Particle Accelerators. An accelerators is a device which is used to impart kinetic energy to the charged particles. Linear Accelerator.
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An accelerators is a device which is used to impart kinetic energy to the charged particles
Principle – An oscillator electric field is applied across the electrodes joined in series. The charged particle when passed through them is accelerated if the frequency of the applied field is in resonance with the motion of the particle.
It consists of a series metallic hollow cylinders called electrodes (E) or drift tubes of successively increasing lengths arranged co-axially within tube (G). Alternate electrodes are connected to the terminals of high frequency oscillator i.e. the even numbered electrodes are connected to one terminal while the odd number electrodes are connected to the second terminal of the oscillator.
The average potential difference between the gap of any two electrodes = V
The energy acquired by ions in passing one gap = ZqVo
The total number of gaps = n
Total energy of ions E = ZqnVo =1/2mv
Tn =Vn /2v=(2ZqnV/m)1/2 1/2v
1-They are inconveniently long in size.
2- They require extremely high frequency and high – voltage oscillator.
Accelerate electrons beyonds ~ 2 MeV, alternate version of linear accelerator was based on wave – guides. These accelerators are known as wave guide accelerators. In such accelerators drift tubes are completely eliminated. These accelerators consist of a circular wave – guide loaded with metallic annular disc.
Device used to accelerate heavy charged particles like proton, deutron, alpha particles etc. by passing them again and again in radio frequency electric field along a closed path
It is based on the principle that charged particles can acquire high energy when they are repeatedly passed through an alternating electric field
The charged particle (say a positively charged proton) is released near mid point of the face of one of the Dees. Being in the electric field from one Dee to another, it is accelerated by the electric force in the direction of electric field. As the particle enters the adjoining Dee, the magnetic force, being perpendicular to it, renders the charged particle to move along a semicircular path within the Dee. By the time, it emerges again in the narrow gap separating the two Dees, the electrical polarity of Dees changes so that the particle is again accelerated again with an increase in speed.
The frequency of the oscillator is so chosen
that the time required to describe this semi-circle
corresponds to one half cycle. It is essential that
the resonance condition is maintained throughout,
otherwise the ions will not reach the gap in proper
phase to be accelerated. The ions go on travelling
until they reach the dees periphery and extracted
out through window.
Need:-To prevent the deviation of ion from ideal condition.
Focussing:-Essential thing in operation of cyclotron is resonance condition. To prevent the deviation of ion from ideal condition, restoring forces are applied in such a way that the ions are brought back to median plane. These forces are provided by shaping the pole pieces of main magnet such as to reduce the magnetic field from centre outwards. The central field is little more than ideal condition and peripheral field is little less. The component of M.F. toward centre of Dees keeps the particle in a circular orbit and component toward median plane helps in median plane focussing. Larger the deviations from the median plane, larger will be the vertical restoring forces.
Betatronis a device for speeding up electrons to very high energy by expanding magnetic field. It is perfect example of reality of induced electric fields.
Based on principle of electromagnetic induction an alternating current applied to ‘primary coil’ induces a similar current in the ‘secondary coil’ windings. The primary current produces an ‘oscillatory magnetic field’. This field, in turn, induces an ‘oscillatory potential’ in the secondary coil.
Electrons from the electron gun are injected into doughnut shaped vacuum chamber when the magnetic field is just rising from its zero value into the first quarter cycle.
The electrons now make several thousands revolutions and gain energy
When magnetic field has reached its max.value,the electrons are pulled out from their orbit.
Either they strike a target and produce x rays or emerge from the apparatus through a window.
The maximum energy that a betatron can impart is limited by the strength of magnetic field due to saturation of iron and practical size of the magnet core.
It is a device used to accelerate electrons.
It consist of an electromagnet having annular pole pieces and a doughnut (ring) shaped vacuum chamber which is usually made of glass or ceramic.
The doughnut is placed be tween the pole pieces. The interior part of doughnut is coated with silver or copper to give a resonance cavity .
A very small gap in cavity divided it into two parts and very high frequency electric field is applied across the gap at the proper time in the magnetic cycle. When accelerator is on the electron is accelerated each time it crosses through the resonator.
Now if the potential applied to the resonator at the proper frequency, the electrons are all kept in phase and receive increment of energy at each revolution as they pass through the cavity.
It consists of ring shaped magnet having four quadrants produces normal magnetic field to the doughnut shaped vacuum chamber the orbit radius is held constant by means of a magnetic field that increases with time.
The doughnut chamber is made up of steel or plastic. The doughnut chamber is supported in the gap of annular ring. The magnetic field is applied over four quadrants only and straight sectrons are kept free from magnetic field to be used for injection, acceleration and ejection of particles.
The proton initially is accelerated upto 10Mev in a linear accelerator and is then injected into the doughnut tube, when the magnetic field is small.
The pressure in the doughnut tube is about 1/10⁶ mm of Hg to reduce the loss of proton beam by gas scattering.
The proton recevies an impulse of about 1KV per turn through r.f. supply.
Due to the protons gain energy, its frequency increases gradually.
Since protons are heavier mass particles, their energies for a relativistic velocity will be very high say 5Bev .
In proton synchrotron, the protons could be accelerated to energies of the order of multi Bev.
When protons reach their maximum energy, the oscillator frequency is distorted so that the orbit expands or contracts and the protons strike the target.