ISIS – Rutherford Appleton Cockcroft -Walton LINAC Muons Neutrons Synchrotron

Cockcroft – Walton accelerator This equipment is commonly used to generate the first accelerating voltage. First built in 1932 by J.P. Cockcroft and E.T. Walton

Cockcroft – Walton accelerator A ‘ladder’ of capacitors and diodes generate high voltages to accelerate H - ions to E = 665 keV. Note the RC circuit to smooth the signal.

Cockcroft – Walton accelerator The cabin containing the proton source and feed to the LINAC

ISIS – Rutherford Appleton Cockcroft -Walton LINAC Synchrotron Muons Neutrons

LINAC The hydrogen ions are fed into the linear accelerator (Drift LINAC) to be accelerated by radio frequencies. First the beam is ‘chopped’ to produce 200  s, 22mAH pulses of protons.

LINAC Radio frequency generators create an electric field which accelerate the pulses The pulses ‘hide’ in the drift tubes when the electric field is reversed.

LINAC Radio frequency generators create an electric field which accelerate the pulses The pulses ‘hide’ in the drift tubes when the electric field is reversed. ACCELERATE HIDE ACCELERATE HIDE

LINAC As the velocity increases the gaps between Cu drift tubes get longer and longer.

LINAC The frequency remains constant so the acceleration is maintained by increasing the lengths of the tubes along the accelerator. Drift tubes are held in ‘tanks’ in a vacuum. Magnets are used to focus the beams. Beam direction  Tank (under vacuum)

ISIS – Rutherford Appleton Cockcroft -Walton LINAC Synchrotron Muons Neutrons

Synchrotron On entry, the hydrogen is stripped of its electrons by 0.3  m alumina foil Photograph showing the ring (bottom) and the beam feed above (with kicker and focusing magnets).

Synchrotron Aerial view of CERN,in Switzerland, showing the two rings. The larger one is 5km in diameter, 27km around.

Synchrotron The HEP (high energy protons) are accumulated over many revolutions and reach a final energy of 800MeV, ‘surfing’ on the rising edge of the sinusoidal magnetic field.

Synchrotron

Beams are focused by pairs of quadrapole magnets Direction is changed by dipole ‘kicker’ magnets.

Synchrotron There are high levels of radiation inside the synchrotron area. Heavy shielding is used.

Synchrotron The 80MeV HEP beam is kicked out of the ring towards the neutron production target. On the way, some are used for muon production.

ISIS – Rutherford Appleton Cockcroft -Walton LINAC Synchrotron Muons Neutrons

Muons Some of the protons in the beam (2 or 3%) collide with a thin carbon target before they reach the neutron production target. Pions (  +)are given off, these rapidly decay to muons (  +) and positrons (e+).

Muons Muons sit inside the target sample and it is the decayed positron that is detected. The positrons are emitted in the direction of spin of the muon which is initially spin- polarised. HEP Carbon atom Pion Neutino Polarised Muon Material lattice Positron

ISIS – Rutherford Appleton Cockcroft -Walton LINAC Synchrotron Muons Neutrons

Fixed target In a fixed target experiment the electron beam is directed at a stationary target, such as a piece of metal or a tank filled with gas (the gas is at a very low T – down to 0.25K - and therefore can be considered ‘fixed’) Detection devices are set up to study what comes out from the collision region.