At the heart of ISIS is an 800 MeV proton accelerator producing intense pulses of protons 50 times a second. The accelerator consists of an injector and a synchrotron.
At the very start of the accelerator is an ion source which produces H- ions (negative hydrogen ions - a proton and two electrons) using an electric discharge. The stream of hydrogen ions are accelerated and separated into bunches by a Radio Frequency Quadrupole accelerator. Ion bunches are then further accelerated using a linear accelerator. Four 10 metre long tanks containing copper drift tube electrodes progressively accelerate the bunches. At the end of the linear accelerator, the ions are travelling at 37% of the speed of light.
Acceleration of the ions continues in the synchrotron, a 163m circumference ring of powerful magnets that bend and focus the beam into a circle. As H- ions enter the synchrotron, a thin alumina foil strips away the electrons leaving a beam of protons. Once sufficient protons have been collected into the synchrotron, they are accelerated by radio-frequency electric fields in ten accelerating cavities. After almost 10,000 revolutions, the protons have separated out into two large bunches travelling at 84% of the speed of light. Each bunch is extracted from the synchrotron by fast kicker magnets that rise to 5000 amps in 100 nanoseconds.
The proton bunches then travel on and collide with a tungsten target.
Neutrons are produced in the target (roughly the size of a house brick) by a process called spallation. The tungsten target is bombarded with these pulses of high energy protons which drives neutrons from the nuclei of the target atoms. This gives an extremely intense neutron pulse, with only modest heat production in the neutron target. The neutrons are slowed to speeds useful for condensed matter research by an array of of hydrogenous moderators around the target. They are then directed to a suite of neutron instruments, each optimised to explore different properties of materials
Inside the instrument a material will be positioned for investigation. Neutrons travel into the material and are detected when they come out. The directions in which the neutrons emerge tell us about the arrangement of the atoms inside. This is called neutron diffraction. The amount of energy lost by the neutrons as they travel through the material tells us about the atomic dynamics , a technique called neutron spectroscopy.
An understanding of why individual substances behave as they do is fundamental to the development of new materials with properties tailor-made to their application