Kinetic Complexity in Divertor Modeling

Transcription

1 Kinetic Cmplexity in Divertr Mdeling F. Taccgna, P. Minelli, D. Brun, S. Lng, M. Capitelli, R. Schneider Istitut di Metdlgie Inrganiche e Plasmi IMIP-CNR, Bari (Italy) Dipartiment di Chimica, Università degli Studi di Bari Ald Mr, Bari (Italy) Institute f Physics, Ernst Mritz Arndt University, Greifswald (Germany) francesc.taccgna@cnr.it Internatinal Sympsium n Chemical Physics f Lw Temperature Plasmas, Bari, 1 st February 2011

2 Outline Recmbinatin in Divertr Regin Limitatins in present Mdels Gas-Plasma kinetics interactin: DSMC PIC H 2 (v) wall assciative desrptin Results Cnclusins

3 Divertr Cncept (Spitzer 51) Divertr regin = vlume belw the X-pint - reduces pwer flux n divertr plates - remves helium ash - cntrls impurity Achievable by plasma recmbinatin mechanism. (*) Spitzer, US Atmic Energy Cmmissin Reprt NYO-993 (1951) 3

4 Recmbinatin Mechanisms Electrn-In Recmbinatin (EIR) - radiative recmb.: e H H(n) hv - 3-bdy recmb.: e e H e H(n) Mlecular Assisted Recmbinatin (MAR) - In-cnversin-mediated: H H 2 (v) H H 2 H 2 e 2H - Negative-in-mediated: e H 2 (v) H H - MAR ccur at >T e and <N e than EIR H - H 2H estimatin dne with fixed N e and T e Fluid r Cllisinal-Radiative mdels nt sufficient! MAR prcesses require: - H 2 (v) vibratinal kinetic study - dynamics f the multispecies gas flw (excited states have large decay times) - plasma dynamics/kinetics (magnetized sheath) - accurate x-sect data set (vibratinally reslved) - plasma/gas-surface study (the vlumetric surce f H 2 (v) is usually small in tkamak plasma) (*) Bacal, Reprt INDC(NDS) 331 (1995) 4 (**) Ohn et al., PRL 81(4), 818 (1998)

5 H2(v) released frm the wall (W) Hetergeneus Catalysis H2(v)*W H2(w) desrptin f surface recmbined H(ad)H(ad)*W H2(w) (Langmuir-Hinshelwd mechanism) desrptin f surface recmbined H(g)H(ad)*W H2(w) (Eley-Rideal mechanism) parablic Treanr hyperblic plateau Bltzmann tail (*) Snwdn-Tawara, NIFS-Data 33, (1996); Rayez et al., Mlecular Science 3, A0029 (2009) 5 (**) Rutiglian-Cacciatre, PSST 18, (2009); Mlinari-Tmellini, Chem Phys. 270, 439 (2001) (***) Hall et al., PRL 60(4), 337 (1988); Jacksn-Perssn, J. Chem. Phys. 96(3) (1992)

6 Particle Mdel (PIC-DSMC) Plasma parameters n p, v p, T p, e, H H 2 Slutin f Pissn s equatin Φ, E Plasma surce and bundary effects r i, v i, H(n), H 2 (v) Particle cllisins v i PIC Calculatin f frce acting n particles DSMC F i = E i v i x B i Particle cllisins v i Plasma surce and bundary effects r i, v i Integratin f particle mtin equatins r i, v i H(n=1-3) H 2 (X 1 Σ g (v=0-14)) Gas parameters n g, v g, T g, 6

7 Vlume Prcesses (MCC Mdule) - Plasma Plasma cllisins: - e H 2 -> e H H(n=1) - H H - -> H(n=1) H(n=3) - e H 2 -> H(n=1) H(n=2) - e H 2 -> 2e 2H - e H - -> 2e H(n=1) - Plasma Neutral cllisins: - e H(n) e H(m) - H H(n) H(n) H (el./cx) - e H(n) 2e H - H H 2 (v) H H 2 (w) - e H 2 (v) e H 2 (w) - H H 2 (v) H 2 H(n=1) - e H 2 (v) e H 2 (w) hν - H H 2 (v) H H (n=1) H (n=1) - e H 2 (v) e H 2 * - H H 2 (v) 2H H (n=1) - e H 2 (v) 2e H 2 - e H 2 (v) H (n=1) H(n=1) - H - H(n) -> e H (n=1) H(n=3) - e H 2 (v) 2e H(n=1) H - H - H(n) -> e H 2 (v=14) - e H 2 (v) H(n=1) H - - H - H(n) -> H(n=3) H - - H 2 H(n=1) -> H H 2 (v=1-8) - H 2 H 2 (v) -> H 2 (w=14) H 2 - H 2 H 2 (v) -> H H(n=3) H 2 (w) - H - H 2 (v) e H H 2 (v) (*) H. R. Skullerud, J. Phys. D 1, 1567 (1968). (**) V. Vahedi, M. Surendra, Cmp. Phis. Cmm. 87, 179 (1995). (**) K. Nanbu, IEEE Trans. Plasma Sci. 28(3), 971 (2000). - Neutral Neutral cllisins: - H(n) H 2 (v) H(n) H 2 (w) (el./vt)

8 1D-3V PIC-DSMC Numerical Mdel Input data: - e/h density: n p =10 21 m -3 (detached divertr plasma cnditin) - e/h Temperature : T p =5 ev - B=1 Tesla; θ=85 Simulatin dmain: l=0.3 mm Every Particle carries: - species: e, H, H 2, H - ; H, H 2 (X 1 Σ g ) - axial psitin, velcities: (z, v x, v y, v z ) - quantities averaged ver x,y (unifrmity) - quantum energy levels: - electrnic: n=1s-3s fr H - vibratinal: v=0-14 fr H 2 Cllisin Methdlgy: - Plasma-Plasma (eh 2 /H - H /H - e) - Plasma-Neutral - Neutral-Neutral relaxatin (Vt/VT/VV) Bundary mdule: - H 2 (v) wall relaxatin-dissciatin - H wall recmbinative desrptin (ER/LH) -> H 2 (v) vibratinal excitatin (A-V) - H /H 2 / wall Auger neutralizatin -> H 2 (v) vibratinal excitatin (s-v)

9 Results: Plasma electrstatic sheath magnetic presheath agreement with prbe measurement electrn heating by ev relaxatin nn-maxwellian behavir (many wrks are based n rate cefficient data)

10 Results: Gas nh2(v=0) > nh(n=1) nly clse t divertr wall Tvib, ev

11 Results: Inizatin vs MAR prductin f precursrs peaks clse t the wall due t high vibratinal excitatin H 2 (v) destructin f precursrs mainly due t: - electrn detachment: e H - -> 2e H - dissciative excitatin: e H 2 -> e H H

12 Cnclusins Cmplex cupling between plasma-gas phases Necessity f particle kinetic representatin (nn-unifrmity, detailed wall interactin) Transprt effects nt negligible Nn-Maxwellian behavir -> necessity f x-sect data Strng dependence frm H 2 (v) emitted frm the wall (best H 2 (v) fr MAR). Nr EIR nr MAR sufficient t explain recmbinatin in divertr regin!! FUTURE WORKS Larger simulatin dmain Rtatinal kinetics H 2 / Mlecular in vibratinal kinetics H 2 (X 2 Σ g, v=0,18) (All X_sect invlving H 2 depend strngly n v) Catalytic hydrcarbns C x H y MAR mechanisms