1
Nuclear Pumped Lasing Experiments
on Fast Burst Reactor Bars-6
V.N.Kononov, M.V.Bokhovko, P.P.Dyachenko, V.V.Korobkin,
Yu.A.Prokhorov, V.I.Regushevsky, A.P.Barzilov, A.V.Gulevich,
A.V.Zrodnikov, O.F.Kukharchuk, E.A.Pashin, and V.N.Smolsky
State Scientific Center of Russian Federation
A.I.Leypunsky Institute for Physics & Power Engineering
Fax +7(095)8833112 E-mail: kononov @ ippe. rssi. ru
1, Bondarenko Sq., Obninsk 249020 RUSSIA
Abstract. Experimental setup configuration and lasing experiments results on fission fragments
pumping of gas lasers are presented. 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 oscillatoramplifier» 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
IPPE [1], lasing experiments were performed on 235U fission fragments pumping of 5d-6p
atomic xenon 1.73 m transition.
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.
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 displayed in Fig.2. The laser cell and
quantum amplifier were placed into the cylindrical polyethylene neutron moderator block with

This work was supported by the Russian Foundation for Basic Research, grant #96-02-16922a.
Proc. Intern. Conf. ICENES'96, Obninsk, 1996
 - 1996 Institute for Physics and Power Engineering, Technical Physics Laboratory
http://www-tpl.obninsk.rssi.ru
E-mail: kuh@ippe.obninsk.ru
2
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 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
235
U film the magnetron dispersion method was used [2]. 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.
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
CAMAC modules connected to a personal computer [3]. 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 gline. 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 [4].
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
235
U 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
Proc. Intern. Conf. ICENES'96, Obninsk, 1996
 - 1996 Institute for Physics and Power Engineering, Technical Physics Laboratory
http://www-tpl.obninsk.rssi.ru
E-mail: kuh@ippe.obninsk.ru
3
obtained with Monte Carlo simulation of fission fragment stopping [5]. 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 [6] for simulation of a coupled reactor system neutronics and
dynamics. Green function method was used to simulate the time-dependent distribution of
fissions produced in the laser fissile coatings by reactor neutrons. If a such function G(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 (t) 
 G(t
 )  N r ()d 
(1)
exp(  l j )
(2)

G() =

kj
j
lj
The Green function for that problem was approximated with exponential set (2), and
then the formula (1) was numerically integrated. In (2) kj and lj are a parameters of
approximation, j - the number of exponents in a set.
The simplified analytical formula for the estimation of a power pulse of metal core
BARS type reactor is following
 t 2 
Er
N r t  
exp 

r
  2r 
(3)
here E r 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 (2), after substituting (3) into (1), we shall obtain the simplified algebraical
expression for the time distribution of fissions produced by reactor neutrons in the fissile laser
coating:


 Er k j
  2r

N (t)  
exp 
2
l
j 
 4 l

j
j


 
2

t 
-  1  er f
l j 


  t  r
 l
2 l j
 j

 
 
 
 

(4)
For the comparison, measured and calculated reactor pulses are shown in Fig.5. Thermal
neutron fluence longitudinal distributions for LAEL and the laser cell are presented in Fig.6.
Time-dependent fluence in laser cell uranium coating, evaluated analytically and computed
using methods mentioned above, are shown in Fig.7 in comparison to experimental data. The
Monte Carlo LOCMMO code, which utilizes a local estimation of steady-state and nonsteady-state flux functionals [7], was used for computation. It is obvious that the computed
and algebraically calculated results are in a good agreement with experimental ones.
Proc. Intern. Conf. ICENES'96, Obninsk, 1996
 - 1996 Institute for Physics and Power Engineering, Technical Physics Laboratory
http://www-tpl.obninsk.rssi.ru
E-mail: kuh@ippe.obninsk.ru
4
CONCLUSION
The first 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] P.P. Dyachenko, A.V. Gulevich, A.V. Zrodnikov, V.N. Kononov, and V.Ya. Poupko,
«Energy model of a puls e nuclear reactor pumped laser system,» in 7th Intern. Conf. on
Emerging Nuclear Energy Systems (ICENES’93), World Scientific, 372 (1994).
[2] G.N. Kazantsev, N.Ya. Maximov, V.I. Uporov, A.Yu. Belomytsev, A.Yu. Perekhrest,
V.G. Burdym, E.S. Kononov, and S.G. Samoylov, «Study of metal uranium dispersion
processes into internal surface of laser active element,». 2nd Intern. Conf. on Physics of
Nuclear Induced Plasmas and Problems of Nuclear Pumped Lasers, eds. A.M.Voinov,
S.P. Melnikov, and A.A. Sinyanskii, VNIIEF, Arzamas-16,, 2, 27 (1995).
[3] V.I. Regushevsky, O.E. Kononov, M.V. Bokhovko, and V.N. Kononov, «Storage digital
oscillograph in the CAMAC system,» IPPE, Obninsk, Preprint #2478 (1995).
[4] V.I. Regushevsky, M.V. Bokhovko, V.N. Kononov, R.H. Gubadullin, and A.U. Gonchar,
«High intensity neutron flux measurement by vacuum fission chambers,» IPPE, Obninsk,
Preprint #2531 (1996).
[5] A.A. Androsenko, P.A. Androsenko, and E.D. Poletaev, «Using of Monte Carlo method
for estimation of space-time distribution of fission fragment energy deposition,» IPPE,
Obninsk, Preprint #1968 (1989).
[6] A.V. Gulevich, B.V. Kachanov, and O.F. Kukharchuk, «Models and codes for reactorlaser system dynamics computation,» IPPE, Obninsk, Preprint #2454 (1995).
[7] E.A. Pashin and V.B. Polevoy, «LOCMMO_T - the code for simulation of nonstationary
neutron flux functionals with local estimation methods and mathematical expectation in
the frame MMKFK-2 code system,» IPPE, Obninsk, Preprint #2388 (1994).
Proc. Intern. Conf. ICENES'96, Obninsk, 1996
 - 1996 Institute for Physics and Power Engineering, Technical Physics Laboratory
http://www-tpl.obninsk.rssi.ru
E-mail: kuh@ippe.obninsk.ru
5
Fig.1. Setup for nuclear pumping lasing experiments.
Fig.2. The experimental setup scheme.
1-cores, 2-moderator, 3-master oscillator cell, 4-cavety mirrors, 5,6,7-turning mirrors, 8amplifier windows, 9,10-beamsplitters, 11-lenses, 12-calorimeter, 13-photodiode,
14-digital oscillograph, 15-tuning laser.
Proc. Intern. Conf. ICENES'96, Obninsk, 1996
 - 1996 Institute for Physics and Power Engineering, Technical Physics Laboratory
http://www-tpl.obninsk.rssi.ru
E-mail: kuh@ippe.obninsk.ru
6
80
8
60
6
1
40
120
15
Pump power, W/cm 3
Output power 1.73  m, W
2
2
Thermal neutron flux, 10 /cm s
160
4
80
20
40
2
0
0
0
0
200
400
600
800
1000
s
Fig.3. Neutron (1) and laser (2) pulses.
Time,
40
1.73  m intensity, W/cm 2
2
30
20
10
1
0
0
100
200
300
400
500
600
s
Fig.4. Input (1) and output (2) amplifier intensity.
700
Time,
Proc. Intern. Conf. ICENES'96, Obninsk, 1996
 - 1996 Institute for Physics and Power Engineering, Technical Physics Laboratory
http://www-tpl.obninsk.rssi.ru
E-mail: kuh@ippe.obninsk.ru
7
20.0
Fast neutron flux, rel.units
17.5
- experiment
15.0
- numerical simulation
- analytical formula
12.5
10.0
7.5
5.0
2.5
0.0
0
100
200
Time,
s
300
400
Fig.5. Neutron reactor pulse.
2.5
- experiment
- numerical simulation
Thermal neutron fluense, 10
12
cm-2
3.0
2.0
1.5
1.0
0.5
0.0
0
50
100
150
200
250
Length of laser cell, cm
Fig.6. Thermal neutron fluence distribution along laser cell.
Proc. Intern. Conf. ICENES'96, Obninsk, 1996
 - 1996 Institute for Physics and Power Engineering, Technical Physics Laboratory
http://www-tpl.obninsk.rssi.ru
E-mail: kuh@ippe.obninsk.ru
8
Thermal neutron flux, 10 15 cm-2s
-1
6
5
- experiment
- numerical simulation
- analytical formula
4
3
2
1
0
100
200
300
400
500
600
Time,
700
s
800
900
1000 1100 1200
Fig.7. Thermal neutron pulse on the surface of a laser cell.
Proc. Intern. Conf. ICENES'96, Obninsk, 1996
 - 1996 Institute for Physics and Power Engineering, Technical Physics Laboratory
http://www-tpl.obninsk.rssi.ru
E-mail: kuh@ippe.obninsk.ru