J. Plasma Fusion Res. SERIES, Vol.3 (2000) 47M72

10 Hz Deuterium Pellet Injector for 1000 s
Gontinuous Fuelling
VINIAR Igor*, SKOBLIKOV Sergey and LUKIN Alexander
PELIN Laboratory, Ltd., Moscow, 125212, Russia(Received: 18 January 2000 / Accepted: 24 March 2000)

Abstract
A new deuterium pellet injector for plasma fuelling in a steady state mode has been developed. A
technique for continuous solid deuterium ice extrusion by a screw extruder is suggested for theproduction of an unlimited number of pellets. A cylindrical rod of 2 mm in diameter and over 100 m inlength made from transparent solid deuterium ice was extruded continuously for over 3000 s at thetemperature of 16 K and 35 mm/s speed. Over 25000 deuterium pellets of 2 mm in size were producedby the injector in the steady state mode at the rates from I to 14 Hz and accelerated to 600-700 m/s.
Three series of 12103, 12584 and 14600 deuterium pellets were continuously injected at l0 Hz with thereliabilities of 99.2,98.8 and 99.5 Vo, respectively. All pellets in flight were recorded by a CCD-camera
and a computer and were found to be intact.

Keywords:
fuelling, pellet, injector, extruder

1. lntroduction

2. Pellet Injector Design
A schematic diagram of the pellet injector is shownin Fig. 1. It consists of the following main parts: a highvacuum chamber (l) with an extruder (2), equipped witha helium heat exchanger (3) and a screw (4), a rotating
driver (5) connected to the screw, a propellant gas valve(6), an electromagnetic pellet chopper (7), a gun barrel(8), and a diagnostic chamber (9). The inner barrel
diameter is 2.7 mm and its length is 400 mm. There is aFuture fusion reactors should be equipped with afuelling system operating in a steady state mode. There
are three techniques for plasma fuelling: by gas puffing,by compact toroids and by injection of pellets produced
from solidified hydrogen isotopes. A key task of theinjection is to develop a reliable pellet injector capableof injecting, in the steady state mode, an unlimited

number of pellets into the plasma core. Several
techniques for continuous pellet production have been

narrow slit (1 mm) between the barrel and the extruder
nozzle. Two thermal sensors are installed in the extruder
body. A transparent chamber (10) is attached to theextruder exit. It is equipped with a pumping system (11)proposed. One is an extrusion method using 3 extruders

operating in sequence []. Another technique is toproduce pellets by a porous generator [2]. Recently, thefirst screw extruder for hydrogen pellet production has

and has a scale for the extruded deuterium rod

been designed and tested [3]. The design and test results

measurement. The new injector somewhat differs fromof a pneumatic injector with a new screw extruder for

the injector equipped with a hydrogen screw extruder[4]. The extruder length is increased to 200 mm. The
helium heat exchanger surface is inireased by 3O Vo.

deuterium pellet production are described below.

@2000 by The Japan Society of Plasma
Science and Nuclear Fusion Research*Corresponding author's e-raail: npelin@ delfa.net
470

viniar I. et al., l0 Hz Deuterium Pellet Injector for 1000 s continuous Fuelline

Fig. 2 A series of deuterium pellets injected at 1O Hz.

extruded continuously for 3000 s. Without theFig.1 A schematic diagram of the pneumatic pellet
injector with a screw elrtruder.

withdrawals, over 50000 pellets could be produced fromthis rod. At the same time, a 10 cm3 volume of solid
deuterium (or 1600 pellets) was placed in the extruder
during the operation time.

The diameter and length of the tube between theSeveral pellet production and acceleration runs

transparent chamber and the vacuum pumping system
are increased to 12 mm and 300 mm, respectively. This
has reduced the pre-start injector operation time to 20
minutes from the beginning of the injector cooling andincreased the screw extruder production rate.

were performed in the repetitive steady state mode. Over
25000 deuterium pellets of 2 mm in size were produced
and accelerated to 600-700 m,/s at the rates of l-14 Hz

with a step of I Hz. Three series of 12103, 12584 and14600 pellets were continuously injected into thediagnostic chamber at l0 Hz. The propellant gas

3. Operation and Results of the lnjector

pressure in the diagnostic chamber was maintained at

0.01-0.02 MPa level. All pellets in flight wereilluminated by a nanoflash lamp in the diagnostic
chamber and recorded by a CCD-carirera and aTests
During the test, the screw was rotated continuously

in the extruder at 10-30 rpm, pushing out thecompressed solid deuterium. The chopper moved thetube for the propellant gas admission into the barrel,computer. They were transparent and intact, as shown inthereby cutting off a piece of the solid deuterium rod toform a pellet. The propellant gas valve was open for 50

and the time in seconds between the previous pellet andthe pellet in this frame is indicated behind the bracket's.

ms after that, and the pellet was accelerated inside thebarrel. The chopper was returned to the initial position,and the cycle was repeated.
The steady state extrusion was registered at 16 K at
the rotation rate of 25-30 rpm and the extrusion speed

The pellet velocities are indicated before the brackets inmeters per second. After the intact pellets were counted,

Fig. 2. The pellet number in a series is given in brackets,the reliabilities of pellet injection in the three series
were found to be 99.2,98.8 and 99.5 Vo, respectively.
No temperature deviations of the extruder wereregistered and the injector operation in the steady statemode was terminated because of the high deuterium
cost, since over I kg of solid deuterium was extrudedof 35-45 mm/s. As compared with the previoushydrogen extruder [3], the new extruder production rate

was increased from 65 to 140 mm3/s. A 100 mtransparent deuterium rod of 2 mm in diameter wasduring the tests.
471

viniar I. et al., 10 Hz Deuterium Pellet Injector for 1000 s continuous Fuellingof the PELIN, Inc. (Canada), the owner of the screw

4. Summary

extruder patent in Russia, for the financial support andpermission to use this patent, and to Dr. A. Umov forthe development of the injector electronics'

A reliable pneumatic injector with a screw extruder
providing a continuous injection of an unlimited numberof deuterium pellets in the steady state mode has beensuccessfully tested. The injector screw extruder contains
a 10 cm3 volume of solid deuterium and is capable ofproducing up to 140 mm3/s extruded deuterium ice forReferences[] S. Combs, C. Foust and A. Qualls, Rev. Sci.
Instrum., 69 (l l), 4012 (1998).
[2] I. Viniar and S. Sudo, Rev. Sci. Instrum., 68 (3)'pellet production in the steady state mode. Injection of 2mm pellets was demonstrated at the rate of 10 Hz forover 1000 s of continuous operation with a 997o

1444 0997).

reliability.

[3] I. Viniar and A. Lukin, Tech. Physics, 44 (1)'

Acknowledgements[4] I. Viniar, S. Skoblikov and P. Koblents, Tech.

(2000).
Physics, 43 (5), 588 (1998).

The authors are grateful to Mr. A. Sekler, President

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