1
Theoretical and Experimental Studies of Gaseous
Laser Pumped by a Twin-Core Fast Burst Reactor
Alexander P. Barzilov, Mikhail V. Bokhovko, Andrey V. Gulevich,
Peter P. Dyachenko, Boris V. Kachanov, Victor N. Kononov,
Oleg F. Kukharchuk, Evgeny A. Pashin, Victor I. Regushevsky,
Anatoly V. Zrodnikov
State Scientific Center of Russian Federation
A.I.Leypunsky Institute for Physics & Power Engineering
1, Bondarenko Sq., Obninsk 249020 Russia
Abstract. Experimental setup configuration and lasing experiments results on fission fragments pumping of gas lasers are
presented. The IPPE’s fast burst reactor BARS-6 has been used as a neutron source for nuclear pumping of lasers.
Experimental results on nuclear pumping of «master oscillator-amplifier» pulse laser system and energy parameters of 1.73
m 5d-6p XeI transition of Ar-Xe laser and amplifier are presented. Neutron characteristics of system were compared with
computed ones. It was shown that experimental and calculated results are in a good agreement.
INTRODUCTION
The concept of using nuclear energy to pump a laser by uranium fission fragments could potentially be used
to create large high power nuclear pumped lasers (NPL) that could not be matched by other laser systems. That
is possible owing to the high energy capacity of a fission reactor and high penetration ability of neutrons in
uranium multiplication systems. In the framework of designing an energy model of a pulse nuclear reactor
pumped laser system in the IPPE (1), lasing experiments were performed on 235U fission fragments pumping of
5d-6p atomic xenon 1.73 m transition (2). The objectives of experiments were to observe the laser oscillation
and amplification effects, to evaluate a power parameters of laser and amplifier and to study the stability of
metal uranium coating of laser active elements (LAEL) under pulse neutron and -irradiation.
It was also necessary to develop mathematical methods, computation techniques and codes for simulation of
neutronics, optics and power NPL system characteristics and compare obtained results with experimental data.
FIGURE 1. Setup for nuclear pumping lasing experiments.
Proc. Intern. Conf. LIRPP'97, 1997
 - 1997 Institute for Physics and Power Engineering, Technical Physics Laboratory
http://www-tpl.ippe.obninsk.ru
E-mail: kuh@ippe.obninsk.ru
2
EXPERIMENTAL ARRANGEMENT
The experiments have been performed using especially elaborated facilities for studies of nuclear pumped
lasers. The general view of NPL system is shown in Fig.1. The two-core fast burst reactor BARS-6 was used as
a power pulsed neutron source. This reactor is able to produce thermal neutron fluences of 51012 n/cm2 with
peak neutron flux 1016 n/cm2s at the laser cell. The scheme of the NPL experiment is shown in Fig.2. The
laser cell and quantum amplifier were placed into the cylindrical polyethylene neutron moderator block with
external 2602000 mm and internal 160 mm covered by cadmium sheets. The laser cell is a thin walled
stainless steel tube with outer diameter 49 mm and length 400 mm.
From one side it was equipped with 6-m curvature concave gold high reflection spherical mirror and on the
other side - with a quartz Brewster’s window. A flat dielectric mirror with reflectivity 95% at 1.73 m was used
as an output coupler. A 300-mm-long aluminum cylinder coated with a 235U dioxide layer of thickness 2.7
mg/cm2 was placed into the laser cell. The laser active element was used as a quantum amplifier. It is a similar
stainless steel tube 492500 mm with an internal 5-m-thick metal 235U coating. Both sides of the LAEL
were hermetically sealed with quartz optic windows having a dielectric antireflection coating for 1.73 m. In
order to cover the internal surface of LAEL by metal 235U film the magnetron dispersion method was used (3).
Both the laser cell and LAEL were filled with Ar+0.5%Xe gas mixture at 380 Torr pressure. Moderated reactor
neutrons produce fission reactions in the 235U laser cell and amplifier coatings. A fraction of the fission
fragments escape from the coatings and deposit their kinetic energy into the lasing medium as ionization and
excitation. As a result, an inversion population is created in the lasing medium.
Figure 2. The experimental setup scheme. 1-cores, 2-moderator, 3-master oscillator cell, 4-cavety mirrors, 5, 6, 7-turning
mirrors, 8-amplifier windows, 9, 10-beamsplitters, 11-lenses, 12-calorimeter, 13-photodiode, 14-digital oscillograph, 15tuning laser.
The optic scheme of experiment has two channels which were created by beamsplitter placed on the
amplifier input. The transmission of beamsplitter was 0.32. The high reflection mirror with 10 m radius of
curvature has been used for a two-round-trip amplifier scheme. In order to eliminate the uncertainty connected
with the limitation of laser beam cross section in both channels, a restrictive 16-mm aperture was placed in
front of the splitter plate. As determined computationally, for this case the cross section of the laser beam does
not restrict along whole optical tract in both channels. The plate aluminum and spherical dielectric mirrors were
used as turning ones. Tuning of optical system and transmission measurements were carried out using a He-Ne
laser. The measured transmission in the input channel was 6.310-2, and 1.910-2 in the output channel of the
amplifier.
A thermocouple calorimeter and germanium photodiodes were been used for registration of laser energy and
time behavior of laser pulse. Registration of the photodiode signal was performed with digital system based on
Proc. Intern. Conf. LIRPP'97, 1997
 - 1997 Institute for Physics and Power Engineering, Technical Physics Laboratory
http://www-tpl.ippe.obninsk.ru
E-mail: kuh@ippe.obninsk.ru
3
CAMAC modules connected to a personal computer (4). Synchronization of measuring system was made from
reactor radiation signal. The gold activation indicators attached on the external surface of LAEL were used for
measurement of the thermal neutron fluence distribution and calculation of amount of fissions in uranium
coatings. The induced activation of 198Au was measured by single-crystal NaJ(Tl) 150100 mm spectrometer
on 412-keV g-line. The photoefficiency of the spectrometer was calibrated using standard g-ray sources in wide
energy diapason. The accuracy of induced activation and thermal neutron fluence measurement was ~3%. The
time behavior of thermal neutron pumping pulse was measured by vacuum fission chamber with 235U (5).
80
40
8
2
6
1
40
20
80
40
15
120
4
2
1.73  m intensity, W/cm 2
60
Pump power, W/cm 3
Output power 1.73  m, W
2
2
Thermal neutron flux, 10 /cm s
160
30
20
10
1
0
0
0
200
400
Time,
600
800
s
0
1000
0
Figure 3. Neutron (1) and laser (2) pulses.
0
100
200
300
Time,
400
s
500
600
700
Figure 4. Input (1) and output (2) amplifier intensity.
EXPERIMENTAL RESULTS AND DISCUSSION
Typical time-dependent 1.73-m atomic xenon laser output in a free oscillation mode and thermal neutron
signal are shown in Fig.3. The total laser oscillator output energy without restrictive aperture and beamsplitter
was 200 mJ. The thermal neutron signal from the vacuum 235U fission chamber has been normalized to the
thermal neutron fluence measured by activation method. Laser output signal from Ge-photodiode has been
normalized to total energy measured by calorimeter.
The pump power has been evaluated from thermal neutron flux value and fission fragment energy
deposition into the laser medium. The last value was obtained with Monte Carlo simulation of fission fragment
stopping (6). Input and output amplifier intensity are presented in Fig.4. The registration energy gain in
amplifier was 4.
SIMULATION OF NEUTRONICS
The neutron physical and power characteristics of two-zone fast burst reactor were computed using special
software (7) for simulation of a coupled reactor system neutronics and dynamics. Green function method was
used to simulate the space-time dependent distribution of fissions produced in the laser fissile coatings by
reactor neutrons. If a such function G(r,t) for fissile coatings is known, it is possible to find a time distribution
of fissions in 235U of laser cell controlled by reactor signal of any complex time shape Nr() as Duamel integral:
t
N(r,t) 
 G(r , t   )  Nr ( )dt

Proc. Intern. Conf. LIRPP'97, 1997
 - 1997 Institute for Physics and Power Engineering, Technical Physics Laboratory
http://www-tpl.ippe.obninsk.ru
E-mail: kuh@ippe.obninsk.ru
(1)
(2)
4
G(r,t)= (r )  
kj
j j
exp(    j )
The Green function for that problem was approximated with exponential set (Eq.2), and then the formula (1)
was numerically integrated. In Eq.2 kj and j are a parameters of approximation, j - the number of exponents in a
set, (r) - coefficient of fission nonuniformity. The simplified analytical formula for the estimation of a power
pulse of metal core BARS type reactor is following
 t 2 
Er
(3)
N r t 
exp  2 
r
 r 
here Er and r - represent the net energy and effective pulse duration respectively. The latter one is connected
with a half-duration of the pulse as 1 2  2r
ln 2

. Taking into consideration Eq.2, after substituting Eq.3
into Eq.1, we shall obtain the simplified algebraical expression for the time distribution of fissions produced by
reactor neutrons in the fissile laser coating:



 



2
 Er k j
 r
t  
r  
 

N(t)   (r )   
exp 
t
  1  erf 
(4)
2

j 
j
2   j  
 4 
j  2 j


j


 
 
3.0
Thermal neutron fluense, 10
Approximation
Rel. units
2.5
- experiment
- numerical simulation
12
Monte Carlo computation
10
cm-2
100
1
0
0
0
2.0
1.5
1.0
0.5
0.0
0.0000
0.0004
0.0008
0.0012
Time, s
Figure 5. Approximation of Green function by exponent
set.
0
50
100
150
200
250
Length of laser cell, cm
Figure 6. Thermal neutron fluence distribution along laser
cell.
The Green function approximated by a set of exponents is shown in Fig.5. For pulse in one reactor core,
thermal neutron fluence longitudinal distributions for LAEL and the laser cell, time-dependent fluence in a laser
cell uranium coating (evaluated analytically and computed using methods mentioned above) are presented in
Fig.6 and 7, respectively, in comparison to experimental data. For co-ordinate pulses in two cores, space
distribution of fission fragments energy deposition into a gaseous laser medium is shown in Fig.8 (maximum of
thermal neutron pulse in a laser cell).
Proc. Intern. Conf. LIRPP'97, 1997
 - 1997 Institute for Physics and Power Engineering, Technical Physics Laboratory
http://www-tpl.ippe.obninsk.ru
E-mail: kuh@ippe.obninsk.ru
5
5
Thermal neutron flux, 10 15 cm-2s
-1
6
- experiment
- numerical simulation
- analytical formula
4
3
2
1
Figure 8. Space distribution of fission fragments energy
deposition into a gaseous laser medium of LAEL.
0
100
200
300
400
500
600
700
800
900
1000 1100 1200
s
Figure 7. Thermal neutron pulse on the surface of a laser
cell.
Time,
The Monte Carlo LOCMMO code, which utilizes a local estimation of unsteady-state flux functionals (8),
was used for computation. It is obvious that the computed and algebraically calculated results are in a good
agreement with experimental ones.
CONCLUSION
The nuclear pumped lasing experiments on the fast burst reactor BARS-6 were performed. Laser oscillation
and amplification for 5d-6p atomic xenon transitions at 1.73 m have been observed. Neutron characteristics of
the system were measured and compared to computed ones. Experimental and calculated results were shown to
be in good agreement.
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
Dyachenko, P.P., Gulevich, A.V., Zrodnikov, A.V., Kononov, V.N., Poupko, V.Ya., «Energy model of a pulse nuclear reactor
pumped laser system,» in Proceedings of the 7th Conference on Emerging Nuclear Energy Systems, 1993, p.372.
Kononov, V.N., et al., «Nuclear Pumped Lasing Experiments on Fast Burst Reactor Bars-6,» in Proceedings of the 7th
Conference on Emerging Nuclear Energy Systems, 1996.
Kazantsev, G.N., et al., «Study of Metal Uranium Dispersion Processes into Internal Surface of Laser Active Element,» in
Proceedings of the Conference on Physics of Nuclear Induced Plasmas and Problems of Nuclear Pumped Lasers, Arzamas-16,
1995, v.2, p.27.
Regushevsky, V.I., Kononov, O.E., Bokhovko, M.V., and Kononov, V.N., «Storage Digital Oscillograph in the CAMAC
System,» IPPE, Obninsk, Preprint #2478 (1995).
Regushevsky, V.I., Bokhovko, M.V., Kononov, V.N., Gubadullin, R.H., and Gonchar, A.U., «High Intensity Neutron Flux
Measurement by Vacuum Fission Chambers,» IPPE, Obninsk, Preprint #2531 (1996).
Androsenko, A.A., Androsenko, P.A., and Poletaev, E.D., «Using of Monte Carlo Method for Estimation of Space-Time
Distribution of Fission Fragment Energy Deposition,» IPPE, Obninsk, Preprint #1968 (1989).
Gulevich, A.V., Kachanov, B.V., and Kukharchuk, O.F., «Models and codes for reactor-laser system dynamics computation,»
IPPE, Obninsk, Preprint #2454 (1995).
Pashin, E.A. and Polevoy, V.B., «LOCMMO_T - the Code for Simulation of Nonstationary Neutron Flux Functionals with Local
Estimation Methods and Mathematical Expectation in the MMKFK-2 Code System,» IPPE, Obninsk, Preprint #2388 (1994).
Proc. Intern. Conf. LIRPP'97, 1997
 - 1997 Institute for Physics and Power Engineering, Technical Physics Laboratory
http://www-tpl.ippe.obninsk.ru
E-mail: kuh@ippe.obninsk.ru