Dynamics of carbon and tungsten colliding plumes

Transcription

1 Dynamics of carbon and tungsten colliding plumes H. Sato 2,Y. Hirooka 1, K. A. Tanaka 2 and the Reactor Eng. Group 2 1) National Institute for Fusion Science 2) Osaka University 2009,Oct 8 th -9 th TITAN Japan-US work shop at NIFS

2 Motivation The present work is to investigate fundamental aspects of laser-induced ablation behaviors with the particular emphasis on cluster/aerosol formation by colliding plumes, using a laboratory-scale experimental setup. Therefore, it is extremely important to understand the behavior of colliding ablation plumes Prof. Hirooka s data indicate: *From visible spectroscopy an ion mass spectrometry Colliding C-plumes radiate Swan band, forming Cn + -cluster ion *From ICCD camera image, at high power densities C-plumes have 2 velocity component plumes, the slow component of which seems interactive in collision This study is intended to analyze in detail the colliding ablation plumes behavior of selected ICF target chamber wall materials. 2

3 Table of Contents 1. Motivation 2. Experimental setup and highlight data - LEAF-CAPexps. -Ion mass spectrometry. -ICCD camera and Langmuir probe measurements 3. Modeling details -Adiabatic expansion model -Exp and model comparison 4. Summary and future plans 3

4 Laboratory Experiments on Aerosol Formation by Colliding Ablation Plumes(LEAF-CAP) Mirror Beam expander Beam splitter(50:50) Ablation laser spec Wave length:355[nm] (Nd:YAG 3ω) Pulse width:6[ns] Frequency 10[Hz] Maximum laser power 320[mJ/pulse] Optical fiber for Visible spectroscopy Q-Mass Cylindrical lens Langmuir probe Colliding Plasma ~10mm ~0.1mm Vacuum Rate : <10-5 [torr] Arc-shaped target (C and W) Liner Focus 4

5 Mass Spectra for Carbon Single Plume C + =12

6 Mass Spectra for Carbon Double plumes C + =12 C 2+ =24 C 3+ =36 C 4+ =48 C 5+ =60

7 1 n,where Basic aspects of colliding plumes 1In thehard - sphere model, r 1 wheren is r 2 (1) 2, which is density of the collision energy independent. scattering particles, - collision mean free path is is crosssection and r,r are the radii of twoparticles For A & M processes,the reaction - reaction mean free path is, where v v n v is (2) the reaction rate coffecient, which is energy dependent.

8 Mass Spectra for Tungsten Single plume W +

9 Mass Spectra for Tungsten Double plumes W + W ++

10 Electron Temperature [ev] Electron Density[10 10 cm -3 ] Langmuir Probe Data for Carbon plumes Laser Power=8.7J/cm 2 4 Te Ne Double Double Single Single Time [μs] 0.01

11 Electron Temperature [ev] Electron Density[10 10 cm -3 ] Langmuir Probe Data for Tungsten Plumes Laser Power=8.7J/cm Te Ne Double Double Single Single Time [μs] 1

12 One-Dimensional Adiabatic Expansion Model The electron temperature is C T s e l T e0 l l C t s i 0 ZkT m e 2 3 The radius after t second The sound Velocity (2) (3) (1) 0.3l 0 l l 0 l 0 :Initial Length( at t=10ns) l:later Length T e :electron temperature T e0 :Initial T e (at t=10ns) t:time C s :Sound Velocity m i :Mass of Ion k:boltzmann Constant Z:Atoms Number *Reference plasma Physics, Vol. 16, pp. 247 TEMPERATURE AND DENSITY OF AN EXPANDING LASER PRODUCED PLASMA P. T. RUMSBY* and J. W. M. PAUL Received 20 June 1973 Model of ellipsoidal body plasma

13 Electron Temperature[eV] Electron- Adiabatic Expansion Model fitting with exp. data Experiment Data Target:Carbon Laser Power:8.7J/cm 2 Experiment Data Adiabatic Expansion Model Time[us] 13

14 Plasma Density[cm -3 ] Compare Plasma Density - Adiabatic Expansion Model Initial electron temperature is 16eV Initial(10ns) density is obtained by Langmuir data at 1μs 1.0E E+15 Experiment Data Adiabatic Expansion Model 1.0E E E E E E E Time[μs] 14

15 Electron Temperature[eV] Compare Electron Temperature - Adiabatic Expansion Model Experiment Data Tareget:Tungsten Laser Power:8.7J/cm Experiment Data Adiabatic Expansion Time[ns] 15

16 Plasma density[cm -3 ] Compare Plasma Density - Adiabatic Expansion Model Initial electron temperature is 8eV Initial(10ns) density is obtained by Langmuir Probe data at 10μs Experiment Data Target: Tungsten Laser Power:8.7J/cm 2 1.0E E+17 Experiment Data Adiabatic Expansion 1.0E E E E E E E Time[ns] 16

17 Summary and future plans From the ion mass spectrometry, colliding C plumes lead to the formation of Cn-cluster ions, including C +, C 2+, C 3+, C 4+ and C 5+. The formation of these clusters has been found to favor low laser power densities. Therefore, the mean free path is considered to play an important role. As opposed to that, colliding tungsten plumes did not show any cluster formation, instead, doubly charged ions are identified. Ablation plume plasma parameters have been measured by a Langmuir probe, changing the time delay after laser pulse. Results indicate that both the electron temperature and density decrease as the time goes by. Assuming adiabatic expansion, the electron temperature and density at the origin of plume generation have been estimated to be 16eV and /cc for C plumes, 8eV and /cc for tungsten plumes, respectively. 17

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