V. Mironov, J.P.M. Beijers

Transcription

1 NUMERICAL MODELING OF ION PRODUCTION IN ECRIS BY USING THE PARTICLE-IN-CELL METHOD V. Miroov, J.P.M. Beijers Kerfysisch Verseller Istituut, Uiversity of Groige, The Netherlds 1

2 1. Itroductio. KVI A-ECRIS 3. Code Descriptio 4. Results 5. Coclusios Outlie

3 We develop the 3D Prticle-i-Cell Mote-Crlo Collisios Code. The key igrediet is poderomotive brrier cofiemet Numericl modelig of ECRIS llows better uderstdig of the physicl processes i ECRIS plsms Some experimetlly observed effects c be explied Could help i fidig out how to optimize the source performce 3

4 KVI A-ECRIS lyout d performce Al plsm chmber, hexpole with the slits for better pumpig of the chmber. RF frequecy 14+(11-1.5) GHz B ij =.1 T, B mi =0.36 T B ext =1.1 T, B rd =0.86 T Chmber legth 30 cm Chmber dimeter 7.6 cm Extrctio perture 0.8 cm Q C eµa O eµa F eµa Ne eµa Ar eµa Q Pb eµa ~

5 Code Descriptio (1) Uiformly distribute 50% eutrl eo toms d 50% Ne1+ i the volume. For ech mcro-prticle, defie i which cell it is ow (rectgulr mesh 38x38x64). Clculte i d get e from qusi-eutrlity requiremet. Group the prticles i the cell i rdom order d clculte io-io elstic collisios (Tkizuk-Abe method of groupig + Nbu model for sctterig gles). 5

6 Clculte electro-io hetig. T e =1 kev everywhere, free prmeter Mrti et l. X-ry spectroscopy of 14 GHz ECRIS rxiv: v1 Code Descriptio () 9 V x, y z = V x y z + δ ( e ( ix, iy, iz ) 15. dt Z / m ) 0.5 Clculte ioiztio probbility; if yes, Z=Z+1 1E-7 1E-8 ioiztio recombitio (RR+DR) Rtes re from P.Mzzott, et l., Astro. Astrophys., Suppl. Ser., 133, 403 (1998). Recombitio processes re egligible. 1E-9 1E-10 1E-11 1E-1 1E-13 1E-14 eo ios, 1 kev rte, cm 3 sec -1 Z,,,

7 Code Descriptio (3) Clculte chrge-trsfer d iotom elstic sctterig rtes. Scle it 0.5 s Z (Lgevi). σ Lgevi = Z π 0 ( α Ry / ε ) Eergy relese with Q roud 10 ev! Move io i the sttic B d E fields defied lyticlly. B field is from POISSON- SUPERFISH clcultios for KVI- AECRIS + compoet for the Hlbch hexpole (o edge effects) 7

8 Iside ECR zoe (B<0.5 T) it is set to zero. 1 V/cm towrds the wlls outside the zoe (presheth). C be vried i wide rge. Whe io crosses the ECR zoe boudry, it is either ccelerted to the wlls, or it is reflected bck if V<PB*sqrt(Z) Poderomotive Brrier Electric field 8

9 Poderomotive brrier Electros re expelled from thi lyer roud ECR by the poderomotive force, givig rise to positive potetil brrier. The potetil brrier (PB) cofies ios iside the ECR zoe. It is free prmeter i our clcultios, vries i (0-1) V rge. No sptil vritios. We set its height to zero if the plsm desity exceeds the cut-off limit of.5x10 1 cm -3 (for 14 GHz RF frequecy) reflectios/bsorptio i the plsm empiriclly observed sturtio of plsm desity t cut-off vlue. 9

10 Code Descriptio (4) Whe io hits the chmber wll, it is eutrlized Frctio of the bckscttered sigly chrged ios is less th 1 % If ot i extrctio perture, io is scttered bck with gulr distributio ccordig to the cosielw (diffuse sctterig) Eergy distributio of eutrlized toms is from the experimetl dt J.W.Cuthbertso, W.D.Lger d R.W.Motley, J.Nucl.Mter , 113 (199). Gussi distributio with the FWHM roud 10 ev, mximum t 10 ev idepedet o the iitil eergy 10

11 Code Descriptio (5) Whe tom hit the wll, it looses some eergy. The therml ccommodtio coefficiet α Es-Ei=α (Tw-Ei) We use α(t) for Ne-Al surfce collisios from F.O.Goodm d H.Y.Wchm, J.Chem.Phys. 46, 376 (1967) Ne-Al For smll eergies, α(t) is quite smll hot gs i the chmber Not for ll elemets! α Ei

12 Sptil Distributios of Ios Ne 1+ Ne 6+ Higher chrge sttes re more loclized o the xis 1

13 Sptil Distributio t Extrctio 13

14 ρ = e v B T m p u di, = e B = k e B A crtoo of clssicl flux B T B m Dimgetic velocity depeds o the chrge d cuses frictio betwee differet species, tht drive rdil fluxes. 14

15 15 The clssicl rdil prticle flux (fil result) b b CL b b b b b b b b b CL b b CL CL D m m e e m m T T e e D D ν ρ = + = Γ + = Γ T T Z H H Z Z ZH Z Z CL 1 ν ρ i CL ei e ei e e CL T T T T Γ = = + = Γ 1 ν ρ ν ρ For hevy impurity i hydroge plsm (collisios with electros c be eglected): iwrd outwrd (temperture screeig) For pure hydroge plsm: ie i ei e ν ρ ν ρ = io d electro flux ito the sme directio d of equl size! = T T Z H H Z Z 1 I equilibrium the impurity profile is much more peked th the hydroge profile (rdil flux=0)

16 Ne Sptil Distributio High ccomodtio coefficiet (cold gs) d low PB 1+ Ne6+ 16

17 Extrcted currets experimet, differet RF powers, fixed gs flow W 17

18 Extrcted currets simultios, differet PB height, SW is vried to hve the sme outflow V 18

19 19

20 Extrcted currets experimet, differet gs flows 0

21 Extrcted currets simultios, differet sttisticl weights of mcro-prticles 1

22 Extrcted Ne 8+ curret experimet d simultios

23 Extrcted currets experimet d simultios 3

24 Extrcted currets simultios, differet sttisticl weights of mcro-prticles 4

25 Cofiemet times of ios (01+); (1++);.Z+ is extrcted t=0 t=t c (Z) (cofiemet time fter vergig) 5

26 Isotope Aomly Mixig 0 Ne + Ne d demdig tht the gs flows of isotopes re the sme 6

27 Coclusios -With our 3D PIC-MCC code, we re ble to reproduce the mi fetures of ECRIS performce -Resos for vrious effects c be ivestigted d clrified -Wll cotig -Afterglow -Gs mixig -Isotope omly -HCI cocetrtio o xis -Frequecy tuig d sclig 7

28 Thks! 8

29 Gs-Mixig Mixig He d Ne (1:1) does ot result i the icresed currets of the highest chrge sttes 9

30 Switchig the Ne-He io collisios off 30