Lecture 1. Introduction

Transcription

1 Preparation of the concerned sectors for educational and R&D activities related to the Hungarian ELI project Ion acceleration in plasmas Lecture 1. Introduction Dr. Ashutosh Sharma Zoltán Tibai 1

2 Contents 1. Introduction 2. Application of laser driven energetic ions 3. Short description on laser-driven ion acceleration mechanism 4. Applicability in context of next generation laser facilities 2

3 Introduction When any material is heated to a sufficient degree, its constituent atoms separate into negative electrons and positive ions. This stateof t matter is called plasma. Plasma has unique properties that make it an attractive medium for particle acceleration. Ion/Proton acceleration from plasma (from solid/gas targets) using high power lasers is an exciting field with a variety of applications inscience, i medicine, i and id industry. 3

4 Introduction Conventional accelerator cavities can only sustain accelerating electric field gradients of the order of 10 6 V/m, as they are limitedi by theelectric breakdown of the accelerator materials. il Plasmas are already broken down and so the accelerating fields are not limited by this effect. Plasmas exhibit quasineutrality, i.e. the negative charge density of the electrons is equal to the positive charge density of the ions. Any significant separation of positive and negative charge is accompanied by strong electrostatic restoring fields. These transient fields are of interest as compact ultrahigh-gradient g accelerating structures. 4

5 Introduction Accelerating Field due to Laser driven strong charge separation E L E - acc High quasi-stationary electric (and magnetic) fields are produced E L E acc tens GV/cm efficient charged particle acceleration 5

6 Introduction Cutting edge laser technology is capable of producing pulses of light focusable to intensities of W/cm 2.Atthese intensities the electric field of the laser rips electrons from their atomic orbitals and accelerates them to highly relativistic energies, E kinetic >> m e c 2. These extremely energetic electrons propagate through the surrounding material, causing further plasma formation. Recent studies have indicated that ions can be efficiently accelerated during such interactions via several mechanisms. 6

7 Introduction Laser Driven Ion Acceleration in thin Solid film Targets If an ultraintense and ultrashort laser pulse hits the surface of a thin solid film, intense and energetic (Multi- MeV!) ion beams are effectively produced - Target Fast tions E. L. Clark et al. Phys. Rev. Lett. 84, 670 (2000) A. Maksimchuk, et al., ibid. 84, 4108 (2000) R. Snavely et al. ibid. 85, 2945 (2000) Laser Electron cloud Typical physical parameters of the accelerating system: Laser energy: J, pulse duration: fs, intensity: W/cm 2 solid target type: conductors, insulators, thickness: μm accelerated ions protons in usual conditions, other ions in proper conditions 7

8 Proposed applications of ion beam Radiography (density measurement) Deflectometry (field measurement) Isochoric heating of matter Fusion Energy (Fast Ignition) Injection into conventional accelerators Cancer therapy Production of isotopes for PET Industrial applications (implantation, lithography) Nuclear/particle physics applications 8 Large moderate energy Divergence control Short burst (narrow band) Warn dense matter, solid density ev

9 Proposed applications and requirements Radiography (density measurement) Deflectometry (field measurement) High-energy ( MeV p + ) Isochoric heating of matter Fusion Energy (Fast Ignition) Injection into conventional accelerators Cancer therapy Production of isotopes for PET Industrial applications (implantation, lithography) Nuclear/particle physics applications 9 Narrow band (ΔE/E ~ %) Divergence control/transport + High repetition, stability, beam monitoring (!!!)

10 Proposed applications and requirements Radiography (density measurement) Deflectometry (field measurement) Isochoric heating of matter Fusion Energy (Fast Ignition) Injection into conventional accelerators Cancer therapy Production of isotopes for PET Industrial applications (implantation, lithography) Nuclear/particle physics applications 10 Very high energy > GeV (or >> GeV) High repetition + High repetition, stability, beam monitoring (!!!)

11 Bragg Peak for ions results in localized energy deposition 11

12 Laser driven Ion Acceleration Mechanism IF THE e - POPULATION IS DOMINATED BY A THERMAL SPECTRUM accelerating electric field due to strong charge separation between hot electrons expanding in vacuum and the bulk target Target Normal Sheath Acceleration (TNSA) Wilks et al., Phys. Plasmas 8, 542 (2001) pre-plasma p (underdense) solid target Relativistic e - current Laser IFTHEROLEOFTHETHERMAL e - pulse POPULATION IS SUPPRESSED accelerating electromagnetic field due to 2 charge separation induced by the balance between radiation pressure and electrostatic main force pulse front surface Radiation Pressure Acceleration (RPA) pre-pulse Esirkepov et al., Phys. Rev. Lett. 92,, (2004) Macchi et al., Phys. Rev. Lett. 94, (2005) 12 return current Light ion layer rear surface

13 Target Normal Sheath Acceleration (TNSA) 13

14 TNSA Typical results: Target: 10 µm Al Temperature ~ 1.8 MeV for 12 J ~5MeVfor 85 J Energy conversion η ~ for 12 J η ~ for 85 J η ~ for 400 J Efficieny at MeV η hot ~ Typical divergence: Zepf et al, PRL 84, 670, (2000), Snavely et at., PRL 85, 2945, (2000) 14

15 TNSA Beam quality substantially better than conventional particle accelerators nm scale surface perturbations are still visible Excellent beam quality of <0.004 mm mrad 15

16 TNSA Laser accelerated protons - more than just a nice technology? Unique for short pulse duration - unrivalled for time resolved probing - excellent emittance Compared to conventional accelerators What do we need to be competitive? - Averaged flux - Narrow angular distribution - Narrow energy distribution (not simply slicing) - Higher endpoint energy (200 MeV protons required for 200 mm range in H 2 O, e.g. for hadron therapy) 16

17 TNSA Energy Scaling Early experiments and modeling suggest that extend the tail to 200 MeV. Should be possible with currently extending lasers. 17

18 Radiation Pressure Acceleration (RPA) 18

19 RPA - Using circular polarisation at normal incidence Laser and electric field in force balance. Charge separation due to laser sets up field that accelerates ions. Momentumconservation determines ion velocity. 19

20 20 RPA vs TNSA

21 RPA vs TNSA Almost all protons are in tiny phase space volume Silva et al. PRL (2004) Esirkepov et al., PRL (20 Note: beam is quasineutral 21

22 Shock Wave Acceleration (SWA) A disturbance travels at supersonic speeds through a medium Subsonic Sonic SuperSonic At supersonic speeds, pressure will build at the front of a disturbance shock wave. Characterized by a rapid change in pressure (density and/or temperature) of the medium. In a plasma a shock wave is characterized by a propagating electric field at speeds useful for ion acceleration (v sh > c) 22

23 Shock formation in laser driven plasmas High Intensity Laser Pulse E E Shock acceleration Sheath Field (TNSA) Linearly polarized laser incidence upon an overcritical target creates and heats the plasma Ponderomotive force creates density spike and imparts a velocity drift on a surface plasma Beam quality destroyed by TNSA fields Denavit PRL 1992, Silva PRL

24 CO 2 Laser Interacting with a Gas Jet Target Gas jet target has advantages for Shock Wave Acceleration (SWA) CO 2 laser Ion beam Gas jets can be operated at or above /cm 3 plasma density (n cr for 10µm) Steepend Plasma Extended Plasma 24 Long scale length plasma on the back side of the gas jet inhibits strong TNSA fields preserving proton spectrum High repetition rate source Clean source of ions (H 2, He, N 2, O 2, Ar, etc ) Low plasma densities allows probing of plasma dynamics using visible wavelengths

25 Collisionless shock in laser-produced plasma Experimental setup, the CO 2 laser pulse profile and an image of a CR39 detector. Proton energy spectra Laser-produced plasma profile. Haberberger et al, Nature Physics 8,, 95 (2012) 25

26 Simulated Proton Spectra 1D-PIC Results Osiris PIC Results (Haberberger et. al., Nat. Phys. 8, 95 (2012) 26

27 Applicability in context of ELI facility The proposed course has focus on high power, ultraintense laser interaction with overdense plasma (solid / gas) which has high relevance in the development of laser-driven particle accelerators, X-ray sources and techniques for controlling the shape and contrast of intense laser pulses. The proposed research has high relevance in medical applications and in biomedical imaging, i and has highh relevance inthe implementation i of next generation lasers: linked to existing cutting edge projects in the field, such as Extreme Light Infrastructure (ELI) and High Power Laser Energy Research Facility (HiPER). ELI: HiPER: 27

28 Problems Q1.1. What is Plasma? A Fourth thstate t of fmatter. Q1.2. A1.2. Why do we use plasma for particle acceleration? Accelerating field in plasma is much stronger than conventional accelerator. Q1.3. A1.3. Why proton or ion beam is better for cancer treatment? Suitable for high energy deposition. Q1.4. A1.4. Where the isochoric heating of matter is relevant? Astrophysics, Inertial Confinement Fusion. 28

29 Problems Q1.5. A1.5. Define the fusion energy! It is the process where atomic nuclei collide together and release energy (in the form of neutrons). Q1.6. A1.6. Show the fusion of deuterium and tritium? Q1.7. A1.7. What is the role of proton beam in cancer treatment? Proton charged particles damage the DNA of cancer cells. 29

30 Problems Q1.8. A1.8. What is the reason proton beam is better than x-ray beam for cancer treatment? t t? Due to heavier mass proton beams are less scattered. Q1.9. A1.9. How does ion accelerate in laser driven plasma? Electric field is generated due to charge separation by laser. Q A What is the source of proton emission in metallic target whose chemical composition does not include hydrogen? Impurities in the form of water or hydrocarbon present on solid surface. 30

31 References 1. F. F. Chen, Introduction to Plasma Physics, (Plenum Press, New York, 1974). 2. Macchi et.al., Review of fmodern Physics 85, 751 (2013). 31