低温等离子体表面处
理技术
Plasma and first wall
Introduction
Today I will talk about something about my study on the first wall in the tokamak. Firstly, I will show you that what the plasma is in our life thought the following pictures such as:
Fig.1 Lighning Fig.2 Aurora
Fig.3 Astrospace
Just as the pictures mentioned above , they are all consist of plasma.
But, what does have in the plasma, now our scientist had given a definition that the plasma state is often referred to as the fourth state of matter and contains enough free charged particles（negative ions 、positive ions）and electronics. Like the photo below.
Fig.4 Plasma production
Plasma production
In our research, we produce the plasma through an ICP (inductively coupled plasma)
device as follow：
Through the RF (radio frequency) source、power generator and matching box, we will get the plasma we need in the experiment. The Fig.6 shows us the plasma produced by the RF source.
Fig.6 The ICP plasma
Plasma diagnosis
And then we need to diagnose the plasma characteristics through some methods like spectrum and probe.
Fig.7 The plane probe
We used the plane probe to detection the temperature of electronics and the density of the plasma as the Fig. 8 and Fig. 9.
Fig.8 electronic temperature
We can see among the power of 3000w-8000w, the change of electronic temperature is not sharp. And at the pressure of 0.258Pa, the electronic temperature is going up obviously.
Fig.9 Plasma density
In the Fig. 9 , we can confirm that as the rising of the power, the particle density is also more and more high. And before the pressure of 0.42Pa, the particles density is rising as the increase of the pressure. But the particles density is dropped after the pressure of 0.42Pa.
And than we used the spectrograph to detection the particles of hydrogen as the Fig.
11 shown us.
Fig.10 The PI spectrograph
Fig.11 The hydrogen spectrum
We find that as the increasing of the power, there are four curves occurred. But when the power reachs to about 2000w and 4000w, the βαH H 、 have a capacity.
When we have a clear know about the characteristics of the plasma. We use the plasma to deal with the first wall materials such as W (tungsten) .
Plasma interaction with the fist wall
In our experiments, we put the W in the plasma, and accelerate the He + particles or H + using a static electric field so that they can own a powerful energy to interaction with the materials.
In the experiments, we choice the different powerful particles to deal with the W. And after the experiment, we used SEM to analyze the surface of the materials. The
surface of the W can be clearly observed that have grown some nanostructure through the SEM like the Fig.12.
（A）(B) （C）
1um
（D）（E）（F）
Fig.12 SEM images of samples exposed to a mean ionic flux of 1.28E22 ion/m2/s with helium fluence was 1.0E26 m-2 and an ion incident energy was （A）10eV、（B）20 eV、（C）50 eV、（D）100 eV、（E）400 eV、（F）600 eV.
（c）
（e）（f）
Fig.13 Cross-sectional SEM micrograph of the samples shown in Fig.12, respectively The Fig.13 show us the cross-sectional SEM micrograph of the samples, we can see that there are many nanostructure formed on the surface of the W. And the nanostructure can grow up as the particles own higher energy.
Fig.14 Cross-sectional SEM micrograph of Circular Region, shown in the Fig.13（f）But in our experiments, we find a different phenomenon when the particles have a powerful energy about 600eV, there are many swell on the surface of the W. And through the cross-sectional we can see they are hollow in the swell.
Conclusion
In our research, we have main three steps as follow:
Firstly, we build a device to produce the plasma we need.
Secondly, we diagnosed the characteristics of the plasma such as electronics temperature and plasma density.
Finally, we used the plasma to deal with the first wall materials like W, and analyzed the surface of the W to judge whether the W is fit for the first wall materials or not.。