Proton Synchrotron

Proton Synchrotron
Landua, Fabienne · CC BY 4.0 · source
Name	Proton Synchrotron
Caption	The CERN Proton Synchrotron complex.
Type	Synchrotron
Location	Geneva, Switzerland
Institution	CERN
Energy	28 GeV
Circumference	628 m
Particles	Protons, Antiprotons, Ions
Commissioning	1959
Predecessor	Synchrocyclotron
Successor	Super Proton Synchrotron

Proton Synchrotron. A proton synchrotron is a type of particle accelerator designed to accelerate protons to high energies using synchronized magnetic and electric fields. It represents a major evolution from earlier machines like the synchrocyclotron, enabling the attainment of energies in the GeV range and beyond. These accelerators have been fundamental to the field of high-energy physics, serving as both primary research instruments and as injectors for larger facilities such as the Super Proton Synchrotron and the Large Hadron Collider.

Introduction

The proton synchrotron was developed to overcome the energy limitations of fixed-field accelerators like the Lawrence's cyclotron. Key to its design is the principle of phase stability, independently discovered by Vladimir Veksler and Edwin McMillan, which allows particles to be accelerated in stable bunches. The first machine to successfully demonstrate this principle for protons was the Cosmotron at Brookhaven National Laboratory, which reached 3.3 GeV. This was quickly followed by the Bevatron at the Lawrence Berkeley National Laboratory, famed for the discovery of the antiproton. The most historically significant proton synchrotron in Europe is the CERN Proton Synchrotron, which began operation in 1959 and became a cornerstone of the continent's particle physics research.

Principle of Operation

In a proton synchrotron, protons are first injected from a pre-accelerator, such as a linear accelerator or a synchrocyclotron. As the proton beam circulates in a vacuum pipe, its path is bent by a ring of powerful electromagnets, specifically dipole magnets. Simultaneously, radio frequency cavities provide accelerating electric fields. To maintain a constant orbit radius as the particles gain energy and velocity, the strength of the dipole magnetic field is precisely increased in synchronization with the frequency of the accelerating voltage. This synchronization, governed by the principles of phase stability and transition energy, is managed by sophisticated control systems. Additional focusing is provided by quadrupole magnets, which use the principle of strong focusing to keep the beam tightly collimated.

History and Development

The conceptual foundation for the synchrotron was laid in the 1940s with the work of Vladimir Veksler and Edwin McMillan. The first operational proton synchrotron was the Cosmotron, completed at Brookhaven National Laboratory in 1952. The CERN Proton Synchrotron, approved under the leadership of Director-General Felix Bloch, was a landmark project for European science, achieving its design energy of 28 GeV in 1959. Its success cemented CERN's role as a world-leading laboratory and directly enabled the construction of the Intersecting Storage Rings and the Super Proton Synchrotron. Parallel developments included the Zero Gradient Synchrotron at Argonne National Laboratory and machines in the Soviet Union, such as those at the Institute for High Energy Physics.

Applications and Uses

Beyond fundamental research into quantum chromodynamics and the Standard Model, proton synchrotrons have diverse applications. They are essential for producing secondary beams of particles like pions, kaons, and antiprotons, which are used in experiments such as those at the Antiproton Decelerator. They serve as the primary injector chain for larger colliders, including the Super Proton Synchrotron and the Large Hadron Collider at CERN. In applied fields, the intense proton beams are used for proton therapy in cancer treatment at facilities like the Paul Scherrer Institute. They also play a role in spallation neutron source facilities, such as the ISIS Neutron and Muon Source, which provide beams for materials science and biology.

Technical Specifications

The CERN Proton Synchrotron has a circumference of 628 meters and accelerates protons to an energy of 28 GeV. Its magnet system consists of 100 dipole magnets for bending and 216 quadrupole magnets for focusing. The beam is accelerated by 13 radio frequency cavities operating at a harmonic number of 30. The vacuum system maintains an ultra-high vacuum to minimize scattering. The machine has undergone several major upgrades, such as the installation of the Low Energy Ion Ring to handle lead ions for the Large Hadron Collider's heavy-ion program. Its control and diagnostics systems are highly automated, involving complex feedback loops and beam instrumentation like beam position monitors.

Operational Challenges

Operating a proton synchrotron involves managing significant technical hurdles. Space charge effects can cause beam blow-up at low energies, requiring careful tuning of the injection process. Reaching and crossing the transition energy demands precise control to avoid beam loss from the gamma transition instability. Maintaining beam stability against collective instabilities, such as those driven by impedance from the vacuum chamber, requires active damping systems like feedback loops. Managing radiation and activation of components from lost particles is a major safety and maintenance concern. Furthermore, integrating the machine into a complex accelerator chain, such as the CERN accelerator complex, requires exceptional synchronization and reliability to feed downstream facilities like the Large Hadron Collider.

Category:Particle accelerators Category:CERN