List of Research Projects
13 projects listed below as of 23.2.2009.
Projects 1-4 completed
1. Effect
of reduction of circuit inductance on plasma focus performance
S
Lee1,2,3, S H Saw2, P Lee3, R
1Institute for Plasma
Focus Studies,
2INTI
3Natural Sciences and Science Education,
National Institute of Education, Nanyang Technological University,
Singapore-637616
Status:
Completed: 2 papers published
Pinch
current limitation effect in plasma focus (This version includes an Erratum)
S. Lee and S. H. Saw, Appl. Phys. Lett. 92, 021503 (2008), DOI:10.1063/1.2827579
Numerical
Experiments on Plasma Focus Pinch Current Limitation
S
Lee, P Lee, S H Saw and R
2. Numerical
Experiments on a range of plasma focus machines to determine neutron scaling
Laws
1Institute for Plasma
Focus Studies,
2INTI
`Status:
Completed: 1 paper published
Neutron
Scaling Laws from Numerical Experiments (This
version includes an Erratum)
S Lee and S H Saw, J of Fusion Energy, DOI: 10.1007/s10894-008-9132-7
3. To develop numerical techniques for
determining plasma focus pinch current from measured discharge current
S
Lee1,2,3, S H Saw2, P Lee3, R
1Institute for Plasma
Focus Studies,
2INTI
3Natural Sciences and Science Education,
National Institute of Education, Nanyang Technological University,
Singapore-637616
4International Centre for
Dense Magnetised Plasmas, 00-908,
Status: Completed: 1 paper published:
Computing
Plasma Focus Pinch Current from Total Current Measurement
S. Lee, S. H. Saw, P. C. K. Lee, R. S. Rawat and H. Schmidt, Appl Phys
Letters 92, 111501 (2008) DOI:10.1063/1.2899632
4. Numerical experiments on megajoule plasma focus machines in relation to current, neutron scaling and saturation
1Institute for Plasma
Focus Studies,
2INTI
3Natural Sciences and Science Education,
National Institute of Education, Nanyang Technological University,
Singapore-637616
Status:
Completed: 1
paper published
Current
and Neutron Scaling for Megajoule Plasma Focus Machines
S Lee, Plasma Phys. Control. Fusion, 50
(2008) 105005
Neutron yield saturation in
plasma focus: A fundamental cause
S Lee Applied Physics Lett 95, 151503 _2009 published online 15 October
2009
5. Implementing
Oxygen in the Lee Model
M.
Akel1, Sh. Al- Hawat1 and
1Department
of Physics, Atomic Energy Commission,
2Institute
for Plasma Focus Studies,
The Lee Model [1] computes plasma focus
electrodynamics and produces realistic results of plasma focus properties and
radiation. As of August 2008 it was configured for Hydrogen, Deuterium, Helium,
Neon, Argon, and Xenon. This project implements Oxygen in the code. The
methodology includes extracting ionization energy data from sources such as
NIST; running corona-modeled sub-routines available on the IPFS website to
obtain thermodynamic data such as ionization curves, specific heat ratios and
effective charge numbers for Oxygen. These data are then fed into the latest
Lee code RADPF5.15 (or later versions) to enable plasma focus numerical
experiments to be operated in Oxygen. Additions to these experiments could be
optimizing line and SXR yields in Oxygen. The results could be included into
the websites of the collaborators’ Institutes or published with due reference
and credit given.
Reference
[1] S Lee, Lee Model Radiative Plasma Focus computation package in:
http://www.plasmafocus.net/IPFS%20folders/modelpackage/UPF.htm
Status: On-going
6. Implementing
Nitrogen in the Lee Model:
M.Akel1, Sh. Al- Hawat1
and
1Department
of Physics, Atomic Energy Commission,
2Institute for Plasma Focus
Studies,
The Lee Model [1] computes plasma focus
electrodynamics and produces realistic results of plasma focus properties and
radiation. As of August 2008 it was configured for Hydrogen, Deuterium, Helium,
Neon, Argon, Xenon. This project implements Nitrogen in the code. It is known
that Nitrogen lines includes SXR suitable for studying the water window making
this gas of special importance for the study of biological samples. The
methodology includes extracting ionization energy data from sources such as
NIST; running corona-modeled sub-routines available on the IPFS website to
obtain thermodynamic data such as ionization curves, specific heat ratios and
effective charge numbers for Nitrogen. These data are then fed into the latest
Lee code RADPF5.15 (or later versions) to enable plasma focus numerical
experiments to be operated in Nitrogen. It is intended that this would lead to
experiments to optimizing line and SXR
yields in Nitrogen. The results could be included into the websites of the
collaborators’ Institutes or published with due reference and credit given
Reference
[1] S Lee, Lee Model Radiative Plasma Focus computation package in:
http://www.plasmafocus.net/IPFS%20folders/modelpackage/UPF.htm
Status: On-going
7. Optimizing Line (and SXR) Yields in Nitrogen Through Numerical
Experiments:
M.Akel1,
Sh. Al- Hawat1 and
1Department
of Physics, Atomic Energy Commission,
2Institute for Plasma Focus
Studies,
At some stage in the implementation of
Project 2, it is logical for the project to move on to numerical experiments
for the optimization of line and SXR yields from the AECS plasma focus. To do
this it would be necessary to discriminate the SXR yields by assessing the
temperature range at which line yields are predominantly He-like and H-like. A
matrix of operational and tube parameters including pressure, anode length and
radius needs to be drawn up to ensure systematic numerical experiments covering
all relevant ranges of parameters. The results could be included into the
websites of the collaborators’ Institutes or published with due reference and
credit given.
Status: On-going
8. Pinch Current and
Radiation Yield Limitation Effects in Nitrogen Through Numerical Experiments:
M.Akel1,
Sh. Al- Hawat1 and
1Department
of Physics, Atomic Energy Commission, Damascus, P.O. Box
6091,
2Institute
for Plasma Focus Studies,
Experiments on the AECS Plasma Focus have
shown that its performance in terms of discharge current is inadequate. This
has been confirmed by numerical experiments using the Lee model. All evidence,
laboratory and numerical, point to the need to reduce the inductance of the
AECS capacitor bank circuit. Recent published work [2] has however shown that
for each capacitance there exists a lower limit of inductance below which any
further decrease of inductance would not increase plasma focus performance (in
terms of pinch current and neutron yields). Since the cost of technology
increases with decreasing inductance, it is then prudent to compute this lower
limit of inductance in order to minimize the cost of this technological
feature.
This collaborative project is to establish
that this pinch current limitation also applies to nitrogen line and SXR
yields. As in an earlier project (3 above) it is necessary to assess the
temperature range at which line yields are predominantly He-like and H-like. A
matrix of operational and tube parameters including bank circuit inductance,
pressure, anode length and radius needs to be drawn up to ensure systematic
numerical experiments covering all relevant ranges of parameters. The results
could be included into the websites of the collaborators’ Institutes or
published with due reference and credit given.
Reference
[2]: S Lee and S H Saw,
APPLIED PHYSICS LETTERS 92, 021503 _2008_
http://www.plasmafocus.net/IPFS%20folders/Papers/PP1Published%20APPLAB922021503_1witherratum.pdf
Status: On-going
9.
Modelling of plasma focus with
admixture operation
L.C. Tan1, P. Lee1,
S.V. Springham1, R.S. Rawat1 and
1Natural Sciences and
Science Education, National Institute of Education, Nanyang Technological
University, Singapore-637616
2Institute
for Plasma Focus Studies,
In the
recent research work done at Plasma Radiation Source Lab of NIE, it has been
shown that doping of deuterium with 2% krypton increases the soft x-ray and
neutron yield by an order of magnitude in miniature plasma focus device. These
are remarkable results and we need to get deeper insights into the physics of
plasmas for gas mixtures, for which we plan to modify the current Lee Code
which currently handles one gas as a time. The main objectives of this project
are to incorporate suitable modifications the Lee Code to simulate plasma
dynamics, plasma parameters and radiation yields, particularly the soft x-ray
and neutron emissions, for gas mixtures (especially that of krypton seeded
deuterium) to understand and explain the recent experimental results, and to
understand how the plasma parameters and radiation yield is affected by the
plasma discharge current and stored energy by collecting the current waveforms
and radiation yield result from various plasma focus machines operating at
different storage energies (ranging from few tens of joules to mega joules) and
simulating their results using the modified Lee code.
Status: On-going
10. Understanding
and optimizing operation of miniature plasma focus device using Lee model
Rishi Verma1, P. Lee1,
R.S. Rawat1 and
1Natural Sciences and Science
Education, National Institute of Education, Nanyang Technological University,
Singapore-637616
2Institute for Plasma
Focus Studies,
One of
major ongoing projects at Plasma Radiation Sources Lab of NIE/NTU is the
development of miniature plasma focus device, with the stored energy of about
200 J, as a portable neutron source. The electrical parameters of this device
are different from the other commonly used PF device in our lab with the
quarter time period of about 500 ns. The electrode assembly for this device has
to be optimized for maximising the radiation yield from this device. A greater
insight into the probable electrode assembly designed is obtained with the help
of Lee code. The device operation is optimized and future directions are
decided using the simulation results of Lee code to minimize the experimental
trials. We are now in the process of upgrading our miniature plasma focus
device with new low inductance capacitors with multiple switching for
repetitive operation which will change the electrical parameters again. The Lee
model is used to predict the possible changes in electrode assembly design and
operating pressure condition for optimized operation
Status: On-going
11. Optimising
the UNU/ICTP PFF for Neon soft x-rays
S Lee1,2,3,
S H Saw2, P Lee3, R
1Institute for Plasma
Focus Studies,
2INTI
3Natural Sciences and Science Education,
National Institute of Education, Nanyang Technological University,
Singapore-637616
The
UNU/ICTP PFF, a 3kJ plasma focus, was designed for demonstrating nuclear fusion
in Deuterium. Its 16 cm length is optimum to match its capacitor risetime of
just under 3 usec with a peak axial speed of close to 10cm/us which is optimum
for neutron production. This plasma focus has also been operated in various
gases including in Neon. For Neon a pinch temperature starting at 2.3*10^6 K is
optimum for SXR production. This corresponds to a peak axial speed of around 6
cm/us. This explains why when the standard UNU/ICTP PFF is run in Neon, in
order to get a good yield the focus current dip has to come significantly after
the peak current; ie with a deliberate time mismatch. The first phase of this
project involves numerical experiments to determine the anode configuration
which optimises the Neon SXR yield. For practical reasons associated with later
experiments the outer electrode is left unchanged. A second phase is to modify
the anode of an existing UNU/ICTP PFF accordingly. Experiments are then carried
out to check the results of the numerical experiments obtained in the first
phase.
Status: On-going:
One paper written
Optimizing UNU/ICTP PFF for neon SXR operation
S H Saw, P C K Lee, R
12. Neon
soft x-rays scaling laws through numerical experiments
S
Lee1,2,3, S H Saw2, P Lee3, R
1Institute for Plasma
Focus Studies,
2INTI
3Natural Sciences and Science Education,
National Institute of Education, Nanyang Technological University,
Singapore-637616
The neutron yield in
plasma focus machines has been the subject of study in numerous machines, from
small to very large. As a result scaling laws of neutron yield versus storage
energy as well as versus discharge currents and more importantly focus pinch
currents have been established both from measurements as well as from numerical
experiments. For SXR no such scaling law appear to have been attempted. This
project sets out to systematically map the SXR yield from plasma focus machines
with storage energies ranging from kJ to MJ to determine the scaling laws of
SXR yield in terms of discharge currents and focus pinch currents.
Status: On-going:
Two papers written:
Soft x-ray
yield from NX2 plasma focus- correlation with plasma pinch parameters
Numerical experiments on plasma
focus neon soft x-ray scaling
S Lee, S H Saw, P Lee and R
13. Neutron yield versus operating pressure
through numerical experiments and comparison with measured results
1Institute for Plasma Focus
Studies,
3Nanyang Technological University, National Institute
of Education,
4Comisión Chilena de
Energía Nuclear, Casilla 188-D, Santiago, Chile
5Center for Research
and Applications in Plasma Physics and Pulsed Power, P4,
Numerical experiments
are carried out, using the Lee model code, incorporating a beam-target
mechanism to compute the Yn versus pressure data of plasma focus
devices PF-400J and FN-II. The Lee model
code is first configured for each of these two machines by fitting the computed
current waveform against a measured current waveform. Thereafter all results
are computed without adjusting any parameters. Computed results of Yn
versus pressure for each device are compared with the measured Yn
versus pressure data.
Status:
Ongoing: one paper has been submitted to
Plasma Physics and Controlled Fusion
Numerical experiments on plasma focus neutron yield versus
pressure compared with laboratory experiments
S Lee , S H
Saw2 ,
L Soto, S V Springham, S P Moo
14. Imaging of the plasma focus for
referencing the Lee model code
S H Saw1,2, V
Vengadeshwaran2, Ahmad Shahrazi bin
1Institute for
Plasma Focus Studies,
3 Natural Sciences
and Science Education, National Institute of Education
Nanyang Technological
University, Singapore-637616
Plasma focus imaging has traditionally been used to interpret the radial
phase of the plasma focus, considering the radial implosion and the focus
pinch. It is important to refine the interpretation to include identification
of the shock front and magnetic piston and the reflected shock front to more
closely reference the physical measurements to numerical modeling.
The project will involve
the development of nitrogen laser (see project below) and a
state-of-the-art shadowgraphy system,
extendable to schlieren imaging; then to integrate such a system into the
plasma focus environment. The collection and proper sequencing of images and
Identification of features may require software techniques. Referencing
identified features to the model may require modifications to be made to the
modelling.
Status:
On-going
15. Development of a nitrogen laser and
shadowgraphy system
S H Saw1,2, Ahmad Shahrazi bin
1Institute for
Plasma Focus Studies,
3Natural
Sciences and Science Education, National Institute of Education,
Nanyang Technological
University, Singapore-637616
In this project a
nanosecond nitrogen laser, inclusive of electrical and optical components will
be developed and its output tested and measured for pulse width and energy. A code
for the numerical operation and optimization of the laser will also be
implemented. A triggered electric spark system will also be developed to
produce plasma shock waves. A nanosecond
shadowgraph system synchronized with the nitrogen laser as light source will be
developed. This shadowgraphic system will be used to study the shock waves emanating from the spark. With the aid of
delay units a time sequence of shadowgraphs
will be used to follow the shock waves.
Status: On-going
16 Study of advanced plasma focus systems
including high voltage and current-steps
S Lee1,2,3 S H Saw1,2 Y
1Institute for
Plasma Focus Studies,
3Natural
Sciences and Science Education, National Institute of Education,
Nanyang Technological
University, Singapore-637616
Recent intensive
numerical experiments carried out by the Institute for Plasma Focus
Studies have concluded that the axial phase dynamic resistance (a
constant over the whole range of small to large plasma focus devices) is the
cause of the observed neutron saturation for large plasma focus machines. Hence the necessity for large plasma focus devices to operate at high voltages to go
beyond the present current-saturation regimes. At the same time current-steps
will provide a much desired boost during the radial phase of the plasma focus
just when the increased dynamic resistance of the radial phase is tending to
depress the value of the pinch current.
In applying ultra high
voltages (e.g. 300 kV or more) the interaction of the various elements in the
circuit, e.g storage capacitance, static
inductance and bank resistance with
axial and radial dynamic resistances and the growing time varying tube
inductances may become more crucial to be understood, even without considering
that the high voltages may induce extraordinary machine effects. Furthermore
when current-steps are introduced, the interaction of the second bank , not
only with the plasma focus discharge and pinch but also with the first bank,
makes a parametric study of these two banks of further greater interest. The
Lee model code is ideally suited to study such circuit manipulations. Until
large scale technological installations are available, numerical experiments
remain the way for such studies.
Status: On-going
17 Comparative study of plasma focus
machines
S H Saw1,2,
1Institute for
Plasma Focus Studies,
2INTI
3Natural
Sciences and Science Education, National Institute of Education,
Nanyang Technological
University, Singapore-637616
The scalability of the
plasma focus is now well known, in terms of a constancy of energy density per
unit mass which applies to all plasma focus machines from the smallest sub-kJ
to the largest MJ devices. This means that over an energy range of some 10,000
times, the temperature of the pinched focused plasmas have a range of less than
10 times; indeed the smaller devices generally have a slightly higher temperature
than the larger machines due in part to
a larger, less efficient radius ratio c=b/a.
The significant difference going from small to larger machines is the
increase in size and lifetime of the focused plasma, which contributes to the
increase in yields, e.g, soft x-ray and neutron yields. This project will
collect in a comprehensive manner the configurations and data of as many
existing and past plasma focus devices as possible. Comparative analysis of the
data will be carried out to obtain among
other things: neutron and soft x-ray scaling with respect to device energies,
capacitor peak current and plasma current. This study will provide more data on effects including neutron saturation
or newer alternative concepts such as deterioration of neutron scaling laws.
Status: On-going
18 Model Parameters and variation with
pressure and machines
Sh. Al- Hawat1, M. Akel1,
Department of Physics,
Atomic Energy Commission,
2Institute for
Plasma Focus Studies,
4Natural
Sciences and Science Education, National Institute of Education,
Nanyang Technological
University, Singapore-637616
Experiments will be
carried out on machines at the SAEC and at INTI UC to fit measured current
traces and hence obtain model parameters for the various machines. These
experiements will give valuatble information on the variation of model
parameters with pressure and with machines
Status: On-going
19 Magnetic
field characteristics of the plasma focus
S H Saw1,2, Devi2 ,
1Institute for
Plasma Focus Studies,
3 Natural
Sciences and Science Education, National Institute of Education
Nanyang Technological
University, Singapore-637616
Magnetic probes will be
built and calibrated. A system for calibration of the magnetic field will be
set up. The probes will be used to characterise the plasma focus plasmas
Status: On-going