HAL Id: jpa-00227589
https://hal.archives-ouvertes.fr/jpa-00227589
Submitted on 1 Jan 1988
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
He-LIKE TITANIUM SPECTRA FROM TOKAMAK PLASMAS
T. Kato, K. Masai
To cite this version:
T. Kato, K. Masai. He-LIKE TITANIUM SPECTRA FROM TOKAMAK PLASMAS. Journal de
Physique Colloques, 1988, 49 (C1), pp.C1-349-C1-352. �10.1051/jphyscol:1988175�. �jpa-00227589�
JOURNAL DE PHYSIQUE
C o l l o q u e C1, S u p p l e m e n t a u n 0 3 , Tome 49, Mars 1988
He-LIKE TITANIUM SPECTRA FROM TOKAMAK PLASMAS
T. KATO a n d K. MASAI
Institute of Plasma Physics, Nagoya University, Nagoya 464, Japan
Abstract.- X- ray spectra of titanium He- like ions from JIPPT-IIU, TFTR and Dou- bletIII tokamak plasmas have been analysed by the same computer code. The disagree- ments between measurements and theoretical calculations are discussed in terms of atomic processes.
1. A t o m i c data and analysis.
The line intensities of titanium He-like ions are calculated by a collisional radiative model computer code which includes 60 levels up to n = 20[1]. The rate coefficients for He- like lines and for Li-like satellite lines are adopted from ref.2. For dielectronic Be-like satellite lines, the data i n ref.3 are t s e d . The inner-shell ionization which contributes to line z is calculated by the Lotz formula[4]. Other atomic data used in this code are described in ref.1. The cascade contributions from highly excited states and the recombination of ~ L l i k e ions are taken into account in this model. The following notations are used; w(2'P
-
l l S ) , z ( ~ ~ P ~-
l l S ) , y(23P1-
l l S ) , ~ ( 2 ~ s-
l l S ) , q(ls2s2p 2 P - 1s22s 2S), P ( l s 2 ~ ~ 2 ~ 'P-1s22s2 IS), j, k ( 1 ~ 2 ~ ' 2D-1s22p 'P). The effective excitation rate coefficient calculated by our code for z is smaller than that of ref.3 by a factor of 1.8.The value in ref.3 is overestimated and their corrected value is 20 % larger than ours.
The effective excitation rate coefficients for x and y agree within 10 %. The effective recombination rates agree within 20 %.
The synthetic spectra are fitted to the measurements. The electron temperatures are obtained from the intensity ratios of dielectronic satellite lines (j,k and n = 3) to w. The ion density ratios, n(Li)/n(He) and n(Be)/n(He), are derived from the intensity ratios of q to w and of
p
to w, respectively, where q andp
are produced by inner-shell excitation. Here n(He), n(Li) and n(Be) represent the densities of He-, Li- and Be-like ions, respectively.2. JIPPT-IIU Tokamak.
The time-resolved X-ray spectra were observed from an ohmic discharge in which a large amount of neon was introduced. The observed spectra (dots) and calculated synthetic spectra (solid lines) in 20 ms intervals are shown in Fig.l[5]. In order to explain the discrepancies between the observation and the calculation during the period of 80 - 100 ms, the charge exchange process between titanium ions and neon ions is included. The cross sections of this process are calculated by the method in ref.6. The results are summarised as follows. i))The plasma is in an ionizing phase at the beginning until about 80 ms, and the recombination takes place after 80 ms following the decrease in the electron temperature. The charge exchange recombination possibly explains the ion density ratios in the later period (80
-
100 ms). This rapid recombination process is responsible for vanishing x-ray emission after 100 ms(Fig.1). ii) Large discrepancies between the experimental and theoretical results for the intensity ratios of x, y and z to w are found. The observed values for x and y are always larger than theoretical ones.iii) If the electrons captured by charge exchange recombination between TiXXII and Ne ions are selectively distributed in the 33L) or 4 3 F state, x and y can be more enhanced than z and thus the observed spectrum can be explained(Fig.2).
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988175
C1-350 JOURNAL DE PHYSIQUE
4 0 - 6 0 nsec
1t = 1.2 kcY
a, r
7
n(Li)/o(Hc) -3.0'z
5 0 - n(Be)/n(He)-4.1c
1 0 0 ZOO 3 0 0 4 0 0
Fig.1 Observed(dots) and calculated(so1id lines) spectra from JIPP-T-IIU with neon puffing. The contributions of inner-shell
ionization are hatched.
0 Focal Plans (mm)
1 I I I I I I A
2.60 2.61 2.62 2:63 2.64 2.65 2.66 2.67 WAVELENGTH (A)
I I Fig.2 A calculated spectra taking into ID0 200 300 400 account the charge exchange between TiXXII
Channel Number and neon ions(hatched regions).
3. TFTR tokamak The spectra observed at the initial phase during ohmic heating show that the intensity of w is smaller than those of x, y and z[3]. This suggests that recombination makes a large contribution. Effective recombination rate for w is srnaller than those of x and y at Te < 1 keV. Although Bitter et al neglected the contribution of H-like ions, we introduced the H-like ions to get better spectral fits(Fig.3). The hatched regions indicate the contribution of the recombination. However disagreements for x and y still remains. In the period after 420 ms, x and y are always larger than z. These intensity ratios cannot be attained by only electron excitation and recombination. It is necessary to consider another mechanism which enhances x and y relative to z. This problem will be discussed in Sec.5. As the electron temperature rises with time, the derived ion density ratio n(Li)/n(He) decreases and n(H)/n(He) increases. This indicates the plasma is in a n ionizing phase.
Another point of interest is that the intensity ratio of z to q is nearly constant, 0.8 - 0.9, at Te < 1 keV. In the early phase of discharge, z is remarkably strong. Both z and q are produced by inner-shell processes from Li-like ions. In the periods 180
-
240 ms and 240 -300 ms, we have introduced high energy electrons of 7 keV and 8 keV wit11the concentration of 0.03 % and 0.05 %, respectively, and obtained a good agreement.
Without the high energy electrons, Be-like satellite lines near z are too strong to simulate the observed spectra.
Te= 1.35keV H = O Li = 0.6
Fig.3 Spectra from an Ohmically heated
0 100 200 300 400 500
plasma of TE'TR. Hatched regions represent the contribution of electron-ion recombi-CHANNEL NUMBER
nation.4. Doublet I11 (DIII)
Titanium spectra during ohmic heating and electron cyclotron heating (ECH) have been reported[7-91. The spectra show always large x, y and n = 3 satellite lines compared with theoretical values(Fig.4). The intensity of j is very small compared with those of k and n = 3 satellite lines during ECH. It is difficult to fit overall the spectra especially during ECH even with the high energy component of electrons.
Fig.4 Spectrum from D I I I during Ohmic
CHANNEL NUMBER heating-
Cl-352 JOURNAL DE PHYSIQUE
5. Discussions.
We have analysed the titanium spectra obtained from tokamak plasmas. The most serious problem is the intensities of x and y which are always higher than calculations. Both the effective excitation and recombination rate for z are larger than those for x and y. Thus z must be always larger than x and y with any mixture of n(H) and n(He). Moreover z can be produced by the inner-shell ionization from Li-like ions. But the measurements from T F T R and JIPPT-IIU show the spectra that x and y are stronger than z. For these problems, we assess the atomic data as follows:
i)Excitation rate coefficient
For He-like titanium ions, only the calculation by Bely-Dubau[2] is available Tlle dependence on the nuclear charge Z is studied for the excitation rate coefficients of He- like ions. We have found that it may be possible to increase the rate coefficients for x and y by a factor of 1.5. If the direct excitation rate coefficients for x and y are increased by a factor of 2, effective excitation rate coefficients for x and y become larger than that of a ; we then get a good agreement for x and y during 600
-
660 ms in T F T R and ohmic heating in DIII. The intensity of y is larger than that of x in most measurements, although theoretical calculations always give a larger value of x than y. This cannot be improved even if the branching ratio from 2 3 P to 23S is reduced to make x larger and z smaller.ii)Ion
-
ion and ion-
atom charge exchangeEven if the excitation rate coefficients for x and y are increased by a factor of 2, x and y are too weak to simulate the observed spectra in the early phase in TFTR and the later phase in JIPPT-IIU. This discrepancy may be attributed to charge exchange between H-like ions and neutral hydrogen or impurity ions such as oxygen. The effective charge exchange recombination rate between H-like titanium ions and the other impurity ions is estimated to be of the order of
lo-''
cm3/s a t 1 keV. The line intensity following charge exchange process depends on capture level ne, especially on t. The principal quantum number n can be roughly estimated, bute
distribution is not well known. The larger thee
-value, the stronger the intensities of x and y.iii) others
Cascade processes are very important for the effective recombination rate coefficient.
This needs to be assessed. Also the effect of the radial distribution should be considered.
References [I] T. Fujimoto and T. Kato, Phys. Rev. A 30 (1984) 379.
[2] F. Bely-Dubau, P. Faucher, L. Steenman-Clark, M. Bitter, S. von Goeler, K.W. Hill, C. Camhy-Val and J. Dubau, Phys. Rev. A 26 (1982) 3459.
[3] M. Bitter et al., Phys. Rev. A 32 (1985) 3011.
[4] W. Lotz, ZPP 1/62 (1967)
[5] T. Kato, S. Morita, K. Masai and S. Hayakawa, Phys. Rev. A 36 (1987) 795.
[6] V.A. Bazylev and M.I. Chibisov, Sou. J. Plasma Phya. 5 (1979) 327.
[7] P. Lee, A.J. Lieber and S.S. Wojtowicz, Phys. Rev. A 31 (1985) 3996.
(81 P.Lee, A.J. Lieber and R.P. Chase, Phys. Rev. k t i . 5 5 (1985) 386.
[9] P.Lee, A.J. Lieber, A.K. Pradhan and Y Xu, Plrys. Rev. A 34 (1987) 3210.
