Global View of the Lee Model code S H Saw INTI International University, Nilai, Malaysia.

Global View of the Lee Model code

S H Saw

INTI International University, Nilai, Malaysia

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

3 kJ Plasma Focus Designed for International Collaboration


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


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


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 H2, D2, D-T, N2, O2, 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 .


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.


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


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


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


Numerical Experiments

• Range of activities using the code is so wide

• Not theoretical

• Not simulation

• The only correct description is:

Numerical Experiments


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


Firing the PF1000


Fitting PF1000 27kV-adjusting model parameters until computed current waveform matches

measured (after getting L0 correct)


PF1000 fitted results


PF1000: Yn Focus & Pinch Properties as functions of Pressure


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


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 Yn. They published their L0 as 20 nH

• Using their published current waveform and parameters we showed their L0 =33 nH

that their L0 was already at optimum

that lowering their L0 would be a waste of effort and resources


New General Insight- For every PF there is a

minimum L0 below which yield no longer increase

• It was thought that the lower L0 is the better would be the current and the yield

• Our NE showed that on the contrary every PF system has a minimum L0; no point trying to go below that- very expensive and will not increase yield

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


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.


Results from Numerical Experiments with PF1000 - For decreasing L0- from 100 nH to 5 nH

• As L0 was reduced from 100 to 35 nH - As expected– Ipeak increased from 1.66 to 3.5 MA– Ipinch also increased, from 0.96 to 1.05 MA

• Further reduction from 35 to 5 nH– Ipeak continue to increase from 3.5 to 4.4 MA

– Ipinch decreasing slightly to - Unexpected 1.03 MA at 20 nH, 1.0 MA at10 nH, and 0.97 MA at 5 nH.

• Yn also had a maximum value of 3.2x1011

at 35 nH.


Pinch Current Limitation Effect - (1/3)

L0 decreases higher Ipeak bigger a longer zp bigger Lp

L0 decreases shorter rise time shorter zo smaller La

L0 decreases, Ipinch/Ipeak decreases



• L0 decreases, L-C interaction time of capacitor decreases

• L0 decreases, duration of current drop increases due to bigger a

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



• A combination of two complex effects

– Interplay of various inductances

– Increasing coupling of C0 to the inductive energetic processes as L0 is reduced

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


Neutron yield scaling laws and neutron saturation problem

• One of most exciting properties of plasma focus is

• Early experiments show: Yn~E02

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

• However quickly shown that as E0 approaches 1 MJ, a neutron saturation effect was observed; Yn does not increase as much as expected, as E0 was progressively raised towards 1 MJ.

• Question: Is there a fundamental reason for Yn


Global Scaling LawScaling 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

y = 0.5x0.8

y = 0.001x2

0.0001

0.0010

0.0100

0.1000

1.0000

10.0000

100.0000

1000.0000

10000.0000

0.1 1.0 10.0 100.0 1000.0 10000.0 100000.0

Log Eo, Eo in kJ

Lo

gY

n, Y

n in

10^

10

High E0 (Low Eo)Mid Eo compile expts08 compiled dataPower ( High E0)Power ( (Low Eo))

• 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


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)


Fusion Wall materials testing at the mid-level of IFMIF: 1015 D-T neutrons per shot, 1 Hz, 1 year for 0.1-1 dpa-

Gribkov

IPFS numerical Experiments:


Fast capacitor bank 10x PF1000-Fully modelled- 1.5x1015 D-T neutrons per shot

• Operating Parameters: 35kV, 14 Torr D-T• Bank Parameters: L0=33.5nH, C0=13320uF, r0=0.19m

• E0=8.2 MJ• Tube Parameters: b=35.1 cm, a=25.3 cm z0=220cm

• Ipeak=7.3 MA, Ipinch=3.0 MA

• Model parameters 0.13, 0.65, 0.35, 0.65


Ongoing IPFS numerical experiments of Multi-MJ Plasma Focus


50 kV modelled- 1.2x1015 D-T neutrons per shot

• Operating Parameters: 50kV, 40 Torr D-T• Bank Parameters: L0=33.5nH, C0=2000uF, r0=0.45m • E0=2.5 MJ• Tube Parameters: b=20.9 cm, a=15 cm z0=70cm• Ipeak=6.7 MA, Ipinch=2.8 MA• Model parameters 0.14, 0.7, 0.35, 0.7

Improved performance going from 35 kV to 50 kV


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


Scaling further- possibilities• 1. Increase E0, however note: scaling

deteriorated already below Yn~E0

• 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 E0 and per unit V0.

• We next extrapolate from point of view of Ipinch


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

Model code


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


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


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


Latest development

Modelling

Ion beam fluence

Post focus axial shock waves

Plasma streams

Anode sputtered material


Ion beam post-pinch plasma stream calculationsSome preliminary Results- INTI IU-IAEA

collaboration


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.


Into the fusion era: Plasma focus for training/Research

(a) Experimental facility: TRPF1 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 measurementsSimple materials processing experiments


Into the fusion era: Plasma focus for research training

(b) Numerical Experiments codeTo complement TRPF• Computes dynamics and energy distributions• Plasma pinch evolution, size and life time• Post focus Ion Beam, plasma stream and anode sputtered materialConnection 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


(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


(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


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

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Global View of the Lee Model code S H Saw INTI International University, Nilai, Malaysia.

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