13 Belarusian State University EFRE2016 2 7 October

Лекция 13 Компрессионные источники плазмы В. В. Углов Belarusian State University EFRE-2016 2 – 7 October 2016 Tomsk, RUSSIA 1

Принципы генерации КПП 1) Нагрев плазмы в магнитных ловушках (tokamaks, stellarators, open traps etc. ); ion Magnetic field electron In the magnetic field, magnetized charged particles of plasma revolve around magnetic field lines and do not reach the wall 4

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Принципы генерации КПП В плазменном ускорителе происходит ускорение ионов при их полной нейтрализации. Indeed, due to the low weight of electrons, they have a velocity greater than 100 km/s even at room temperature (~ 300 K). At the same time, for ions of most light gas (hydrogen) to obtain the same velocity (~ 100 km/s), the effective temperature of about 50 e. V is required. 12

Принципы генерации КПП Electrodes Compression plasma flow parameters pulse duration ~ 100 sec peak current 50 120 k. A plasma velocity 30 70 km/s electron density 1016 1018 cm-3 plasma temperature 2 4 e. V energy density 5 40 J/cm 2 21

Diagram of plasma states Hydrogen bomb ПУ Plasma accelerators

Plasma accelerators The first quasi-stationary plasma accelerator operating in the mode of ion current transfer, was called “Magnetoplasma compressor“ (MPC). To provide the ion current transfer, delivery of ions across the anode into an accelerating channel has to be arranged. For this reason, a solid anode of MPC was replaced by a set of metal rods.

Plasma accelerators At high discharge currents typical for MPC, ions are magnetized also (not only electrons). However, because the ions have the large mass, they drift from the anode to the cathode (they "jump" from one magnetic field line to the other), thus providing transfer of current in the accelerating channel. In this case, the ions receive a kinetic energy by moving along electric field. 25

Plasma accelerators: Medium energy magnetoplasma compressor C 0 = 2400 мк. Ф; U 0 = (2 5) k. V; W 0 – до 30 к. J The diameter of external electrode is 16 cm Compression plasma flow: length — 10 – 15 cm; diameter — 2– 5 cm 26

Plasma accelerators: Magnetoplasma compressor of compact geometry C 0 = 1200 F; U 0 = (2 5) k. V; W 0 – up to 15 k. J working gas discharge duration peak current plasma velocity electron density plasma temperature –H 2, N 2 and any gases – 150 sec; – 50 120 k. A; – 30 70 km/sec; – 1016 1018 cm-3; – 2 4 e. V Discharge device Compression plasma flow: length — 5 – 10 cm; diameter — 1 – 2 cm 27

Plasma accelerators: Miniature MPC C 0 = 400 F, U 0 = (1 3) k. V W 0 — до 2 k. J Gas-discharge compression plasma flow: length — 1 cm; diameter — 0, 4 cm Erosive compression plasma flow : length — 0, 5 – 1 cm; diameter — 0, 4 cm 28

Plasma accelerators Further progress of plasma accelerators is associated with the development of physical principles of radically new Quasistationary High-current Plasma Accelerator (QHPA), proposed by Professor A. I. Morosov 29

Plasma accelerators Unlike previous accelerators, the QHPA represents twostage plasmadynamic system with magnetic shielding of accelerating channel elements. QHPA operates in ion current transfer mode and provides ion-drift acceleration of magnetized plasma. The function of the QHPA AIC first stage is to inject Та completely ionized plasma flows into the second stage, IIC Тc i. e. the main accelerating channel formed by so Cjet called anode and cathode General scheme of QHPA transformers (electrodes). 30

Plasma accelerators Developed at the Laboratory of Plasma Accelerated Physics is the quasi-stationary high-current plasma accelerator (QHPA) of P-50 type 31

Plasma accelerators Quasi-stationary high-current plasma accelerator (QHPA) of P-50 type discharge duration peak current plasma velocity electron density plasma temperature — 500 sec; — 200 450 k. A; — 70 200 km/sec; — 1016 1018 cm-3; — 10 15 e. V Compression plasma flow: length – 30 -50 cm; diameter – 3 20 cm 32

CPF possibilities Produce functional surface layers Direct influence Morphology modification • • Disperse microstructure • Nitriding Materials mixing • Alloying • Phase transformation • Hardening Surface erosion • Ablation Coating deposition • Nano-coatings producing • Erosion

CPF possibilities: Fast melting and crystallization - activation energy of atom transition through phase interface - melting heat per atom Si 1 – 0, 5 MW/cm 2 2 – 0, 8 MW/cm 2 3 – 1, 0 MW/cm 2 Cooling rate ~ 107 K/s 34

CPF possibilities: surface morphology modification Si (111)Si (100)Si Al By exposing silicon wafers to compression flows, the regular bulk structures of 100 -700 nm in diameter and more than 500 microns long were first obtained. 35

CPF possibilities: surface morphology modification - formation of elastic oscillations under the melt (107 – 1012 Гц) - initiation of Kelvin-Helmholtz instability at melt-plasma interface Si treated by CPF - strong anisotropy of crystallizing matter surface energy z=z(x, y) – crystal surface equation α(p, q) – density of surface energy α 0 и β 0 – const Segment of calculated equilibrium surface of Si 36

CPF possibilities: formation of nanoparticles and nanostructured materials CPF loaded with highly dispersed metal particles have been used formation of nanostructured metal coatings on surfaces. The obtained coating looks like a monolayer of nanostructured metal clusters (20– 300 nm) which consist of nanoparticles 10 -30 nm. 38

CPF possibilities: structure dispersion Iron cross-section I - zone with disperse grains (thickness 6 -7 µm) II - zone with columnar grains (thickness ~15 µm) III - transition zone Thickness of the modified layer can be controlled by treatment parameters (Q) 39

CPF possibilities: structure dispersion Iron 40

CPF possibilities: homogenization of phase composition AISI M 2 high-speed steel Q=5 J/cm 2 g. C, N, M Q=10 J/cm 2 M 6 C - Fe 3 W 3 C type MC - VC type • dissolution of MC and M 6 C carbides • formation of austenite alloyed with N, W, V Hard alloy cross-section origin after treatment WC (Ti, W)C (W, Ti)C solid solution formation 41

CPF possibilities: homogenization of element composition Al-12%Si alloy cross-section I – melted layer I + II – modified layer Hv=1, 9 GPa Distribution of Si (mapping) Hv=1, 3 GPa 42

CPF possibilities: surface nitriding Ti. N, Ti 2 N formation in Ti Titanium e-Fe 2+x. N, g-Fe formation in AISI T 1 steel Nitrogen content (and nitrides volume fraction) can be controlled by treatment parameters (energy, number of pulses, pressure) AISI T 1 steel 43

Practical CPF application Hard alloy cutting tool After treatment wear Without treatment 3 -7 times increase of cutting tool lifetime after plasma treatment (depending on plasma treatment parameters) Untreated ~ 13 GPa 44

Interaction of CPF with “coating-substrate” system I stage: coating deposition Coating I stage: Injection of doping elements II stage: treatment by CPF Result: Mixed layer ~ 5 -70 m Substrate Fe Al Ti Mixed layer, m 5 -20 20 -70 5 -15 Plasma mixing of “coating/substrate” system (plasma surface metallurgy) allows to modify mechanical, corrosion, magnetic and other properties of surface layer of a substrate material by corresponding choice of alloying elements. 45

Interaction of CPF with “coating-substrate” system: Ti on steel Ti coating Carbon steel ~100 nm After CPF treatment Alloyed layer (Fe-10% Ti) 46

CPF possibilities: stabilization of metastable phases Mo/Si system 8 J/cm 2 6 J/cm 2 β-Mo. Si 2 formation 5 J/cm 2 Ti/Si system C 49 -Ti. Si 2 formation 10 J/cm 2 8 J/cm 2 6 J/cm 2 47 47

Control of alloying element concentration: I. Change of treatment parameters (Q, n) (limitation: cmax=tcoating/tmixed layer) in steels with tcoat ~ 2 μm cmax ~ 15 at. % II. Change of coating thickness (limitation: tcoating<tmixed layer) III. Hybrid methods (e. g. repetition of deposition and treatment processes) 48

Surface ablation CPF sample Weight loss (22 J/cm 2, 1 pulse): 1. 9∙ 10 -4 g/cm 2 Area surface profile of steel St 3 sample (52 x 52 mm) Direction of the melt motion 50

CPF possibilities: Cleaning of steel surface before treatment Oxides layer (~27 μm) Fe 2 O 3 Fe 3 O 4 Fe. O Ст3 after CPF treatment (20 J/cm 2, n=1) 51

The main factors ensuring the efficient modification of a material surface exposed to compression plasma flow are: 51

Part 1. Compression plasma flows (CPF) generated by quasi-stationary plasma accelerators • principles of CPF generation • plasma accelerators Part 2. CPF possibilities for materials modification • direct interaction • interaction CPF with “coating-substrate” system • formation of nanoparticles and nanostructured materials Part 3. New possibilities of CPF • quasi-stationary spherical plasma formation • powerful emitting source 52

CPF: new possibilities The collision of two oppositely directed compression plasma flows 53

CPF: new possibilities Compression plasma flows open up essentially new opportunities for fundamental research into dynamics of plasma formations in electromagnetic fields of the complex configuration. The interest to such plasma accelerators is connected with investigations for controlled thermonuclear synthesis based on collision of two compression plasma flows within the magnetic Quasi-stationary magnetic trap with β ≈ 1 trap. 55 54

CPF: new possibilities Studying of interaction processes of opposing compression plasma flows generated by gas-discharge MPC of compact geometry are conducted. V. M. Astashynski, et al. Dynamics of interaction between opposing compression plasma flows // V International conference "Plasma Physics and Plasma Technology", Minsk, 2006. – V. 2. – P. 915 -917. 56 55

CPF: new possibilities (spherical plasma formation) The collision of plasma flows produces a quasistationary spherical plasma formation whose life time is longer than the MPC discharge duration. As we show, the deceleration of a compression flow with magnetic field frozen in plasma results in the formation of closed current loops (vortices) which persist for some time upon the discharge termination in the MPC. 57 56

CPF: new possibilities (emitting sources) Experimental estimations of basic thermodynamic parameters of plasma have shown that in the collision area of compression flows they are at least twice as high as those in a free (non-colliding) flow. The collision area of two compression plasma flows represents a powerful emitting source. 58 57

Summary • Several models of quasi-stationary high-current plasma accelerators of MPC type were developed. These plasmadynamic systems operate in the ion current transfer mode and provide the ion-drift acceleration of magnetized plasma • The findings showed that quasistationary plasmodynamic systems of new generation offer the challenge for synthesis of new materials and for effective modification of materials surface properties. • High-speed heating and cooling, long duration of melt existence, additional alloying by almost any element are the main factors providing materials surface properties modification. 60 58