Accelerators are devices that use electric and magnetic fields to accelerate charged particles to high speeds. There are several types including linear accelerators (LINACs), pelletrons, and cyclotrons. The document discusses the types of accelerators at IUAC New Delhi including a 1.7 MeV and 15UD pelletron accelerators and a superconducting LINAC. It provides details on how pelletrons and LINACs work, describing the use of electric fields to speed up particles. The LINAC at IUAC uses niobium quarter wave resonators cooled with liquid helium to achieve superconductivity and accelerate beams up to 250 MeV for research.

1. Accelerators

2. Layout of Presentation
Introduction
History
Types of Accelerator
LINAC
Pelletron
HCI

3. Types
Need
How

5. • To probe in to the structure of nuclei
(matter) using different energy beams
to study nature of matter.

6. Use of Accelerator
Research
Ion
implantation
Material
Characterization
Industrial
processing
Radiotherapy
Biomedical
purposes

7. Accelerators @ IUAC, New Delhi
Atom beam sputtering system: ~1.0keV
Low energy ion beam facilities: Few tens of
keV – MeV
1.7 MeV Pelletron Accelerator
15UD Pelletron Accelerator
Superconducting LINAC

9. Accelerators

10. Particle Accelerator:-
Any device that accelerates charged
particles to very high speeds using electric
and/or magnetic fields.
They all have the same three basic parts:
• Source of elementary particles or ions
• Tube pumped to a partial vacuum in which
the particles can travel freely
• Some means of speeding up the particles.

11. Electrostatic
Accelerators-
Cockroft-
Walton, Van
de Graaff
Induction
Accelerators
-
Betatron
Types
RF
accelerators-
LINAC,
Cyclotron,
Synchrotron

12. Development of
Accelerators

13. 1870
• William Crookes- Cathode rays
1895
• J.J. Thomson- Electrons.
1896
• Röngten- X-rays
1909
• Rutherford- Scattering of alpha particle on a gold foil
1929
• E. O. Lawrence- Cyclotron (circular device)
1931
• Robert Jemison Van de Graaff - Van de Graaff accelerator
1932
• John D. Cockcroft and Ernest Walton- Cockroft-Walton
generator
1940
• Donald W. Kerst - Betatrons

14. Van de Graff Accelerator
 Builds up a potential
between two electrodes
by transporting charges
on a moving belt.
 Charges are mechanically
carried by a conveyor
belt from a low potential
source to a high potential
collector.
 Van de Graaff
accelerators can
accelerate particles to
energies as high as 15
MeV.
 Capable of producing
particles of higher energy
than the energies
of radioactive decay.

15. PELLETRON
ACCELERATOR

16. Pelletron - 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)
Beam energies-up to 1 MeV of kinetic energy, to the
Largest system DC voltage- over 25 MV
Beam energies- over 900 MeV

17. The IUAC Pelletron
- ve Ion Source
Injector Magnet
Terminal
Analyzing Magnet Switching Magnet
Buncher
Ion
Source
Room
Tower
Vault
Beam Hall
Tank
Radio-biology
Atomic Physics
HIRA
Materials Science
GDA
Scattering
Chamber
Tank ht: 26.5 m
Diameter: 5.5 m
Pressure: 86 PSI
of SF6 gas
Ions accelerated:
H to Au beams
Ion Currents:
Typically
5 - 50 pnA
Energy : 30 -
250 MeV

18. Generating electric charge is done by a mechanical
transportation system made of a chain of pellets (short
conductive tubes connected by links made of insulating
material), that is used to build-up high voltages on the
Pelletron terminal.

19. The system is enclosed by a pressure vessel filled with
insulating gas , such as SF6 (sulfur hexafluoride), and an
evacuated beamline. The potential difference between the
terminal and ground is used to accelerate several kinds of
particles, such as positron, electrons and negative and
positive ions.

22. Comparing with Van de Graaff Generator
Compared to the Van de Graaff generator, the pellet chain can
operate at a higher velocity than a rubber belt, and 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, so the stability of the terminal voltage and the particle
energy is also higher.

23. Applications of Pelletron Accelerators
Pelletron accelerators are used as analytical tools in many
fields, including -
• Materials analysis,
• Nuclear physics,
• Semiconductor development and production,
• Pharmaceutical research, and as
• Ultra-sensitive mass spectrometers for carbon dating
and the
• Measurement of other rare isotopes.

24. Linear Accelerators
The Principle : Rolf Widroe
• In Linear accelerators the charged particle receives several
small energy kicks in acceleration gaps between drift tubes that are
powered by a radio frequency voltage source.
• The length of the drift tubes is so adjusted that the time taken by the
particle to traverse a drift tube is integral multiple of half RF period.
• The Drift tube length is thus particle velocity dependent and increases
with particle energy.
• Very high particle
energies can be achieved
through multiple
acceleration.
SLAC : 25 GeV electrons
ILC : 250 GeV electrons L=v/2f
L

25. Linear Accelerators
The Principle : Alvarez
 The Widroe structure becomes inefficient at high frequencies due to
dissipation of electromagnetic energy.
 Alvarez structure is enclosed in a metallic tank to form a resonant
cavity.
 Unlike the Widroe structure the drift tubes are passive structures
and the accelerating field arises from the electromagnetic radiation
flooding the tank.
L
L=v/f

26. Linear Accelerators
Superconducting Linear Accelerators
Why Superconductivity ??
Q
EUω
P
P
U
Q
cycleRFperdissipatedEnergy
StoredEnergy2π
(Q)FactorQuality
2
a00
0ω




Suppose, stored energy = 0.1 J/(MV/m)2 &  = 2  x 108 Hz
the resonator @ room temp, Q = 10000
to generate a field of 1 MV/m Power ~ 6 KW
the resonator @ LHe temp, Q = 108
to generate a field of 1 MV/m Power ~ 0.6 W

27. Linear Accelerators
Superconducting Linear Accelerators
Why Superconductivity ??
However
From the concept of efficiency of Carnot Cycle,
The electrical power required at R.T.(300K) to remove
1 watt heat at 4.2 K (Refrigeration)
= (300-4.2)/4.2 = 70 watts
Assuming refrigerator efficiency = 0.2 (i.e. 20%)
Power required to keep LHe @ 4.2K ~ 70 x 5 ~ 350 watts
So, power required to produce 1 MV/m field inside the
SC resonator = 350 x 0.6=210 Watts << 8 KW of power for
R.T. QWR

28. Linear Accelerators
Materials for Superconducting LINAC
 Requirements
• High critical temperature (Tc)
• High Critical magnetic field (Hc)
• Good machinability
Niobium Lead
Hc 1980G 803G
Tc 9.2 K 7.2 K
Rs 7x10-9 W 3x10-8 W
@4.5 K, 150 MHz

29. Linear Accelerators
Alternatives Materials to bulk Niobium
Nb3Sn
• Tc 18.2 K
• Hc 5350 G
 Cavities are formed by vapor diffusion of tin into Niobium
 Fields achieved are of the order of ~15 MV/m
Niobium thin film sputtered on copper
High Tc Superconductors
 Performances deteriorate at high fields.
 Fields achieved are of the order of ~15 MV/m

30. Linear Accelerators
The Superconducting Quarter wave
Resonator at IUAC
Material - Niobium (inside)
Stainless Steel(outside)
Bath cooled by LHe (4.2 K)
Four important ports on QWR
to put power (coupler)
to take back small amount
of power (pick up)
to pass the beam thru QWR
A niobium bellow acts as tuner

31. Linear Accelerators
The Superconducting Quarter wave
Resonator at IUAC
Frequency 97MHz
Length of central conductor
~l/4
TEM mode, EM wave
propagation along the length
High voltage at the open end,
high current at the shorted end.
bopt0.08, distance between
the mid points of the two gaps:
d boptl/2

32. Linear Accelerators
The Superconducting Linac

33. Beam Acceleration through Linac: Bunching
•Beam is bunched before injection into Linac
•Bunch width ~ 200ps.
•Bunching in two steps:
Pre-tandem buncher ~ 1.5ns
Post tandem superbuncher ~ 200ps.
• Bunching : Velocity modulation, retard the early arriving particle
and accelerate the late arriving particle.
Time
Early
On Time
Late
Voltage
+
-
+ ve particles

34. Beam Acceleration through Linac: Acceleration
• Acceleration is done @ 70° phase angle for phase stability
Time
Early
On Time
Late
Voltage
+
-
+ve particles

35. Beam Acceleration through Linac: Energy Gain
• For a single Resonator:
If gap voltage is Vg &
q is the charge
Maximum energy gain= 2Vgq
However, the voltage is varying with time and a charged particle
takes finite time to cross the Resonator
Hence the actual energy gain is less that the maximum value
Transit time effect
Thus actual energy gain (DE)2Vg qT(b)
DEEa L q T(b)
Ea=2Vg/L is the accelerating field
L is the active accelerating length

36. Beam Acceleration through Linac:Energy gain
T(b) is the transit time factor and a function of particle velocity
Beta Vs TTF Plot for the IUAC QWR
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
0 0.04 0.08 0.12 0.16 0.2 0.24 0.28 0.32 0.36
Beta
TTF(Absolute)

37. Beam Acceleration through Linac:Energy gain
Further since acceleration is done at 70°phase angle the
energy gain is still lesser
Energy gain from one Resonator(DE)Ea  L q  T(b) Sinf
If there are N Resonators in Linac the total energy gain
Etotal=N DE

38. Beam Acceleration through Linac:Energy gain
For our linac, accl. Field Ea ~ 4 MV/m (say) @ 6 watts power
Accelerating length of QWR = 16 cm = 0.16 m
So if the linear accelerator contains contains 24 resonators,
total energy of the beam per charge state
Etotal /q = 24 x 0.64 x 0.8 x0.94 = 11.6 MV/q (assuming T(b)=0.8,
and f=70°)
Suppose from Tandem, O-beam of energy 100 MeV enters
into linear accelerator with a charge state of 8+ . Then
at the exit of the linac, the total energy will be
= 100 + 11.6 x 8 = 192.8 MeV

39. HCI

40. High Current Injector : Motivation
High Current More Species
Present : Typically few nA
Aim : few hundred of nA
Noble Gases etc…

41. Major Components of HCI
HTS ECR Ion Source
(PKDELIS)
Room Temperature RFQ,
48.5 MHz
Room Temperature DTL,
97 MHz
Eout = 8 keV/amu
Eout = 180 keV/amu
Eout = 1.8 MeV/amu*
SC Low Beta QWR
Module, 97 MHz
b = 0.05
Design Value A/q  6

43. Bunching Technique
A dc/long bunch enters an RF cavity;
the reference particle is the one
which has no velocity change. The
others get accelerated or
decelerated. After a distance L
bunch gets shorter while energies
are spread: bunching effect.L

44. Radio Frequency Quadrupoles
Radio Frequency Quadrupoles (RFQ) is a Linear Accelerator for
high current low velocity ion beams which focuses, bunches and
simultaneously accelerates with the help of RF quadrupole fields
These accelerators follow the ion source and serve as injectors to
Widroe or Alvarez type Linacs.
The principles of operation of the RFQ were first presented by
two scientists (Kapchinsky and Teplyakov) from ITEP Moscow
in the former Soviet Union (now Russia) in the late 1960’s.
First practical RFQ was realized by LANL (then LASL) in
1980. This 425 MHz RFQ accelerated a 100keV proton beam to
640 keV.

45. Radio Frequency Quadrupoles
The Quadrupole Lens
+
-
+
-
N S
NS
Magnetic Quadrupole
Lens
Electric Quadrupole
Lens
Focusing in one plane, de-focusing in the other

46. Radio Frequency Quadrupoles
F F
F F
F
D D D F
D D D Horizontal
Vertical
A focusing RFQ

47. Radio Frequency Quadrupoles
RFQ with acceleration
Vertical electrodes
Horizontal electrodes
Vertical electrode
Horizontal electrode
Quadrupole
focusing field
Axial
acceleration
field

48. Radio Frequency Quadrupoles
Four Vane type RFQ
Capacitance between the vane tips, inductance in the intravane space.
Frequency depends on the cylinder dimensions. High frequency
structures (frequencies of the order of ~200MHz).
Each vane behaves as a resonator. Suitable for low energy protons.

49. Radio Frequency Quadrupoles
Four Rod type RFQ
Capacitance between the rods, Inductance with the holding bars.
Frequency independent of the cavity dimensions.
Each cell is a resonator. Low frequency structures suitable for very
low velocity heavy ions.

50. Radio Frequency Quadrupoles
Frequency: 48.5 MHz
Length : 4m
A/q : 7
RF power : ~100kW
8 keV/u  180 keV/u
The IUAC RFQ

51. Drift Tube Linac
Features

52. Tank Diameter 85 cm
Tank Length 38.5 cm
Operating
Frequency
97.000 MHz
A/q 6
Input Energy 180 keV/u
Output Energy 320 keV/u
No. of Cells 11
Prototype DTL Development
Chamber
Stem
Ridge

53. Transit Time Factor (TTF) Curve
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.04 0.08 0.12 0.16 0.2 0.24 0.28 0.32
Beta (v/c) ->
TTF(Absolute)
Beta = 0.060 (TTF~80%)
E/A ~ 1.8 MeV/u

54. Need of low beta module…

55. Parameter Value
b 0.05
f 97 MHz
U0 26 mJ
Features
Low Beta Cavity
SC low b module located so that it can accelerate beams from
HCI as well as Pelletron accelerator.