Dr. Abdul Ahad
Dr. Abdul Ahad
Dr. Abdul Ahad
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An Overview of 5MV<br />
Pelletron Accelerator at<br />
NCP<br />
<strong>Dr</strong>. <strong>Abdul</strong> <strong>Ahad</strong>
Contents<br />
• Electrostatic Accelerators<br />
• 5UDH-2 Pelletron at NCP<br />
– introduction<br />
– Control System<br />
– Ion Sources<br />
– RC43 Setup<br />
– RS61 Setup<br />
• Applications (Ion Beam Analysis)
Electrostatic Accelerators<br />
• True DC<br />
• Low Energy Spread<br />
• Current<br />
• All Masses<br />
100% duty cycle<br />
100e V to few KeV<br />
(1 MeV to 100’s s MeV)<br />
nano to micro amp<br />
(Mass independent)<br />
3
Electrostatic Accelerators<br />
Single Ended<br />
• Higher Currents<br />
• Ne, Ar, Xe<br />
• Less energy spread (microprobes)
Electrostatic Accelerators<br />
Tandem<br />
• Source, etc. outside accelerator tank<br />
• No molecular interferences - He++ vs. H2+<br />
• Flexibility – Multiple sources<br />
• Easy to upgrade<br />
• Higher E for Vt, especially for heavy ions<br />
THE NCP 5UDH-2 IS A TANDEM
Electrostatic Accelerators<br />
Belt Charging system<br />
Current transported by belt<br />
Characteristics of Ideal Belt<br />
- high resistivity<br />
- little stretch<br />
- moisture resistant<br />
- smooth surface<br />
- sufficient mechanical strength<br />
• Dust Generation
Electrostatic Accelerators
Electrostatic Accelerators<br />
• Pelletron charging System By NEC (1960)<br />
• Metal cylinders with rounded ends joined by nylon<br />
• Move at at bout 15 m/s<br />
• Delivers charging currents of 100 - 200 µA<br />
• motors are supported on movable platforms which<br />
are counterweighted, automatically providing proper<br />
chain tension
Electrostatic Accelerators<br />
Pelletron Chain<br />
• Spark damage well<br />
protected.<br />
• Better voltage stability.<br />
- High efficiency.<br />
- Insensitive to moisture.<br />
- Long life (50,000 hours).<br />
- Simple and reliable.<br />
- Go to over 30 MV
Pelletron Charging<br />
11
The NCP 5UDH-2 2 PELLETRON<br />
• 5 MV Terminal Voltage<br />
• Dual Ion Sources<br />
– SNICS II for wide range of light and heavy ions<br />
– RF-Charge Exchange for He<br />
• Beam currents<br />
– 5 – 10 microamps for most probable charge states,<br />
– 100's of pA for high charge state heavy ions<br />
• Energies<br />
– 10 MeV for Protons, 15 MeV for He++<br />
– Useful currents for heavy ions to over 50 MeV<br />
• 15 degree beamline for Materials Analysis<br />
• 30 degree beamline for Ion Scattering/Nuclear Physics<br />
13
The NCP 5 MV Pelletron
The NCP 5 MV Pelletron<br />
15
The NCP 5 MV Pelletron<br />
16
The NCP 5 MV Column<br />
17
Control system<br />
Control & Data<br />
Acquisition<br />
• LINUX based<br />
computer user<br />
interface<br />
• MCA CARDS for data<br />
acquisition<br />
18
Control system
Beam Energy<br />
• Tandem accelerates the negative ion to the<br />
positive terminal<br />
• Then strips to many charge states, Q<br />
• Each state picks up Q x MV<br />
• Total Energy = (Q+1)MV<br />
• Charge state probability depends on terminal<br />
voltage, ion mass, and stripper<br />
20
Beam Currents<br />
• The next slide shows the wide variety of<br />
beam energies and currents from a<br />
tandem at 3MV<br />
• Higher energies are possible in the 5UDH<br />
21
ION SOURCES<br />
• The purpose of the ions sources are to<br />
produce either positive or negative ions<br />
from neutral atoms of elements of interest.<br />
• the ions beams are injected to the<br />
accelerator tube for gaining high energy.<br />
23
SNICS II Ion Source<br />
• “Source of Negative Ions by Cesium<br />
Sputtering” from solid materials.<br />
• Cs ions from hot “ionizer” surface are<br />
accelerated to the cathode.<br />
• Cathode contains element (s) for beams.<br />
• Simple operation; rapid cathode change.<br />
• Currents up to 100's of micoramps<br />
depending on material.<br />
24
SNICS II Ion Sources
Principle Of Operation<br />
• Cs vapor comes from the cesium oven into<br />
an enclosed area between the cooled<br />
cathode and the heated ionizing surface.<br />
• Some of the cesium condenses on the<br />
front of the cathode and some of the<br />
cesium is ionized by the hot surface.<br />
26
Cont..<br />
• The ionized cesium accelerates towards the<br />
cathode, sputtering particles from the cathode<br />
through the condensed cesium layer.<br />
• Some materials will preferentially sputter<br />
negative ions.<br />
• Other materials will preferentially sputter neutral<br />
or positive particles which pick up electrons as<br />
they pass through the condensed cesium layer,<br />
producing negative ions.<br />
27
SNICS II Ion Sources<br />
28
Alphatross Ion Sources
RF Charge Exchange Source<br />
30
Operation Principle<br />
• There are two main components in this device.<br />
The first one is the radio frequency positive ion<br />
source.<br />
• Helium gas is bled into a quartz discharge bottle<br />
through a metering valve to maintain a pressure<br />
of 10-50 millitorr.<br />
• An RF oscillator induces a plasma in the bottle<br />
which is intensified by the solenoid magnet.<br />
31
Cont..<br />
• A DC potential is applied across the<br />
plasma by probe power supply.<br />
• This potential extracts ions from the<br />
plasma and accelerates them through the<br />
Ta exit canal.<br />
• Then they enter the charge exchange<br />
chamber.<br />
32
Cont..<br />
• The charge exchange is the second main<br />
component of the Alphatross.<br />
• In it He + ions are neutralized by Rb vapor.<br />
• A few He atoms then undergo a 2 nd charge<br />
exchange reaction and become negative<br />
He ions.<br />
33
RF Charge Exchange Source<br />
Schematic<br />
34
15 Degree NEC RC43 Setup<br />
• RBS with channeling<br />
• Elastic Recoil Detection (ERD)<br />
– Surface hydrogen analysis<br />
• Nuclear Reaction Analysis<br />
(NRA)<br />
– Element specific analysis<br />
– E.g.:<br />
• 15N + H (Hydrogen depth<br />
profiling)<br />
• 4He + 16O (enhanced<br />
oxygen detection)<br />
• Particle Induced X-Ray<br />
Emission (PIXE)<br />
• Particle Induced Gamma<br />
Emission (PIGE)<br />
– Trace element analysis<br />
35
RC43 RBS Data Collection<br />
37
NEC RS61 Scattering System<br />
• Ion Scattering Studies<br />
• Nuclear Physics<br />
• Atomic Physics<br />
• Ion Implantation<br />
• Radiation Damage<br />
Studies<br />
38
5UDH-2 2 APPLICATIONS<br />
40
Ion Beam Analysis
Ion Beam Analysis<br />
• The 5UDH-2 accelerator systems is equipped for materials analysis with ion<br />
beams at MeV energies, using one or more of the following analytic<br />
techniques:<br />
• RBS (Rutherford Backscattering): for elemental depth profiling<br />
• Channeling: for measuring crystalline perfection and impurities in crystals<br />
• ERD (Elastic Recoil Detection): primarily for Hydrogen depth profiling<br />
• NRA (Nuclear Reaction Analysis): for measuring selected isotopes with<br />
enhanced sensitivity<br />
• PIXE (particle Induced X-Ray Emission): for trace element analysis
Rutherford Back Scattering (RBS)<br />
• Rutherford scattering is simple, central force,<br />
elastic scattering.<br />
• The effects of nuclear reactions are avoided by<br />
operating at beam energies below the Coulomb<br />
barrier.<br />
• This is basically billiard ball scattering.<br />
Kinematices and absolute cross sections can be<br />
calculated directly from first principles.
Rutherford Back Scattering (RBS)<br />
• The thickness of the surface layer is determined<br />
from the energy width of the surface peak, using<br />
standard dE/dx energy loss calculations.<br />
• The elemental concentration as a function of<br />
depth can also be determined from the number<br />
of counts as a function of energy for both the<br />
surface layer and the substrate.<br />
• Channeling Measures crystal perfection, which<br />
is especially valuable in silicon technologies.
PIXE<br />
• Non-destructive, quantitative analysis of heavier<br />
elements.<br />
• Generally used for trace element analysis 1-100ppm.<br />
• Identify high-Z elements (11
PIXE<br />
• Protons at an energy of a<br />
few MeV are used to<br />
excite the atoms in a<br />
sample.<br />
• The excited atoms emit<br />
characteristic X-rays.<br />
• The energy of the X-ray<br />
identifies the element<br />
from which it came, and<br />
the number of X-rays of a<br />
given energy is a<br />
measure of the element’s<br />
concentration.
PIXE<br />
• Probed depth tens of µm.<br />
• Sensitivity up to 1ppm.<br />
• Accuracy 10%.<br />
• Higher signal to background ratio as<br />
compared to electron beam induced x-ray<br />
spectroscopy.<br />
• Low velocities changes as compared to<br />
electron, hence no bremsstrahlung.<br />
• PIXE is 100 times more sensitive than EDX.
Thanks<br />
48
Control & Data Acquisition<br />
• Control & Data<br />
Acquisition<br />
• LINUX BASED COMPUTER<br />
CONTROLLED SYSTEM<br />
• MCA CARDS<br />
• Data Analysis Software<br />
• RUMP FOR RBS/ERDA<br />
SPECTRUM ANALYSIS<br />
• GUPIX FOR X-RAY<br />
SPECTRUM ANALYSIS<br />
• SIMNRA FOR NUCLEAR<br />
REACTION ANALYSIS<br />
49
Ion Beam Analysis
RBS<br />
E o<br />
E<br />
E=KEo