Biomedical Engineering Reference
In-Depth Information
Fig. 30.3
Artist's rendering of a Dielectric Wall Accelerator based Particle Therapy System
strengths in such a wakefield can exceed a hundred gigavolt per meter. With the
development of ultra intense lasers in the last decade the possibility is suggested
that compact accelerating systems could be build at a fraction of the size and cost of
standard systems available today.
During the last decade the field has evolved rapidly. Ultrahigh intensity lasers
have been shown to achieve accelerating fields in the range of 10 TV/meter,
surpassing the field strength of standard accelerators by sixth orders of magnitude,
and the generation of mono energetic electrons of GeV energies have been reported
[
24
-
26
]. Laser-based acceleration of protons and ions also has seen significant
progress in recent years and many authors have suggested this technology as an
alternative for particle beam therapy [
27
-
29
].
Laser-driven ions in the MeV/u range also have been reported to exhibit short
pulse length, high intensity, and low transverse emittance. Unfortunately their
exponential energy spectrum had an almost 100% energy spread [
30
,
31
].
The underlying physics of laser plasma acceleration of ions is the process of
target normal sheath acceleration (TSNA) [
32
]. Initially the ultra-high intensity laser
pulse incident on a target accelerates a significant number of electrons to energies of
several MeV. These electrons can traverse thin target foils, generating electric fields
in excess of 1 TV/m. This field ionizes material present on the back surface of the
foil and accelerates the ions. Predominantly one finds protons from hydrocarbon
contamination on the the target surface, but heavier ions can be generated after
careful cleaning of the surface. Experiments have reported acceleration of protons
to more than 60 MeV [
30
], fluor ions to above 100 MeV [
31
], and palladium to 225
MeV [
33
].
