John T. Costello
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Transcript of John T. Costello
John T. Costello
National Centre for Plasma Science & Technology (NCPST)/ School of Physical Sciences, Dublin City University
www.physics.dcu.ie/~jtc
Stagnation Layers at the Collision Front between Two Colliding
Plasmas: Prospects for Materials Growth and (VUV) LIBS
EU COST MP0601 Salamanca May 14 - 2009
Ph.D StudentsJohn Dardis (Imaging/Spectroscopy)Padraig Hough (Interferometry)Thomas ‘Mossy’ Kelly (Image Processing)
PostdocPaddy Hayden
International Visiting FellowSivandan Harilal (Purdue University)
Former Group MembersKevin 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)
Talk contains elements of the work of:
EU COST MP0601 Salamanca May 14 - 2009
Ph.D StudentsMr. Conor McLoughlin (PLD)
PostdocPaddy Hayden (LIBS)
ColleaguesJean-Paul Mosnier (PLD)Eugene Kennedy (LIBS)
Former Group MembersEoin O’Leary (LIBS)
InternationalLeo Gizzi et al.
Talk contains elements of collaboration with:
EU COST MP0601 Salamanca May 14 - 2009
• Colliding Plasmas - Introduction
• Optical Diagnostics
• Prospects for PLD & LIBS
Outline of the Talk
EU COST MP0601 Salamanca May 14 - 2009
EU COST MP0601 Salamanca May 14 - 2009
Colliding Plasmas - IntroductionMaking Stagnation Layers
Laser Pulse Energy: 50 - 500 mJ/ beamLaser Pulse duration: 170 ps, 6 ns, 15 nsFocal Spot Size: ~ 100 mIrradiance: 109 - 1011 W.cm-2 €
d = γf n −1( )
Colliding Plasmas - Introduction
EU COST MP0601 Salamanca May 14 - 2009
Not a new idea !
‘Seed’ Plasmas
‘Stagnation Layer’
When plasma plumes collide there are two extreme scenarios:1. Interpenetration - interactions are mostly via binary collisions2. 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
Colliding Plasmas - IntroductionHuge 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
1. T R Dittrich et al., Phys. Plasmas 6 2164 (1999)2. R W Clark et al., Phys. Plasmas 4 3718 (1997)3. J L Horwitz and T E Moore, IEEE Trans. Plasma. Sci. 28 1840 (2000)4. C Sanchez Ake et al., J. Appl. Phys 100 053305 (2006)5. C D Gregori et al., Ap. J. 676 420 (2008)
EU COST MP0601 Salamanca May 14 - 2009
Colliding Plasmas - Introduction
Collisionality Parameter:
€
ξ =D
λ ii
Plasma - Plasma Separation
Ion - Ion Mean Free Path (mfp)
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λii 1−2( ) =mi2v124
4πe4Z 4ne ln Λ12( )For collisions between opposing plumes (1, 2)
Slow moving and dense plumes are
more likely to stagnate !
λii >> D Interpenetrationλii ~ D ’Soft’ Stagnationλii << D ’Hard’ Stagnation
EU COST MP0601 Salamanca May 14 - 2009
Colliding Plasmas - Introduction
Collisionality Parameter:
€
ξ =D
λ ii
Plasma - Plasma Separation
Ion - Ion Mean Free Path (mfp)
€
λii 1−2( ) =mi2v124
4πe4Z 4ne ln Λ12( )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, λii) - application specific…..
EU COST MP0601 Salamanca May 14 - 2009
Stagnation layer growth
1. Time resolved (ICCD) imaging
2. Time-space resolved spectroscopy
3. Faraday ion cup
Plasma Diagnostics
n Time-space resolved spectroscopy - ne & Te
n Time resolved interferometry - ne
Part 2. Optical Diagnostics
EU COST MP0601 Salamanca May 14 - 2009
Part 2. Optical Diagnostics
EU COST MP0601 Salamanca May 14 - 2009
Optical Diagnostics
Time Evolution:
Ca - Emission Imaging @ 423 nm
Tight point focus on each Ca face:120 mJ per beam
ICCD: 5 ns gate10 ns interval
EU COST MP0601 Salamanca May 14 - 2009
Optical Diagnostics Broadband image - 200ns Stagnation Layer Evolution
~100 mJ/170 ps/’seed’ beam
Colliding aluminium plasmas
EU COST MP0601 Salamanca May 14 - 2009
Stagnation Layer Evolution:(Al) - Charge resolved !
Optical Diagnostics
300mJ/6ns/’seed’ beam
‘Growth rate’ - 10 m/ns
EU COST MP0601 Salamanca May 14 - 2009
Stagnation Layer (Al): Electron density & temperature
Optical Diagnostics
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ne ≈1017cm−3
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Te ≈ 2.2eV
‘Seed’ spectrum
‘Seed’ spectrum
Stagnation zone
EU COST MP0601 Salamanca May 14 - 2009
Optical DiagnosticsStagnation Layer (Al): Electron density & temperature
Spectroscopy - only works well for t > 100 nsSpectra dominated by continuum emission - solution - time resolved interferometry
Experimental Setup-
Nomarski Interferometry
EU COST MP0601 Salamanca May 14 - 2009
Optical DiagnosticsSeparation of electron and ion stagnation - Ambipolar effects
Electrons -‘Nomarski’
Al+ ions -ICCD
Al plume -ICCD
EU COST MP0601 Salamanca May 14 - 2009
Colliding Plasma - PLD PLASMA
GENERATIONPLASMA
EXPANSIONFILM
GROWTH
Target
IncidentLaserbeam
Expanding PlasmaPlume
Substrate
Replace single plume with stagnation layer……..
NeoceraTM PLD system
EU COST MP0601 Salamanca May 14 - 2009
Colliding Zn Plasma - PLD VacuumSingle Plume
VacuumColliding Plumes
1 mbar O2
Single Plume
1 mbar O2
Colliding Plumes
SEM IMAGES
EU COST MP0601 Salamanca May 14 - 2009
TISR-VUV-LIBS, Ambient Gas
Sulphur/Steel in N2 Background Gas
Line: S4+ (78.65 nm)
EU COST MP0601 Salamanca May 14 - 2009
VUV - LIBS, Ambient N2
Sulphur/ Steel in N2 Background Gas - strong enhancement of S4+ 78.65 nm line - S5+ + e S4+*….?
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LOD(Vacuum ) =3σ BS= 28ppm
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LOD(N2) =3σ BS= 6ppm
S4+ 78.65 nm
EU COST MP0601 Salamanca May 14 - 2009
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…..
Support
Science Foundation Ireland
Irish Research Council for Science, Engineering and Technology
EU COST: MP0601
EU COST MP0601 Salamanca May 14 - 2009
What have we learned to date ?
1. Strong stagnation in table top colliding plasmasdue to large value of the collisionality parameter ()
2. Degree of confinement/ hardness of the stagnationlayer can be controlled by designing the value of
3. Stagnation layer becomes quite uniform after 100s nsand so looks attractive for investigation as alternativepulsed 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