J. Plasma Fusion Res. SERIES, Vol. 3 (2000) 449451

A Tracer-Encapsulated Pellet Injector TECPEL-2
VINIAR lgor*, SUDO Shigeru' and REZNICHENKO Pavel
PELIN Laboratory, Ltd., Moscow, 125212, Russia
lNational InstituteFusion Science, Toki 509-5292, Japanfor(Received: 18 January 2000 / Accepted: 19 May 2000)

Abstract
A new technique and a device for producing tracer-encapsulated cryogenic pellets (TECPEL) havebeen designed for local deposition of the tracer ions in a steady state plasma and for an accurate
measurement of the particle transport in magnetic confinement devices. The technique allows
manufacturing TECPEL in the form of a solid deuterium (or hydrogen) cylinder of 3 mm diametercontaining an impurity core of 0.1-0.2 mm in size as a tracer. To increase the TECPEL injection
reliability, the process of core loading into the hydrogen pellet was made visible. A brief injector design
and the first experimental results are presented.

Keywords:
plasma diagnostics, particle transport, impurity pellet, injector

2. Injector Design and Operation

1. lntroduction
The plasma transport in fusion devices is one of theTECPEL-2 is a pellet injector which produces amost important problems to be studied before a bigmachine such as ITER is designed. The main difficultyin analyzing the plasma transport is the lack of accurate
experimental information, because the laser blow-off
method [1] and impurity pellet injection [2] give a broad
source profile of the impurities. A new diagnostic
method is based upon the localized particle source as a
tracer within a limited small volume of about I cml in
the plasma [3]. The tracer particles are deposited by a
TECPEL consisting of the small tracer core of a light
atom and the major outer layer of a hydrogen isotope,
which is the same species as the bulk plasma ions. The
first TECPEL-I injector was designed and successfully
tested [4]. To increase the TECPEL injection reliability,
to simplify the injector operation and to increase theamount of cores capable of being loaded into thecryogenic pellet in a steady state mode, a new techniqueand a device named TECPEL-2 were developed. Thesesolid hydrogen (or deuterium) pellet by in-situ
condensation [5] with an impurity core inside andare discussed below.

the barrel center.

*accelerates this TECPEL by a single-stage light gas gun.

The new technique of producing and accelerating theTECPEL involves the following procedures: 1) loadinga core from a storage into the injector barrel andkeeping the core on the barrel axis by a special needle,2) formation of the solid hydrogen inside the barrel
around the core, 3) pulling out the needle from thepellet, leaving the core inside,4) ejection ofthe formed
TECPEL with a propellant gas.
A schematic diagram of the barrel cross section
with a core storage is shown in Fig. l. The barrel innerdiameter is 3 mm and the core size varies between 0.1
and 0.2 mm. There are 50 holes of 0.23 mm diameter inthe storage where the cores are housed before theinjector is cooled down. A special needle of 0.6 mm
diameter is placed inside the storage and can move to@2000 by The Japan Society of Plasma
Science and Nuclear Fusion Research

Corre sponding author's e-mail : tvpelin@ delfo.net
449

Viniar I. et al., A Tracer-Encapsulated Pellet Injector TECPEL-2

Fig. 1 The barrel cross section with a core in the center.

Fig.2 A schematic diagram of the TECPEL-2 injector.

A schematic diagram of the injector is shown inFig. 2. A copper plate of 3 mm thickness is brazed tothe barrel and connected to the core storage. This plateis equipped with a helium heat exchanger. There is achannel of 3 mm diameter inside the plate for hydrogencondensation. A small chamber with a window and apropellant gas valve is attached to one end of the barrel.
The second end is inserted into the gate valve with aFig. 3 Stages of TECPEL formation inside the barrel.

injector operation is illustrated in three photos in Fig. 3.
The needle captures a core in the storage and moves it
into the copper plate channel. The cross section of theplate with the core (small dark circle) on the top of theminiature lamp. The lamp illuminates the inner barrel
surface when the gate valve is closed. There is also a
diagnostic chamber attached to the gate valve. The

needle is shown in Fig. 3, (a). A hydrogen gas is450

Viniar I. et al., A Tracer-Encapsulated Pellet Injector TECPEL-2

pellets in flight were made to prove the TECPEL

admitted into the barrel and condensed on the barrel
walls within the copper plate cooled by liquid helium to10 K. The dark O-ring of the solid hydrogen on thebarrel walls is shown in Fig. 3, (b). After the wholebarrel cross section is frozen and the formed pellet
becomes transparent, the needle is pulled out of thepellet. The core remains inside the pellet, as shown inFig. 3, (c). A small amount of hydrogen gas is admittedand frozen in the channel which remains after the needle
removal. The gate valve is opened and the TECPEL isaccelerated by the propellant gas admitted through theconfiguration after the acceleration.

4. Conclusion
A new device TECPEL-2 for producing adiagnostic pellet to measure the particle transport bothparallel and perpendicular to the magnetic field lines offusion devices has been constructed and operated. The
TECPEL-2 shows some advantages over the TECPEL-I

design and operation; in particular, the posibility ofvisual observation of core loading and pellet formation.
It has been shown that no injection can be performed
without a core. Only one driver is used for the coreloading, which simplifies the loading process. A large
number of cores (50 instead of 24 in the previousinjector) can be loaded into the injector before cooling.
Cores have no contact one another and can not behindrance for the next core loadins.

valve.

3. Experimental Results
For technical demonstration of the device
producing TECPEL, we used spherical stainless steel
cores of 0. l5-O .22 rnm diameter. Here, we present somepreliminary results of the injector operation. Three seriesof 50 cores were loaded into the barrel before the pellet

References

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[3] S. Sudo. J. Plasma and Fusion Research 69 (ll),observation of the loading process and the pellet

1349 (1993').

formation through the window and barrel, the injector
operation was recorded by a CCD-camera. The
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Instrum., 6E, 27 l7 (1997).
[5] J. Lafferranderie et al., Fusion Technology 1986:
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a hydrogen propellant gas. We registered steel cores that

had penetrated into the surface of an aluminum target
installed at the end of the diagnostic chamber. Photos of451