UDC 533.9.01
1*Kunakov S., 2Son E., 1Shapiyeva A.
1International IT University, Almaty, Kazakhstan
2Joint Institute of High Temperature, Moscow, Russian Federation
*e-mail: [email protected]
Probe diagnostics in helium plasma, generated by a volume source of fission fragments
Abstract. In the present paper experimental results of probe measurements in nuclear induced helium plasma are presented and analyzed. Both parts of volt–ampere characteristics (VAC) of the probe are used to get the density of electrons and positive ions in plasma. Plasma is formed by products of the reaction
3�� � � � � � � � �.����� and studied under the pressure to be equal 760 torr and neutral flux about 1013–14 cm–2 s–1. The linear part of VAC and its slope might be used to evaluate density and temperature of the studied plasma. In some special cases like plasma diagnostics in the core of active of nuclear reactor the probe diagnostic methods is the only one possible experimental technique which makes possible to extract nuclear induced plasma property information. Electrostatic probe represents substantially a metal electrode placed in the diagnostic cell, inserted in the active zone of nuclear reactor and within which the tested mixture is uploaded.
Key words: helium, plasma, nuclear induced plasma, flux of thermal neutrons, volt ampere characteristics.
Introduction
Commonly known that electrostatic probe is used as a primary diagnostic tool in the measurement of the local parameters of the ionized gas in a variety of me- dium [1], such as the electrical discharge and after- glow, the ionization boundary region behind the shock waves, flames, MHD generators, plasma jet, as well as atmospheric and space plasmas. Despite its limited area of application the probe techniques of experimen- tal measurements are very successful and rapidly de- veloped in recent years. The probe diagnostics expe- rimental set in nuclear reactor is schematically pre- sented on the figure 1.
The plasma apparatus [3,7] is relatively simple, however, the theory of electrical probes complicated by the fact that the probe is boundary surface to the nuclear induced plasma, and the equations describ- ing the behavior of the plasma near the interface are nonlinear [2]. The plasma created in the active zone of a nuclear reactor has a number of specific fea-
tact with the experimental set due to induced ra- dioactivity, making all of the experimental appara- tus is only a one-time use as well as the obligatory remote control of the experiment set due to the irre- versible structural changes in the measurement and diagnostic devices connected with strong radiation [3]. Plasma, created by fission fragments was initial- ly described in the following papers by Leffert C.B.
Reese D.B., Nguyen D. H., Grossman L.M. and Guyot J.C., Miley G.H., Verdeyen J.T. [4–6]. But direct probe measurement was undertaken in the present paper and the experimental studied in [3].
Experimental volt ampere characteristics analysis The test ampulla of the 3He gas was inserted in the flux of thermal neutrons absorbs thermal neu- trons creating highly energetic particles, which cause in its own turn the ionization of the working medium through the following channel:
64 Probe diagnostics in helium plasma,generated by a volume source of fission fragments
1 –Vial o Di Figure 1 tics of the
Reaction is 5400 barn portional to among the p of tritium
of the test mixt iagnostic chan 1 – Experimen e plasma gas m
of a stationa
n cross secti ns and increa o ���.�. The
proton and t
�5������a
ture; 2 – the re nnel; 4 – signa ntal setup for p mixtures in the ary nuclear rea
ion (1) for t ases as its en e energy rele triton as follo and 1������
Figure 2
eactor core; 3 al wires.
probe diagnos e radiation fie actor.
thermal neut nergy varies eased distrib ows: the nuc
� proton ene
– Ion branche – eld s-
trons buted pro- cleus ergy.
Thevolu
whe serte shapbott mixbase gurawire Nontact Pumcarr
conswith thorion neutteste
es of VAC of
e input power ume, estimat
� � ere Φ – neutr The diagnost ed is made of pe of a cylind tom of the ce
ture that is to e of the cell th ations are we es. The probe n–operating p
with plasma mping, heatin ied out with a In the prese sideration of h experimen rs [7]. On th and electron tron fluxes ed plasma.
probe in heliu
r of the react ed by the fol 1.65 ∗ Φ ∗ � ron flux dens tic channel in f steel pipe. T der with a di ell special tip o be studied.
he probes of lded, sealed a es are moun part of the pro
by insulator ng and filling
a high–vacuu ent paper, th f this problem ntal data real he figure 2 a n branch ar and differen
um plasma.
tion 3He (n, p llowing expr
� � �
cm
3sity.
nto which the The diagnosti
iameter of 40 ps are made t
In the center different geo and mounted nted on a cer obe is protect made of the g cells with um unit [8].
he detailed m is made an lized by one and figure 3 re presented nt geometry
3He
p) T per unit ression:
, (2) e test cell in- c cell has the 0 mm. At the o fill the gas r of the upper ometry confi- d to the signal ramic holder.
ted from con- quartz tubes.
gas mixture quantitative nd compared e of the au- the VAC of at different of probe in t
) e - e s r - l . -. e d e -f n t
At any s
where ���– c
where ���– c We also
From e ion and ele region are l en out from In the ch
and the radi
Figure 3–
surrounding
∮ ������ �� current of po
∮ ����� �� current of ele o accept that
�� � � xperimental ctron branch inear and the m the experim
harged volum
���
ius of the lay
– Electronic b
probe surfac
��� � ���, ositive ions o
��� � ���, ectron on the at any point
�� ��. curve, we hes of VAC e slope migh mental VAC.
me layer, we
���� �, yer is equal to
branches of VA
ce we have:
on the probe.
e probe.
:
may notice at some def ht be exactly e may state th
o:
AC of probe in
(3)
(4)
(5) that finite tak- hat:
(6) whe
whe coef we c
whe
pera
n nuclear indu ere e – electro From this w
���� 4 ere ����������
fficient, ���– To get conce come to the f
ere
ta Then we als ature:
e i
i
e em
T m
uced helium p on’s charge.
e may obtain 4����������
� – probe’s p length charg entration of p following:
���������� ��
a� ���∆���∆
so may evalu
2
tan tan
e i e
i
plasma.
n, that:
����������, potential, b+–
ge layer.
positive ions
�
��� ,
∆��
�������. uate the elect
3 2
1 1
i p
e p
I I
(8) – mobility
s in plasma
(9)
(10) tron’s tem-
, (11) )
) )
)
66 Probe diagnostics in helium plasma,generated by a volume source of fission fragments
On the V
Precedin the probe p probe VAC
From (6 the potentia ation:
VAC in figu
Figure 4–
ng our evalu potential the
we get:
��� � 4 6) and Poisso al obeys to th
[
3 3
re 4 it is show
– The ion and ch
uations for p en for electr
4�����������
on equation f he following
[
wn how the
d electronic br haracteristics f
ositive value ronic part of
������. for charged l differential
1 ]
]
2
,4 3
eS
estimation mranchesof expe for plane and
es of f the
(12) layer equ-
(13) whe
the in th
p3
Sr
might be done
erimentally m spherical prob
ere
T T r
r
p
,
Boundary co
The solution linear depen his part of ap
e.
measured curre bes.
S n D T
Te,
onditions are , ) 1
(
p
n of (2.13) gi dence of exp pplied electri
ent–voltage
r r
p
d
, ( )2,
e as follows:
0 ) 1
''(
.
ives the conf perimental pr ic potential (F
e kTe
.
(2.14) firmation of
robe’s VAC Figure 5).
)
Electric
r
where
Table 1 – characteristic
W, 2 5 8
Figu
c field in the
r
0( 1
ݎൌ ݎ
The concen cs.
kWh 200 500 800
re 5 – Numer of
charged laye
20)
21,
ݎ ሺଷଶହఝఉమሻభర
ntrations of e
Н
rical solution o f probe potenti
er
b
eS 4
,భ
ర .
electrons and
Не+, sm–3 х107
3.7 9.3 14.9
of the equation ial within one
(15)
(17) He+ comprim coolwith solvmet 1015 plas d ions derive
n (2.13–2.14) probe’s size.
Results and The balance
+3 and the ele mposed, whic
mary electro ling of elect h helium ato ved for the hod. At
5–1016cm–3s– sma close to ed from exp
Не2+, sm–3 х107
1.3 3.2 5.0
shows the dro
d conclusion equations fo ectron energy ch take into ons [10]. It trons occurs oms. System case of qua
rates of
1, the electr the temperat perimentally
op
or particles o y balance equ o account all t is assume due to elast of these equ asi–stationary
ion for ron tempera ture of heavy measured cu
Не3+, sm х101
1.7 2.8 3.6
of He+, He+2, uations were l sources of ed that the tic collisions uations were y numerical rmation at ature of the y particles.
urrent–voltage
m–3
1
e , e f e s l t e
e
68 Probe diagnostics in helium plasma,generated by a volume source of fission fragments of molecular ions He+2. He+2 recombination time is
large, and time conversion to He+3 ions is small, so the ions He+2 are also negligible.The ratio of the concentration of ions He+ and He+2, He+3 concentration
is around of 10–3– 10–2. In connection with the above, the main channel for electron loss is a reaction of dissociative recombination with ions He3 +. The results of these calculations are presented in Figure 6.
Figure 6 – Time dependence of ions and electrons density in nuclear induced helium plasma.
The concentrations of electrons and ions derived from experimentally measured current–voltage characteristics are shown in Table 1. The results are in good agreement, both among themselves and with the results of numerical calculations.The experimental VAC in some regions is linear from probe potential and the slopes of the curve might be used to evaluatethe density and temperature of electrons in nuclear induced plasma.
References
1. Huddlestone, S.L. Leonard R.H. Plasma Di- agnostics Techniques. – New-York: Academic Press, 1965.
2. Chung P.M., Talbot L., Touryan K.J. Elec- tric probes in stationary and flowing plasmas. – New-York: Theory and Application, 1975.
3. Kunakov S.K. Zondovaya diagnostika ya- dreno–vozbuzhdaemoj plazmy, soderzhashhej otri- catelnye iony. // Zhurnal problem evolyuciiotkrytyx system. – 2009. – Vol.1. – N. 11. – P.45–48.
4. Leffert C.B., Reese D.B., Jamerson F.E.
Noble Gas Plasmas Produced by Fission Frag- ments// J.Appl.Phys. – 1966. – Vol.37. – P.133–142.
5. Nguyen D.H., Grossmsan L.M. Ionization by Fission Fragments Escaping from Source Me- dium// Nucl. Sci. and Engin. – 1967. – Vol.30. – P.233–241.
6. Guyot J.C., Miley G.H., Verdeyen J.T. Ap- plication of a Two Region Heavy Charged Particle Model to Noble Gas Plasmas Induced by Nuclear Radiation. // Nucl. Sci. and Engin. – 1972. – Vol.48.
– P.372–386.
7. Kunakov S.K., Son E.E. Probe Diagnostics of Nuclear Excited Plasma of Uranium Hexafluo- ride.// High Temperature. – 2010. – Vol. 48. – N.6.
– P.789–805.
8. Kunakov S.K. Zondovaya diagnostika ya- derno–vozbuzhdae mojplazmy geksaftoridaurana.//
Vestnik kazaxskogo gosudarstvennogo universitetia Al-farabi. – 2010. – Vol.33. – N. 2. – P.15–17.
9. Benilov M.S. Teoriya elektricheskix zondov v potokax slaboi onizirovannoj plazmy vysokogo davleniya. // TVT – 1988. – Vol.26. – N. 5. – P.993–1004.
10. Benjamin S.W., Geoge H.M. Monte Carlo Simulation of Radiation–Induced Plasmas. // Nuc- lear Science and engineering. – 1973. – Vol.52. – P.130–140.
