Applications and Modeling of Non-Equilibrium Plasmas

Transcription

1 1 Applications and Modling of Non-Equilibrium Plasmas J.P. BOEUF CNRS-CPAT, Univ. P. Sabatir, Toulous Franc

2 2 Non-Equilibrium Plasmas Dfinition of non-quilibrium plasmas Low dgr of ionization (δ) n lctron dnsity, N gas dnsity Gas dnsity >> plasma dnsity n δ = < n + N 3 4 Collisions btwn chargd particls and nutrals ar dominant Transport quation = Boltzmann quation Non-quilibrium Elctron tmpratur >> ion and nutral gas tmpratur T >> Ti TN

3 3 Non-Equilibrium Plasmas Elctron Tmpratur (K) Earth Magntosphr Solar Wind Ionosphr Solar Corona RELATIVISTIC PLASMAS Magntic fusion CLASSICAL PLASMAS Non Equilibrium Thrmal Plasmas Plasmas Lightning Inrtial fusion sun Whit dwarfs QUANTUM PLASMAS 1000 V 100 V 10 V 1 V Dnsity n (cm -3 )

4 4 Non-Equilibrium Plasmas Gnration of non-quilibrium plasmas Currnt through a gas For larg nough applid lctric fild gas bcoms conductor Elctron avalanchs (ionization) + lctron mission by surfacs gas brakdown Slf-sustaind plasma: volum ionization + surfac gnration = losss to walls + rcombination Various ways of gnrating a non-quilibrium plasma DC or pulsd voltag HF (high frquncy AC voltag), capacitiv or inductiv coupling Microwav sourc, microwav + magntic confinmnt, ECR (lctron cyclotron rsonanc) Larg rang of oprating prssur At low prssur: difficult to sustain th plasma confinmnt by magnctic fild or HF fild At high prssur: difficult to gnrat a larg volum plasma micro-plasma

5 5 Non-Equilibrium Plasmas Applications Elctric Enrgy Luminous Enrgy Sourc of photons Lamps Lighting Watr purification Visualization Plasma displays Lasrs PLASMA Kintic Enrgy Sourc of chargd particls Ion sourcs Ion implantation Propulsion Surfac tratmnt Elctron bams X-ray sourc Switchs Chmical Enrgy Sourc of activ spcis Surfac procsss Microlctronic Surfac tratmnt Strilization Volum procsss Pollution control Exhaust gass Wast dstruction Matrial analysis Chmical synthsis Bio-mdical aplications

6 6 Non-Equilibrium Plasmas Spcificity of non-quilibrium plasmas Gnrat activ chmistry at low gas tmpratur (nrgy dposition by lctrons) Non Maxwllian vlocity distribution of chargd particls Elctron hating mchanisms can b complx Dscription of lctron hating oftn nds a kintic tratmnt. Exampls: Elctron hating in a small rgion with high lctric fild (cathod shath) Non-collisional hating in a HF fild at low prssur Elctron oscillations in a hollow cathod High non linarity of lctron impact ionization Ionisation dpnds xponntially on lctric fild or lctron nrgy

7 7 Non-Equilibrium Plasmas Applications in microlctronics industry: plasma tching and dposition Plasma ractor for microlctronics Low prssur plasma (1 mtorr-1 torr) Plasma gnrats ractiv spcis (du to high lctron tmpratur) at low gas tmpratur (no damag of th substrat) Lasr intrfromtr RF gnrator substrats élctrods wafr Substrat holdr injction pump Gas in

8 8 Non-Equilibrium Plasmas Plasma tching 0.4 µm

9 9 Non-Equilibrium Plasmas Pollution control Dstruction of NOx Rducing missions in light-duty vhicls. Combin plasma tratmnt with spcializd catalyst matrial to convrt oxids of nitrogn (NOx) into componnts of clan air. 90% incras of NOx dstruction by combining catalysis and non quilibrium plasma

10 10 Non-Equilibrium Plasmas Diamond synthsis All CVD tchniqus for producing diamond films rquir a mans of activating gas-phas carbon-containing prcursor molculs. This gnrally involvs thrmal (.g. hot filamnt) or plasma (D.C., R.F., or microwav) activation, or us of a combustion flam (oxyactyln or plasma torchs). Diamonds grown with 10% argon in th mthan/hydrogn mixtur Microwav plasma sourc for diamond film dposition about 50 hours to mak a diamond film 0.1mm thick

11 11 Non-Equilibrium Plasmas Atmosphric prssur plasma procssing A plasma sourc may b viwd as an lctrical switch that turns chmical ractions on and off. Whn it s on, a high concntration of atoms and radicals ar dlivrd to a surfac to clan, rmov, modify, or dposit a matrial of your choic. By using lctricity instad of hat to turn ractions on and off, you can indpndntly control th tmpratur of th surfac. Atmosphric prssur plasma procssing is alrady an stablishd surfac tratmnt mthod in svral larg industris. Traditionally, ths plasma tools hav bn basd on arc dischargs, which can dstroy many matrials du to th xtrmly high tmpraturs gnratd insid th plasma. Surfx s nw products dlivr a similar high dnsity of ractiv spcis to th working surfac, but at vry low tmpratur and undr a control gas atmosphr that guarants th dsird chang is mad quickly, fficintly, and th sam way vry tim.

12 12 Non-Equilibrium Plasmas Strilization - dcontamination «Th tchnology of cold ionizd gass has rcntly rachd a lvl of maturity at which applications can b considrd. Cold plasmas consist of lctrons and ions in gass at high prssur, up to and vn xcding atmosphric prssur. Th chargd particls in ths cold plasmas ar succssfully usd to dcontaminat surfacs».

13 13 Non-Equilibrium Plasmas Bio-Mdical applications RadioFrquncy «Plasma ndl» Potntial Applications - Claning of dntal cavitis - Rmoval of unwantd clls/tissus - Plasma inducd modification of artry walls - Tratmnt of cancr clls 1 millimtr plasma glow at 250V (about 0.1 W). Th glow is cold nough to b touchd (imag crdit: E Stoffls t al J. Phys. D: Appl. Phys )

14 14 Non-Equilibrium Plasmas Plasma Display Panls JP Bouf, J. Phys. D: Appl. Phys 36, R53 (2003), adrssing UV light mittd by th discharg sustaining Plasma Display Panl micro-discharg

15 15 Non-Equilibrium Plasmas Flow control by surfac micro-plasmas Flow Attachmnt at High Angl of Attack Using Plasma Actuators Plasma Off Plasma On J.R. Roth t al., Univ. Tnnss

16 16 Non-Equilibrium Plasmas Ion thustr for satllit propulsion: Hall Effct thrustr Europan lunar prob SMART 1, launchd by ESA on with Stationary Plasma Thrustr from SNECMA: PPS1350 Smart 1 will arriv at th moon in January 2005 Will sarch for signs of watr-ic in cratrs nar th Moon's pols, provid data on th still uncrtain origin of th Moon and rconstruct its volution by mapping and th surfac distribution of minrals and ky chmical lmnts.

17 17 Non-Equilibrium Plasmas Modl Chargd Particl Transport EM Fild Fluid Hybrid Particl-In-Cll Mont-Carlo Maxwll Poisson Photon Transport Nutral Transport Fluid Navir Stoks DSMC Chmistry Volum Surfac

18 18 Non-Equilibrium Plasmas Choic of th modl approximations Chargd particl transport Fluid - Closur rlations? Hybrid Particl-In-Cll Mont Carlo Collisions Coupling Chargd Particl Transport Elctric Fild Solv Poisson s quation? Constraint on tim stp Quasinutrality assumption? xplicit intgration of Poissontransport quations: constraint on tim stp t < t < 1 ω p ε0 ν = σ ω m 2 p PIC modl ω p Fluid modl = 2 ε m 0 n

19 19 Non-Equilibrium Plasmas Quasinutrality or not? «In a plasma, it is usually possibl to assum n = n i and.e 0 at th sam tim. This is a fundamntal trait of plasmas, on which is difficult for th novic to undrstand. Do not us Poisson s quation to obtain E unlss it is unavoidabl.» F.F. CHEN can assum quasinutrality if spac charg shath rgion do not play an ssntial rol in sustaining th discharg

20 20 Non-Equilibrium Plasmas Exampls of modls of non-quilibrium discharg plasmas Outlin 1. Hall ffct thrustr for satllit propulsion 2. Non quilibrium discharg plasma in collisional rgim Atmosphric micro-plasmas and applications

21 21 Thrustrs for Satllit propulsion Elctrothrmal hating of a gas + xpansion thrugh a nozzl Arc Jt, rsistojt Magntodynamic Plasma xpansion du to Lorntz (Laplac) forc Pulsd Plasma Thrustr Lorntz Forc Acclrator Ion thrustrs plasma sourc + xtraction and acclration of ions by polarizd grids Stationary Plasma Thrustr (Hall Effct Thrustr) No acclrating grids

22 22 Hall Effct Thrustrs Principls xnon injction anod cathod lctrons ions Cost rduction / chmical Prop Gridlss Ion Engin High Thrust Efficincy > 50 % Spcific impuls ~1800 s Thrust to Powr Ratio ~ 70 mn/kw Orbit Transfr N/S Station Kping anod xhaust cathod acclration channl coils Coils coils

23 23 Hall Effct Thrustrs Principls xnon injction anod cathod lctrons ions Cost rduction / chmical Prop Gridlss Ion Engin High Thrust Efficincy > 50 % Spcific impuls ~1800 s Thrust to Powr Ratio ~ 70 mn/kw Orbit Transfr N/S Station Kping acclration channl Coils

24 24 Principls Hall Effct Thrustrs r cathod lctrons Larg radial B fild at xhaust (200 G) Man fr paths >> dimnsions Collisionlss ions Collisional lctrons (l confinmnt) Nutral flow ~ fully ionizd B EXB configuration ions x Typical numbrs Voltag 300 V Typical dimnsions φ 10 cm, L 3 cm xnon mass flow rat 5 mg/s ion vlocity ~ 18 km/s thrust 80 mn currnt 4 A

25 25 Principls Hall Effct Thrustrs r cathod radial B fild trappd lctrons -J low axial lctron conductivity J = σ E B EXB configuration x low σ -> larg E ν σ = nµ = n m ω 2 B

26 26 Principls Hall Effct Thrustrs r cathod radial B fild trappd lctrons B E nhancd ionization low axial lctron conductivity larg axial lctric fild ION ACCELERATION EXB configuration x

27 27 Elctron transport in SPT Collisionlss trajctoris (spcular rflxion on shath) E x = 100 V/cm B r = R 1 /r x 100 G No axial transport 5 r (cm) 3 B r E x R 1 3 cm X (cm) R 2 5 cm anod xhaust

28 28 Elctron transport in SPT Elctron trajctoris with collisions E x = 100 V/cm B r = R 1 /r x 100 G collision with atom or scattring with wall Axial transport 5 r (cm) 3 R cm X (cm) R 2 5 cm anod xhaust Azimutal motion

29 29 Principls Hall Effct Thrustrs r cathod ionization radial B fild trappd lctrons low axial lctron conductivity S i E x acclration nhancd ionization larg axial lctric fild ION ACCELERATION EXB configuration x

30 30 Hall Effct Thrustrs Ionization and acclration Collisional lctrons Collisionlss ions Ionization zon upstram of acclration zon fficint ion acclration Part of th potntial drop outsid th channl ffct on bam divrgnc V V 50 V color = ionization rat contours = potntial

31 31 Ordrs of magnitud Hall Effct Thrustrs Applid voltag Xnon mass flow rat Canal lngth Diamtr of xtrnal cylindr Total currnt Ion currnt Ion bam nrgy 300 V 5 mg/s 2.5 cm 10 cm 4 A 3 A V Atom dnsity at anod cm -3 Atom dnsity at xhaust cm -3 Max plasma dnsity cm -3 Max lctron man nrgy 30 V

32 32 Hall Effct Thrustrs Charactristic tims invrs plasma frquncy 1/ω p invrs cyclotron frquncy 1/ω c lctron-wall collision tim lctron-atom collision tim ion transit tim in acclration zon ion-atom collision tim atom transit tim Tim (s)

33 33 Hall Effct Thrustrs Charactristic lngth lctron Dby lngth lctron cyclotron radius magntic fild gradint dvic lngth lctron man fr path Lngth (cm) ion cyclotron radius

34 34 Hall Effct Thrustrs Choic of modl approximations Particl-In-Cll Mont Carlo simulation of Hall thrustr is not practical Evn implicit PIC modl would nd tim stps lss than s 1D PIC modl in ths conditions tak svral wks of computation on fast computrs Elctric fild is inducd by a dcras of plasma conductivity Quasinutrality should b a good approximation

35 35 Quasinutral hybrid modl Hall Effct Thrustrs Nutral atoms transport injction at anod, collisions with walls, losss by ionization Ion transport gnration by ionization, collisionlss transport rcombination at walls Elctron transport gnration at cathod & by ionization collisional transport (trapping by magntic fild) Elctric fild quasinutrality is assumd fild dducd from lctron momntum quation and currnt consrvation quation PARTICLE MODEL PARTICLE MODEL FLUID MODEL QUASINEUTRALITY

36 36 Hall Effct Thrustrs Quasinutral hybrid modl Ion & nutral transport (PIC) Elctron momntum quation + quasinutrality Currnt continuity Tim t k, lctric fild & ionization rat E k, S k j = f( n, E) nw fild E k+1. = 0. j =. j j T plasma dnsity n k+1, ion currnt dnsity j i k+1 i Elctron nrgy quation Elctron nrgy + Ionization rat S k+1

37 37 Hall Effct Thrustrs Elctron momntum quation u n. ( ) m + u u = n E + u B p mn vmu t lctric forc lctron kintic prssur p = n kt T = lctron tmpratur lctron-nutral collisions v = N Q v m m

38 38 Hall Effct Thrustrs Elctron momntum quation mnv u = n E+ u B p ( ) m n nu = E+ u B ( nkt) mν m n 2 ν m * * E B j = σ 0 E E n ω c B E σ * E * 0 2 n m E B * E nkt = E+ n = m ν Hall currnt

39 39 Hall Effct Thrustrs r Elctron momntum quation j H, j, cathod j, j ν 2 m, = σ 0 ω 2 c j = σ, 0 j E = n * E * E B B H, 2 x In a Hall thrustr: ν 10 < < 10 ω 1 m 4 c

40 40 Hall Effct Thrustrs Calculation of lctric fild from lctron momntum quation j = f( n, E) lctron momntum transport quation n = n = n (1) (quasinutrality) known from ion transport (2) i. j =. j = S i (currnt continuity) known from ion transport + boundary condition: total currnt (1) + (2) quation for th lctric fild Ε

41 41 Hall Effct Thrustrs Calculation of lctric fild from lctron momntum quation. j =. j = S i 2 ν m * *. j =. σ 0 E E 2 + ωc 2 * * ν m * * E = V. σ 0 V V S 2 + = * ωc V = V kt n ln n 0 Simpl lliptic quation for V* but cofficint in on dirction >> cofficint in th prpndicular dirction Difficult to solv numrically

42 42 Hall Effct Thrustrs Calculation of lctric fild from lctron momntum quation Approximation: Boltzmann quilibrium along th B fild lins nkt j σ E σ V *, = 0 = n V x r kt ( λ) n( x, r) = ( λ ) + n 0 * (, ) V ln λ stram function, constant along B fild lins ( ) * V λ obtaind by intgrating th currnt quation along a B fild lin

43 43 Hall Effct Thrustrs Calculation of lctric fild from lctron momntum quation stram function λ λ = rbr x λ = rb r intgrating th currnt quation along a B fild lin jds= I jds T i x * * V V rb = λ ν 2 m * jds = σ 0 E ds 2 ω c α E * V kt + β = IT i λ λ n kt = V + 1 ln * * n0 jds

44 44 Hall Effct Thrustrs Ionization and acclration Collisional lctrons Collisionlss ions Ionization zon upstram of acclration zon fficint ion acclration Part of th potntial drop outsid th channl ffct on bam divrgnc V V 50 V color = ionization rat contours = potntial

45 45 Hall Effct Thrustrs Nw concpts of Hall thrustrs Nd for vrsatil thrustrs for GEO and probs orbit top up orbit raising high thrust (rduction of mission duration) high mass flow rat/low voltag (nhanc ionization) North/South Station Kping probs high Isp to minimis gas consumption high voltag/low mass flow rat to nhanc acclration Singl Stag Hall Effct Thrustr - Ionization/acclration strongly connctd - difficult to optimiz thrustr for svral opration mods Doubl Stag Hall Effct Thrustr - Sparation of ionization and acclration procsss - promising candidat for multi-mod opration

46 46 Hall Effct Thrustrs Doubl Stag Hall Effct Thrustr (DSHET) Ionization Chambr Hall acclration cathod lctrons RF sourc? Hlicon? Magntic confinmnt? B ions

47 47 Hall Effct Thrustrs SNECMA Patnt , Authors : Schrss Olivir, Bougrova Antonina, Morozov Alxi filld : 9 July 2003 Cathod 0 V xnon injction Anod 2: 300 V lctrons ions Ion trap Anod 1 : 350 V Coils

48 48 Hall Effct Thrustrs Doubl Stag Hall Effct Thrustr (DSHET) Anod 1 : 350 V Cathod 0 V Anod 2: 300 V myxina sparatrix Zro magntic fild

49 49 Hall Effct Thrustrs DSHET: Elctron trajctoris 350 V 0 V 300 V

50 50 Hall Effct Thrustrs DSHET: Potntial distribution Ionization chambr Hybrid simulations CPAT Simulations basd on channl quasinutral plasma assumption Particl-In-Cll ions and nutral atoms lctric fild from Ohm s law lctron nrgy and ionization from fluid modl or Mont Carlo simulation

51 51 Potntial Distribution Ionization chambr Hybrid simulations CPAT Ions channl trappd in th potntial wll bounc back & forth ar guidd to th chanl whr thy ar acclratd out

52 52 Hall Effct Thrustrs Othr qustions 1. Anomalous lctron transport Classical (collisional) conductivity not sufficint in th xhaust rgion Nd to account for «anomalous» conductivity du to plasma turbulnc Exprimnts and PIC modls can hlp quantify anomalous conductivity 2. Elctric fild calculation Assumption of Boltzmann quilibrium along fild lins not good for small B Not good in th 0 B rgion of th Doubl Stag Hall Effct Thrustr Nd for improvmnt of lctric fild calculation

53 53 (x,ϕ) Particl-In-Cll Modl R m ϕ J.C. Adam t al., Physics of Plasmas 2003 E x E ϕ r ϕ (cm) X (cm) x100 V/cm X (cm) x100 V/cm

54 54 Rfrncs Hall Effct Thrustrs Hybrid, quasinutral modl JP Bouf and L Garrigus, J. Appl. Phys. 84, 3541 (1998) G Haglaar, J Barills, L Garrigus, JP Bouf, J. Appl. Phys. 91, 5592 (2002) G Haglaar, J Barills, L Garrigus, and JP Bouf, J. Appl. Phys. 93, 67 (2003) J Barills, G Haglaar, C Bonifac, L Garrigus, JP Bœuf, Phys Plasmas 11, 3035 (2004) Kintic modl of lctron transport P Dgond, V Latocha, L Garrigus, JP Bouf, Transp. Thory Stat. Phys (1998) V Latocha, L Garrigus, P Dgond, JP Bouf, Plasma Sourcs Sci. Tchnol. 11, 104 (2002) PIC modl and anomalous conductivity JC Adam, A Hron, G Laval, Phys. Plasmas 11, 295 (2004) Attmpts to dvlop quasinutral PIC modls G Joyc, M Lamp, S Slinkr, W Manhimr, J. Comp. Phys. 138, 540 (1997) M Lamp, G Joyc, W Mannhimr, S Slinkr, IEEE Trans. Plasma Sci. 26, 1592 (1998)