Fueling Pellet Injectors
R. Sakamoto, G. Motojima
e-mail: sakamoto@nifs.ac.jp

1.

Objective
Inject hydrogen isotope pellets into core plasma to control plasma density

2.

Apparatus
The in-situ pipe gun type 20-barrel injector and the screw extruder type repetitive pellet injector areintegrated on the B-stage (Fig. 1). Solid hydrogen isotope pellets are injected from 3Ｏ-AL01-01 port.
In both pellet injectors, pellet is accelerated pneumatically with high pressure propellant gas (He). The
three-stages differential pumping system is employed to minimize the undesirable propellant gas flow into
the LHD vacuum chamber.

Fig. 1. Fueling pellet injectors

2.1. In-situ pipe gun type 20-barrel solid hydrogen pellet injector- 20 pellets can be injected independently at arbitrary timing.

2.2.

Nominal size
[mmφ]Number of atoms

Number of barrels

3.0

1.0×1021

4

3.4

1.5×1021

6

3.8

2.0×1021

10

Screw Extruder type repetitive pellet injector- Pellet can be injected steadily at a frequency of up to 11 Hz.
- Pellet size and velocity: 3.0 mmφ and 200 – 500 m/s.

3.

Operation- Pellet injection timing control+ Preprograming pellet injection timing control based on the t=0 trigger

Pellet velocity[m/s]1000 - 1400

+ Realtime pellet injection timing control based on the CO2 interferometer or bremsstrahlung signal- Pellet materials can be selected from hydrogen and deuterium.

4.

Available data by “Retrieve”- Diagnostics name: “FPellet”
Ch.

Signal nameExplanation

1

LG1

Light gate at the 1st expansion chamber

2

LG2

Light gate at the 2nd expansion chamber

3LG3Light gate at the 3rd expansion chamber

4ReP-LG0

Light gate at the auxiliary expansion chamber for RePellet

5ReP-LG1

Light gate at the 1st expansion chamber for RePellet

6DAC

Target value for the realtime pellet injection timing control

7CO2/Brems

Reference signal for the realtime pellet injection timing control

8HalphaPellet ablation light intensity with narrow band pass filter for Balmer α

9Hbeta5

Pellet ablation light intensity with narrow band pass filter for Balmer β

10Hbeta20

Pellet ablation light intensity with wide band pass filter for Balmer β11Hgamma

Pellet ablation light intensity with narrow band pass filter for Balmer γ

12ContPellet ablation light intensity with wide band pass filter between Hα and Hβ13

FCgateExposure control signal for fast camera

14TS_Trigger

Pellet injection synchronized Thomson laser driving trigger

15165.

Remarks
It takes around 6 hours to cooling down the cryo-unit from the room temperature to the operationaltemperature (~10 K). Therefore, injection plan should be submitted at least one day before the experiment.

References[1] R. Sakamoto et al., “Twenty barrel in situ pipe gun type solid hydrogen pellet injector for the Large
Helical Device”, Review of Scientific Instruments 84 (2013) 083504.
[2] R. Sakamoto et al., “Development of Advanced Pellet Injector Systems for Plasma Fueling”, Plasmaand Fusion Research 4 (2009) 002.
[3] H. Yamada et al., “Repetitive fueling pellet injection in large helical device”, Fusion Engineering andDesign 69 (2003) 11-14.
[4] H. Yamada et al., “Development of pellet injector system for large helical device”, Fusion Engineeringand Design 49-50 (2000) 915-920.