Laser acceleration system for generating monoenergetic protons

• US 8,264,174 B2
• Filed: 07/26/2010
• Issued: 09/11/2012
• Est. Priority Date: 07/24/2009
• Status: Active Grant

• Current Assignee: University of Maryland
• Original Assignee: University of Maryland
• Inventors: Liu, Chuan Sheng, Shao, Xi, Tripathi, Vipin, Liu, Tung-Chang, Su, Jao-Jang
• Primary Examiner(s): LE, DON P
• Application Number:
  US12/843,520
• Publication Number:
  US 20110273115A1
• Time in Patent Office: 778 Days
• Field of Search: 315500-507, 600/1, 250/396.R
• US Class Current: 315/500
• CPC Class Codes: A61N 2005/1088 generated by laser radiation
• CPC Class Codes: H05H 15/00 Methods or devices for acceleration of charged particles not otherwise provided for , e.g. wakefield accelerators

Abstract

A proton acceleration system is provided for accelerating protons within a target. The system includes a laser source generating a laser beam having a wavelength λ_L and intensity and a target formed of foil having a selected thickness. The target is irradiated by the laser beam and transformed into a plasma that has a target density. This causes a treatment energy to be emitted from the foil due to the irradiation. The thickness of the foil of the target is selected so that the foil has a thickness within a range of optimal thickness Δ_s to 2×Δ_s, wherein Δ_s is less than the laser wavelength and is a function of the laser intensity, laser wavelength, and target density sufficient to achieve radiation pressure acceleration (RPA).

Claims

1. A proton acceleration system for accelerating protons within a target comprising:

a laser source generating a laser beam having a wavelength λ

_L and intensity; and

a target formed of foil having a selected thickness, wherein the target irradiated by the laser beam and transformed into a plasma having a target density causing a treatment energy to be emitted from the foil due to the irradiation;

wherein the thickness of the foil of the target is selected so that the foil has a thickness within a range of optimal thickness Δ

_s to 2×

Δ

_s, wherein Δ

_s is less than the laser wavelength and is a function of the laser intensity, laser wavelength, and target density sufficient to achieve radiation pressure acceleration (RPA).

2. The proton acceleration system according to claim 1, wherein achieving RPA includes balancing a ponderomotive force of the laser radiation accelerating electrons in the foil with a space charge force due to electric field produced by the charge separation pulling the electrons back, wherein protons in the foil are stably trapped due to the balance.

3. The proton acceleration system according to claim 1, wherein

4. The proton acceleration system according to claim 1, wherein:

the laser beam is circularly polarized and has a high intensity with laser power between 100-1000 TeraWatt; and

the treatment energy includes 50-350 MeV monoenergetic protons.

5. The proton acceleration system according to claim 1, wherein the laser beam includes pre-pulses and a main pulse having a contrast ratio of >

10⁹.

6. The proton acceleration system according to claim 2, wherein the electron layer with the trapped protons is accelerated as whole by laser radiation, achieving an acceleration gradient in the order of >

100 GeV/cm.

7. The proton acceleration system according to claim 6, wherein a distance from a reflection mirror of at least one reflection mirror reflecting the laser beam to an area on an object that is treated with the treatment energy is less than three meters.

8. The proton acceleration system according to claim 1, wherein the target density is greater than critical density.

9. The proton acceleration system according to claim 1, wherein the target is formed of C₂H₄.

10. The proton acceleration system according to claim 1, wherein the target is shaped to suppress Rayleigh-Taylor (R-T) instability in the target caused by the irradiation.

11. The proton acceleration system according to claim 10, wherein the target is shaped to have a convex front surface that has a maximum thickness substantially at its center and a minimal thickness at its edges.

12. The proton acceleration system according to claim 10, wherein the front surface has a surface level and the shape of the target includes providing the front surface of the target with a plurality of periodic variations in the surface level.

13. The proton acceleration system according to claim 12, wherein the variations in the surface level include at least one of protrusions or indentations.

14. The proton acceleration system according to claim 12, wherein the variations in the surface level are periodical in two-dimensions.

15. The proton acceleration system according to claim 10, wherein the system the target comprises a plurality targets each target having a different combination of thickness and shape, wherein one target is selected from the plurality of targets based on its combination thickness and shape for achieving at least one of maximum RPA and minimal R-T instabilities.

16. The proton acceleration system according to claim 1, wherein the target is provided with a radial density gradient to suppress R-T instability.

17. The proton acceleration system according to claim 1, wherein the treatment energy is tuned by adjusting power of the laser beam that irradiates the target.

18. The proton acceleration system according to claim 1, wherein the laser beam includes pulses and the treatment energy is tuned by controlling duration of the pulses.

19. The proton acceleration system according to claim 1, further comprising a controller having:

a tangible processor; and

a memory with instructions to be executed by the tangible processor for tuning the treatment energy by selecting at least one property of the laser beam selected from the group of properties consisting of intensity, time profile, beam width, intensity profile, and contrast ratio.

20. The proton acceleration system according to claim 1, further comprising a controller having:

a tangible processor; and

a memory with instructions to be executed by the tangible processor for tuning the treatment energy by selecting the thickness of the target.

21. The proton acceleration system according to claim 1, wherein the laser beam travels along at least one longitudinal path having a transverse profile normal to the at least one longitudinal path;

the system further comprising at least two mirror shapers impacted by the laser beam before the target is impacted for shaping the intensity distribution of the laser beam'"'"'s transverse profile.

22. The proton acceleration system according to claim 21, wherein the at least two mirror shapers are shaped so that the intensity distribution is selected from one of double Gaussian, flat top, double super Gaussian, and super Gaussian.

23. The proton acceleration system according to claim 1, wherein the laser beam travels along a longitudinal path;

the system further comprising a magnet for generating an external magnetic field directed along the longitudinal axis.

24. The proton acceleration system according to claim 1, wherein a particle beam is emitted from the irradiated target, the system further comprising:

a steering bending magnet for generating a magnetic field that acts on the particle beam; and

a selector gap for selecting energy of the particle beam that can pass through the selector gap as the treatment energy;

wherein at least one of energy spread and spot size of the particle beam are determined by a combination of the steering bending magnet and the selector gap.

25. The proton acceleration system according to claim 24, wherein:

the steering magnet includes at least one coil through which an adjustable current flows for generating the magnetic field; and

the selector gap includes movable first and second plates that form an adjustable gap between them; and

the system further comprises a controller having;

a tangible processor; and

a memory with instructions to be executed by the tangible processor for controlling at least one of the energy spread and spot size of the particle beam by controlling at least one of;

the current flowing through the at least one coil; and

relative positions of the first and second plates for adjusting the size of the gap.

26. A controller for a proton acceleration system including a laser source generating a pulsed laser beam having a wavelength λ

_L and intensity; and

further including a target formed of foil which is irradiated by the laser beam and transformed into a plasma having a target density causing a treatment energy to be emitted from the foil due to the irradiation, wherein the controller comprising;

a tangible processor; and

a memory with instructions to be executed by the tangible processor for selecting a thickness of the foil of the target so that the foil has a thickness within a range of optimal thickness Δ

_s to 2×

Δ

_s, wherein Δ

_s is less than the laser wavelength and is a function of the laser intensity, laser wavelength, and target density sufficient to achieve radiation pressure acceleration (RPA).

27. The controller according to claim 26, wherein:

28. The controller according to claim 26, wherein the system includes a plurality of targets and the selecting the thickness of the foil of the target by the controller includes selecting a target from the plurality of targets for achieving maximum RPA.

29. The controller according to claim 26, wherein the a memory further includes instructions to be executed by the tangible processor for adjusting the treatment energy by adjusting a parameter of the laser beam selected from the group of laser beam parameters consisting of:

power, duration of the laser beam'"'"'s pulses, time profile, beam width, intensity profile, and contrast ratio.

30. The controller according to claim 28, wherein:

the system further comprises a plurality of moveable mirror shapers impacted by the laser beam before the target is impacted for shaping the intensity distribution of the laser beam'"'"'s transverse profile; and

adjusting the intensity profile includes selecting at least two mirrors from the plurality of mirrors and adjusting positions of the selected at least two mirrors for achieving a desired intensity distributing.

31. The controller according to claim 26, wherein:

the laser is propagated longitudinally and the system further comprises a solenoid through an adjustable current flows for generating an external magnetic field directed along its longitudinal axis for confining electron'"'"'s of the foil about the longitudinal axis; and

the a memory further includes instructions to be executed by the tangible processor for adjusting the current for controlling the external magnetic field and the confining.

32. The controller according to claim 26, wherein:

the system further includes;

a steering bending magnet having at least one coil through which an adjustable current flows for generating a magnetic field that acts on the particle beam; and

a selector gap having movable first and second plates that form an adjustable gap between them for selecting energy of the particle beam that can pass through the selector gap as the treatment energy;

wherein the a memory further includes instructions to be executed by the tangible processor for controlling at least one of the energy spread and spot size of the particle beam by controlling at least one of;

the current flowing through the at least one coil; and

relative positions of the first and second plates for adjusting the size of the gap.

33. A method for controlling a proton acceleration system including a laser source generating a pulsed laser beam having a wavelength λ

_L and intensity; and

further including a target formed of foil which is irradiated by the laser beam and transformed into a plasma having a target density causing a treatment energy to be emitted from the foil due to the irradiation comprising;

selecting a thickness of the foil of the target so that the foil has a thickness within a range of optimal thickness Δ

_s to 2×

Δ

_s, wherein Δ

_s is less than the laser wavelength and is a function of the laser intensity, laser wavelength, and target density sufficient to achieve radiation pressure acceleration (RPA).

34. The method according to claim 33, wherein: