paulp@tekcad.UUCP (09/02/83)
#N:tekcad:11200002:000:6270
tekcad!paulp Sep 1 14:45:00 1983
I thought this might be of interest to the physics community at large.
Paul Pomes
Usenet: {ucbvax,decvax,pur-ee,ihnss,chico}!teklabs!tekcad!paulp
CSnet: paulp@tek
ARPA: paulp.tek@rand-relay
US Mail: Paul Pomes, Tektronix, Inc.
Box 500 MS 59-323, Beaverton OR 97077
Phone: 503-627-2341
******
Floating Accelerator: Progress at Last
It has been a pleasure to observe, during the last 6 weeks, increasing
interest among policy makers in the proposal that the 200-Gev proton
accelerator be located on a large, specially designed, floating
platform. Long recognized as offering unique advantages of
flexibility of use and economy of construction, the plan has been
plagued by questions of safety. Happily, these have been solved, and,
according to a report soon to be issued by the Conference of Eastern
Coastal Universities (CECU), full-scale consideration of the plan is
now warranted.
The report stresses two main design goals: (i) avoidance of extensive
use on land and (ii) transferability of the accelerator from one
harbor to another at approximately 6-month intervals. Preliminary
engineering surveys show that the harbors of New York, Philadelphia,
Baltimore, Boston, and Norfolk, Virginia, are almost ideal for the
purpose, and West Coast harbors could be used after the widening of
the Panama Canal is completed.
The accelerator, of strong focusing (alternating gradient) type, would
be incorporated in four floating platforms, each about the length and
width of a modern 100,000-ton oil tanker. Each would have the form of
a quadrant of a circle, and the four units would be joined (by a
precision key system and giant hydraulic clamps) to form a single
rigid ring. Prior to the clamping operation, ballast tanks in each
quadrant would be flooded with sea water to appropriate depth to bring
the quadrants to the same level. Thanks to the slight elasticity in
the integrated structure, fine-scale alignment of the quadrants of the
synchrotron can be accomplished by fine adjustment of the water levels
in these tanks.
The diameter of the accelerator is relatively small: 400 meters.
Correspondingly more powerful magnetic guide fields are provided by
60-kilogauss superconducting magnets of low-inductance design in a
multiple-pyramiding arrangement which provides especially tight
control of the betatron oscillations without significant increase in
the period of the synchrotron oscillation (except at injection, when
special pentapole magnets of diamagnetic ferrite are superimposed on
interphased counterfields).
Plans for the linac injector are still tentative, but may call for a
1500-foot 1-Gev traveling-wave assembly mounted on two aligned
concrete barges to be held by slender, prestressed-concrete equants in
rigid tangential orientation.
The ring of 1024 magnets, located in a common circular tunnel running
through all four platforms, will be situated 6 meters below the
waterline, so that adequate shielding is provided, at no expense, by
the surrounding water. A protective screen of nylon netting will
probably be mounted some 10 or 20 meters from the quadrants to keep
fish away and thus prevent radiation damage to them. The use of such
a screen was suggested by the Izaak Walton League.
Although shielding, cooling, and electrical grounding present no
problems (thanks to the unlimited amount of sea water available), the
provision of adequate power poses problems. Because city electric
power, supplied to the accelerator via submarine cables, may be in
short supply during the daytime, the accelerator may have to be
operated at night only. (If so, tourists could visit the accelerator
during the day, and the entrance fees charged might pay a significant
fraction of the operating cost.)
When repair work must be performed in the circular tunnel, which would
soon become highly radioactive, accelerator engineers would fill the
entire tunnel with sea water. Mechanics employing aqualungs or diving
suits could then work in complete safety.
A separately constructed central area of the assembly would contain
machine shops, special power supplies, a large control room,
administrative headquarters, and also a kind of motel (with parking
for helicopters rather than cars) for the crew of approximately 1000
engineers and technicians. Recreation facilities would include a
movie theater, squash courts, swimming pools, and a specially stocked
fishing pool.
The plan circumvents rivalry from groups in different parts of the
country. (The possibility of building the quadrants in smaller units
that could pass through the St. Lawrence Seaway and be assembled in
Lake Erie or Lake Michigan has not been ruled out.) Also, four
different parts of the country could be given contracts for the four
arc-shaped platforms. (Already, a bid has been received from a
Japanese shipbuilding firm experienced in building supertankers.)
Since these four quadrants-and linac structure and the experimental
hall structures-could be built simultaneously in different shipyards,
as much as 2 years could be saved relative to the time needed to
construct a fixed synchrotron.
Only in the last few weeks has the last and thorniest problem been
solved: the problem of radiation beamed toward a particular part of
the city adjacent to the harbor in question. If an emergent beam were
aimed toward a certain portion of the city, persons living there would
receive, during a typical month, five or ten times the permissible
dose (from muons, which are fundamentally aquatic and can travel
freely in water). The solution is to mount a 5-hp outboard motor
tangentially at the outer edge of the platform and keep the motor
running continuously, so as to rotate the entire accelerator at the
rate of one revolution per week and thus distribute the radiation
uniformly along the entire harbor-front. The direction of rotation
will be the same as that of the protons in the accelerator, so as to
add to their speed; even a slight increase is significant if the
particles are already traveling at a speed almost equal to that of
light.
WILLIAM A. SHURCLIFF
Underwater Consultant, CECU
42 Oxford Street
Cambridge, Massachusetts
(Re-printed without permission from Science (Letters, 26 August 1983,
p. 808))