SEPARATION OF CARBON ISOTOPES IN THE SEPARATOR WITH
TWO OPPOSING AXYSYMMETRIC MAGNETIC FIELD REVERSALS
L.A. Bondarenko, N.P. Gladky, Ye.V. Gussev, P.L. Makhnenko, L.I. Nikolaichuk,
V.A. Popov, E.I. Ponomarchuk
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
E-mail: [email protected]
The results of studies on the use of the separator with two reversals of opposing axially symmetric magnetic field
for the separation of carbon isotopes are presented. The dynamics of the isotope separation process is analyzed numerically for different modes of isotope separation with and without reflection of a lighter component of the isotope
mixture. Consideration is given to the use of the annular multiaperture injection or the annular beam injection, and
also, the antiparallel injection to the magnetic system of the separator in order to increase the installation capacity.
PACS: 29.27.-a
INTRODUCTION
The isotopes of chemical elements, both stable and
radioactive, are widely used in everyday practice.
Among areas of application we mention nuclear power
engineering and defense industry with products estimated at tens and hundreds of tons, and also, analytical and
medical investigations handling tens of grams, etc.
While previously medicine had used short-lived radioisotopes as markers, now a diversity of diagnostic techniques using stable isotopes have been developed. They
are based on the isotopic composition change of stable
substances in the human body when compared to the
natural balance.
By now, the rare stable carbon isotope 13C has found
extensive use [1, 2]. The currently used technology to
produce highly enriched isotope 13C (natural concentration of 1.1%), time-consuming, energy-consuming and
inefficient [3, 4]. For widespread use of stable isotope
13
C is necessary to improve existing and develop new
methods of producing isotopes. In this connection it is
interesting to study the possibility of creating a simple
and user-friendly operation of the plant.
One of the promising methods is the electromagnetic
separation of isotopes in magnetic fields of acute geometry having axial symmetry. Its advantages are the ability to work in a wide range of atomic masses, achieving
almost 100% separation, even with a single-stage cycle.
Separators using this separation method, favorably high
speed and ease the transition to work from the masses of
other isotopes, as well as small size, allows to create
mobile devices.
The theoretical basis of the method for isotope separation in cusped magnetic fields having axial symmetry
has been described in ref. [5].
Fig. 1. Principle of isotope separation
in opposing axially symmetric magnetic fields
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Particles from the source A, located in the left-hand
magnetic-mirror (Fig. 1) at a distance r0 from the magnetic axis 0Z (symmetry axis), are injected along the
axis at a rate v0. The trajectories of particles moving
toward the region of a zero magnetic field are essentially dependent on the parameter η, which is described by
the expression
r0 qH 0
,
(1)
mv0
where q and m are, respectively, the charge and mass of
the particle; v0 is the velocity at the moment of injection; H0 is the magnetic field strength on the axis. The
particles, injected parallel to the axis of the system at
η<0.75, while passing the zero magnetic field plane,
come over to the right-hand mirror of the trap, rotating
round the axis of the system and forming a helix with a
pitch
h
2 r0
1
2
.
(2)
Hence, if the ions, injected from the source at the
same r0, have the same velocity v0 but different masses,
then in the right-hand mirror the ions move in helix with
different pitch distances; that finally results in a spatial
separation of particles having different masses. At η≈1,
the particles injected parallel to the axis of the system,
reflect from the zero magnetic field plane and leave the
trap through the left-hand mirror or the annular slit.
Those it has two methods of particle separation: after
passing through the region of zero magnetic field by
using a difference in a spiral step or picking up the
magnetic field conditions and the velocity of the particles, to achieve different masses reflect conditions or
passing through the region of zero magnetic field (ie
because of the mass difference one particle
0.75 in
the while for others
1 even greater spatial separation of the particles can be achieved).
The theoretical findings of paper [5] were confirmed
experimentally [6 - 8], and that gave grounds to further
investigations. Various improvements of the magnetic
system were proposed, and methods of taking into account parameters of isotope sources were developed [9].
To attain a higher dispersion, the ion drift region in the
uniform axially-symmetric magnetic field located after
the cusped field was proposed to be made more extendISSN 1562-6016. ВАНТ. 2016. №3(103)
ed [6], or the field strength should be linearly varied
along the axis [10]. It has been shown in [11] that the
use of the second region with a cusp field (second reversal) instead of the drift space [6, 10] substantially improves the process of separation and makes it possible
to reduce the facility size. While passing over to the
plane of the second-reversal zero magnetic field, the
particles show some dispersion on the radius of intersection of the plane; that provides attaining a higher dispersion of isotopes on the radii. This sort of the separating
system permits the use of annular injection to the separator.
For verification of the suppositions used in numerical studies and optimization of technological issues, a
pilot separator with two magnetic field reversals is being created.
EXPERIMENTAL FACILITY
The based on the above-described principle of separation (Fig. 2), involves the ion source, ion optics, the
electromagnetic system, diagnostic devices, the vacuum
volume and technological systems (power-supply, vacuum and cooling systems).
The ion source with thermal ionization (and other
types of ionization) is used for isotope production. The
process admits the use of both single- and multiaperture sources, holes of which are located on the radius r0 given by eq. (1). The ion beam at the magnetic
system inlet is formed by the multielectrode ion optics.
The magnetic system of the separator consists of
eight solenoids, grouped in pairs. The outer diameter of
the coils is equal to 0.4 m, the inner diameter is
~ 0.28 m, the coil length is ~ 0.096 m, and the coil separation is 0.04 m. To energize the magnetic system, a
powerful constant-current supply, providing a load current up to 500 A, that allows you to create a magnetic
field at the injection radius r0 = 0.07 m more 0.85 T.
Fig. 2. General view of the separator
By varying the coil connection circuit, different
magnetic field configurations can be created in the separator. A version of the magnetic system with two successive cusp field regions is illustrated in Fig. 3, where the
zero magnetic field planes are depicted in red, and the
green line shows the vacuum chamber of the separator.
Fig. 3. Magnetic system geometry
of the two-reversal separator
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To measure the magnetic field distribution in the
separator volume, a mechanical robot was created. The
Hall probe was moved by means of stepping motors.
The device control as well as the information data input
and processing were realized by a personal computer
according to the prescribed algorithm.
The complexity of theoretical description of particle
behavior in the magnetic field of the geometry under
study, as well the nonavailability of the codes developed
by other authors have induced to develop the original
computer code BonParticlePaths.
The code makes it possible to calculate 2.5Dtrajectories of the isotopes in the magnetic field generated by a set of solenoids. For convenience in operation
with the code, a shell program was developed.
The developed code has enabled us to carry out numerical studies on the particle behavior in the separator,
to investigate the influence of separator parameters on
the separation process, and to determine their optimum
values without experimentation.
STUDIES ON THE POSSIBILITY
OF CARBON ISOTOPE SEPARATION
IN THE SEPARATOR BEING CREATED
For numerical simulation, the parameters of the
above-described separator were used.
The earlier studies, both experimental and numerically simulated, were based on the assumption that the
injection plane is located at the place, where there is
only the direct-axis component of magnetic field, i.e., in
the plane passing through the center of the coil that
forms the first magnetic mirror. In actual practice, for
some technological reasons, it is not always possible to
make the injection plane coincide with the mentioned
plane. Therefore, we investigated the effect of the injection plane position on the separation characteristics. The
studies were performed in the mode of reflection of a
lighter component of the isotope mixture. The isotope
injection plane was between two coils (the first mirror
field is formed by two coils, Fig. 3) or at a point of
magnetic field maximum on the radius of injection, and
also, on the left boundary of the magnetic system of the
separator. In all our calculations, the coil current was
taken to be 100 A, and the injection was carried out at
radial distance of 0.07 m.
The studies have shown that in each of the cases under consideration there was the range of injection voltage values (ΔUinj), which enabled the realization of the
mode of reflection of a lighter isotope-mixture component from the second magnetic barrier.
If injection is realized in the plane halfway between
the first two coils, where the magnetic field B z0 induction is equal to 1347.84 Gs, then the ΔUinj values lie in
the range between 735 and 797 V. Fig. 4 illustrates the
behavior of isotope trajectories at an injection voltage of
736 V.
Now we consider the case when the injection plane
is at the left boundary of the first coil (z=-6.61 cm). This
arrangement may be required to improve the heat removal from the ion source, or to reduce considerably the
expenses for magnetic field generation if the magnetic
system is encased in a magnetic shield. The mode of
129
separation at Bz0=1242.04 Gs is
637 Uinj 690 V.
realized
within
Fig. 5 shows the carbon isotope separation for the
case when both isotopes arrive at the exit of the tworeversal magnetic system.
The injection was carried out in the plane, where the
longitudinal component of the magnetic field is the
maximum, and the radial field equals zero. The angular
velocity spread amounts to ± 0.026 rad. It can be seen in
the 3D picture (Fig. 6) that the isotopes of different
masses are successfully separated on the radius in the
cross-sectional plane.
Fig. 4. Carbon isotope trajectories: 12С – red curve,
and 13С – blue curve
The positioning of the injection plane at the field
maximum offers the best efficiency. At Bz0=1452.58 Gs,
the separation occurs in the widest range of Uinj from
797 to 864 V, thereby enabling one to choose most exactly the operating conditions for collecting the separated components. In this case, it is possible to use higher
injection voltage, to increase the isotope current and
thus to increase the facility capacity.
If the magnetic field is determined and the injection
position is chosen, then it is possible to calculate the
injection voltage, at which the isotope of mass Mi will
come back to the left mirror:
U крит
1
R л Bz
Mi
144,2
0
2
,
(3)
where Rл is the Larmor radius of the isotope. This is
confirmed by the results given in ref. [5]. The existence
of the ΔUinj. range permits one to exclude the modes, at
which the trajectory of the lighter isotope reflected from
the magnetic mirror would intersect the injection trajectories or coincide with them, and that would adversely
affect the process of separation.
The separation based on the retrace of the lighter
isotope-mixture component to the left magnetic trap
mirror (the “heavy-light” principle) is appropriate for all
the elements, both light (ΔM/M ≈ 0.1) and heavy
M / M 0.005 [11]. In some cases, the separation on the
“heavy-light” principle turns out to be the only possible
method of attaining high separation selectivity for heavy
elements.
The above-given results of the investigation were
obtained in the assumption that the particles were injected from the point source at a rate of v0 along the axis. In actual practice, the particles are injected from a
certain region and are spread not only in values, but also
in the initial velocity direction. In the studies presented
below, the particles are injected from the hole of diameter 2ri=1.4 mm (parameter of the source in use), and the
radial velocity at start is determined as v0 r tg v0 z .
Fig. 5. Trajectories of 12С (red) and 13С (blue) isotopes
at injection voltage of 1031 V
130
Fig. 6. 3D image of isotope trajectories
Fig. 7 shows the distributions of 12C and 13C isotopes
(red and blue points, respectively) in the cross-sectional
plane at the output of the magnetic system at injection
from several emitting holes situated at different angles
on the 7 mm radius of injection. The width of the ring,
on which the 13C isotope falls (blue), is equal to
~ 1.1 cm, and the ring width for 12C (red) is about
4.3 cm. It can be seen that the isotopes are well separated, the spacing between the rings being ~ 1 cm. As is
obvious, the radial separation of the isotopes in the tworeversal magnetic field system permits the use of circular injection.
Fig. 7. Cross-section for carbon isotope beams
at the output of the magnetic system
So, the separator efficiency can be considerably increased [11] due to the application of circular injection.
Fig. 8. Carbon isotope trajectories:
12
С – red line, and 13С – blue line
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To ensure high purity of separated isotopes, it is
necessary that the separator operation conditions should
be carefully maintained. If however the mode of lighter
component reflection is used, then it is easier to attain
practically a 100% isotope separation.
Fig. 8 shows the behavior of isotope trajectories in
the mode of reflection. In this case, the separated isotopes will be collected from the opposite sides of the
magnetic system of the separator.
The separator capacity can be doubled if making use
of the magnetic system symmetry along the longitudinal
axis and injecting the isotope mixture from two opposite
ends of the separator (antiparallel injection). In this
case, both the modes of isotope passage through the
magnetic system and of lighter component reflection
can be used.
Fig. 9 shows one of the variants of isotope separation at opposite sides injection in the mode of lighter
component reflection.
Fig. 9. Antiparallel carbon isotope injection:
12
С – red line, and 13С – blue line
The 12C isotope, which undergoes reflection, is collected from two opposite sides of the separator, and the
heavy 13C component is collected at the center of the
separator.
CONCLUSIONS
Analysis of the results shows that the prepared separator with fields acute geometry can successfully separate the isotopes of different elements [11 - 13] (carbon
paper), without making design changes to the plant,
only by changing the magnetic field strength and the
injection pressure.
We derive the conditions imposed on the injector for
isotope separation depending of type of bias injection
from the plane, where there are only pro-longitudinal
component of the magnetic field.
Two- reversible advantage of the system is the possibility of one- reversible isotope separation radius (not
in azimuth due to the difference in the helix step in onereversible mode). This feature allows both to reduce the
length of the separator and reduce the cost, and using
circular injection improve performance. Separators of
this type may be carried out isotope separation beams
which are spread in the radial and angular characteristics (within certain limits) without focusing in the separation device.
It also shows that high purity separated isotopes
(particularly heavy isotopes) is easier to achieve when
using the reflection mode, the lighter components of the
isotopic mixture.
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Article received 26.02.2016
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РАЗДЕЛЕНИЕ ИЗОТОПОВ УГЛЕРОДА В СЕПАРАТОРЕ С ДВУМЯ РЕВЕРСАМИ ВСТРЕЧНЫХ
АКСИАЛЬНО-СИММЕТРИЧНЫХ МАГНИТНЫХ ПОЛЕЙ
Л.А. Бондаренко, Н.П. Гладкий, Е.В. Гусев, П.Л. Махненко, Л.И. Николайчук, В.А. Попов,
Е.И. Пономарчук
Приведены результаты исследования использования сепаратора с двумя реверсами встречных аксиальносимметричных магнитных полей для разделения изотопов углерода. Численным методом анализируется
динамика процесса разделения изотопов при различных режимах сепарации изотопов как с отражением более легкой компоненты изотопной смеси, так и без отражения. Рассмотрено использование многоапертурной кольцевой инжекции либо инжекции кольцевого пучка, а также встречной инжекции в магнитную систему сепаратора с целью повышения производительности установки.
РОЗДІЛЕННЯ ІЗОТОПІВ ВУГЛЕЦЮ В СЕПАРАТОРІ З ДВОМА РЕВЕРСАМИ ЗУСТРІЧНИХ
АКСІАЛЬНО-СИММЕТРИЧНИХ МАГНІТНИХ ПОЛІВ
Л.О. Бондаренко, М.П. Гладкий, Є.В. Гусєв, П.Л. Махненко, Л.І. Ніколайчук, В.О. Попов, Є.І. Пономарчук
Наведено результати дослідження використання сепаратора з двома реверсами зустрічних аксіальносиметричних магнітних полів для розділення ізотопів вуглецю. Чисельним методом аналізується динаміка
процесу розділення ізотопів при різних режимах сепарації ізотопів як з відображенням легшою компоненти
ізотопної суміші, так і без відображення. Розглянуто використання багатоапертурної кільцевої інжекції або
інжекції кільцевого пучка, а також зустрічної інжекції в магнітну систему сепаратора з метою підвищення
продуктивності установки.
132
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