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)

€

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

€

ne ≈1017cm−3

€

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+*….?

€

LOD(Vacuum ) =3σ BS= 28ppm

€

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