Laser acceleration of electrons and ions: principles, issues, and applications

1. Laser accelerationof electrons and ions: principles, issues, and applications Alexander Lobko Institute for Nuclear Problems, BSU Minsk Belarus

2. Motivation • Way to table-top accelerators with relatively low energy for various applications in nuclear medicine, material science, biology, chemistry, and industry (e.g. sterilization of food) • Basic research in laser and plasma physics, physics of radiations, nanoscience, high density energy physics, detector development, etc • Seeking collaborations of Belarus physicists doing research in above fields, both theoretically and experimentally

3. Classical acceleration process

4. Evaluation of electric fieldat plasma wave where - plasma wave amplitude

5. Classical and plasma acceleration

6. Laser-induced ionization For the hydrogen atom, the binding electric field is given (in SI units) by This is the intensity at which any target material will be ionized solely by the laser electric field In fact, with laser intensities exceeding the photon density is high enough so that enables the multi-photon ionization process

7. Relativistic laser intensity where normalized vector amplitude The maximum kinetic energy of the electron can be written as Focused laser with a normalized amplitude of is commonly referred to as relativistic.

8. Motion of an electron in the laser field

9. Chirped pulse amplification (CPA) Before the invention of the CPA in 1985, laser pulses could be focused only in the two transverse dimensions by corresponding sets of lenses. The CPA technology has allowed the compression of the laser pulses in the third, longitudinal dimension, and this technological breakthrough has immediately led to a jump in the achievable powers and focused intensities. The Petawattshots, where an adaptive mirror has been employed, have resulted in the focal intensity Now, three classes of laser amplifiers – CPA based on Ti-Sa, CPA based on Neodymium glass, and Optical Parametric CPA based on DKDP crystals can deliver approximately the same level of power, about 1.0 PW.

10. Chirped pulse amplification (CPA)

11. Examples of lasers at operation

12. Laser pulse and plasma wave N. Matlis et al // Nat. Phys. 2 (2006) 749 The maximum amplitude of the plasma wave was measured to be in the range 20%–60% [C. E. Clayton at al // Phys. Rev. Lett. 81 (1998) 100)].

13. External injection

14. Supersonic jet target schematics One of the solutions to control electron injection is injection at downwarddensity ramp with a density gradient scale length greater than the plasma wavelength.

15. Beam quality Comparison of self-injection (top) and injection at a density transition (bottom)

16. Bubble regime-transverse injection The laser pulse that propagates from left to right, expels electrons on his path, forming a positively charged cavity. The radially expelled electrons flow along the cavity boundary and collide at the bubble base, before being accelerated behind the laser pulse. The fact that electrons are trapped behind the laser, where they no more interact with the laser field, contributes to improving of quality of the electron beam.

17. Transition between acceleration regimes Electron beam distribution for different plasma densities showing the transition from the self modulated laser wakefield and the forced laser wakefield to the bubble/blow-out regime.

18. Colliding laser pulses Two laser pulses propagate in opposite directions

19. Colliding laser pulses During the collision, some electrons get enough longitudinal momentum to be trapped by the relativistic plasma wave driven by the pump beam

20. Colliding laser pulses Trapped electrons are accelerated in the wake of the pump laser pulse

21. Experimental setup

22. Beam energy tunability

23. Beam energy spread

24. Beam properties

25. Ion accelerationTarget Normal Sheath Acceleration (TNSA) The obliquely incident laser heats electrons on the front side of the target. The electrons penetrate the target, that is several micron thick and opaque to the laser light. A charge separation field is created by these hot electrons on the back side of the target due to subsequent field ionization of the target surface. Protons (and ions) are accelerated in this virtual cathode target normal to the back surface

26. TNSA mechanism features

27. Ion accelerationBreak-out afterburner (BOA) The laser starts to ionize the surface of the initially opaque target and successively heats more and more electrons to relativistic energies. Provided, the target is thin enough and has not blown apart under the irradiation of the laser pedestal, the laser will eventually promote all electrons within the focal volume to hot electrons and turn the target relativistically transparent. At this time, which is referred to as t1, strong acceleration of the plasma ions over the whole volume occurs, where the accelerating electric field co-moves with the ions and the laser continuously replenishes the energy, the electrons transferred to the ions. The acceleration ceases, when the plasma turns classically underdense.

28. BOA regime features

29. BOA regime demands In order to enter the BOA regime with the laser systems available today (i.e. 100 TW to a PW) targets of 5-500 nm are necessary; with thicker targets the relativistic transparency will not be reached and acceleration will be dominated by the TNSA mechanism. The use of ultra-thin nm-scaled targets also demands ultra-high laser contrast, so that premature expansion does not destroy the target prior to arrival of the peak pulse.

30. Particle spectra Particle spectra measured by ion spectrometers at different angles for shots that yielded peak energies (a) for carbon ions and (b) for protons.

31. Maximal energies forcarbon ions and protons For protons maximum energies are emitted on-axis regardless of the target thickness, whereas maximum carbon ion energies are emitted off-axis in the BOA regime ( <<1 μm) and on-axis in the TNSA regime (> 1 μm)

32. Average ion energy Thickness dependency of the average particle energy for carbon (a) and protons (b) for thicknesses ranging from 30 nm up to 25 μm.

33. Particle numbers Thickness dependency of particle numbers for carbon ions (a) and protons (b) for thicknesses ranging from 30 nm up to 25 μm. The peak at 200 nm corresponds to the optimum BOA target thickness

34. CONCLUSIONFUTURE OF THE LASER PLASMAACCELERATORS

35. Century of Progress

36. Literature V. Malka Electron and X-ray beams with Laser Plasma Accelerators // Presentation at Channeling-2012 Conference В.Е. Фортов Экстремальные состояния вещества М.:-2009, - 304 с. А.В. Коржиманов и др. // УФН 181 (2011) 9 D. JungIon accelerationfrom relativisticlaser nano-target interaction//PhD thesis / Munchen 2012 V. Malka // PoP19, 055501 (2012) A. Pukhov // Rep. Prog. Phys. 66 (2003) 47 Ч.Джоши // В мире науки №5 2006

37. Thank you for attention