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系統識別號 U0026-2508202012511400
論文名稱(中文) 實驗室電漿中激發朗謬爾波超連續光譜與紊流狀態
論文名稱(英文) Generation of Langmuir Wave Supercontinuum and Turbulence in Laboratory plasma
校院名稱 成功大學
系所名稱(中) 太空與電漿科學研究所
系所名稱(英) Institute of Space and Plasma Sciences
學年度 108
學期 2
出版年 109
研究生(中文) 吳哲亘
研究生(英文) Che-Hsuan Wu
學號 LA6071051
學位類別 碩士
語文別 英文
論文頁數 110頁
口試委員 指導教授-河森榮一郎
口試委員-張博宇
口試委員-藍永強
中文關鍵字 朗謬爾波  超連續光譜  實驗室電漿  紊流 
英文關鍵字 Langmuir wave  Supercontinuum  Laboratory plasma  Turbulence 
學科別分類
中文摘要 超連續光譜激發是指單色波入射波傳遞介質產生周邊頻譜拓寬的現象,其源自於初始波與波傳遞介質所產生的非線性效應,非線性效應則包含了四波混和以及拉曼散射,而波傳遞介質的例子有光纖、玻色-愛因斯坦凝態以及電漿,本研究的目的是於實驗室電漿中演示朗謬爾波超連續光譜與紊流狀態激發,由於朗謬爾波的非縣性行為能夠被非線性薛丁格方程式所描述,而在過往光學上的發展也以非線性薛丁格方程式描述超連續光譜形成,因此激發朗謬爾波超連續光譜是能夠成立的。我們實驗進行於國立成功大學電漿所的線性磁化電漿腔,此腔體由於外加背景磁場,一維的設置能夠被滿足,到此在激發朗謬爾波超連續光譜狀態的實驗中,我們發現了以下的結果:

在低能量電子束入射模式中,我們激發了朗謬爾波超連續光譜,當電子束能量約為3至4倍的電子溫度時,其頻譜拓寬的範圍 ∆ω/ω_pe ≳0.1,其中此連續頻譜狀態的朗謬爾波傳遞了2000λ_De仍舊有很高的空間相干性g (1) > 0.5以及擁有相當高的四波相干性 |t^2| > 0.5這顯示了此連續頻譜狀態的朗謬爾波有顯著的四波交互作用也驗證其物理機制為初始朗謬爾波與周邊頻譜產生調變不穩定性。在考量了入射電子束能量的尺度我們認為初始的朗謬爾波是產生於電子束與電漿中電子不穩定性(bump-on-tail),在實驗驗證中,採用平板式朗謬爾探針進行電子速度分布函數的測量,其實驗結果可觀察出有類bump-on-tail結構的電子分佈函數且與入射電子束能量有相關性,但更進一步的調查與驗證仍是必需的。

此外,我們也實行了由背景電漿產生裝置的熱陰極入射高能電子束模式的實驗,電子束能量大小為100eV約25倍電子溫度,此模式下的朗謬爾波被觀測出顯著的頻譜拓寬範圍 ∆ω/ω_pe ≳0.3、高度的空間相干性g (1) > 0.5以及高度的四波相干性 |t^2 | > 0.5
雖然此模式的頻譜特徵與定義上的朗謬爾波超連續光譜非常相似,但其波傳遞方向則在兩個空間點中量測出相反的傳遞方向。
在相同的熱陰極模式中,熱陰極的電子束強度較低的條件下,我們以熱陰極電子束產生的朗謬爾波紊流狀態,紊流狀態的朗謬爾波有著顯著的頻譜拓寬範圍 ∆ω/ω_pe ≳0.3、極低的空間相干性g (1)≈ 0且沒有四波相干性 |t^2 |≈ 0。在考量了電子束能量尺度,我們認為朗謬爾波紊流狀態的機制是源自於高能電子束與電漿中電子的雙流不穩定性(OTSI),而另一個OTSI特徵則是在色散關係量測中顯示初始朗謬爾波的波數近乎為0。
英文摘要 Supercontinuum (SC) generation is a drastic spectral broadening of a seed wave, which results from nonlinear interaction including four-wave mixing and Raman scattering of the seed wave with the wave propagation medium, such as optical fibers, Bose-Einstein condensates, and plasmas. This research aims at demonstrating generation of SC states of Langmuir waves (LWs), a novel state of LWs, and turbulence state of LWs, in laboratory plasmas. This is motivated by the fact that LWs having finite amplitude can be described by nonlinear Schrödinger equation (NLSE), which describes conventional optical SC generation as well. To this end, we conducted Langmuir waves SC (LWSC ) generation experiments in a quasi-one-dimensional configuration using linear plasma device MPX by application of background magnetic field. From the experiments, we found the followings:

In the low energy electron beam injection mode, LW supercontinuum (LWSC), whose spectral broadening ∆ω/ω_pe ≳0.1 was generated when the energy of the electron beam was 3−4 times of "T" _"e" , where ∆ω and ω_pe are spectral broadening and the plasma angular frequency, respectively. The seed LW is considered to be excited by the bump-on-tail instability. The LWSC exhibited a high spatial coherence g (1) > 0.5 along the distance corresponding to "2000 " λ_"Debye" (the Debye length) and a high tricoherence |t^2| > 0.5 indicating a significant four-wave interactions between the seed LW and its side bands. The main mechanism of the LWSC generation is a modulational instability. Velocity distribution functions of electrons were measured with the use of a planer Langmuir probe using the one-dimensional Druyvesteyn method. A bump-like structure was observed at the energy tail of the electron distribution functions when the electron beam was injected, and the energy of the bump was correlated with the injected electron beam energy. To conclude this result, further investigation is needed.

On the other hand, when a high energy electron beam (~ 100 eV ~ 25 times of Te) was injected using a hot cathode, which was also utilized for the background plasma
production, a LW state showing a considerable spectral broadening ∆ω/ω_pe > 0.3, high spatial coherence g (1) > 0.5and high tricoherence |t^2 | > 0.5 was observed. Although it showed characteristics similar to those of LWSC, propagation directions measured at the two distant locations were different.
In certain conditions of low intensity of the electron beam from the hot cathode, LWT was generated in the HC modes. LWT states showed remarkable spectral broadening ∆ω/ω_pe ≥0.3, low spatial coherence g (1) "≈ 0" and low tricoherence |t ^2 |≈ 0. It was considered that the LWT was generated dominantly by OTSIs from seed waves. This is because the seed LW, which is considered to be generated by two-stream instability, had wave numbers ~ 0 from the two-point correlation measurement using the monopole antennas.
論文目次 Abstract………………………………………………………………...……...………...I
contents…………………………………………………………………………..….... IV
List of figures………………………………………………………………….….…. VII
Chapter 1 Introduction…….……………………………………...…………….……1
1.1 Langmuir wave…………….…………………………….………………...……1
1.2 History of supercontinuum phenomenon research…………………...…2
1.3 Langmuir wave supercontinuum and turbulence…………………………3
1.4 Purpose of this research…………………………………………………….…4
Reference…………………………………………………………..……………….......5
Chapter 2 Theory of LWSC&LWT……………………………………….……………7
2.1 Linear Langmuir wave………………………………………………………..….7
2.1.1 Derivation of linear dispersion relation of Langmuir wave………….…7
2.2 Ponderomotive force……………………………………………………....….…9
2.2.1 Derivation of ponderomotive force………………………………......…...9
2.3 Nonlinear Langmuir wave – Zakharov equations………………………...10
2.3.1 Derivation of Zakharov equation……………………………………….…10
2.4 Nonlinear Schrödinger equation……………………………………………..13
2.4.1 Derivation of nonlinear Schrödinger equation……………………….…13
2.5 Generation of LWs by instabilities……………………………….….…….…14
2.5.1.1 Two-stream instability………………………………..……………..……15
2.5.1.2 Bump on tail (BOT) instability…………….…………………….….……15
2.5.2 Instability to generate Langmuir wave packet – wave-wave interactions............................................................................................16
2.5.3.1 Decay instability……………………………………………………….......16
2.5.2.2 Oscillating two stream instability (OTSI) ………………..……...….…17
2.5.2.3 Modulational instability (MI) …………………….…………….……..…20
2.6 Langmuir wave supercontinuum and Langmuir wave turbulence ……25
2.7 Summary ………………………………………………………..………..………26
Reference………………………………………………………………………………26
Chapter 3 Experimental Setup of Generation of LWSC in MPX ……….……27
3.1 Vacuum chamber and pumping system ……………………………………27
3.2 Magnetic coil system……………….……………………………………..……28
3.3 Plasma emitter – Hot cathode mode……………………………..…………29
3.4 The MPX remote control system …………………………………………….29
3.4.1 Operation control part ………………………………………………………29
3.4.2 Data acquisition part ………………………………………………………..29
3.4.3 Data acquisition for measurement tool for LWs ……………………….29
3.5 Langmuir wave exciters ……………………………………………………....30
3.5.1 Principle of Langmuir wave exciter – Microwave mode ………………30
3.5.2 Configuration of Langmuir wave exciter – Microwave mode ……….31
3.5.3 Principle of Langmuir wave exciter – Electron beam injection mode......................................................................................................33
3.5.4 Configuration of Langmuir wave exciter – electron beam injection mode ……..…..…..…..…..…..…..…..…..…..…..…..…..…..…..…..…..…...…34
3.6 Measurement tools ………………………....……………………………….…34
3.6.1 Basic tools ………………………………………………..…………………...34
3.6.1.1 Langmuir probe ……………………………………………………………35
3.6.1.2 Microwave interferometer ……………………………………………….37
3.6.2. Newly developed diagnostic tools for LWSC experiment….…………38
3.6.2.1 Plasma absorption probe…………………………………….....……..…38
3.6.2.2 Langmuir wave receiver – double monopole antenna……………...42
Reference…………………………………………………………………………..…..44
Chapter 4 Experimental results and discussions of generation of Langmuir wave supercontinuum and turbulence state in laboratory plasma ………..45
4.1 Experimental target and idea for verification……………………………..45
4.2 LWSC generation by LW exciter – Microwave (MW) mode……………….45
4.2.1 Experimental setup of LWSC – Microwave (MW) mode………………..45
4.2.2 Experimental result of LWSC – Microwave (MW) mode………………..47
4.2.3 Summary of LWSC - MW mode…………………………………………….53
4.3 LWSC generation – HC mode (high energy electron mode) ……………53
4.3.1 Experimental setup of Hot cathode (HC) mode ………………………..53
4.3.2 Experimental result of LWSC – Hot cathode (HC) mode ……………..53
4.3.3 Experimental result of LWT – Hot cathode (HC) mode ……………….65
4.3.4 Discussion and summary of experiment in HC mode ………………..70
4.4 LWSC generation – Electron beam injection (EBI) mode (low energy injection Ebeam ~ Te) ……………………………….....……………………….....73
4.4.1 Experimental setup of EBI mode ………....………………………………73
4.4.2 Experimental result of EBI mode ………………………………………….74
4.4.3 Discussion and summary of experiment in EBI mode…..………..…. 90
4.5 Verification of bump-on-tail instability in LWSC-EBI mode……………92
4.5.1 Experimental setup of distribution function measurement of electron in LWSC-EBI mode…………………….……………………………………………..92
4.5.2 Experimental results of distribution function measurement of electron in LWSC-EBI mode……….…………………………………………...…..94
4.5.3 Discussion and summary of distribution function measurement of electron in LWSC-EBI mode…... …………………………………………………106
Reference…………………………..…………………………………………………108
Chapter 5 Summary ……………………………....……………………………...109
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