Global view of the Lee Model code

Global View of the Lee Model code

S H Saw

INTI International University, Nilai,

Malaysia

3 kJ Plasma Focus Designed for International

Collaboration

Seminar on Plasma Focus Experiments 2012,(SPFE2012), 12 th July 2012

S H Saw

Design of the UNU/ICTP PFF- 3kJ Plasma Focus System??


S H Saw

UNU/ICTP PFF- narrow trolley to fit ICTP lift???


S H Saw

The Code

• From beginning of that program it was realized that the laboratory work should be complemented by computer simulation.

• A 2-phase model was developed in 1984

• We are continually developing the model to its present form

• It now includes thermodynamics data so the code can be operated in H

2

, D

2

, D-T, N

2

, O

2

, He, Ne, Ar, Kr,Xe.

• We have used it to simulate a wide range of plasma focus devices from the sub-kJ PF400 (Chile) , the small 3kJ

UNU/ICTP PFF (Network countries), the NX2 3kJ Hi Rep focus (Singapore), medium size tens of kJ DPF78 &

Poseidon (Germany) to the MJ PF1000, the largest in the world.

• An Iranian Group has modified the model, calling it the

Lee model, to simulate Filippov type plasma focus .


S H Saw

Philosophy of our Modelling

• Experimental based

• Utility prioritised

• To cover the whole process- from lift-off, to axial, to all the radial sub-phases; and recently to post-focussed phase which is important for advanced materials deposition and damage simulation.


S H Saw

Priority of Basis

•

Energy consistent for the total process and each part of the process

•

Mass consistent

•

Charge consistent

• Connected to the reality of experiments


S H Saw

Priority of Results

•

Applicable to all PF machines , existing and hypothetical

• Current Waveform accuracy

•

Dynamics in agreement with experiments

• Consistency of Energy distribution

•

Realistic Yields of neutrons, SXR, other radiations;

Ions and Plasma Stream; in conformity with experiments

•

Widest Scaling of the yields

•

Insightful definition of scaling properties

•

Design of new devices ; e.g. Hi V & C-S

•

Design of new experiments


S H Saw

Philosophy, modelling, results and applications of the Lee Model code


S H Saw

Numerical Experiments

• Range of activities using the code is so wide

• Not theoretical

• Not simulation

• The only correct description is:

Numerical Experiments


S H Saw

PF1000

Lo nH Co uF b cm a cm z0 ro mW

33.5 1332 16 11.6 60 6.1

fm fc fmr fcr

0.13 0.7 0.35 0.65

Vo Po Mw A At/Molecular

27 3.5 4 1 2


S H Saw

Firing the

PF1000


S H Saw

Fitting PF1000 27kV-adjusting model parameters until computed current waveform matches measured (after getting L

0 correct)


S H Saw

PF1000 fitted results


S H Saw

PF1000: Y n

Focus & Pinch Properties as functions of Pressure


S H Saw

Plasma Focus- Numerical Experiments leading Technology

• Numerical Experiments- For any problem, plan matrix, perform experiments, get results- sometimes surprising, leading to new insights

• In this way, the Numerical Experiments have pointed the way for technology to follow


S H Saw

NE showing the way for experiments and technology

• PF1000 (largest PF in world): 1997 was planning to reduce static inductance so as to increase current and neutron yield Y n

. They published their L

0 as 20 nH

• Using their published current waveform and parameters we showed their L

0

=33 nH that their L

0 was already at optimum that lowering their L

0 resources would be a waste of effort and


S H Saw

New General Insight- For every PF there is a minimum

L

0 below which yield no longer increase

• It was thought that the lower L

0 the current and the yield is the better would be

• Our NE showed that on the contrary every PF system has a minimum L

0

; no point trying to go below thatvery expensive and will not increase yield

• This was a surprising result- and changes one frontier area of plasma focus technology


S H Saw

Determination of Pinch Current

• by fitting a measured current trace with reliable neutron yield to the computed current trace.

- by fitting a measured current trace with reliable neutron yield to the computed current trace .


S H Saw

Results from Numerical Experiments with PF1000

For decreasing L

0

- from 100 nH to 5 nH

•

As L

0 was reduced from 100 to 35 nH - As expected

– I peak

– I pinch increased from 1.66 to 3.5 MA also increased, from 0.96 to 1.05 MA

• Further reduction from 35 to 5 nH

– I peak continue to increase from 3.5 to 4.4 MA

– I pinch decreasing slightly to -

 1.03 MA at 20 nH,

Unexpected



1.0 MA at10 nH, and



0.97 MA at 5 nH.

• Y n also had a maximum value of 3.2x10

11 at 35 nH.


S H Saw

Pinch Current Limitation Effect - (1/3)



L

0 decreases

 bigger L p

 higher I peak

 bigger a

 longer z p



L

0

L a decreases

 shorter rise time

 shorter z o

 smaller

L

0 decreases, I pinch

/I peak decreases


S H Saw


•

L

0 decreases, L-C interaction time of capacitor decreases

• L

0 decreases, duration of current drop increases due to bigger a

 Capacitor bank is more and more coupled to the inductive energy transfer




S H Saw


• A combination of two complex effects

– Interplay of various inductances

– Increasing coupling of C

0

L

0 is reduced to the inductive energetic processes as

Leads to this Limitation Effect

Two basic circuit rules: lead to such complex interplay of factors which was not foreseen; revealed only by extensive numerical experiments


S H Saw

Neutron yield scaling laws and neutron saturation problem

•

One of most exciting properties of plasma focus is

• Early experiments show: Y n

~E

0

2

• Prospect was raised in those early research years that, breakeven could be attained at several tens of MJ .

• However quickly shown that as E

0 approaches 1 MJ, a neutron saturation effect was observed; Y n does not increase as much as expected, as E

0 was progressively raised towards 1 MJ.

• Question: Is there a fundamental reason for Y n


S H Saw

Global Scaling Law

Scaling deterioration observed in numerical experiments (small black crosses) compared to measurements on various machines (larger coloured crosses)

Neutron ‘saturation’ is more aptly portrayed as a scaling deterioration-

Conclusion of IPFS-INTI UC research

LogYn vs LogEo

10000.0000

1000.0000

100.0000

10.0000

1.0000

0.1000

0.0100

0.0010

0.0001

0.1

y = 0.001x

2

1.0

y = 0.5x

0.8

H ig h E 0

( Lo w E o )

M id E o

c o m p ile e xp t s

0 8 c o m p ile d d a t a

P o we r ( H ig h E 0 )

P o we r ( ( Lo w E o ) )

10.0

100.0

1000.0 10000.0 100000.

0

Log Eo, Eo in kJ

•

S Lee & S H Saw , J Fusion

Energy, 27 292-295 (2008)

•

S Lee , Plasma Phys. Control.

Fusion, 50 (2008) 105005

•

S H Saw & S Lee .. Nuclear &

Renewable Energy Sources

Ankara, Turkey, 28 & 29 Sepr

2009.

•

S Lee Appl Phys Lett 95 , 151503

(2009)

Cause: Due to constant dynamic resistance relative to decreasing generator impedance


S H Saw

Scaling for large Plasma Focus

Targets:

1. IFMIF (International fusion materials irradiation facility)-level fusion wall materials testing

(a major test facility for the international programme to build a fusion reactor)


S H Saw

Fusion Wall materials testing at the mid-level of IFMIF:

10 15 D-T neutrons per shot, 1 Hz, 1 year for 0.1-1 dpa-

Gribkov

IPFS numerical Experiments:


S H Saw

Fast capacitor bank 10x PF1000-Fully modelled- 1.5x10

15 D-T neutrons per shot

•

Operating Parameters: 35kV, 14 Torr D-T

•

Bank Parameters: L

0

=33.5nH, C

0

=13320uF, r

0

=0.19m

W

•

E

0

=8.2 MJ

•

Tube Parameters: b=35.1 cm, a=25.3 cm z

0

=220cm

•

I peak

=7.3 MA, I pinch

=3.0 MA

•

Model parameters 0.13, 0.65, 0.35, 0.65


S H Saw

Ongoing IPFS numerical experiments of Multi-MJ Plasma

Focus


S H Saw

50 kV modelled- 1.2x10

15 D-T neutrons per shot

•

Operating Parameters: 50kV, 40 Torr D-T

•

Bank Parameters: L

0

=33.5nH, C

0

=2000uF, r

0

=0.45m

W

•

E

0

=2.5 MJ

•

Tube Parameters: b=20.9 cm, a=15 cm z

0

=70cm

•

I peak

=6.7 MA, I pinch

=2.8 MA

•

Model parameters 0.14, 0.7, 0.35, 0.7

Improved performance going from 35 kV to 50 kV


S H Saw

IFMIF-scale device

• Numerical Experiments suggests the possibility of scaling the PF up to IFMIF mid-scale with a PF1000-like device at

50kV and 2.5 MJ at pinch current of

2.8MA


S H Saw

Scaling further- possibilities

• 1. Increase E

0

, however note: scaling deteriorated already below Y n

~E

0

•

2. Increase voltage, at 50 kV beam energy

~150kV already past fusion x-section peak ; further increase in voltage , x-section decreases, so gain is marginal

• Need technological advancement to increase current per unit E

0 and per unit V

0

.

• We next extrapolate from point of view of

I pinch


S H Saw

Scaling Plasma Focus from Ipinch using present predominantly beam-target in Lee

Model code


S H Saw

SXR Scaling Laws

• First systematic studies in the world done in neon as a collaborative effort of IPFS,

INTI IU CPR and NIE Plasma Radiation

Lab

• Scaling laws extended to Argon by AECS


S H Saw

Special characteristics of SXR-for applications

• Not penetrating; for example neon SXR only penetrates microns of most surfaces

•

Energy carried by the radiation is delivered at surface

• Suitable for lithography and micro-machining

• At low intensity - applications for surface sterilisation or treatment of food

• at high levels of energy intensity, Surface hammering effect;, production of ultra-strong shock waves to punch through backing material


S H Saw

Compression- and Yield- Enhancement methods

• Suitable design optimize compression

• Role of high voltage

• Role of special circuits e.g current-steps

• Role of radiative cooling and collapse


S H Saw

Latest development

Modelling

Ion beam fluence

Post focus axial shock waves

Plasma streams

Anode sputtered material


S H Saw

Ion beam post-pinch plasma stream calculations

Some preliminary Results- INTI IU-IAEA collaboration


S H Saw

6. Developing the most powerful training and research system for the dawning of the

Fusion Age .

Integrate:

6a the proven most effective hardware system of the UNU/ICTP PFF with

6b the proven most effective numerical experiment system Lee Model code with emphasis on dynamics, radiation and materials applications.


S H Saw

Into the fusion era: Plasma focus for training/Research

(a) Experimental facility: TRPF

1 kJ focus: 10 kV 20 uF 80 nH

Measurements:

• current, voltage sufficient to deduce dynamics and estimate temperatures

•

Fibre-optics, pin diodes; magnetic probes directly measure speeds, ns imaging

• SXR spectrometry, neutron counters & TOF, ion collectors for radiation & particle measurements

Simple materials processing experiments


S H Saw

Into the fusion era: Plasma focus for research training

(b) Numerical Experiments code

To complement TRPF

• Computes dynamics and energy distributions

• Plasma pinch evolution, size and life time

• Post focus Ion Beam, plasma stream and anode sputtered material

Connection with reality: through fitting computed current to measured current trace

Behaviour of plasma focus and yields as functions of pressure, gases, storage energies, circuit currents and pinch currents.

Carry out above experiments with any plasma focus.

Optimization of planned plasma focus


S H Saw

(a) The proven most effective 3 kJ PF system

The trolley based UNU/ICTP PFF 3 kJ plasma focus training and research system will be updated as a 1 kJ system


S H Saw

(b) The proven most effective and comprehensive

Model code

• Firmly grounded in Physics

• Connected to reality

• From birth to death of the PF

• Useful and comprehensive outputs

• Diagnostic reference-many properties, design, scaling

& scaling laws, insights & innovations


S H Saw

(b) Philosophy, modelling, results and applications of the Lee Model code


S H Saw

Global view of the Lee Model code - Institute for Plasma Focus Studies

The Code

Philosophy of our Modelling

Priority of Basis

Priority of Results

Numerical Experiments

PF1000

Firing the

NE showing the way for experiments and technology

L

Scaling for large Plasma Focus

IFMIF-scale device

Scaling further- possibilities

SXR Scaling Laws

Latest development

Into the fusion era: Plasma focus for training/Research

Into the fusion era: Plasma focus for research training

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Global view of the Lee Model code - Institute for Plasma Focus Studies