B V Kuteev

S V Krylov

T-10

V G Skokov

V M Timokhin

V Yu Sergeev

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T-10 DISCHARGE CONTROL BY METHOD OF LITHIUM PELLET-
INJECTION AND BY INJECTION OF SUPERDENSE SUPERSONIC 
GAS JETS 
V.M. Timokhin
1
, V.G. Skokov
1
, V.Yu. Sergeev
1
, S.V. Krylov
2
, B.V. Kuteev
2
, and T-10 team
2
1 State Polytechnical University, St.Petersburg, Russia 
2 Nuclear Fusion Institute, Russian Research Center “Kurchatov Institute”, Moscow, Russia 
Introduction 
The high temperature plasma discharge control is one of important tasks in the program 
of the controlled fusion achievement [1]. The first wall lithium (Li) conditioning in T-11M, 
TFTR, CDX-U tokamaks was found as a factor of an essential increase of plasma energy 
content, energy confinement time due to obtaining the lower Zeff discharge with low impurity 
content [2-4]. On the other hand it had not been confirmed in either Heliotron E [5] or Alcator 
C MOD [6] Li pellet experiments. Results of the sequential Li pellet injections in T-10 aiming 
to study its conditioning capability are presented. Recently, supersonic jets of hydrogen and 
impurity gases are being considered for plasma fueling [7] and disruption mitigation [8]. First 
operation of the T-10 supersonic helium jet injector is described in the report. 
Discharge conditioning exper iments 
In experiments, cylindrical pellets of 0.75-0.78 mm in diameter and 0.9±0.1 mm in 
length which corresponds to (1.6–2.2)x10
19
 content of lithium atoms were injected. The pellet 
size was limited by the injector barrel diameter. Prior to loading of Li pellets in the injector 
they were coated by the nitride shell (LiN3) of the 10 mkm thickness. This procedure was 
used for avoiding the undesirable effect of the lithium sticking with injector material and 
allowed to accelerate Li pellets up to 650 m/s velocities into the plasma with fairly good 
reproducibility. The pellet ablation was observed using CCD camera, wide-view 
photodetector and a set of the narrow collimated photodetectors. Details of the injector 
experimental setup are described in Ref. [10]. Injections were carried out in the ECRH heated 
plasmas with following main parameters: <ne> = 3x10
13
 cm
-3
, aL= 30 cm, Ipl = 270 kA, 
BBt = 2.4 T, PECRH = 800 kW. In these conditions, Li pellets penetrated up to r/aL = 0.3  and 
deposited a main part of lithium nearby a half of plasma minor radius aL. 
Li pellet injection time was 600 ms from the plasma current start-up and with the 
100 ms delay relative to the start of ECRH heated pulse. A special regime of the discharge 
shutdown without the toroidal magnetic field cessation has been used to exclude the lithium 
33rd EPS Conference on Plasma Phys. Rome, 19 - 23 June 2006 ECA Vol.30I, P-4.092  (2006)
washout at this discharge stage. A sequence of 4 shots with the Li pellet injection was realized 
(##42313, 42315, 42316, and 42317). Two reference shots without Li injection before 
(#42312) and after (#42319) this sequence has been analyzed in order to observe conditioning 
effects. In the shots #42314 and #42318 where were no plasma due to technical reasons. 
Fig. 1. Evolution of main plasma parameters in the reference shots before (#42312 red curve) and after 
(#42319 yellow curve) series with Li injection. All data are in arbitrary units. 
The time evolutions of signals measured by the microwave interferometer, Hc detector 
and one of peripheral AXUVD bolometer channels (30 cm of minor radius) are presented in 
Fig. 1. It is seen that there are no obvious effects of discharge conditioning. In particularly, 
Hc signal did not decrease after a sequence of Li pellet injections as might be expected for 
successive conditioning experiments (see Ref. [3]). 
33rd EPS 2006; V.Yu.Sergeev et al. : T-10 Discharge Control By Method of Lithium Pellet-injection and by Inj... 2 of 4
Considering the peripheral bolometer signal in Fig. 1, one can conclude that a 
qualitative composition of peripheral impurities had no noticeable disturbance after Li pellet 
injections. No difference of main impurities lines radiation (CIII, OII) behavior before and 
after Li injections confirms this suggestion as well. 
Electron density evolutions in Fig. 1 
have an indication of decreasing the 
hydrogen recycling. Behavior of the 
density till 600 ms is provided by feed-
back operation of the programming gas 
puff. After 600 ms gas puff was switched 
off in all shots. Therefore, lower plasma 
density (t > 600 ms) in shot #42319 after a 
sequence of Li pellet injections indicates 
lower particle flux from the wall. The same 
conclusion can be done by analysis of the total gas puff amount (shown in Fig. 2) which is 
needed to provide the programming electron density behavior till 600 ms of the shot. From 
Fig.2 one can see that it was necessary to increase the total gas puff amount in shots after Li 
pellet injections. It means that Li pellet injection gradually decreased the hydrogen recycling 
from the wall. 
Fig. 2. Comparative increasing of hydrogen puffing 
during series of Li injection. 
The possible reason of absence of the conditioning effects was insufficient total amount 
of the injected Li atoms to cause conditioning effect on the vacuum vessel. Estimation of a 
lithium amount for the monolayer coating of the T-10 first wall surface gives a number of 
2.5x10
20
 atoms that 10 times higher than the pellet content. On the other hand it is enough 
~10
18
 Li atoms to coat the T-10 limiter surface. One can propose to perform the further 
conditioning experiments with smaller limiter radius to increase the limiter coating by the 
available lithium content of the pellet injector. A peripheral Li jet injection can be also 
proposed for increasing the Li amount in order to improve the conditioning efficiency. 
Supersonic He jets injection 
The gas injection was arranged using the supersonic jet source developed and mounted 
at T-10 recently. The source is based on an electromagnetic fast valve with a Laval nozzle. 
The nozzle has 3 mm in length and 0.3 mm throat size. The valve was opened during about 
2 ms that allowed to inject (1-20)x10
19
 He atoms depended on the PHe gas pressure (PHe = 5-
100 bar) at the valve inlet. A formation of the compact helium jet with ~1.5 km/s velocity was 
expected. He jet was injected from top to bottom toward the plasma core. Injections were carried 
33rd EPS 2006; V.Yu.Sergeev et al. : T-10 Discharge Control By Method of Lithium Pellet-injection and by Inj... 3 of 4
out in Ohmically heated plasma with <ne> = 
3x10
13
 cm
-3
 and I = 270 kA and a varied 
number of injected helium atoms. It was 
shown that injection of more than 3x10
19
 He 
(PHe > 15 bar) atoms caused a T-10 discharge 
minor disruption. In a case of injection of the 
moderate amount atoms, high deposition 
efficiency of the He jet was found. For 
instance, in shot #42683, the 1.2x10
19
 He 
atom amount calculated the from nozzle flow 
dynamics was found in a good agreement 
with those measured in test-bed experiments 
(1.6x10
19
 atoms) with the jet source and 
evaluated from the electron density jump after injection (1.5x10
19
 atoms). 
Fig. 3. He supersonic jet penetration in T-10 
plasma. 
The jet emission in plasma was observed using the CCD camera (see Fig. 3). The 
luminescent part of the plasma periphery gives a rough estimation of the jet penetration up to 
r/aL = 0.6. The further experimental program studies of jet penetration depth versus jet 
velocity, sort of injected gas, and density are foreseen. Furthermore discharge shutdown 
experiments with a massive Ar gas jet injection is planned. 
Acknowledgements 
This work was partially supported by RFBR grants ## 05-02-17269, 06-02-17333 and 
grant of RF President to young scientist supporting # MK-7792.2006.2. 
References 
[1] Technical Basis for the ITER Final Design Report (2001). 
[2] Mirnov S V et al., Plasma Phys. Control. Fusion 48 (2006) 821–837. 
[3] Mansfield D.K. et al., J. Phys. Plasmas 3 (1996) 1892. 
[4] Majeski R. et al., Nucl. Fusion 45 (2005) 519–523. 
[5] Sergeev V.Yu. et al., Plasma Phys. Control. Fusion 40 (1998) 1785. 
[6] J. Rice, private communication. 
[7] Bucalossi J. et al., EPS Conf. on Plasma Phys. Tarragona, Vol.29C, O-4.005 (2005). 
[8] Hollmann E.M. et.al, Nuclear Fusion 45 (2005) 1046. 
[9] Rozhansky V. et.al, Nucl. Fusion 46 (2006) 367-382. 
[10] BelopolskyV.A. et al., Europhys. Conf. Abs., St. Petersburg, Vol.27A, P-3.117 (2003). 
33rd EPS 2006; V.Yu.Sergeev et al. : T-10 Discharge Control By Method of Lithium Pellet-injection and by Inj... 4 of 4


T-10 DISCHARGE CONTROL BY METHOD OF LITHIUM PELLET- INJ ECTION AND BY INJ ECTION OF SUPERDENSE SUPERSONIC GAS J ETS

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T-10 DISCHARGE CONTROL BY METHOD OF LITHIUM PELLET- INJ ECTION AND BY INJ ECTION OF SUPERDENSE SUPERSONIC GAS J ETS

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