Capture, focusing and energy selection of laser driven ion beams using conventional beam elements
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Transcript of Capture, focusing and energy selection of laser driven ion beams using conventional beam elements
Capture, focusing and energy selection of laser driven ion beams using conventional beam elements
Morteza AslaninejadImperial College
13 December 2012
TNSA(Target Normal Sheath Acceleration) For relatively thick targets (μm thick AL foils) Acceleration of surface ions(60 MeV protons). For TNSA scaling considerations predict that laser intensities of a few 1022
W/cm2 are required to reach the 200 MeV proton energies of interest for ion therapy.
RPA(Radiation Pressure Acceleration )Radiation Pressure Regime proposed by Esirkepov et al., 2004 Laser acts like a piston that accelerates foil as a whole. Promises several hundred MeV protons (or carbon) “mono-energetic”. Major challenges are to fabricate the required ultrathin target foils that have a typical thickness in the order of 10 nm only.
Laser acceleration:Beyond 1018 W/cm2 , laser pulses can produce particle beams.There are different regimes of ion acceleration depending on target thickness and laser parameters:
Laser ion acceleration potential candidate for therapy applications :available energies are getting interesting (65 MeV p) high "quality" of beams at origin (small 6D phase space) abundance of protons per shot (total ~ 1010…1013) high rep rate lasers emerging (10 Hz) laser accelerator "compact" (acceleration length < 1mm)
Focusing and the transport of laser driven protons a challenging problem .Large energy spread Large angular divergence, Beam handling: though the emittance of particles bunches produced by laser acceleration are very favourable, the hardware necessary to match these beams to a therapy scanning system is unwieldy, expensive and impractical.
BUT
Aperture collimation (no focusing) Development of a Laser –Driven Proton Accelerator for Cancer TherapyC.M. Ma et al., Laser Physics, 2006, Vol. 16, No. 4,pp. 639-646.• Energy selection (bends + apertures) 250 MeV • Passive elements to form dose
Very compact particle selection not requiring much more than 1 m distance laser target to tumour.1. Transverse collimation by a small aperture immediately behind the target limiting transmission to a production cone angle of
Ω≈±10 mrad (0.5 degrees), 2. A dispersive energy separation device 3. A Second aperture close to the tumour
Obviously, the available particle flux density form the source and the need for keeping the distance low are critical issues here.
PMQ Parameters
Magnetic field strengths
55 and 60 T/m
Repetition rate 1 Hz
Proton beam energy
2.4 MeV
Focused to a spot with a size of
3 x 8 mm2 at a distance of 650 mm from source
Lens collection by quadrupoleMore flexibility can be expected if active lens focusing by a solenoid or quadrupole is applies which allows using a larger production cone angle
Focusing and Spectral Enhancement of a Repetition-Rated, Laser-Driven,Divergent Multi-MeV Proton Beam Using Permanent Quadrupole MagnetsM. Nishiuchi et al Appl. Phys.Lett.94,061107(2009)
Solenoid Parameters
Solenoid Length L=360 mm
Inner radius Rin=44 mm
Outer radius Rout=76 mm
Magnetic Field B=13 T
Focal distance F=1 m
Beam ParametersEnergy E=200 MeVEnergy Spread ∆E/E=±0.05Special Angle Ωmax=50 mradRadius R=10 μmEmittance ε=0.5 mm-mradPulse duration 140 ps
Lens Collection by SolenoidCollection and Focusing of Laser Accelerated Ion beam for Therapy Applications:Ingo Hofmann et alPhysical Review Special Topics Accelerators and Beams 14, 0313304 (2011).
Sample trajectory through solenoid collector and ∆E/E=±0.05
Distance target to
solenoid= 240 mm
Linear behaviour for energy spreadQuadratic dependence on the initial cone angle
An emittance scaling law for the Chromatic emittance at the focusing : ε=αcΩ2(∆E/E) αc=0.3 m/rad
Phase space at the trajectory crossover
Usable intensities of 200 MeV protons as a function of selected production cone angle and energy window
∆E/E=±0.1 and Ω=40 mrad I=3.5x1010
20 times as high as the fluence requirement of 1.7x109/cm2
∆E/E=±0.01 and Ω=40 mrad I=3.5x109
5 times as high as the fluence requirement of 7x109/cm2
PHELIX laser system at GSI:The proton beams accelerated are contained within an angular distribution with up to a half-angle divergence of 7° for high energy protons and 20° for low energy protons. Exponentially decaying proton spectra had a maximum cut-off near 23 MeV.
Intensities of 2.9*1019W/cm2
With 72 J of normal incident linearly polarized 1.054 μm laser light in 500 fs.The laser light focused to an 8.5μm by 17 um diameter spot size(FWHM) on a flat 25 μm thick Au foil.
Laser Accelerated protons Captured and Transported by a Pulse power SolenoidT. Burrins-Mog, et alPhysical Review Special Topics Accelerators and Beams 14, 121301 (2011)
8.5 Tesla solenoid for beam energy up to 23 MeV.Solenoid as the initial capture and collimating elements for a 250 MeV proton is scaled to 32 T.
Electrostatic lenses on the other hand have several advantages.Space charge plasma lenses of the Gabor type might be a cost effective alternative.
See talk by Juergen Thank you
Gabor Lenses for Capture and Energy Selection of Laser Driven Ion Beams In Cancer TreatmentJuergen Pozimski
Magnetic lenses are very sensitive to the energy of the particles and the extremely high –energy spread of the raw beam from the laser would render the design of such a transport system challenging.
Conventional optical systems like solenoids or quadrupoles will be operating at the technical limits which would be contradictory to the cost and space argument.
Back up slides
Spectral Yield
Pure aperture collimation:dN/dE=0.25x109
E=200 MeV∆E/E=±0.01 →→∆E=±2 MeV →→∆E=4 MeV dN=(0.25x109)=109
The standard proton fluence of 7x108/cm2
Required at the distal layer with a spot radius of 10 mm (resulting at 1 m distance according to the assumed divergence)requires, 2x109which would be missed by a factor of 2 for a single laser shot.
Laser parameters considered by I. Hofmann:
Spot radius = 10 μmPulse duration = 66 fsSpecific power = 3x1021 W/cm2
Peak power = 10 PWPulse energy = 620 JAverage power = 6 kW(10 Hz)
Nishiuchi expriement
Divergence half angle=10°±1°The beam diameter(FWHM)= 28±1 mmPMQ used.J-KAREN laser100 TW