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A few comments on Opacity Calculations Using ADAS214 Cadarache, Sept. 2012 K. Behringer

A few comments on Opacity Calculations Using ADAS214 Cadarache, Sept. 2012 K. Behringer. escape factors for line radiation (pec-files) – or – population simple(r) case: excited state population negligible (only resonance lines optically thick) opacity of excited states (iteration)

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A few comments on Opacity Calculations Using ADAS214 Cadarache, Sept. 2012 K. Behringer

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  1. A few comments on Opacity Calculations Using ADAS214 Cadarache, Sept. 2012 K. Behringer • escape factors for line radiation (pec-files) – or – population • simple(r) case: excited state population negligible • (only resonance lines optically thick) • opacity of excited states (iteration) • additional remark: the importance of diffusion • summary K. Behringer

  2. when is opacity important? absorption coefficient Doppler profile: • optical thickness (re-absorption) of line radiation is mainly important at • high lower state densities (→ resonance lines) • high transition probabilities • narrow lines (low Tg) • in technical Plasmas (neutral H, He, Ar ….. in arcs also ions) • in divertor plasmas (neutral H, He) • → here mainly neutral He K. Behringer

  3. line escape factor K. Behringer

  4. absorption of greenhouse gases measurement from 19.6 km altitude (stratosphere) surface temperature CO2 brightness temperature: O3 temperature in 19.6 km blackbody ceiling approached from above! K. Behringer

  5. population escape factor the collisional-radiative particle balance is modified by absorption: population escape factor  K. Behringer

  6. escape factors in the ASDEX Upgrade divertor k(0): line centre ne = 41020 m-3 nH = 31019 m-3 ionisation and recombination coefficients are also affected K. Behringer

  7. pec files with optical thickness ADAS214 calculates these escape factors. ADAS214 changes A-values in adf04 files according to population escape factors, subsequent ADAS208 calculations correct the population structure for opacity. however: the reduced A-values are also being used for line emission in the pec output files! This may not be what you want(fortunately line and population factors are similar for the longer plasma dimension). It may be necessary to use the paper.text output and multiply by the proper A-values later! K. Behringer

  8. lower state densities do we know the lower state densities? resonance lines: yes if excited state population negligible - fortunately often the case lines between excited states? if excited state population matters, iteration is required manual input in ADAS214: default = Boltzmann distribution! cannot input small numbers – are set to zero by program must use tricks K. Behringer

  9. ADAS214 input – excited state factors K. Behringer

  10. transitions between excited states run ADAS214 with a first guess of excited state population run ADAS208 to calculate excited state densities use output for ADAS214 – iterate (tedious procedure by hand) input of ADAS208 paper.text densities and output of excited state information in adf04 file provided in my off-line escape factor program – text output of ADAS214 is pretty useless caution: ADAS208 equilibrium population output includes recombination with ni = ne(not the case in mixture plasmas). K. Behringer

  11. output of my off-line program (in part) C 06-04-2012 escape factor program C produced with ADASESCV.BAS (V. 31/3/98) from d:\adas\adf04\helium\behringer_he\p04he0.dat and the following data: C parab. case; cyl.; profile#: 1 (underpop: 6.00e-03 1.00e-06) C m = 4, te = 3.50 eV, tg = 500.00 K, l = 6 cm, na (or nion) = 1.00e+15 cm-3 C KB He microwave 10Pa, 3.5 eV, metastables according to ADAS208, M o'M ionisation lines C---------------------------------------------------------------------------- C level= 2; Te= 3.5 2.15e+11 fraction/Boltz= 2.15e-042.07e-02 C level= 3; Te= 3.5 1.99e+10 fraction/Boltz= 1.99e-05 7.21e-03 C level= 4; Te= 3.5 7.28e+10 fraction/Boltz= 7.28e-053.24e-03 C level= 5; Te= 3.5 1.71e+10 fraction/Boltz= 1.71e-05 2.45e-03 C level= 6; Te= 3.5 2.13e+08 fraction/Boltz= 2.13e-07 4.69e-05 C -----------------d:\adas\henew\1.00e+15\p0435_1E12.1E4; ne= 1.00e+12----------------- ADAS208 output with this file (3.5eV/1e12cm-3): LEVEL = 2 - EQUILIBRIUM POP LEVEL = 3 - EQUILIBRIUM POP LEVEL = 4 – EQUILIBRIUM POP ----------------------------------- ----------------------------------- ----------------------------------- NE (CM-3) 1.00D+12 NE (CM-3) 1.00D+12 NE (CM-3) 1.00D+12 TE (EV) -------------- TE (EV) -------------- TE (EV) -------------- 1.00D+00 | 1.19D-05 1.00D+00 | 7.46D-07 1.00D+00 | 1.37D-06 1.30D+00 | 6.94D-06 1.30D+00 | 4.61D-07 1.30D+00 | 1.12D-06 1.50D+00 | 5.41D-06 1.50D+00 | 3.66D-07 1.50D+00 | 1.01D-06 1.80D+00 | 5.76D-06 1.80D+00 | 4.08D-07 1.80D+00 | 1.27D-06 2.00D+00 | 8.90D-06 2.00D+00 | 6.61D-07 2.00D+00 | 2.12D-06 2.30D+00 | 2.09D-05 2.30D+00 | 1.65D-06 2.30D+00 | 5.51D-06 2.50D+00 | 3.57D-05 2.50D+00 | 2.90D-06 2.50D+00 | 9.93D-06 2.80D+00 | 7.02D-05 2.80D+00 | 5.94D-06 2.80D+00 | 2.10D-05 3.00D+00 | 1.02D-04 3.00D+00 | 8.90D-06 3.00D+00 | 3.19D-05 3.50D+00 | 2.16D-04 3.50D+00 | 2.00D-05 3.50D+00 | 7.29D-05 K. Behringer

  12. additional process: diffusion diffusion of metastable particles out of the plasma volume must be taken into account – possibly by an artificial transition probability to the ground state. for a cylindrical plasma with radius a and a parabolic source the confinement time is metastable He in He, 500 K, 1 Pa, D = 8 m2/s, 1 cm, tau = 210-6 s Diffusion and Excitation Transfer of Metastable Helium in Normal Gaseous Helium, R. A. Buckingham and A. Dalgarno, Proc. Roy. Soc. A, 506 (1952) in technical plasma diffusion times are of the order of 10-4 – 10-6 s. important at low electron densities. K. Behringer

  13. helium 388.9 nm, 2s - 3p3S -  3P°, Te = 3 eV, nHe = 1015 cm-3 triplet system! K. Behringer

  14. neutral helium, “Boltzmann plot” He I experiment: ECR discharge, emission spectroscopy, n=2 from absorption (Augsburg University: Berger, Fantz, Dietrich) clear proof of optical thickness rate coefficients pretty well confirmed similar in Haas’ ionisation gauge K. Behringer

  15. summary •  in some plasmas optical thickness of spectral lines is important • influences (differently) population and emitted intensities • using ADAS214 and ADAS208, the same escape factors are used for population and pec files – may have to use paper.text files • ADAS214 uses Boltzmann population of excited levels by default some problems to put in low values (→correct code) • when optical thickness between excited levels is really important, iteration of population calculations is required – hard with ADAS214 better text output of ADAS214 desirable • in many plasmas, diffusion of metastable ions must be taken into account – possibly by an artificial transition probability K. Behringer

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