Movable Sample Holders
M. Shojie-mail: shohji.mamoru@nifs.ac.jp

1.

Purpose / Application

The movable sample holders are for exposing samples to the LHD plasma periphery or moving to the positionof the vacuum wall for investigating plasma-material interaction processes. This device can also be used fora movable electron gun for magnetic surface measurements, magnetic/electrostatic probes for peripheral
plasma measurements, an electrode for electric bias experiments, and so on.

3. General Description
3.1. Movable sample holder (4.5-L)
3.1.1 Overview
Two movable sample holders are installed in two lower ports (4.5-L and 10.5-L), which can vertically insert
the samples into the LHD vacuum vessel up to near the equatorial plane (see Figure 1). These devices arevertically mounted on a middle stage in the LHD basement hall. Figure 2 shows a side view of theconfiguration of the movable sample holder installed in 4.5-L port. The length of the stroke for the verticalmovement is about 4m. The device consists of a movable rod, an upper vacuum chamber, welded bellows, alower vacuum chamber and a driving gear (air motor). The device is electrically disconnected to the LHD
vacuum vessel by an insulator inserted at the top of the upper chamber. Two network cameras routinely
monitor the device for the safe operation. The cameras are controlled from the LHD control room via Web
browsers on personal computers. An analog CCD camera (NTSC video signal output) is also set at the frontof a remote control system on the middle stage for real-time monitoring. Most of gate valves and vacuum
gauges are remotely controlled from the control room. The movable rod inserted in the vacuum vessel isroutinely monitored with an unti-radiation plasma monitor camera mounted in an upper port (4.5-U). One
can insert the movable rod to near the equatorial plane, because the divertor leg is intersected by divertor
plates in closed helical divertor components near the lower port (4.5-L).

Fig. 1. Top view showing the positions of the movable sample holders installed in 4.5-L and 10.5-L ports.

3.1.2.

Movable rod

An insulator on the top of the movable rod enables to electrically bias the samples. The central part of therod (tube) is rotatable on the axis of the rod, which can be used as mask for controlling exposed areas of thesamples and so on (see Figure 3). The rotation angle is controlled with a pulse motor mounted at the bottomof the lower vacuum chamber. The length of the vertical movement and the rotation angle of the tube arecontrolled from the control room via optical fibers, a media convertor, and a four port RS-232 serial device
servers (NPort 5410). Two power supply cables (φ1.7mm×2), eight general-purpose cables (φ0.5mm×8),and eight thermocouples (K-type, φ1.6mm×8) are mounted at the top of the rod for experimental use. Twocooling pipes pass through the inside of the rod for cooling the top of the component.

Fig. 2. Side view of the configuration of the movable sample holder installed in 4.5-L port.

3.1.3.

Upper vacuum chamber

The samples mounted on the top of the rod can be replaced by opening a flange (ICF305) in the upper vacuumchamber. At the replacement of the samples, a specially designed container with a manipulator are mounted
on the flange, which enable to check the residual tritium and to replace the samples quickly. The samples canbe seen through a view port on the upper chamber. A cyopump (the pumping speed is 500l/s) is connected tothe chamber via gate valves which are remotely controlled. A turbo molecular pump (the pumping speed is350l/s) is connected to the chamber via a gate valve which is also remotely controlled.

3.1.4.

Lower vacuum chamber

The lower vacuum chamber is vertically moved by the driving gear with the air motor. The electrodes for thepower supply and the cables are mounted at the both sides of this chamber. A turbo-molecular pump (thepumping speed is 550l/s) with a flexible tube can be connected to the chamber for efficient residual gas
pumping if necessary.

3.1.5.

Driving gear (air motor)

The driving gear (an air motor) is controlled by a control unit by the remote control system.

Fig. 3. Side view of the configuration of the top of the movable rod installed in 4.5-L port.

3.2. Movable sample holder (10.5-L)
3.2.1 Overview
The movable sample holder installed in a lower port (10.5-L) can insert the samples into the LHD vacuum
vessel to near the equatorial plane. The structure of this device is almost same as another one installed in 4.5L (see Figure 4). Two network cameras monitor the device for the safe operation. The movable rod inserted
in the vacuum vessel is routinely monitored with a plasma monitor camera in an upper port (10.5-U). It
should be noted that a lower/outer divertor leg plasma intersects the side of the movable rod, which candamage the rod in plasma discharge operation. It is recommended that this device is used for exposing thesamples to the divertor plasma or is inserted up to the position of the vacuum vessel surface except for low
power plasma discharge operation.

Fig. 4. Side view of the configuration of the movable sample holder installed in 10.5-L port.

3.2.2.

Movable rod

The structure of the top of the movable rod is illustrated in Figure 5. The central part of the rod (tube) isrotatable. The rotation angle is controlled with a pulse motor mounted at the bottom of the lower vacuumchamber. The length of the vertical movement and the rotation angle of the tube are controlled from thecontrol room via optical fibers, a media convertor. Two power supply cables, ten general-purpose cables, andsix thermocouples are mounted at the top of the rod. Two cooling pipes pass through the inside of the rod inorder to cool down the top of this component.

Fig. 5. Top view and side view of the configuration of the top of the movable rod installed in 10.5-L port.

3.2.3.

Upper vacuum chamber

The samples mounted on the top of the rod can be replaced by a specially designed container with amanipulator. A cryopump (the pumping speed is 800l/s) is connected to the chamber via a remotely controlled
gate valve. A turbo molecular pump (the pumping speed is 300l/s) is connected in the chamber via a gatevalve.

3.2.4.

Lower vacuum chamber

The lower vacuum chamber is vertically moved by the driving gear with the air motor which is same as thatin the sample holder (4.5-L). The electrodes for the power supply and the cables are mounted at the side of
the vacuum chamber.

3.2.5.

Driving gear (air motor)

The driving gear (an air motor) is controlled by a control unit by the remote control system.

3.3

Specification- The nominal precision of the vertical movement of the rod is ±1mm.
- The nominal precision of the rotation angle of the tube at the top of the rod is about 0.1° (4.5-L) and 0.01°(10.5-L), respectively.
- The rotation speed of the tube at the top of the rod is about 18°/sec.

- The speed of the vertical movement of the rod is about 150mm/min.
- After venting to the air, it takes about two day to evacuate the chamber to 1.0×10-5Pa which is necessarypressure to open the gate valve connecting the LHD vacuum vessel.
The remote control systems for the movable sample holders (4.5-L & 10.5-L) locates on the middle stage inthe LHD basement hall. While the neutron and gamma-ray fluxes at the controllers is not high, the fluxes
directly under the lower ports on the stage is not negligible. The web cameras, the pulse motors for rotating
the rod, and rotary encoders are covered with polyethylene blocks and tungsten sheets for protecting it fromthe neutron and gamma-ray fluxes coming down from the LHD lower ports.

4.

Requirement in use

When the samples are replaced, the containers with a manipulator have to be set on the gate-valve on theupper vacuum chamber, which is for preventing the spread of radioactive materials. The procedure such as
venting the chambers and replacing the samples must follow an operational manual for this device. There isa limitation of the maximum size, weight and material for the samples, which must be under a regulation for
the radiation control.

5.

OthersIn near future, infrared cameras will be installed in 10.5-U ports for monitoring the temperature of the surfaceof the samples mounted at the top of the rod. In opening the flange on the chambers after exposure of thesamples to the plasmas, residual tritium has to be measured in the chamber. Time for completely taking out
the rod to the outside of the LHD vacuum vessel is about 25 minutes (in the case where the position of thetop of the rod is the equatorial plane). When the samples are exposed to plasmas at vertical positons beyond
the level of the vacuum vessel surface during the LHD plasma discharge operation, an approval from theLHD experimental board is necessary as a special experimental proposal.

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