PFC/JA-82-11 R
OBSERVATION OF H- AND He-LIKE X-RAY LINE EMISSION
IN HIGH DENSITY TOKAMAK PLASMAS
E. Kaline, J. K91lne and J. E. Rice
Plasma Fusion Center
Massachusetts Institute of Technology,
Cambridge, MA
02139
June 1982
This work was supported by the -U.S. Department of Energy Contract
No. DE-AC02-78ET51013. Reproduction, translation, publication, use
and disposal, in whol-e or in part by or for the United States government is permitted.
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Observation of H- and He-like X-ray Line Emission
.in High Density Tokamak Plasmas
E. Killne and J. Kallne
Harvard-Smithsonian Astrophysical Observatory
Cambridge, Massachusetts
02138
and
--
J.E. Rice
Plasma Fusion Center
Massachusetts Institute of Technology
Cambridge, Massachusetts
02138
Page 2
Abstract
been
measured
in
the
region
=
X
4.3-5.1 K.
observation of the principal n=2 to n=l X-ray
sulphur,
and
for
range Ne = (1-6) x
inner
shell
He-like
sulphur
1014 cm-3.
excitation
results are compared with current
We report the
B-like
for
and chlorine in the density
recombination
and
only weakly seen.
The
Dielectronic
satellites
lines
have
ions
impurity
Characteristic X-ray spectra of plasma
are
atomic
calculations
of
line
spectra -and transition rates, and are of interest for both atomic
physics and plasma diagnostic applications.
1
I
X-ray spectroscopy of highly ionized
classical
the
with
started
which
atoms,
work on spark discharges in the 40's (Edl'n
and Tyr'n 1939), has received renewed interest with the advent of
the
laboratory produced hot plasmas as well as
of
range
broad
with improved observations of X-rays from
In
plasmas.
stellar
magnetically confined plasmas, steady and controllable conditions
for
periods of time (>100 ms).
extended
be
can
of electron density (Ne) and temperature (Te
sustained
With temperatures of a
few keV medium Z impurity atoms, frequently found in plasmas from
plasmas produce characteristic X-ray emission from H-,
Li-like
just
transitions
on
X-ray
the
emission
from sulphur and chlorine
density
high
P1/2,3/2
the abundance of these ions
and 1s2 1 S0 - ls2p
the
in
to with letter symbols as in Gabriel (1972)).
coronal equilibrium) (Jacobs et al. 1979),
temperature diagnostic or, if Te
by
x
The wH
equilibrium.
satellites
of
the
ground
P1) reflect
(Transitions
plasma.
are
Since the
(for a plasma in
abundance ratio is a predictable function of Te
this
(Ne < 8.5
He-like
(w) transitions to the H- and
(s 21/2 - 2p
related
first
tokamak Alcator C located at MIT.
The resonance
states
the
Here we report on
present as natural impurities in the
10 14 cm 3 )
and
states
the application of such knowledge
as
allows one to diagnose the plasma.
measurements
and
He-,
The resulting line spectra are relatively simple
ions.
and can provide information on highly ionized atomic
related
These
are stripped of all but the last few electrons.
tokamaks,
the wH/He
ratio is a
is known, it provides a test of
and wHe
type
transitions are accompanied
ls (nl.)
J
-
2p (nl.)
J
and
Page 4
2
is 2ni.) - ls2p (nl).
(n > 2) are mainly
nli
orbitals
The
satellites
populated through dielectronic recombination so these
have
a
strong dependence on T e .
Inner shell excitation of the
relative
intensity
its
so
satellite
nl. -orbit is predicted to be strong for the q
can be used to detect departure from
to w H
the coronal equilibrium abundance ratio of Be- to Li-like ions in
(Bhalla
plasma
the
3p2,1
transitions is 2
1 S0
- ls 2 p
is 2
1 S0
- ls2s 3S1
transition
transitions between the
density
long
a
the X-ray decays
of
those
to
with
increase
states
n=2
lived
comparable
become
and
over
to- wHe
However, the rates of collisionally induced
and Te.
range of Ne
in the He-like charge state
relative
should appear with fixed intensities
forbidden
the
and
y)
(x and
(z)
intercombination
The
al. 1975).
et
cm 3
observed at some critical value of N e (N * = (2-4) x 1013
: e
The most direct manifestation
(Gabriel 1972).
for S and Cl)
in
hereof is predicted to be a decrease
23 P2,1 (Pradhan et al. 1981).
wH
is
N
> 1013
e
the
et
suggested
also
cm- 3
and P1/2
information
exists,
wH (P1/2
3/2)
however,
ratio.
induced
et
2
al. 1979).
on
confronted
with
state
1/2
,transitions
of
in
(Vinogradov
experimental
Little
the density dependence of the
Neither has the density
dependence
of
(Pradhan et al. 1981) re-distribution (or
excitation) of the He-like n=2 states 2 1 S , 23S1
0
been
components
to
density dependent in the region
be
induced 22 S2 +2 2 P3
Bei.gman
al. 1977;
collisionally
to
The P3/2
because of a preference for the P
collisionally
H
z/x+y
ratio
line
collisional transfer of population from 23S
the
reflecting
the
much
experimental
and
2 3pOl,2
information.
letter we report new measurements of the H- and He-like
In this
emission
Pajte .5
sulphur and chlorine under varying plasma conditions
of
spectra
for densities near and above N e*.
The experiment was performed at the Alcator C tokamak with a
high through-put, high resolution Bragg crystal
installed
newly
re-entry tube located at
circular
(r
port
a
16 cm) Mo plasma limiters.
=
is viewed through a
plasma
which
also
accommodates
two
The vertical entrance
slit of the spectrometer was placed about 70 cm frdm
center.
1933;
Bamos
(Van
geometry
The
1977).
Taylor
and
Schnopper
Samos
van
the
in
spectrometer
plasma
the
photons are diffracted off a cylindrically curved,
The
highly reflective PET crystal (R = 58.5 cm and 2d = 8.742 A)
and
sensitive proportional counter.
The
detected
position
a
with
dispersion (C0.3 mm/mA at
cylinder
focussing
and
axis
AX/X
horizontal
the
along
takes place in the non-dispersive
The overall resolution of
vertical direction.
is
A -4 A) occurs
spectrometer
the
-1/2000 corresponding to a spatial line width of 0.7 mm
(FWHM), partially limited by the detector.
at
Plasmas of deuterium or hydrogen were produced
magnetic
fields
toroidal
of 60 to 80 kG and at plasma currents of 350 to
500 kA.
The discharges were typically 300 ms long with a
current
condition
prevailing for 100-150 ms, which was selected
Besides the readily available
for our measurements.
on
the
macroscopic
(Alcator
group
1980).
obtained
from
Te
and
Ne .
A
independent
This allowed us to observe
line spectra of X-ray emission under known plasma
varying
information
plasma parameters, the electron density and
temperature of each plasma shot were
diagnostics
steady
conditions
of
typical example of an X-ray emission
Page 6
is
spectrum from a single plasma shot
The
Fig. la.
in
shown
results on selected spectral regions are shown in the lower three
panels of Fig.
l, namely He- and Li-like
(Fig. lb)
sulphur
and
and H-like emission in sulphur
(Fig. lc),
molybdenum
in
along with Ne-like emission
plasma conditions [Ne (10
14
cm
-3
-
),
Te (keV)]
the
for
Line identification was made with spectroscopic
atomic
Cl
by
the
w
line
(Figs. lb,c).
Besides-these main lines of
some
predicted
of
the
present.
Among
n=2
1s2 2s
the
satellites
-
ls2s2p
the
the
strongest one, the
about
k
j
given
q
should
the
satellites
S
of Li-like systems are
from
2
Of the ls 2p
singly
-
1s2p 2
dielectronic
line is observed, while the theoretically
line, is unseparable from z;
j
is estimated
1.4 times the-intensity of k (Bhalla et al. 1975).
From the predicted intensities of the n=2 satellites, only
and
of
system,
Bfe-like
satellites from doubly excited states (populated by
recombination)
Cowan
with x,y, and z
along
satellites
excited states, we see the q and r lines.
be
information
It- is thus found that the spectra
dominated
are
a-d
cases
calculations (Vainshtein and Safronova 1978;
Safronova 1981).
1981;
to
The
(3.2,1.2), and (3.5,1.3).
(3,1.1), (2.3,1.2),
were:
and
Several
(Fig. ld).
shots of similar parameters were added in Fig. lb-d.
plasma
from
chlorine
in
emission
j,
k
give finitec.ontributions to our S and Cl spectra
observed
intensity
of
k.
Higher
orbital
(n>3)
are probably the cause of the contributions appearing
on the long wavelength side of wHe'
Pag.e 7
ld)
Sulphur in the H-like charge state is manifested (Fig.
doublet seen at 4.726/4.731 A (separation 5.3
by
the
mA)
which agrees with the
were
resonance
to
fitted
which
are
(Vainshtein
of the wH
predicted
locations
1981).
Peaks
intensity which is
an
of
the
w
E
satellites
They amount to less than 1/20
Safronova 1978).
and
(Safronova
measured spectrum at X = 4.760 and 4.784
the
the
prediction
upper
limit
since
the
line
identification is impeded by the presence of molybdenum emission.
The Mo spectrum is dominated by principal Ne-,
Na-,
and
Mg-like
ld) along with dielectronic
2p-3d transitions (indicated in Fig.
The satellite intensities
recombination satellites (Cowan 1981).
or Cl and Mo spectra from the same plasma exhibit the
4
expected trend of a -Z dependence (Gabriel 1972).. We also note
in
that
our
S
single most-significant difference between our He-like
the
Princeton PLT tokamak
at
measured
spectra of S and Cl and those of Fe previously
the
2 keV) (Bitter et al. 1979) is the
(at Te
order of magnitude larger relative intensity of n=2 satellites in
the
Fe
this
spectra;
is
a manifestation of the Z4
largely
dependence and the difference in wavelengths
Typical values of relative satellite
and
0.07
observed
as
Comparison
with
dependence
on
and
k
calculated
electron
k
the
for
e)
et
al. 1975).
temperature
at
transitions
in Cl.
and
their
intensities
1.0 keV and
Tz
Z
0.7
keV
This Te-value is somewhat lower than the
1.2 keV set by other diagnostics.
the
q
q
0.09
are
intensities
ionization (Tz) temperature,
and
would imply plasma conditions of Te,
(Bhalla
and
(4.4 resp 1.8 A).
The parameter
Tz
represents
which the abundance ratio of Li- to He-like
Patge 8
a
in
plasma
a
indicate
would
use
make
however,
z
Tz
available.
We
in this context.
wH/w He
He
The result on wH
Fig. 2
measurements of the ratios wH/wHe
principal
and
this
we
of
and qLi wHe
always
transitions
He-like
0.13(0.19),
give
We envisage the value
and plan experiments for simultaneous
Tz
of
diagnostics
spectra
the
deviation from equilibrium or could be accounted
true
for within experimental uncertainties.
The
whether
It is not clear
among the individual data points.
indicates
Although
trend of the data there -is some scatter
the
follows
prediction
in
dependence based on
al. 1979).
et
(Jacobs
equilibrium
e
presented
is
as a function of Te
with the predicted T
compared
and
coronal
dual
> T
measurement of the ratio
own
our
of
e
state of transient ionization.
There is no other diagnostic measurement on
can,
T
result
i.e., our
ions represents coronal equilibrium;
dominate
our
0.25(0.28), and 0.50(0.47) as
typical relative intensities for the x, y, and z transitions in S
(Cl).
calculations of Gabriel
The
ratios, namely, 0.13 (0.17),
densities
below
its
(1972) predict quite similar
0.25(0.25),
critical
value.
but
and 0.64(0.60)
Data
from
for
solar flare
measurements have already confirmed these predictions for the low
density regime N e << N e* (Doschek et al. 1981).
it now appears that
densities
an
order
x,y,
the
and
z
lines
of magnitude above N *.
e
From our results
remain
strong
In particular, the
lack of a significant decrease in the ratio z/x+y at our
densities
of Ne
~3 x 10
14
cm
-3
is noteworthy.
at
typical
There is also no
clear indication of a simple Ne-dependence in the observed x,
y,
Pae9
and z intensities for our plasmas of varying density in the range
(1-6) x 101- cm
3.
higher
a
of
suggestive
are
These results
value for the critical density than predicted in the framework of
standard theories.
the
in
observed
fluctuations
results
our
of
A conspicuous feature
line ratios for
z/x+y
and
X/y
seemingly similar plasma discharges even though the average
vary
intensities of x,y and z can
the
from
two
of
factor
for nearly constant w emission.
even
averages
a
line
In particular, the
predictions.
atomic
to
close
fall
ratios
of
degree
the
is
These variations
the
sometimes occur in connection with unusual time histories of
Therefore,
emission.
X-ray
one
seek
might
the cause in the
the
plasma
such
as
equilibrium.
Under
such
conditions,
ionization
excitations could contribute significantly to the
the
3
2
-3
p2 ,1
and
2
S
from 2 3
a
to 2
(Vinogradov et al. 1977;
the
of
n=2
collisional
population
population
3 P1,2.
(Pradhan
transfer
measured
et
Of note here is the predicted
Beigman et al. 1979) collisional mixing
states for H-like ions affecting even the P 1 / 2
3 /2
We
states and resulting in line ratios wH(Pl/2)/wH(P3/2) > 0.5.
have
of
states and affect the line ratios in a
more complex way than just
al. 1981)
from
departure
transient features of the
this line ratio for H-like S and find values that
indeed are larger than O.5.' 'The observed range of
variation
0.5 to 0.8 for densities in the range (1-4) x 1014 cm
3
is
but with
no apparent correlation in the variation of wH (P/2 )/wH (P3/2 ) and
N
.
A
common cause of these line ratio variations and those of
the principal He-like transitions might be suspected which
calls
Page 10
for
of
measurements
simultaneous
both
the B-like and He-like
parts of the spectra.
He-
In conclusion, we have measured H-,
for
spectra
S
identified
and
Cl
and
transitions and the satellites.
weak
which
can
qualitatively
as
can
the
theories
relative
satellite
intensities
be
explained
within
but
predicted
the
of
intensities
the
regime
manifestation
of
structure
components
of
both
+
ln
are
existing
resonance
the
(Ne > 1014
such effects,
Instead,
depletion of the forbidden.line, is not observed.
fine
line
Collisional mixing of the
2n states should be important in our density
cm-3 )
principal 2n
the
The
and He-like sulphur.
transitions of H-
Li-like
and
H-like
the
the
resonance and
He-like intercombination transitions show quite large variations,
might
which
suggest
that density dependent collisional effects
are of a complex nature or that transient plasma effects such
as
departure from ionization equilibrium are important.
acknowledge
We gratefully
discussions with Dr.
for us.
Dr. .
R.
R.D.
many
and
supported by the U.S.
the
interpretational
Cowan who also performed calculations
We are also thankful for the
Parker
friendly
Alcator
support
group.
Department of Energy.
we
enjoyed
from
The experiment was
Page 11
References
17, 258.
Alcator Group,1980, J.Vac.Sci.Technol.
I.L.,
Beigman,
Bureeva,
Sov.Astron.
I.,1979,
Skobelev,
Yu
and
L.A.,
23, 725.
Presnyakov,
Bhalla, C.P., Gabriel, A.H., and
L.P.,1975,
MNRAS,
172, 359.
Bitter, M.,
43, 129.
et al.,1979, Phys.Rev.Lett.
Cowan, R.D.,1981, unpublished, private communication.
Doschek, G.A., et al.,1981, Astroph. J..
249, 372.
Edlen, B. and Tyren, F.,1939, Nature 143, 940.
Gabriel, A.H.,1972, MNRAS 160, 99.
Jacobs, V.L.., et al.,1979, Astroph.J.
230, 627.
Pradhan, A.K., Norcross, D.W., and Hummer,
J.
246, 1031,
D.G.,1981,
Astroph.
ibid 249, 821.
Safronova, U.I., 1981, Physica Scripta, 23, 241.
Schnopper,
and
H.W.
Taylor,
DOE
P.O.,1977,
Report
E4-76-S-02-4021.
Vainshtein, L.A.
and
Safronova,
U.I.,1978,
Atomic
Data
and
Nuclear Data Tables 21, 49.
Van Hamos, L. 1933, Ann.der Physik 17, 716.
Vinogradov,
A.V.,
Yu
Skobel,
Sov.J.Plasma Physics 3, 389.
I.,
and
Yukov,
E.A.
/ 1977,
Pagg 12
Figure Captions
Fig.
1
Example of X-ray spectrum recorded for
discharge
showing
detector [a].
of
He-like
X -range
single
covered
plasma
by
the
Partial spectra showing the X-ray emission
Cl
[b]
emission from Mo [d].
1972;
full
the
a
and
S [c),
and H-like S along with
Wavelengths of predicted
Vainshtein and Safronova 1978;
(Gabriel
Safronova 1981) S
and Cl lines are indicated relative to the resonance line
(w);
Fig. 2
for the letter symbols used, see the text.
Measured intensity ratios of the resonance transitions in
H- and He-like sulphur plotted vs.
electron temperature.
Comparison is made with coronal equilibrium prediction.
4.30
4.40
4.50
4.60
X (A)
a)
-wxy
100
50
z
----------
4.48d
4.460
4.440
4.50d
X(A)b)
400 I
w
x y
k z j
q r
200-J
w
z
z
r
5.040
0
400
w
5.060
5.080
x y
q r
5.100
.X(A)k zj
0
c)
200
I
4.800
4.7o6
X (A)
200
(0
o~
to)Cl
0
(D)
-;
M
I0
to
(n
0
100
/
*
?~
;co A..
.. ~.
..
.
POSITION (CHANNEL NO.)
d)
REL. INTENSITY wH
/W He
0
(n1
I
I
U
-1
0
0
P~
-H
CD
0
0
Ie
0
P
N
Cr)
C
0
N
I
C
QI
I0
-L
z
-Hi
P1
0
0
C
01
CD
N.
0
0
0
I
I