International Workshop On Plasma Diagnostics & Applications

INTERNATIONAL WORKSHOP ON PLASMA DIAGNOSTICS & APPLICATIONS

IWPDA2009 2-3 July 2009

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Plasma focus device The dense plasma focus devices were developed by J.W.Mather in the USA and N.V.Filippov in former Soviet Union. It is a device which produces an electrical discharge in a rarefied gas with current that can vary from a few kA to several MA.

Mather type

Filippov type

1)insulator sleeve, 2)anode, 3)cathode, 4)current sheath 2

Importance and the goal - Dense

Plasma Focus:

Density: ~1025 m-3 Temperature: ~1keV -Plasma focus discharges hot plasma bunches and fast streams fast neutrons hard and soft X-rays energetic ions and electrons 3

Simulation and design of system -The three phase current sheath dynamic model by MATLAB

-input parameters

Results: anode length=14.8cm cathode radius=4.47cm current sheath velocity=10.86 cm/µs axial phase time=2.94µs

anode radius=1.39cm axial peak current=224kA radial motion time=0.013µs S factor =92.52 4

computed discharge current

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(a)

a) computed current sheath curvature at the end of breakdown phase b) simulated velocity of current sheath in the axial phase 6

Design of mechanical structure - The anode is a cylindrical tube with a length of 14.8cm, and a diameter of 2.78cm. - The cathode is in the form of a squirrel cage consisting 6 rods arranged concentrically around the anode with a diameter of 4.47cm, and a length of 14.5cm. - These electrodes are made of copper and they are mounted on a knife edge copper collector plate. 7

Design of mechanical structure -The Pyrex glass insulator with a length of 5.1 cm and a thick of 3mm slides over the anode - A thick Perspex disc is used as the insulator between collector plates. - The discharge chamber is a stainless steel cylinder of 26.5cm in internal diameter and 38cm height. - Upper cover of the cathode is a stainless steel plate with diameter of 34.5 cm. 8

Design

1-anode, 2-cathode bars, 3-lateral wall, 4-pyrex insulator, 5-knife edge cathode disc, 6-copper cathode disc, 7-perspex insulator disc, 8-anode brass disc, 9-lateral window, 10-vacuum chamber 9

Design -The vacuum system is intended for evacuation of the chamber up to pressure ~5×10-3 Torr and for puffing the working gases into the chamber with density ~ 1015-1017 particle/cm3. -The electrical structure is used for charging the capacitor up to the adjusted voltage, its discharging both through the discharge chamber, and in the case of necessity, from it to the ground. 10

Design -Energy is stored in 36µf, 16kV, and 100nH capacitor by charging up to 15kV. -Transfer of energy from capacitor to coaxial electrodes is made by a rail gap switch. -The rail gap is mounted directly on the top of the capacitor using parallel plate configuration. -This switch consists of three parallel 35.5 cm electrodes which act as multiple spark channels. 11

1- plexi disc between anode and cathode plates, 2- soft robber, 3- cathode disc, 4- knife edge disc, 5- cathode bars, 6- anode, 7- rail gap switch, 8-coaxial cables, 9- upper cover of chamber, 10- control and command unit, 11-capacitor, 12- six lateral windows, 1312 pinhole camera, 14- gas puffing system

APF plasma focus device

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diagnostics The diagnostic systems consist of PC based oscilloscopes to record the output of the following diagnostics: - Rogowski coils to measure the current flowing into the anode and the current derivative signals. - NaI

scintillators and fast plastic scintillators followed by an appropriate photomultiplier to register neutron and HXR yields. - Pinhole camera with single and two emission zones to study SXR and HXR signals - Magnetic probes to study the dynamics of current sheath in the axial phase. -SXR spectrometer to X-ray spectroscopy in the range of 5-14 Å. 14

Experiments

Pinch current

current signals measured by a rogowski coil (I) Ar(11.5kV, 0.95torr) with high intensity plasma pinch , (II) Ar(11.5kV, 0.95torr) without plasma pinch( simple RLC) 15

Experiments

Focusing time

(a)- current signals (I)- Ar(11.5kV, 2 torr), (II)- Ar(11.5kV, 0.95torr), (III)- Ne(11.5kV, 1.2torr), (IV)- Ne(11.5kV, 2.5torr), (b)- Focusing

time

Ar : (I)- 11.5kV, (II)- 13.5kV

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Experiments

Pinch visible light

Visible light emitted by plasma pinch. a) Ar(11.5kV,0.95torr) b) Ar (14.5 kV, 2torr) c) Ne (11.5kV,1.2torr) d) Ne (14.5kV,2.5torr)

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Experiments

Insulator effect

Signals of current discharge (Ar,11.5kV, 0.95torr) with different insulator sleeve dimensions: (a)- (I) - L=4.8cm, DL=3.2cm, (II) - L=4.8cm, DL=3 cm, (III) -L=4.8cm, DL=3.4cm, (b)-(I)-L=6.5cm, DL=3cm, (II) - L=4.6cm, DL=3cm, (III)-L=5.2 cm, DL=3cm. 18

Experiments

Optimum pressure

(a)-Optimum pressure vs. applied voltage with Ar and Ne (b)- discharge current vs. applied voltage at the optimum pressure. 19

Experiments

HXR intensity

Time profile of HXR signals (I)-Ar(11.5kV,0.95torr) and Ne(11.5kV,1.2torr) (b): HXR intensity as a function of applied pressure when Ne puffed to the chamber 20

Experiments

HXR anisotropy

Angular distribution of HXR by APF plasma focus 21

Experiments

magnetic probe

As the current sweeps past the probe, the coils of magnetic probe will pick up a sudden increase.

(a) - Magnetic probe structure (b) - Setting positions of magnetic probes 22

Experiments

magnetic probe

recorded signals by three symmetric magnetic probes and discharge current signal with Ar (11.5kV, 0.95torr) 23

Experiments magnetic probe

recorded signals by three symmetric magnetic probes and discharge current signal with Ar (11.5kV, 0.95torr) 24

Experiments

Velocity of current sheath

the measurement of the passing time of current sheath through the magnetic probes Shots

Z (cm)

tfirst probe tsecondprobe tthird probe (µs)

(µs)

(µs)

Current signal

Average

behavior

velocity (cm/µs)

Shot-1

4.3

2.42

2.39

2.42

High intensity pinch

Shot-2

6.3

3.6

3.63

3.61

High intensity pinch

Shot-3

4.3

2.38

2.36

2.40

High intensity pinch

Shot-4

6.3

3.48

3.52

3.51

High intensity pinch

Shot-5

4.3

2.76

3.83

1.9

Weak pinch

Shot-6

6.3

3.91

4.32

2.1

Weak pinch

Shot-7

4.3

2.4

1.68

3.49

Simple RLC

Shot-8

6.3

2.1

4.2

4.8

Simple RLC

1.72 1.80 1.51 1.7 25

Experiments

intensity of HXR signals correlated with the magnetic probes signals

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Results -Variation of pinch current versus working voltages at the optimum pressure was obtained experimentally when we used Ar and Ne as working gases. -optimum pressure has an important effect on plasma pinch formation and when we applied non optimum pressures, intensity of plasma pinch was weak. 27

Results -Effect of the insulator sleeve length on plasma focus operation investigated by others and the experimental results by different diameters of insulator sleeve show that insulator diameter can influence on plasma pinch quality. -optimum pressure tends to increase as we tried to higher voltage levels for any of working gases. 28

Results -HXR signal intensity versus operating pressure, when Ne puffed into the chamber obtained among 20 shots at the nearly constant conditions. -Decrease of HXR intensity with the increase of working pressure was obvious. 29

Results -The distribution of HXR intensity shows a large anisotropy with a maximum intensity between 22.5o and 45o at the right hand and between -22.5o and 67.5o at the left hand. -The anisotropic distribution of HXR indicates that their origin isn’t due to a simple mechanism. 30

Results - when discharge resulted to a high intensity plasma pinch, the first peak of signals recorded by three magnetic probes occurred at the same time obviously. - when the first peak of magnetic signals registered at the different times, occurrence of plasma pinch disruption at the first peak of discharge current wasn’t observed. - there is a noticeable correlation between plasma pinch intensity and current sheath symmetry.

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Results

-velocity of current sheath computed by these recorded signals and average velocity of current sheath at this point obtained 1.68 cm/μs at the optimum condition. -in the case of a symmetric plasma layer formation between the electrodes, intensity of HXR signal is more intense than a bad shot which results to an asymmetric plasma sheath. 32

Results -Close correlation among plasma sheath symmetry, HXR intensity, and current signal behavior illustrate that not only quality of pinched plasma column influence on HXR yield, but also symmetry of plasma layer at the axial acceleration phase has a direct relationship with the yield of HXR. 33

Refrences [1] J. W. Mather, Dense Plasma Focus, Methods of Experimental Physics, Vol.9, Part B, Academic Press, New York, (1971), pp. 187-249 [2] J. W.Mather, Formation of high density deuterium plasma focus, Physics of Fluid, 8 (2) (1965), pp. 366377 [3] M. G. Haines, Dense Plasma in Z-pinches and the Plasma Focus, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and PhysicalSciences,300(1456) (1981), pp.649-663 [4] Y. H. Chen and S. Lee, Coaxial plasma gun in mode 1 operation,International journal of electronics, 35(3) (1973), pp.341-352 [5] S. Lee, T. Y. Tou, S. P. Moo, M. A. Eissa, A. V. Golap, K. H. Kwek, S. Mulyodrono, A. J. Smith, Suryadi, W. Usada, and M. Zakaullah, A simple facility for the teaching of plasma dynamics and plasma nuclear fusion, American Journal of Physics, 56 (1) (1988), pp. 62-68 [6] L. Soto, New trends and future perspectives on plasma focus research, Plasma Physics and Control Fusion, 47(5A) (2005), pp. 361-381 [7] H Bruzzone , D Grondona, Magnetic probe measurements of the initial phase in a plasma focus device, Plasma Physics and Control Fusion, 39(9) (1997), pp.1315–1326 [8] J. O. Pouzo, Application of the Dense Plasma Focus to Nuclear Fusion and Plasma Astrophysics, IEEE TRANSACTION OF PLASMA SCIENCE, 31(6) (2003), pp.1237-1242 [9] M. Mathuthu, T. G. Zengeni, and A. V. Gholap, The Three-Phase Theory for Plasma Focus Devices, IEEE TRANSACTION OF PLASMA SCIENCE,25(6) (1997),pp.1382-1388 [10] M. Habibi, R. Amrollahi, M. attaran, R. Etaati, Design, Construction and the First Experiments on the Amirkabir Plasma Focus (APF) Facility, Plasma Device and Operations, 16(3) (2008), pp.163-169 [11] M. Mathuthu, T. G. Zengeni, A. V. Gholap, Measurement of magnetic field and velocity profiles in 3.6 kJ United Nations University/International Center For Theoretical Physics plasma focus fusion device, Physics of Plasmas 3 (12) (1996),pp.4572-4576 34

 Thank You for Your Attention

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