Transcript ISIS - physicsinfo.co.uk

ISIS – Rutherford Appleton
Muons
Neutrons
Synchrotron
LINAC
Cockcroft
-Walton
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 Hions 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
Muons
Neutrons
Synchrotron
LINAC
Cockcroft
-Walton
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
HIDE
ACCELERATE
HIDE
ACCELERATE
The pulses
‘hide’ in the
drift tubes
when the
electric field
is reversed.
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.
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Tank (under vacuum)
Beam direction ----------------------------------------
Drift tubes are held in ‘tanks’ in a vacuum.
Magnets are used to focus the beams.
ISIS – Rutherford Appleton
Muons
Neutrons
Synchrotron
LINAC
Cockcroft
-Walton
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
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
Muons
Neutrons
Synchrotron
LINAC
Cockcroft
-Walton
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 spinpolarised.
HEP
Carbon
atom
Polarised
Muon
Pion
Neutino
Material
lattice
Positron
ISIS – Rutherford Appleton
Muons
Neutrons
Synchrotron
LINAC
Cockcroft
-Walton
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.