Elementary-Particle Physics (1986) / Chapter Skim
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5 Accelerators for Elementary-Particle Physics
5 Accelerators for Elementary-Particle Physics
Pages 98-131
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From page 98... ...
A bunch of electrically charged particles, either electrons or protons, passes through an electric field. The particles gain energy because they are accelerated by the electric field, hence the name accelerator.
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From page 99... ...
Accelerators are either linear or circular (Figure 5.21. In the linear accelerator the particle is propelled by strong electromagnetic fields to gain all of its energy in one pass through the machine.
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From page 100... ...
secondary particles during the collision, and the transformation of the incident and target particles into new kinds of matter. Not only are the primary reactions of the accelerated particles on fixed targets studied, but also in many experimental situations the secondary particles (such as pions, muons, and K mesons)
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From page 101... ...
Particle Colliders A simplified example of a particle collider is shown in Figure 5.3. In a circular machine, a bunch of electrons and a bunch of positrons circulate in opposite directions, the particle bunches being held in the machine by a magnetic guide field.
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From page 102... ...
In higher-energy storage rings, the particles are accelerated after injection to their full energy. The following combinations of particles are now used or will be used in colliders: e+- e~ P - P P - P e~- p e+- P electrons colliding with positrons protons colliding with protons protons colliding with antiprotons electrons colliding with protons positrons colliding with protons A critical property of colliders is called luminosity, which is a measure of the rate at which particle collisions occur.
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From page 103... ...
The present largest accelerators have a four-mile circumference and consume many tens of megawatts of power. An innovation that has led to much higher available energy for circular proton accelerators and storage rings has been the development of superconducting magnets.
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From page 104... ...
ELEMENTARY-PARTICLE PHYSICS AND THE VARIETY OF ACCELERATORS In the last section we described how accelerators work. We now turn to the reasons for the variety of accelerators used in elementaryparticle physics: fixed-target accelerators and particle colliders, proton accelerators and electron accelerators, low-energy accelerators and high-energy accelerators.
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From page 105... ...
The highest energies have been achieved by storage rings, the latest invention in accelerator technology. In this figure the energy of storage rings is denoted by the equivalent energy that a fixed-target accelerator would have to possess to give the same useful energy.
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From page 106... ...
But electron-positron collisions should provide the cleanest and easiest way to create Z° particles in great numbers so that their properties can be studied in great detail. Indeed, studying the physics of the Z° is the first purpose of two electron-positron colliders now under construction, the Stanford Linear Collider (SLC)
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From page 107... ...
The classic way to study the weak interaction has been to collide neutrinos with protons or with neutrons in a fixed-target experiment. The neutrinos must come from a secondary neutrino beam produced at a proton accelerator.
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From page 108... ...
To achieve this mass range both high energy and high luminosity are necessary. To reach the mass scales of the theories discussed in Chapter 4, colliders should have the following general properties: 10-TeV minimum total energy proton-proton or proton-antiproton electron-positron 1032 cm~2 so minimum luminosity 1-TeV minimum total energy 1032 cm~2 s~ ~ minimum luminosity As will be described in the section below on The Superconducting
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From page 109... ...
On the other hand, we do not yet have the knowledge and experience needed to build an electron-positron collider in the TeV range. The development work being done toward that goal is described below in the section on Research and Development for Very-HighEnergy Linear Colliders.
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From page 110... ...
+After energy upgrade Particles Most Used protons, neutrinos, muons, pions, koons, photons, ant i protons protons, neutrinos, muons, pions, goons, photons, ant i protons protons, pions, koons, antiprotons electrons, positrons, photons, protons, neutrinos, pions, koons, an t i protons proton protons, pions, koons FIGURE 5.6 The world's high-energy fixed-target accelerators ordered according to their maximum energy. There are no new fixed-target accelerators under construction, but some, such as the SLAC electron accelerator, are being increased in energy, and the AGS at Brookhaven may be increased in intensity.
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From page 111... ...
The proposal for the highest-energy collider, the SSC in the United States, is now being developed. Proton Accelerators: Fixed Target The only high-energy proton accelerators in the United States today are the 30-GeV AGS at Brookhaven National Laboratory and the Tevatron at the Fermi National Accelerator Laboratory, both of which can produce energies up to 1 TeV.
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From page 112... ...
All of these machines have provided extensive data on the systematics of the strong and weak interactions over the past two decades. The Tevatron will provide for the extension of these experiments into a new energy domain, and, as described later, it will also be used as a proton-antiproton storage ring.
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From page 113... ...
SLAC The PEP and SPEAR electron-positron storage rings will continue to operate. However.
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From page 114... ...
Proton Are' Center East ` -- _PE '~WB 15' \ Bubble Cham her Primary Beam Secondary Beam · Pri mary Target Locat ion Research Foci I ity FIGURE 5.9 The 1-TeV fixed-target proton accelerator called the Tevatron at Fermilab is shown here schematically. The large number of secondary beams that can be produced by this accelerator are shown.
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From page 115... ...
Later, the asymmetry in the scattering of polarized electrons on deuterium at SLAC provided the first definitive evidence of the interference between the electromagnetic and the weak interactions, thus confimning the theory of the unification of the weak and electromagnetic forces. The electron linear accelerator has also been used to provide secondary beams of photons and hadrons for the study of strong interactions and other phenomena such as those described for fixed-target proton accelerators.
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From page 116... ...
Recently, experimenters at PEP and PETRA have succeeded in measuring the lifetime of the B meson, a property that is important in understanding the weak interactions of the b quark, as well as the overall relations among the quark generations. The TRISTAN and LEP Electron-Positron Circular Colliders At present, there are two new high-energy electron-positron storage rings under construction (Appendix B)
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From page 117... ...
The development of superconducting accelerator cavities has made encouraging progress at Cornell in the United States and in several laboratories in Europe and Japan. The use of this technology would reduce the operating costs of high-energy electron storage rings and would increase the maximum energy of LEP, for example, to over 200 GeV.
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From page 118... ...
This energy must be continuously replaced by a radio-frequency accelerating system, which becomes a major capital investment and major operating expense as the desired beam energy increases. This leads to the rapid increase in the size and cost of electron storage rings as the design beam energy is increased.
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From page 119... ...
/ \,~ ACCEl ERA TORS FOR ELEMENTARY-PARTICLE PHYSICS 119 / ~ F inol Focus Collider Arcs \ Positron Booster ~ 1 Posi tron Production Target L Posi tron Return /1 Line ~ 6 Tronsport from . I_ L i nac Electron Booster Existing Linac , Spectrometer ~ Emittonce my/ M oni tots Domping Rings Existing Linac ~ Electron Gun FIGURE 5.11 A schematic illustration of the SLC.
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From page 120... ...
Then, in a later upgrade, one of the linear accelerators can be modified to accelerate protons, or an additional proton accelerator can be added. THE SUPERCONDUCTING SUPER COLLIDER, A VERY-HIGHENERGY PROTON-PROTON COLLIDER Physics Goals As described in Chapter 4, we are now faced with a set of fundamental questions that require experiments to be carried out in the mass
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From page 121... ...
Collider Goals These physics goals, searching for answers to fundamental questions and exploring new physics in the several-Ted mass range, require a hadron-hadron collider of very high energy and large luminosity. Our knowledge and experience in accelerator technology enables us to set the practical goals for the collider of a maximum energy of 40 TeV and a maximum luminosity of 1033 cm~2 S-~.
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From page 122... ...
elementary-particle physics community has been developing a plan for the construction of a high-luminosity proton-proton collider in the energy range of 40 TeV. The work began in the summer of 1982 at a meeting in Snowmass, Colorado (see Proceedings of the 1982 Division of Plasma and Fluids Summer Study on Elementary Particle Physics and Future Facilities, June 28-July 16, 1982, Snowmass, Colorado, R
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From page 123... ...
This collider has been named the Superconducting Super Collider (SSC) because it requires the use of superconducting magnets to keep its size and its operating power costs within reasonable bounds.
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From page 124... ...
Preliminary Collider Designs and Considerations The design studies, particularly the National SSC Reference Designs Study, have shown that a conservative extension of existing or near-term technology can lead to the successful achievement of an SSC. Several design options exist' and the selection of a particular design to optimize the cost is one of the most important considerations.
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From page 125... ...
(b) Schematic layout of the SSC indicating the injector complex and the main ring, where protons are accelerated to 20 TeV in counterrotating bunches that collide at six points around the circumference.
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From page 126... ...
Very high magnetic fields, 8 teslas or more, can be achieved with a niobium-tin superconductor, but there is little experience at present with such magnets. a The choice among these systems is complex.
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From page 127... ...
The Reference Designs Study has considered the construction schedule, as follows: .'In this study, we have assumed a six-year construction period, which would lead to completion in early 1994 if construction were to begin in PY 1988. The optimum duration of the construction period should itself be an object of study.
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From page 128... ...
incidentally, although most of the thought and work on linear colliders is for electron-positron machines, the concept may also be applicable to electron-proton colliders. Present Technology and Concepts As described above in the section on Accelerators We Are Using and Building, the first application of linear collider principles is now being made in the construction at SLAC of the Stanford Linear Collider, a facility with a maximum total energy of 100 to 140 GeV.
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From page 129... ...
(At these shorter wavelengths there is increased energy spread in the accelerated beam, and further development in chromatic corrections of the final focusing systems is required to handle this energy spread.) The repetitive nature of linear accelerators naturally suggests automated production techniques to reduce construction costs.
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From page 130... ...
Accelerating fields as high as 2 TeV per kilometer have been discussed, but there remains great uncertainty about the stability, energy efficiency, and suitability of such a mechanism to the construction of a highenergy linear collider. Many such ideas have been suggested.
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From page 131... ...
While such developments are important, they do not promise a radical saving or access to much higher energies. Mechanical forces will limit the usable magnetic fields no matter what conductors become available.
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