Laser-Wakefield Acceleration Application to Endoscopic Oncology - - PowerPoint PPT Presentation

Laser-Wakefield Acceleration Application to Endoscopic Oncology

Scott Nicks, Toshi Tajima, Dante Roa, Ales Necas Workshop on Beam Acceleration in Crystals and Nanostructures June 25, 2019

Laser Wakefield Acceleration (LWFA)

• Collective force ~𝑂2
• Coherent, smooth, robust (not stochastic)
• Driven by laser or beams
• High acceleration gradient: ~ GeV/cm
• Wake phase velocity 𝑤𝑞ℎ ≫ bulk velocity 𝑤𝑐𝑣𝑚𝑙

𝒘𝒒𝒊 ≫ 𝒘𝒄𝒗𝒎𝒍

• Coherent, robust
• No turbulence
• Deep-ocean tsunami

𝒘𝒒𝒊~𝒘𝒄𝒗𝒎𝒍

• Wavebreak
• Turbulence
• Near-shore tsunami

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• T. Tajima and J. M. Dawson, Phys. Rev. Lett. 43, 267 (1979)
• E. Esarey, C. B. Schroeder, and W. P. Leemans, Rev. Mod. Phys. 81, 1229 (2009)

𝑤𝑞ℎ ≫ 𝑤𝑐𝑣𝑚𝑙 No bulk coupling 𝑤𝑞ℎ 𝑤𝑐𝑣𝑚𝑙

Laser Wakefield Theory

• Laser group velocity: 𝑤𝑕 = 𝑑 1 −

Τ 𝑜𝑓 𝑜𝑑

• Wake phase velocity 𝑤𝑞ℎ = 𝑤𝑕
• Low-density regime  𝑤𝑞ℎ ≫ 𝑤𝑐𝑣𝑚𝑙
• High-density regime  𝑤𝑞ℎ~𝑤𝑐𝑣𝑚𝑙
• Electron energy gain: ∆ℰ = 2𝑛𝑓𝑑2

Τ 𝑜𝑑 𝑜𝑓

• Robust wave saturation  Tajima-Dawson field:

𝐹𝑈𝐸 = 𝑛𝜕𝑤𝑞ℎ 𝑓 𝒘𝒒𝒊 ≫ 𝒘𝒄𝒗𝒎𝒍 ∆ℰ ≫ 𝑛𝑓𝑑2 𝒘𝒒𝒊~𝒘𝒄𝒗𝒎𝒍 ∆ℰ ≲ 𝑛𝑓𝑑2

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Laser critical density Plasma density

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Wakefields as Tsunamis

4 SurferToday.com

Blue wave 𝑤𝑕 ≈ 0 𝑤𝑕 ≫ 𝑤𝑐𝑣𝑚𝑙 Black wave Clean, no dredging Extensive sediment dredging, mass transport Pristine wakefield Bulk solid-target interaction (TNSA)1

• 1B. M. Hegelich et al., Nature 439, 441-444 (2006)

ProtoThema.gr

Plasma wavelength

Endoscopic Oncology

• Bring radiation directly to tissue
• Endoscopic or intra-operative
• No collateral tissue damage
• Low-energy particles
• LWFA  LINAC alternative

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• A. Giulietti, ed., Laser-Driven Particle Acceleration Towards

Radiobiology and Medicine, 2016

• A. S. Beddar et al. Med. Phys. 33, 1476 (2006)

Professor Dante Roa, Radiation Oncology, UCI

Linear accelerator

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Fiber lasers for LWFA

• Coherent Amplification Network (CAN)
• Optical lasers
• Many lasers together
• Technology reached critical stage
• Fiber laser for endoscopic LWFA

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• G. Mourou, W. Brocklesby, T. Tajima, and J. Limpert, Nat. Photonics 7, 258 (2013)

Nanomaterials for LWFA

Nanomaterials:  Wakefield guide  Optical laser 𝑜𝑑

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• N. V. Myung, J. Lim, J-P Fleurial, M. Yun, W. West, and D. Choi, Nanotech. 15, 833 (2004)
• X. Zhang et al., Phys. Rev. Accel. Beams 19, 101004 (2016)
• T. Tajima, Eur. Phys. J. Spec. Top. 223, 1037 (2014)

Nanotube Uniform Solid Porous alumina

• n SI substrate

LWFA for Endoscopic Oncology

• Putting the pieces together

 low-energy electrons  near-critical density LWFA  Nanomaterial provides density/guide  CAN laser (optical) for endoscopy

• Next steps

 Wakefield physics at Τ 𝑜𝑓 𝑜𝑑 ≈ 1  Scaling: density, intensity  Self-modulation

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Paper and Collaborators Submitted, Phys. Rev. Accel. Beams (2019)

Modeling Critical-Density Wakefields

• Critical density  𝑤𝑕 = 0
• Laser enters plasma  sheath formation
• Sheath accelerates electrons
• Simulation  laser injected from vacuum
• 1D 3V Particle-in-cell (PIC) code
• Ti:Sapphire laser, 𝜇 = 1 μm
• Laser 𝐹𝑧 = 𝐹0 sin 𝑙𝑦 − 𝜕𝑢 − 𝜚 ℎ 𝑦, 𝑢
• ℎ 𝑦, 𝑢  flat-top, resonant profile

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Uniform Plasma Slab 𝑦 = 0 Laser Impedance-matching boundary 𝑦 = 0 𝑦~𝜇𝑞 Laser (dispersed) Sheath Electrons Early Later

Density Scaling of Electron Energy

• Electron energy gain: ∆ℰ = 2𝑛𝑓𝑑2

Τ 𝑜𝑑 𝑜𝑓

• Linear dependence on

Τ 𝑜𝑑 𝑜𝑓

• Scan over

Τ 𝑜𝑑 𝑜𝑓  linear ∆ℰ trend agrees

• Low density  wakefield not constant 

deviation from linearity

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Low-Density Regime

• Typical wakefield regime,

Τ 𝑜𝑑 𝑜𝑓 = 10

• Clear, robust wakefield
• Wakefield  train of trapped electrons
• “Blue” wave  no bulk coupling/turbulence

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Laser 𝐹𝑧 Wakefield 𝐹𝑦 Electron phase space

𝜇𝑞 = 2𝜌𝑑 𝜕𝑞

Plasma wavelength

Early Later

High-Density Regime

• Critical density regime,

Τ 𝑜𝑑 𝑜𝑓 = 1

• 𝑤𝑕 = 0  sheath oscillation
• Sheath  low-energy electron streams
• Streams build up  sheath exhausted
• Novel regime
• “Black” wave  bulk coupling

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Sheath 𝐹𝑦 Sheath 𝐹𝑦

Transition Regime

• Intermediate regime,

Τ 𝑜𝑑 𝑜𝑓 = 5

• Modest electron trapping
• Transition  sheath physics beginning
• “Grey” wave

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𝐹𝑦 Proto-sheath 𝐹𝑦

Intensity Scaling of Electron Energy

• Electron energy gain in high-density regime
• 𝑏0  Normalized laser intensity
• Energy gain 𝑏0 dependence: ∆ℰ ∝ 𝑕 𝑏0
• Ponderomotive potential 𝑕 𝑏0 = 1 + 𝑏0

2 Τ 1 2 − 1

• Density fixed, ∆ℰ scanned over 𝑏0
• ∆ℰ compared  𝑕 𝑏0

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Τ 𝑜𝑑 𝑜𝑓 = 3 Τ 𝑜𝑑 𝑜𝑓 = 10

Self-Modulation

• Fiber lasers  long pulse better
• Self-modulation: long pulse breaks  small pulses
• Pulse length

Τ 𝜇𝑚 𝜇𝑞 scanned, Τ 𝑜𝑑 𝑜𝑓 = 10, 𝑏0 = 1

• Long pulses  Laser/wakefield modulated

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• J. Krall, A. Ting, E. Esarey, and P. Sprangle, in Proceedings of the 1993 Particle Accelerator Conference, Vol. 4
• E. Esarey, C. B. Schroeder, and W. P. Leemans, Rev. Mod. Phys. 81, 1229 (2009)

Τ 𝜇𝑚 𝜇𝑞 = 5 Τ 𝜇𝑚 𝜇𝑞 = 3 Τ 𝜇𝑚 𝜇𝑞 = 0.5

Self-Modulation at the Critical Density

• Critical plasma + long laser pulse 𝜇𝑚 = 8𝜇𝑞
• 𝑤𝑕 = 0  huge sheath oscillation
• Violent sheath  huge electron acceleration
• Laser  initial burst
• Sheath  later streams

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Resonant pulse Long pulse Initial burst from laser Later streams from sheath Sheath

Electron Tissue Penetration

• Critical plasma + long laser pulse 𝜇𝑚 = 8𝜇𝑞
• Electron energy spectrum  tissue penetration
• Continuous slowing-down approximation (CSDA)
• Penetration  tuned by

Τ 𝑜𝑑 𝑜𝑓, 𝑏0

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Summary

• Laser evolution  CPA to fiber
• Endoscopic therapy  keV electrons
• Fiber  tiny keV accelerator
• Technology exists  quick deployment
• Low-hanging fruit for large medical benefit
• Critical-density wakefield  Novel physics regime

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Linear accelerator

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