ISIS is a high power accelerator that fires high energy protons into two targets to release neutrons for experiments. A world leading centre for research, ISIS provides facilities for over 2000 scientists from 30 countries visiting each year.
The accelerator starts with the ISIS ion source which creates negatively charged hydrogen ions made up of two electrons and one proton. These are then fed into the first of three accelerators. This accelerates the ions and focuses them, like an optical lens, for entry into the second accelerator, a linac. The linac accelerates the ions up to 34% of the speed of light. The ions are then transported to the third and final accelerator, a circular synchrotron. As they enter, the ions are stripped of their electrons by a thin foil, leaving the bare protons. The synchrotron is made up of 10 sections each consisting of a bending magnet, to keep the protons on their circular path, and five focussing magnets. The total distance around the synchrotron is 163 metres. Electric fields provide the accelerating forces in ISIS. They also separate the protons into two bunches.
As the proton beam is accelerated by the electric fields the bending magnets need to become stronger and stronger to keep the beam on a circular orbit. The magnetic fields are over 10 thousand times more powerful than the magnetic field on the surface of the Earth.
After 10,000 revolutions of the synchrotron the protons are now travelling at 84% of the speed of light. At this speed they could travel 6 times around the Earth in one second. Now they are extracted from the synchrotron using three fast kicker magnets in which the current rises from zero to 6,500 amps in under 100 nanoseconds.
The proton beam passes through a thin carbon target producing muons for experiments before hitting the primary target to produce neutrons. Each proton can produce about 20 neutrons. A separate beamline takes protons to the ISIS second target station. This target is optimised for low energy neutrons providing greater capacity at ISIS and opening up new areas of research. Neutron instruments are used like powerful microscopes to study the atoms in materials. Scientists can work out where atoms are and measure the forces between them.
The whole ISIS cycle repeats 50 times every second, 24 hours a day. This requires a sophisticated controls system so that everything can be managed by trained specialists. With both targets in use, four pairs of bunches go to the first target station and one pair of bunches goes to the second target station.
ISIS employs around 360 people to continually develop and maintain the accelerator and research instruments. Together they enable world-class researchers from across the globe to get the very best results.
Based at the Rutherford Appleton Laboratory in Oxfordshire, ISIS, and similar facilities such as Diamond Light Source, are the driving force behind UK science. With plans for further instruments for the second target station and continuing research, development and investment, ISIS will continue to be at the forefront of UK science.
