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John T. Costello

Stagnation Layers at the Collision Front between Two Colliding Plasmas: Prospects for Materials Growth and (VUV) LIBS. John T. Costello National Centre for Plasma Science & Technology (NCPST)/ School of Physical Sciences, Dublin City University www.physics.dcu.ie/~jtc.

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John T. Costello

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  1. Stagnation Layers at the Collision Front between Two Colliding Plasmas: Prospects for Materials Growth and (VUV) LIBS John T. Costello National Centre for Plasma Science & Technology (NCPST)/ School of Physical Sciences, Dublin City University www.physics.dcu.ie/~jtc EU COST MP0601 Salamanca May 14 - 2009

  2. Talk contains elements of the work of: Ph.D Students John Dardis (Imaging/Spectroscopy) Padraig Hough (Interferometry) Thomas ‘Mossy’ Kelly (Image Processing) Postdoc Paddy Hayden International Visiting Fellow Sivandan Harilal (Purdue University) Former Group Members Kevin Kavanagh (Founder - Brand Plate Media - http://brandplate.com) Hugo de Luna (Now Lecturer - Federal University of Rio de Janeiro) Jofre Pedregosa (Now Maitre de Conference, Universite de Provence) EU COST MP0601 Salamanca May 14 - 2009

  3. Talk contains elements of collaboration with: Ph.D Students Mr. Conor McLoughlin (PLD) Postdoc Paddy Hayden (LIBS) Colleagues Jean-Paul Mosnier (PLD) Eugene Kennedy (LIBS) Former Group Members Eoin O’Leary (LIBS) International Leo Gizzi et al. EU COST MP0601 Salamanca May 14 - 2009

  4. Outline of the Talk • Colliding Plasmas - Introduction • Optical Diagnostics • Prospects for PLD & LIBS EU COST MP0601 Salamanca May 14 - 2009

  5. Colliding Plasmas - Introduction Making Stagnation Layers Laser Pulse Energy: 50 - 500 mJ/ beam Laser Pulse duration: 170 ps, 6 ns, 15 ns Focal Spot Size: ~ 100 mm Irradiance: 109 - 1011 W.cm-2 EU COST MP0601 Salamanca May 14 - 2009

  6. Colliding Plasmas - Introduction Not a new idea ! ‘Seed’ Plasmas ‘Stagnation Layer’ When plasma plumes collide there are two extreme scenarios: Interpenetration - interactions are mostly via binary collisions Stagnation - plumes decelerated at collision plane, rapid accumulation of material, kinetic energy converted into excitation energy (glow), rapid growth of dense (stagnated) layer,……… EU COST MP0601 Salamanca May 14 - 2009

  7. Colliding Plasmas - Introduction Huge body of literature on colliding plasma fundamentals - but mainly from work at high power laser facilities ! Motivations - they are many and varied……….. 1. Fusion (Hohlraums) 2. X-ray Lasers 3. Space Weather Observations 4. Pulsed Laser Deposition 5. Laboratory-Astrophysical Model Experiments T R Dittrich et al., Phys. Plasmas 6 2164 (1999) R W Clark et al., Phys. Plasmas 4 3718 (1997) J L Horwitz and T E Moore, IEEE Trans. Plasma. Sci. 28 1840 (2000) C Sanchez Ake et al., J. Appl. Phys 100 053305 (2006) C D Gregori et al., Ap. J. 676 420 (2008) EU COST MP0601 Salamanca May 14 - 2009

  8. Colliding Plasmas - Introduction Plasma - Plasma Separation Collisionality Parameter: Ion - Ion Mean Free Path (mfp) For collisions between opposing plumes (1, 2) Slow moving and dense plumes are more likely to stagnate ! ii >> D Interpenetration ii ~ D  ’Soft’ Stagnation ii << D  ’Hard’ Stagnation EU COST MP0601 Salamanca May 14 - 2009

  9. Colliding Plasmas - Introduction Plasma - Plasma Separation Collisionality Parameter: Ion - Ion Mean Free Path (mfp) For collisions between opposing plumes (1, 2) Key point: One can engineer stagnation layer characteristics; ‘hardness’, density, temperature, shape, etc. by varying geometry (D) and laser-target interaction physics (mfp, ii) - application specific….. EU COST MP0601 Salamanca May 14 - 2009

  10. Part 2. Optical Diagnostics Stagnation layer growth • Time resolved (ICCD) imaging • Time-space resolved spectroscopy • Faraday ion cup Plasma Diagnostics • Time-space resolved spectroscopy - ne & Te • Time resolved interferometry - ne EU COST MP0601 Salamanca May 14 - 2009

  11. Part 2. Optical Diagnostics EU COST MP0601 Salamanca May 14 - 2009

  12. Optical Diagnostics Time Evolution: Tight point focus on each Ca face: 120 mJ per beam ICCD:5 ns gate 10 ns interval Ca - Emission Imaging @ 423 nm EU COST MP0601 Salamanca May 14 - 2009

  13. Optical Diagnostics Stagnation Layer Evolution Broadband image - 200ns Colliding aluminium plasmas ~100 mJ/170 ps/’seed’ beam EU COST MP0601 Salamanca May 14 - 2009

  14. Optical Diagnostics Stagnation Layer Evolution: (Al) - Charge resolved ! ‘Growth rate’ - 10 m/ns 300mJ/6ns/’seed’ beam EU COST MP0601 Salamanca May 14 - 2009

  15. Optical Diagnostics Stagnation Layer (Al): Electron density & temperature ‘Seed’ spectrum Stagnation zone ‘Seed’ spectrum EU COST MP0601 Salamanca May 14 - 2009

  16. Optical Diagnostics Stagnation Layer (Al): Electron density & temperature Spectroscopy - only works well for t > 100 ns Spectra dominated by continuum emission - solution - time resolved interferometry Experimental Setup- Nomarski Interferometry EU COST MP0601 Salamanca May 14 - 2009

  17. Optical Diagnostics Separation of electron and ion stagnation - Ambipolar effects Electrons - ‘Nomarski’ Al+ ions - ICCD Al plume - ICCD EU COST MP0601 Salamanca May 14 - 2009

  18. Colliding Plasma - PLD NeoceraTM PLD system Replace single plume with stagnation layer…….. EU COST MP0601 Salamanca May 14 - 2009

  19. Colliding Zn Plasma - PLD Vacuum Single Plume Vacuum Colliding Plumes SEM IMAGES 1 mbar O2 Colliding Plumes 1 mbar O2 Single Plume EU COST MP0601 Salamanca May 14 - 2009

  20. TISR-VUV-LIBS, Ambient Gas Line: S4+ (78.65 nm) Sulphur/Steel in N2 Background Gas EU COST MP0601 Salamanca May 14 - 2009

  21. VUV - LIBS, Ambient N2 S4+ 78.65 nm Sulphur/ Steel in N2 Background Gas - strong enhancement of S4+ 78.65 nm line - S5+ + e  S4+*….? EU COST MP0601 Salamanca May 14 - 2009

  22. LIBS with Colliding Plasmas ? 1. Results give us some confidence that colliding plasmas could also be engineered to improve the efficacy of LIBS……. 2. Also, could be used in ‘double pulse’ LIBS experiments to separate ‘sampling’ from excitation….. EU COST MP0601 Salamanca May 14 - 2009

  23. Support Science Foundation Ireland Irish Research Council for Science, Engineering and Technology EU COST: MP0601 EU COST MP0601 Salamanca May 14 - 2009

  24. What have we learned to date ? 1. Strong stagnation in table top colliding plasmas due to large value of the collisionality parameter (z) 2. Degree of confinement/ hardness of the stagnation layer can be controlled by designing the value of z 3. Stagnation layer becomes quite uniform after 100s ns and so looks attractive for investigation as alternative pulsed laser materials deposition source, target for LIBS 4. Preliminary PLD results are promising….. 5. Colliding Plasma LIBS efficacy to be proven…….. EU COST MP0601 Salamanca May 14 - 2009

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