The document discusses a Pelletron tandem accelerator. A Pelletron uses a chain of metal pellets and insulating connectors to generate a high voltage on its terminal, allowing for tandem acceleration of ions. It operates similarly to a Van de Graaff generator but can achieve higher voltages and currents. Ions are produced, accelerated twice in opposite directions, steered, and directed into scattering chambers. Applications include materials analysis, medical uses, and industrial processes like radiation production and sterilization.

1. PELLETRON
( TANDEM ACCELERATOR )
Hira Rafiq M.Phil. Department of Physics Q.A.U

2. HISTORY:
• The first accelerator was hand made in the late 1930’s, consisting of a copper sheet
hammered into place over a pine wood frame to form the terminal electrode.
• This hand-made accelerator was capable of approximately 2 MV in air,
depending upon the local weather conditions.
• Shown here is a “spark”, or electrical discharge, along one of the supporting columns
when the accelerator was operating at approximately 1.2 MV
• The next accelerator was a “modern” Van de Graaff accelerator, housed in the
Lafortune Building, which was the science building during the 1940’s.
• The FN Tandem accelerator was purchased and brought to the facilities in the late
1960’s
and has been the primary accelerator for the laboratory since that time.
It has been upgraded several times over the years, including new accelerating tubes,
new column resistors, and the installation a new charging system known as a
pelletron

3. INTRODUCTION:
• A pelletron is a type of electrostatic particle accelerator similar to a Van de
Graaff generator.
• Pelletrons have been built in many sizes.
• Small units producing voltages up to 500 kV and beam energies up to 1 MeV
of kinetic energy.
• Largest system, which has reached a DC voltage of over 25 megavolts and
produced ion beams with energies over 900 MeV.
• Built by the National Electrostatics Corporation
accelerator has 4 main components
 Ion production
 Two-Stage (tandem) acceleration of ions
 Steering of ions
 Scattering chambers

4. COMPARISON WITH VAN DE GRAAFF
• Compared to the Van de Graaff generator, the pellet chain
can operate at a higher velocity than a rubber belt.
• Both the voltage and currents that can be attained are far
higher.
• The chain is charged more uniformly than the belt of a Van
de Graaff.
• The stability of the terminal voltage and the particle
energy is also higher.

5. GENERATING ELECTRIC CHARGE
• Generating electric charge is done by a mechanical transportation system
made of a chain of pellets.
• Chain pellets are short conductive tubes connected by links made of
insulating material that is used to build up high voltages on the Pelletron
terminal.
• For example in tandem acceleration of ions:
• The negative ions are accelerated toward the center of the pressure tank by a
difference in potential.
• The center of the pressure tank is made positive with
respect to the charge exchanger.
• The potential difference is developed by the Pelletron
Charging system, which consists of metal pellets and
insulating connectors.
The terminal is charged by induction and is a very stable and
reliable system.

6. • The chain is housed inside of this tank.
• The terminal is in the center.
• From right edge of the photo to the terminal is where P.D is applied.
• A Nitrogen gas is bled from the left end of the photo to the terminal
to pull off the added electron in another charge exchange collision.
• The resultant positive particle is accelerated away from the terminal
towards the left edge and thus produces the tandem acceleration.
• The charging chain for high voltage generation exhibit an excellent
voltage stability, a high reliabilty and a long lifetime (over 50 000
hours).
terminal

7. THE ACCELERATOR – WHAT’S INSIDE THE TANK…
Low Energy ColumnHigh Energy Column Terminal

8. Accelerating Rings Pellet
Inductor

9. EXPLANATION BY A VIDEO:

10. WORKING:
1: HOW TO GET THE BEAM THROUGH THE TANDEM ACCELERATOR:
• In the case of a Tandem accelerator the terminal is charged to a positive
potential.
• This means that a negatively charged beam must be provided by some type
of external ion source and are accelerated from ground to the positively
charged terminal.
• The advantage of doing things this way is that one can get “two accelerations
for the price of one”.
• The new positively charged ions experience a second boost of acceleration
(hence the name ‘Tandem’ accelerator) as they exit the terminal and travel
down the acceleration tube to ground at the high-energy end of the
machine.

11. 2:MAKING BEAMS FOR THE TANDEM:
• Negatively charged beams for use in the
Tandem are produced by ion sources outside
the accelerator.

12. ILLUSTRATION OF THE BEAM:

13. 3: THE STRIPPER FOIL:
• A thin carbon foil is placed in the beam tube at the center of
the terminal. As the negatively charged beam strikes the foil (at
fairly high energy), electrons are stripped from the ions, leaving
them positively charged.
• Inside the terminal is a stripper, which uses a gas canal (usually
nitrogen) or a very thin carbon foil (areal density about 3
µg/cm2) to remove electrons from the incoming negative ions.
• The resulting kinetic energies T of the beam depend on the
charge q of the positive ions,
T = eU + qU = (e + q)U
• The positive charge q of heavy ions can
be multiples of e. Thus the maximum possible kinetic energy
depends on the ions, e.g.,
p, d : T = 2 eU
32S16
+ : T = 17 eU
•
Positively Charged
Beam Exits the
Stripper Foil
3 mg/cm2
Carbon
Stripper Foil
Negatively Charged Beam
Enters the Stripper Foil

14. 4: BASIC DIAGRAM OF THE FN TANDEM:
• The terminal is supported by a structure known
as the column, which is a sandwich of glass
blocks and metal planes. The column is held in place by
compression supplied by a huge spring.
The beam tubes are mounted along the side of the column.
• The resistors are actually mounted on the column instead of along the tube, and each plane of the
column is connected to the corresponding plane in the tube by a metal spring.
• The entire accelerator is housed inside a large steel tank that is pressurized to approximately 12.41
bar with an insulating gas to help prevent electrical discharges and to protect lab personnel.

15. 5: VOLTAGE CONTROL ,THE CORONA SYSTEM
• To be useful in nuclear physics, the particle accelerator must be
able to maintain an extremely constant accelerating voltage over a
very long period of time. Regardless of the method of charging the
terminal, it is necessary to devise a way to compensate for
variations in the terminal voltage due to charging inconsistencies,
minor discharges, etc. This is done in nearly all Van de Graaff
accelerators by using a coronal discharge system.
• This system consists of a set of very sharp needles mounted inside
a mushroom shaped electrode. The entire assembly is mounted on
a long rod through the wall of the pressure vessel so that the
needles can be moved close to or far away from the terminal
electrode.

16. 6: CORONA SYSTEM
• As the needles are moved toward the terminal, a coronal discharge is established, with a small amount of charge
continually flowing from the terminal to the tips of the needles, due to the breakdown of the electric field at the
very sharp points.
• This current flows from the needles through an electrical circuit that contains a “radio tube”, which acts as a
variable resistor. By controlling the amount of bias on the grid in the tube, we can either inhibit or enhance the
amount of current flowing through the needles.
• This can be done in a very rapid time frame, and by controlling the grid bias we can control the corona current,
and this allows us to account for variations in the terminal voltage.
• Note that this corona current tends to reduce the terminal voltage, and so must be replaced by the charging
current.

17. 7: MEASURING THE TERMINAL VOLTAGE
THE GENERATING VOLT METER
• The terminal voltage can be measured in real time by a device known as a
Generating Volt Meter.
• This device is mounted in the tank wall, and the rotor blades spin in front
of the stators, alternately covering and exposing the various stator plates.
• As the stators are exposed to the electric field of the terminal, an
electrical signal is generated that is proportional to the terminal voltage.
• In GV Control, the terminal voltage as measured by the Generating
Voltmeter is compared to the terminal voltage specified by the
experimenter via a setting on the front panel.
• The difference between the measured voltage and the requested voltage
is used by the stabilizer to adjust the corona tube grid bias. For example, if
the measured voltage is too high, the stabilizer adjusts the corona tube
grid bias to allow more current to flow through the corona needles,
reducing the terminal voltage until it agrees with the requested value.

18. EXPLANATION BY VIDEO:
•

19. APPLICATIONS OF PELLETRON ACCELERATOR:
Pelletron accelerators are used as analytical tools in many fields e.g.
– Materials modification
– Ion implantation and ion beam mixing
– Materials analysis
– Rutherford backscattering spectroscopy (RBS),
– particle induced X-ray emission (PIXE),
– particle induced gamma ray emission (PIGE),
– nuclear reaction analysis (NRA),
– elastic recoil detection (ERD),
– resonance scattering analysis (RSA),
– accelerator mass spectrometry (AMS) and
– ion micro beam applications (µ-beam).
– Particle production
– Medical, security
– Radiation production
– X-ray imaging

20. INDUSTRIAL APPLICATION:
– Production of X-rays,
– Sterilization of medical products,
– Wire and cable cross-linking,
– Tyre and rubber pre-cure treatment,
– Shrink wrap sheet products,
– Thin films polymer cross-linking,
– Heat shrinkable tubing and plastics,
– Polymer tube cross-linking,
– Bulk polymer modification,
– Sheet foam materials,
– Silicon wafer processing,
– Specialty automotive wire,
– Food irradiation,
– Purification of gases,
– Treatment of waste water and toxic wastes,
– Advanced composites modification and
– Scissioning of long chain polymers.

21. PELLETRON
NOW
A DAYS:

22. CONCLUSION:
• The FN accelerator was installed in 1968. The accelerator works under the same concept of a Van de Graaff
generator. The accelerator starts with the ion source. The ion source sends negative ions in a vacuum towards
the accelerator.
• In the accelerator there is a centralized metal electrode known as the terminal. The terminal is charged
to a very high positive potential. The negatively charged ion beam is accelerated towards the
positively charged terminal.
• Just as the ion beam is about to enter the terminal it passes through a thin carbon foil. The carbon foil strips
the electrons from the ion beam. The ion beam is now positively charged as it enters the terminal. The
terminal is now repelling the positive ion beam out the opposite side of the accelerator.
• It is a tandem accelerator because there are two points of acceleration. Before passing through the carbon
foil and after passing through the carbon foil.
• The accelerator is housed in a steel tank . This is so that the high voltage surfaces are isolated
from the outside world. This keeps the surfaces of the accelerator from discharging.
• The system that charges the terminal uses a "Pelletron chain" in the same way that a Van de Graaff generator
uses a belt to charge itself. After the leaving the accelerator, the beam can be steered through the use of
magnets. The beam is steered through the next room, past it, and into the next room. At the end the beams
smashes into the sample and the x-rays are detected.

23. END RESULTS BY DETECTORS:

24. REFERENCES:
• www.pelletron.com
• J.D. Cockcroft and E.T. Walton, Proc. Roy. Soc. (London) A136 (1932) 229, A144 (1934) 704.
• H. Greinacher, Z. Phys. 4 (1921) 195.
• R.J. Van de Graaff, Phys. Rev. 38 (1931) 1919A.
• http://en.wikipedia.org/wiki/ParticleInduced_Xray_Emission (http://en.wikipedia.org/wiki/ParticleInduced_X-
ray_Emission)