1

P. Kubes, D. Klir, J. Kravarik, K. Rezac,

Czech Technical University Prague,

Collaboration with teams from IPPLM Warsaw,

KI Moscow, TRINITY Troitsk, IHCE Tomsk

Transformation of the plasma column

during neutron production in plasma focus

discharge

2

Active study of plasma column during HXR and

neutron production in CTU Prague 2012 -2013

Transformation of the pinch structure during acceleration of the deutron

beams on PF-1000 in IPPLM Warsaw

Influence of the applied magnetic field on the pinch dynamic and

neutron emission on PF-1000 in IPPLM Warsaw and on PFZ-200

in CTU Prague

Study of implosion of deuterium with heavier gases and

generation of the MeV electron and ion beams on GIT-12

Study of the fusion neutrons on the laser system PALS and

tokamak COMPASS in Prague

3 3

Plasma source 1: PF-1000 IPPLM Warsaw, Poland Laboratory of Internatinal Centre for Magnetized Plasma

23 kV, 2 MA, 350 kJ, D-D reaction, D2 gas

neutron yield 1010-1012 ,

Source of deuteron beams

Ed ~20 – 300 keV

Nd ~1017 per pulse

Energy a few kJ in pulse

P. Kubes et al, IEEE TPS39,

(2011), 562-568

4

Neutron diagnostics

scintillator BC-408 + photomultiplier Hamamatsu

registration outside the chamber

HXRs – product of fast electrons, neutrons – product of fast deuterons

velocity of neutrons with energy 2.45 MeV ….. 2.16 cm/ns

5

Signals of HXRs and neutrons

side-on 900

downstream 00

upstream 1800

50 – 70 ns

1. neutron pulse

smaller anisotropy 2. neutron pulse

higher anisotropy

detectors in 7 m distance

HXR neutrons 7 m neutrons 16 m

-200 0 200 400 600 800 1000

ns

arb

itra

ry u

nit

s

8585n7u

8585n16u

energy distribution

6

Scenario of neutron production in PF

beam of fast deuterons:

1-10 keV heat the plasma, Ti above 1 keV due to Coulomb interaction

10-300 keV neutrons with probability 10-6

fusion neutrons

2-3 MeV

Dominant beam-target mechanism downstream

3 MeV

2.45 MeV

2 MeV

anode face

7

Interferometry – PF-1000 16 pictures in one shot (Dr. M. Paduch, E. Zielinska)

evolution of the plasma column during HXR and neutron emission E. Zielinska, M. Paduch, M. Sholz, Contrib. Plasma Phys. 51, 279-283 2011

system of 52 mirrors and prisms

0, 10, 30, 40, 60, 70, 90, 100, 120, 130, 150, 160, 180, 190, 210, 220 ns

reference beam

films dignostic beam

8

Different structures in the pinched column

plasmoids

helical tubes-

coalescence of

axial and toroidal I

living 120 n s

lobules – part of

toroidal tubes

prolapsed through

the surface

anode

cathode disc

3 cm

shot 9181_-21 ns

shot 9181_+99 ns

shot 9209_+91 ns

Existence of

toroidal currents and

poloidal magnetic fields

anode face

dense plasma

column

constriction

9

Correlation of interferometry and neutron diagnostics 1st HXR and neutron pulse

-28 ns -8 ns +2 ns 22 ns

2 steps:

transport of the plasma from boundary to the axis

formation of the plasmoid and its transport downstream

instant and region of HXRs ; 5-20 ns time delay of maximum neutrons after HXRs

region of neutron production

mean density 3x1024m-3

dimension ~ 2 cm

anode

10

2nd HXR and neutron pulse

Shot 8406, NY: 9×1010

1. evolution of m=0 instability

2. formation of the plasmoid in the

constriction

3. radial jets of the plasma from the

constriction and formation of

plasmoids in the neighbouring

column

3. explosion of the rests of the

constriction and plasmoids

130 ns 160 ns 180 ns 220 ns

0 200 400 600 800

ns

arb

itra

ry u

nit

s

HXR

neutrons 7 m

dow n, side, up

2 m side

anode

dense plasma column

11

Existence of closed toroidal currents and

their poloidal magnetic field ?

The toroidal currents with poloidal magnetic field are self-generated

during evolution of the pinch (magnetic dynamo)?

Conditions for generation:

transport of the plasma through magnetic field

inhomogeneities in densities, velocities and magnetic fields,

turbulences toroids, plasmoids

Experimental evidence by magnetic probes at PF-1000: 1. V. Krauz, K. Mitrofanov et al: PPCF 54 (2012) , 025010.

2. V. Krauz, K. Mitrofanov et al: EPL, 98 (2012) 45001.

12

Conclusions folowing from results obtained from B probes

1. Bz exists in front and in imploding current sheath

2. Bz onset correlates with formation of toroidal and plasmoidal

structures and Bz decrease correlates with decay of constrictions and

plasmoids

3. Values of Bz in the toroids and plasmoidal structures reache 6-8 T;

10-30% of B.

4. Neutron production correlates with changes of Bz

5. In z-pinch column exist the closed currents

6. Bz is component of poloidal magnetic field

7. Neutron production correlates with transformation of magnetic lines

Results were published: P. Kubes, V. Krauz, K. Mitrofanov, et al: PPCF 54 (2012), 105023.

It is possible to describe an evolution of magnetic field in PF ?

13

Dense magnetized plasma is example of magnetic confinement in

which poloidal magnetic field is self-generated and plays

important role in its dynamic.

Acceleration of fast electrons and ions correlates with

transformation and decay of internal magnetic fields.

The energy of produced fast particles increases with velocity of

transformations of internal structures and with velocity of

decay of magnetic fields.

Publication: P.Kubes: Scenario of Pinch Evolution in a Plasma Focus Discharge,

Plasma Phys. Control. Fusion 55 (2013), 035011.

Conclusion from interferometry and neutron diagnostics

on PF-1000 Possible scenario of magnetic field evolution in the plasma column

14

Possible scenario of magnetic field evolution

Dense plasma layer Current sheath

Toroid Toroidal disk

Plasma jet

Opposite currents

Layer of azimuthal current

constriction

1NP

2NP

15

anode

IzIt

Implosion of current sheath

1. Existence of toroidal current during plasma implosion

B and Bz helical current; I 20-30% Iz, sign of Bz

Azimuthal current I 1% Iz, sign of Bz

16

anode

Formation of toroids

2. Tearing of toroidal current into a few toroids

1. Tearing of the azimuthal current into toroidal loops It

2. Stable toroidal current stabilized with discharged current helical

form existence of poloidal component Ip

3. Opposite –Ip to Iz in axis

4. Existence of point B = 0

5. Toroidal current depresses implosion

6. Higher pressure near anode inject the plasma in the center of toroid

It

Ip

It >Ip

anode

IzIt

Implosion of current sheath

17

3. Transformation of toroid

into toroidal disk

anode

Formation of toroidal disk

1. Jet of plasma into helical B

2. Increase of plasma density in toroidal centre

3. Increase of the poloidal current Ip due to α effect

4. Existence of both closed currents It and Ip

Ip

anode

Formation of toroids

18

4. Transformation of toroidal

disk into plasmoid

Start of 1. neutron pulse

anode

Formation of plasmoids

1. Spontaneous transformation of poloidal and toroidal I and B .

2. Formation of the plasmoidal structure due to reconnection

of magnetic lines.

3. Pumping of energy into plasmoid through turbulent structures

4. Formation of intense closed currents

5. Production of 1. neutron pulse

anode

Formation of toroidal disk

19

anode

Stagnation after 1. neutrons

5. Decay of plasmoid and

continuation of 1. neutron pulse

1. Decay of plasmoid and closed internal currents

2. Plasma column expands

3. Penetration of the discharge current into column

4. Stabilization of the column with azimulhal current

5. Orientation of Ip ?

anode

Formation of plasmoids

20

anode

Evolution of instabilities

6. Start of instabilities

Formation of toroids and

toroidal disks

1. Tearing of the layer I into toroidal loops It

2. Stable toroidal current is stabilized with discharged current helical

form increase of Ip

3. Opposite component of poloidal component of the current in axis

4. Existence of point B = 0

5. Toroidal current depresses implosion

6. Higher pressure in neck injects the plasma in the center of toroid

analogy with plasma implosion

anode

Stagnation after 1. neutrons

21

anode

Formation of plasmoids

8. Formation of constrictions and plasmoids

Start of next neuron pulse

Jet of plasma into toroidal B

Increase of plasma density in toroidal centre

Existence of turbulence

Self-generation of the Ip due to α effect

Pinch in the axis region

Pumping of energy into plasmoid

anode

Evolution of instabilities

22

anode

Disintegration of constriction and plasmoid

9. Decay of constrictions and plasmoids

Production of next neuron pulses

1. Decay of closed currents and magnetic field

2. Production of neutrons due to reconnections and decay of magnetic

lines

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Possible scenario of pinch evolution

During pinch evolution the closed toroidal and poloidal currents and their B are

generated in forms of toroidal and helical structures.

These structures are compressed with discharge pinching current.

The toroidal structures depress the implosion and plasma from neighborhood

more compressed regions is injected into the center of toroids.

Plasma streams interact with Bp inside the toroids, are confined inside them and

form toroidal disks. During this process the turbulent structures are produced and

support dynamo effect.

The kinetic energy of plasma streams transforms into the magnetic energy in the

toroidal disk and in the final phase in the plasmoid.

The neutrons are produced during formation and dis-integration of plasmoids and

constrictions. The reconnection and decay of closed internal currents and their

magnetic fields contribute to the deuteron acceleration.

24

Influence of the tungsten evaporated in anode

on the pinch dynamic and on the neutron emission

anode

tungsten plate

ca

thode r

ods

MCP view

view of four X-ray PIN

Diagnostics:

multiframe interferometry, 16 figures, t=10, 20 ns

scintillation detectors 7m: 0°, 90°, 180°,

MCP filtered by polyster 10 m,

4 PIN in positions 0-3, 1.5-4.5, 3-6,6-9 cm

filtered with beryl

25

Conclusions from experiments with tungsten anode

a. 1% tungsten admixtures after 1. neutron pulse

b. neutron yield decreased to 40%

c. decrease of the mean energy of fast deuterons to 80% to 90 keV

d. reduction of the DD cross-section about 40%

e. lower velocity of transformations of the constrictions and the

plasmoids enabled the more detail description of the plasma

column evolution

f. Recombination radiation of tungsten makes possible its localization

26

Influence of applied magnetic field

on pinch dynamic and neutron emission on PF-1000 in IPPLM Warsaw

PF-1000 (2 MA) 20-50 mT

Compression ratio 10x => Bz≈ 2-5 T

the same order as the Bz which is generated spontaneously

Without application of permanent magnets

27

Conclusions which follows from application of magnetic field

on the pinch dynamic and neutron emission

on PF-1000 in IPPLM Warsaw

The magnetic field of permanent magnets of 40-70 mT was compressed 100times

to the value of 4-7 T.

This value is comparable with the magnetic field registered by magnetic probes.

This magnetic field decreases the total neutron yield to 20-50%.

The smooth, symmetry and stability of the plasma focus was increased.

The life-time of internal structures - plasmoids, constrictions and toroids or helicals

was increased and velocity of transformations was depressed.

The magnetic field dissipates from the dense column after evolution of instabilities

after 150-200 ns.

The anisotropy of fast deuterons producing observed neutrons is higher, the side-

on component is depressed

28

Conclusions which follows from application of magnetic field and tungsten anode

on the pinch dynamic and neutron emission

on PF-1000 in IPPLM Warsaw

HXR and neutrons are produced in correlation with formation and decay of

plasmoids and constrictions

The plasmoid formation is possible to interpret by confinement of the plasma

streams containing the current Iz associated with B with the Bp field in

toroidal or helical structures.

At this interaction, B increases in the centre, as Bt. Both components relax to

state of minimal energy, spheromak-like structure, plasmoid.

At the decay of the plasmoid, Bt in the central region decays, the plasmoid

expands due to released Bp.

During neutron production the reconnection of the magnetic lines occurs at the

increase and decay of internal closed magnetic lines.

Energy necessary for acceleration of electron and ion beams is delievered (i)

by kinetic energy of plasma beams injected to the plasmoid, which is partially

transformed into magnetic energy of plasmoids and (ii) by decay of magnetic

energy released at the expansion of the plasmoid and constriction

29

Thank you for your attention

30

1. D. Klir, P. Kubes, M. Paduch, T. Pisarczyk , T. Chodukowski, M. Scholz, Z. Kalinowska, E. Zielinska, B. Bienkowska, J.

Hitschfel, S. Jednoroh, L. Karpinski, J. Kortanek, J. Kravarik, K. Rezac, I. Ivanova-Stanik, K. Tomaszewski, Response to

Comment on Experimental evidence of thermonuclear neutrons in a modified plasma focus, Appl. Phys. Lett. 100, (2012)

016101.

2. P. Kubes, D. Klir, J. Kravarik, K. Rezac, M. Paduch, T. Pisarczyk , M. Scholz, T. Chodukowski, I. Ivanova-Stanik, L.

Karpinski, K. Tomaszewski, E. Zielinska, M. J. Sadowski: Energy Transformation in Column of Plasma Focus Discharges

with Megaampere Currents, IEEE Transactions on Plasma Science 40 (2012), 481-486.

3. P. Kubes, D. Klir, M. Paduch, T. Pisarczyk , M. Scholz, T. Chodukowski, Z. Kalinowska, K. Rezac, J. Kravarik, J. Hitschfel, J.

Kortanek, B. Bienkowska, I. Ivanova-Stanik, L. Karpinski, M. J. Sadowski, K. Tomaszewski and E. Zielinska: Characterization

of the Neutron Production in the Modified MA Plasma-Focus, IEEE Transactions of Plasma Science 40 (2012) 1075-1080.

4. V. Krauz, K. Mitrofanov, M. Scholz, P. Kubes: Experimental Study of the Structure of the Plasma-Current Sheath on the PF-

1000 Facility, PPCF 54 (2012) , 025010.

5. D. Klir, A. V. Shishlov, P. Kubes, K. Rezac, F. I. Fursov, V. A. Kokshenev, B. M. Kovalchuk, J. Kravarik, N. E. Kurmaev, A. Yu.

Labetsky, and N. A. Ratakhin: Deuterium Gas Puff Z-Pinch at CVurrents of 2-3 MA, Physics of Plasma, 19 (2012),

19 032 706.

6. V. Krauz, K. Mitrofanov, M. Scholz, M. Paduch, P. Kubes, L. Karpinski, E. Zielinska: Experimental Evidence of the Axial

Magnetic Field in a Plasma Focus, EPL, 98 (2012) 45001.

7. P. Kubes, D. Klir, K. Rezac, M. Paduch, T. Pisarczyk , M. Scholz, T. Chodukowski, Z. Kalinowska, J. Hitschfel, J. Kortanek, J.

Kravarik, I. Ivanova-Stanik, B. Bienkowska, L. Karpinski, E. Zielinska, M. J. Sadowski, K. Tomaszewski: Interferometry of the

Plasma Focus Equipped with Forehead Cathode, Nukleonika 57, 189-192.

8. M. Scholz, L. Karpinski, V.I.Krauz, P. Kubes, M. Paduch, M.J. Sadowski: Progress in MJcPlasma Focus Research at IPPLM,

Nukleonika 57 (2012), 183-188.

9. P. Kubes, V. Krauz, K. Mitrofanov, M. Paduch, M. Scholz, T. Pisarczyk , T. Chodukowski, Z. Kalinowska, L. Karpinski, D. Klir,

J. Kortanek, E. Zielinska, J. Kravarik, K. Rezac: Correlation of Magnetic Probe and Neutron Signals with Interferometry

Figures on the Plasma Focus Discharge, Plasma Phys. Control. Fusion 54 (2012), 105023.

10. K. Rezac, D. Klir, P. Kubes and J. Kravarik: Improvement of time-of-flight methods for reconstruction of neutron energy

spectra from D(d,n)3He fusion reactions. Plasma Phys. Control. Fusion 54 (2012), 105011.

11. P. Kubes, J. Kravarik, D. Klir, K. Rezac, J. Kortanek: Neutron Production from a Small Modified Plasma Focus Device, IEEE

Transactions of Plasma Science 40 (2012), 3298-3302.

12. P. Kubes, D. Klir, J. Kravarik, K. Rezac, J. Kortanek, V. Krauz, K. Mitrofanov, M. Paduch, M. Scholz, T. Pisarczyk , T.

Chodukowski, Z. Kalinowska, L. Karpinski, E. Zielinska: Scenario of Pinch Evolution in a Plasma Focus Discharge, Plasma

Phys. Control. Fusion 55 (2013), 035011.

Publications 2012-2013