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Measurement
of
the
Temperature
of
Cold
Highly Charged Ions Produced in an
Electron Beam Ion Trap
P.
Beiersdorfer
V.
Decaux
K.
Widmann
Prepared
for
Submittal
to
7th
International Conference on the Physics
of
Highly Charged Ions
September 19-23,1994, Vienna,
Austria
September 14,1994
This
is
a preprint of a paper intended for publication in a journal or proceedings. Since
changes may be made before publication, this preprint
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of
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author.
c
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..
.,
7.
International Conference on the Physics
of
Highly Charged Ions
September
19
-
23,
1994,
Vienna, Austria
Paper:
Mo62
Measurement
of
the Temperature
of
Cold Highly Charged Ions
Produced in an Electron Beam Ion Trap
P.
Beiersdorfer,
V.
Decaux,
K.
Widmam
Department
of
Physics and Space Technology
Lawrence Livennore Nationul Laboratory, Livemre,
CA
94551,
USA
The temperature
of
highly charged titanium ions produced and trapped
in
an
electron
beam
ion
trap
was determined by precisely measuring the broadening
of
the emission line profile caused by the
thermal Doppler
motion.
The
measured
temperature ranges from about
700
eV
for
deeply trapped
ions to about
70
eV for ions
in
a
shallow
trap.
The
latter
value
represents the lowest temperature at
which the
x-ray
emission
of
collisonally excited heliumlike
Tim
ions has ever been recorded,
and
the measured transitions represent the narrowest
x-ray
lines
observed
from highly charged
titanium
ions.
Author to whom
all
correspondences should
be
se
nt:
Peter Beiersdorfer, Lawrence Livermore National Laboratory, P.
0.
Box
808,
Mailstop
L-421,
Livermore, CA
9455
1,
USA.
Phone:
(5
10)
423-3985,
FAX
(5
10)
422-5940.
La;srFUBUTlON
OF
THIS
DOCUMENT
IS
UNLlMtTEIJ
-
1
9;a
I.
Introduction
Characteristic x-ray lines
of
highly charged ions
from
virtually all plasma sources are
broadened by the thermal motion
of
the emitting
ions.
In
fact, the line broadening induced by the
thermal motion represents a standard technique for measuring the ion temperature of high-
temperature plasmas
[l].
The line emission from laser-produced plasmas may
be
broadened
further by opacity or density effects.
The line emission observed
in
accelerator-based
measurements is broadened by the Doppler effect, because the necessity
for
a finite acceptance
angle entails viewing relativistic ions
with
different velocity components. The
line
emission
from
any
of these sources may
be
broadened further
by
satellite lines populated by
single
or multiple
electron capture into high-lying spectator levels.
As
a result of
this
broadening,
the
resolution and
the precision
with
which measurements
can
be
made
is
limited.
I
The
electron
beam
ion
trap
(EBIT)
facility uses a monoenergetic electron
beam
to
produce
and excite highly charged ions
in
a trap
[2].
Because excitation processes can
be
selected by
choosing
the
appropriate
beam
energies, the population of satellite transitions that may broaden
a
given
line
in
plasma and accelerator sources
are
avoided
131.
Moreover, the
electron
density
is
less
than
5
x
1012
cm-3
so
that opacity
or
density effects
are
unimportant and broadening effects that
may affect highdensity plasma sources are absent.
On
the
other
hand, interaction with the electron
beam
causes strong heating of the ions; thus ion thermal broadening is expected
to
play a role
in
determining the
widths
of
x-ray lines produced
with
an
EBIT device
[2].
The tempemure
of
the
ions, however, must
be
limited
by the fact that ions with enough kinetic energy
to
overcome the
trapping potential
will
leave the trap and
are
lost. By adjusting the trapping potential
it
should
thus
be
possible to reduce the ion temperam.
In
the absence of
any
other line-broadening
mechanism
we
thus
expect to observe x-ray lines
with
widths
much less
than
achievable
with
any
other
som,
provided the temperature of the ions trapped
in
the
EBIT
device
is
reduced sufficiently.
4
In
the
following,
we present a measurement
of
the line widths of the transitions (is2p2)5~
+
(ls22p)3,2
and
(ls2p2)3~
-+
(ls22p)1/2
in
lithiumlike Ti19+. These transitions,
in
standard
I
I)
-
2
~
__
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