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The Next Big Accelerator

by John G. Cramer

Alternate View Column AV-110
\
Keywords: linear, electron, positron, collider, e+e-, high, energy, particle, physics, accelerator, tunnel, USA, Japan, Germany
Published in the February-2002 issue of Analog Science Fiction & Fact Magazine;
This column was written and submitted 8/4/2001 and is copyrighted ©2001 by John G. Cramer.
All rights reserved. No part may be reproduced in any form without
the explicit permission of the author.
 

In 1993, the U.S. Congress canceled the Superconducting Super-Collider Project (SSC), the Department of Energy’s $8 billion high-energy proton-proton collider synchrotron that was then under construction in Waxahachie, Texas.  About $2 billion had been spent, the ring tunnel was 2/5 complete, the first prototype superconducting magnets had shown excellent performance, and the project was moving forward at a rapid pace, when Congress shot it down.  The SSC was to have been the next great leap forward for particle physics in the United States, the project that was to take us into the 21st century with leadership in this forefront area of physics.  Instead, the plug was pulled, producing a disaster for all of particle physics.  A fictionalized account of the events leading up to the project’s cancellation can be found in my hard SF novel Einstein’s Bridge.

In the aftermath of the SSC cancellation, the rival European project, the CERN Laboratory’s Large Hadronic Collider (LHC) was delayed after the SSC’s competitive pressure had been removed, and it’s target date of first operation was pushed back from 2000 to about 2005.  Many particle physicists-refugees from the SSC collapse managed to reach some accommodation with CERN and have joined the LHC construction effort or one of the three LHC detector groups (ATLAS, CMS, and ALICE).  Many others, particularly the younger SSC physicists, have had to abandon their careers in physics altogether and now work as bankers, software developers, Wall-Street brokers, etc.  Some attribute the recent instability of the stock market to the influx of former-SSC physicists with new schemes for market manipulation.

Accelerator physicists in this country, that sub-group of physicists who specialize in the design and construction of large accelerators, have suffered the devastating impact of two successive cancellations of major high-energy physics collider facilities by the U.S. Government, ISABELLE in 1985 and the SSC in 1993.  Nevertheless, they are pushing forward again with the design for a new multi-billion dollar collider facility, which they call the Next Linear Collider (NLC).  In this effort they are in direct competition with a design group at the DESY laboratory in Hamburg Germany that is proposing the Tera Electron Volt Energy Superconducting Linear Accelerator (TESLA) facility, and a design group at the KEK laboratory in Japan that is promoting the Japan Linear Collider (JLC).  All of the proposed machines are “linear”, using a long straight line of accelerating structures as opposed to the circular magnet-ring design of the SSC and LHC.  This is because high-energy electrons lose energy rapidly due to synchrotron radiation when bent in a curved path, with the energy loss rising as the 4th power of the particle energy.  Above some critical energy on the order of 100 GeV, electrons and positrons must be accelerated in a straight line.

At the recent high-energy physics gathering at Snowmass, Colorado, with the theme “The Future of Particle Physics”, there were detailed presentations from all three of these rival projects.   The projects are very similar in many ways.  All would collide electrons and positrons at an energy of 0.5 to 1 TeV (1012 electron volts) in the center of mass of the collision, with a luminosity (rate of collisions in a given area) of about 1034 collisions per cm2 per second.  Each facility would be constructed in a tunnel about 30 km (19 miles) long containing two linear accelerators, each 15 km long, aimed at a collision point and detector complex at its center.  Each would accelerate the electrons and positrons in several tens of thousands of superconducting cavity resonators that develop average accelerating electric fields of about 50 million volts per meter of cavity length.  Each would require 6 to 8 years to construct, once funding was secured.  And each would have a large cost.  At this stage the cost is not well specified, but informed guesses range between 2 and 6 billion dollars, (or roughly this year’s cost overrun for NASA’s International Space Station Project).

In the present design studies, the two non-US facilities would be located in places that would exploit existing accelerator complexes in Japan and Germany.  In one JLC design study, the collider would be centered at the KEK laboratory near Tokyo, with the linac arms extending away in oppositely-directed tunneled under suburban neighborhoods.  Another JLC study, however, envisions using highway construction techniques to blast the accelerator tunnel from the stone under a mountain range near Tokyo, saving about a factor of 10 in tunnel construction costs but requiring more equipment construction because the existing KEK infrastructure could not be used.  The JLC facility would also use the high-energy electron beams of the facility to create an x-ray laser.  The free-electron laser formed by the ultra-low emittance electron beam would produce both incoherent and coherent beams of hard x-rays for applications in condensed matter physics and in molecular biology.

The design study for the TESLA facility would use the DESY laboratory in Hamburg as one injection station of the facility, with the village of Westerhorn 30 km away as the other injection station.  The collision point and detector complex would be located at the village of Ellerhoop half way between Hamburg and Westerhorn.  The tunnel would be bored under urban and suburban neighborhoods and farmland in the vicinity of Hamburg.  The Germans anticipate no not-in-my-back-yard (NIMBY) problems with local residents in doing this, because the DESY facility has been constructed in the same way, in tunnels deep under the city of Hamburg.

No site in the United States has been specified for the NLC design study done here.  However, if the project goes forward one can envision extensive site-selection hearings and site proposals similar to those that preceded the selection of the SSC site.  The site-selection process for the SSC was very interesting to watch, because it brought the united interests of basic science, pork-barrel politics, and regional boosterism into direct conflict with the NIMBY concerns of the nearby residents and with the sizable fraction of the population that has a deep-seated superstitious fear of anything nuclear.  The culmination of the site selection process, with the selection of Waxahachie, Texas, ultimately based on the geology of the Austin Chalk beneath the site, was controversial, with many of the losers accusing the powerful Texas Congressional delegation of stacking the deck.  If the NLC ultimately goes forward, the site selection should be a three-ring circus.


In about 2005 the new CERN LHC will bring pairs of protons into head-on collision at 7 TeV   That collision energy is about seven times greater than the energy of the three proposed linear colliders that were showcased at Snowmass.  Therefore, it’s fair to ask why we would need these machines at all if they run at lower energies than the LHC.  The answer is in the details.

Protons are composite particles made of three quarks pasted together with gluons.  The proton has a mass of about 936 MeV, but the quarks that form it have masses of only about 10 MeV each.  The remainder of the proton’s mass is contained in the gluons and in the “Fermi motion” of the quarks, the kinetic energy of the quarks as they rattle around in their little box.  The result of this is that when the quarks in two protons collide, they carry into the collision only a small fraction of the proton’s total energy.  Moreover, their collision energy is somewhat indefinite, because it is smeared by the quark Fermi motion.  Thus, a proton collider is a shotgun, propelling multiple pellets at each other, each with a somewhat indefinite energy.

On the other hand, the proposed electron-positron colliders are more like a high-precision rifle.  The electron and positron in collision are “pointlike” particles.  They therefore bring all of their energy to each central collision.  For this reason, a 1 TeV electron-positron collider is roughly equivalent to t 10 TeV proton-proton collider.  Moreover, the electron-positron collision energy is not smeared by Fermi motion.  Therefore, a 1 TeV electron-positron collider has particle production capabilities that compare very favorably with those of the LHC collider, and it offers many advantages in experiments where precise collision energy is important.

The problem facing contemporary particle physics is that the Standard Model, the current theory of fundamental particles and their interactions, works too well.  It is in good agreement with the complete body of data collected by particle physics experiments during the past decades.  However, it is not a theory that provides any deep understanding of the inner workings of the universe.  It is a paste-up theory that depends on about two dozen arbitrary "constants": particle masses, force strengths, and interconnection strengths.  We have no idea where these constants come from or how they are related to each other.  We are sure that there must be a better, more fundamental theory behind the Standard façade, but we cannot discover it without data at higher energies.  We need an accelerator with enough energy to make the Standard Model "break".  We must find places where its predictions fail, so that we can learn what lies beyond.  It is not clear that the LHC, with its 7 TeV proton collision energy will be able to do this job.  The proposed electron-positron collider is a complementary machine, a rifle that complements the LHC shotgun approach.

One dark cloud on the e-e+ collider horizon appeared during a panel on new facilities at the Snowmass Meeting.  Michael Holland of the Bush Administration’s Office of Management and Budget stated that in order to make the case for the new machine, be it the NLC or U. S. participation in the other projects, the particle physics community would have to demonstrate that the new facility was important not only to their own area of research, but also important to “science as a whole”.  Since no one can speak for science as a whole (except perhaps this column), this requirement would be almost impossible to satisfy.

Another panelist, Luciano Maiani, Director-General of CERN, declared that he found such a stringent criterion for federal support “unfriendly to science” and an inhibition to progress in basic research.  Several members of the audience asked why NASA’s Space Station and various defense-related projects were not being held to the same standard.

One key point on which the SSC Project foundered was the lack of international participation.  The Europeans were pushing their own smaller project, the LHC, and President Bush (the Elder) failed to directly ask Japanese Prime Minister Miyazawa for Japanese participation in the SSC construction during his famous up-chuck visit to Japan in January, 1992.  This time around, if there is to be a 1 TeV electron positron collider somewhere in the world it must be an international collaboration, with the strong American, European, and Japanese groups all working as a team to construct it and extract the physics lessons it will provide.  Deciding where it will be built will be a major problem for all of the competitors.  Persuading the chauvinistic and mercurial U. S. Congress and the Bush Administration, which has so far been accumulating an anti-science record, to become a major contributor to the project will be a major problem for the particle physicists of this country, particularly if the machine is constructed elsewhere.

Since no one else has yet had the temerity to venture into these waters, let me make a modest proposal.  I suggest building the new electron positron collider in the Australian Outback.  Then, like most U. S. National Laboratories, it would be located in a remote and forbidding place, roughly equidistant from all of its designers and users, and constructed on inexpensive neutral ground where none of its promoters will have an advantage and everybody will be equally uncomfortable.


References:

Background on the cancellation of the SSC Project:
Einstein’s Bridge,
John Cramer, Avon (1997), ISBN 0-380-78841-4; http://bookviewcafe.com/bookstore/?s=Cramer .
See also the URL: http://faculty.washington.edu/jcramer/EBridge/EOS.html

The Japanes JLC Project:
See the URL: http://www-jlc.kek.jp

The US NLC Project:
See the URL: http://www-project.slac.stanford.edu/lc/nlc.html

The German TESLA Project:
See the URL: http://tesla.desy.de  


SF Novels by John Cramer:  my two hard SF novels, Twistor and Einstein's Bridge, are newly released as eBooks by Book View Cafe and are available at : http://bookviewcafe.com/bookstore/?s=Cramer .

AV Columns Online: Electronic reprints of about 177 "The Alternate View" columns by John G. Cramer, previously published in Analog , are available online at: http://www.npl.washington.edu/av.


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