formation at high concentrations. This suggests, Dr. Yarmolinsky says, that it may act by a different mechanism. Although the aminonucleoside fragment alone is not as potent as puromycin, it is not necessary to have attached to the nucleoside the specific amino acid found in the antibiotic. When one of a variety of amino acids is attached to this nucleoside in place of the p-methoxyphenylalanine of puromycin, an equally effective compound results, Dr. Yarmolinsky says.
MURA Readies Fixed Field Synchrotron Will test stacking and collision of beams as route to high energies A small accelerator with a big mission and a big name is nearing completion at Madison, Wis. The unit: a double, beam, 40 m.e.v. fixed field alternating gradient (FFAG) synchrotron, built by Midwestern Universities Research Association. The mission: to test concepts that may lead to particle accelerators that can produce 500 b.e.v. At the start, says technical director Keith R. Symon, MURA's s^ichrotron will test the "beam stacking" idea. In stacking, one group of particles is accelerated to a high energy and left to coast. Successive groups are brought to the same energy level. This permits building up very intense beams. Once this is done, MURA's scientists will induce two electron beams to collide. When this happens, the beams are expected to produce large amounts of energy for creating other particles. The 40 m.e.v. synchrotron, for example, may produce electron collisions that will yield as much energy as a single 6 b.e.v. beam striking a target, SQr. Symon says. Intensities of the electrons, circulating in opposite directions, will range from 25 to 50 amperes. Ultimately, if AEC makes funds available, MURA hopes to build a 15 b.e.v. proton accelerator embodying the principles tested in the smaller machine. Two colliding 15 b.e.v. proton beams would develop as much energy as a 540 b.e.v. beam hitting a target.
FFAG Concept. The high beam intensities and collision energies of MURA's accelerator are due to the fixed field alternating gradient principle. The FFAG synchrotron accelerates particles in a doughnut-shaped vacuum tank. The particles' orbits are maintained by a fixed magnetic field provided by a series of magnets placed in a ring. These are designed so that the magnetic field is weak at the inner edge of the vacuum tank and strong at the outer edge. Low energy particles can then circulate near the inside edge while high energy particles go around the outer edge. Two kinds of FFAG magnetic field patterns were tried in previous experiments. One is the radial sector pattern, a variation of which is used in the new unit; the second is the spiral, sector pattern. In the first pattern, which MURA used for an earlier accelerator, positive and negative magnets placed alternately about the ring provide an alternating magnetic field gradient. The positive magnets curve particles around the center of the ring; sole purpose of the negative magnets is to stabilize the orbits. Without them, the particles would fly out vertically, striking the top and bottom of the vacuum tank. The negative magnets, though, make the accelerator larger than desired. The radial sector pattern used in the new accelerator was devised by Japan's Dr. T. Ohkawa. His theory holds that it's possible to design an accelerator in which both the positive and negative magnets are made exactly alike. And beams of particles circulating in opposite directions can
revolve simultaneously in the magnets. The spiral sector pattern, which cuts down the size of an FFAG accelerator, was suggested by MURA's Dr. D. W. Kerst. This pattern is equivalent to twisting the positive magnets of a radial sector pattern into a spiral. Negative magnets are then unnecessary. MURA built a smaller accelerator of this kind in 1957. System Is Flexible. A fixed field accelerator, says Dr. Symon, makes for a lot of flexibility in designing systems to accelerate particles. Once a suitable magnetic field is set up, it can hold particles in stable orbits at all energies. These energies can range from the low levels—at which particles are injected into the unit—to the highest to which they're accelerated. Particles can then be accelerated further by applied radio frequency (rf) voltages at any desired schedule. Important point: Many groups of particles can be accelerated at the same time. For example, the 15 b.e.v. proton accelerator may work this way: • A pulse of protons is injected 10 times a second at 50 m.e.v. and accelerated to 1.4 b.e.v. with rf voltages. • These particles are left to coast at 1.4 b.e.v. until 10 successive particle groups are accelerated to the same energy level (beam stacking). • Once a second, another rf system picks up 10 groups of particles stacked at 1.4 b.e.v., kicks them up to 15 b.e.v. Two such beams can be made to collide. Intensity of these beams, says Dr. Symon, is such that 100,000 or more collisions will occur every second. And all the energy of any two colliding protons is available for study.
UNDER CONSTRUCTION. Working on MURA's experimental synchrotron are (from left) James D. Hogan, Dr. Charles H. Pruett, and Dr. William A. Wallenmeyer APRIL
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