The present invention relates generally to the production of relativistic particles, and, more particularly, to the production of relativistic particles by colliding a plasma with electromagnetic pulses.
The sustainable acceleration of charged particles is a major challenge in both basic plasma physics and astrophysics. Current conventional particle accelerators have an energy gain per distance of only about 1GeV/m. Recent advances in ultra-intense lasers (ULs) (e.g., with intensity I>2×1018Wcm−2) open up a new frontier in the acceleration of particles via intense electromagnetic (EM) fields. (See e.g., G. A. Mourou, C. P. J. Barty, M. D. Perry, Phys. Today 51(1), 22 (1998), the SAUUL Report, T. Ditmire, Ed. (UT Austin, 2003), for and by L Lontano et al., Eds., Superstrong Fields in Plasmas, AIP Conf. Proc. No. 611 (AIP, NY 2002)).
Most proposed laser acceleration schemes, for example, Laser Wake Field Acceleration (LWFA), Plasma Wake Field Acceleration (PWFA), Plasma Beat Wave Acceleration (PBWA), as described by E. Esarey, P. Sprangle, J. Krall, A. Ting, IEEE Trans. Plasma Sci. 24, 252 (1996), P. Sprangle, E. Esary, A. Ting, Phys. Rev. Lett. 64, 2011 (1990), V. Malka, in AIP Conf. Proc. No. 611, p. 303, Ed. M. Lontano et al. (AIP, NY, 2002), A. Pukhov, J. Meyer-ter-Vehn, Phys. Rev. Lett. 79, 2686 (1997), T. Tajima and J. M. Dawson, Phys. Rev. Lett. 43, 267 (1979), and Free Wave Acceleration (FWA), as described by M. S. Hussein, M. P. Pato, A. K. Kerman, Phys. Rev. A 46, 3562 (1992), M. S. Hussein, M. P. Pato, Phys. Rev. Lett. 68, 1992, S. Kawata, T. Maruyama, H. Watanabe, I. Takahashi, Phys. Rev. Lett. 66, 2072 (1991), J. G. Woodworth, M. N. Kreisler, A. K. Kerman, The Future of Accelerator Phys. p. 378, Ed. T. Tajima (AIP, N.Y. 1996), involve the propagation of lasers in an underdense plasma (ωpe=(4πne2/me) 1/2<ωo=2πc/λ, where λ=laser wavelength, me is the rest mass of an electron e− or a positron e+, e is the absolute value of the electric charge of an electron e− or a positron e+, c is the speed of light in a vacuum, and n=electron density). In such schemes both the acceleration gradient (energy gain/distance) and the particle beam intensity are limited by the underdense plasma requirement. (See e.g., E. Esarey, P. Sprangle, J. Krall, A. Ting, IEEE Trans. Plasma Sci. 24, 252 (1996), P. Sprangle, E. Esary, A. Ting, Phys. Rev. Lett. 64, 2011 (1990), V. Malka, in AIP Conf. Proc. No. 611, p. 303, Ed. M. Lontano et al. (AIP, NY, 2002), A. Pukhov, J. Meyer-ter-Vehn, Phys. Rev. Lett. 79, 2686 (1997), T. Tajima and J. M. Dawson, Phys. Rev. Lett. 43, 267 (1979)).
When a single ultra-intense laser (UL) irradiates a plasma surface through a variety of nonlinear collisionless processes, as described, for example, by W. L. Kruer, E. J. Valeo, K. G. Estabrook, Phys. Rev. Lett. 35, 1076 (1975), W. L. Kruer, K. G. Estabrook, Phys. Fluids 28, 430 (1985), and S. C. Wilks, W. L. Kruer, M. Tabak, A. B. Langdon, Phys. Rev. Lett. 69, 1383 (1992), the single ultra-intense laser (UL) as described, for example, by S. C. Wilks, W. L. Kruer, M. Tabak, A. B. Langdon, Phys. Rev. Lett. 69, 1383 (1992), and A. Pukhov, J. Meyer-ter-Vehn, Phys. Rev. Lett. 79, 2686 (1997), couples a significant fraction of the energy of the single ultra-intense laser (UL) to superthermal electrons with characteristic energy E given by the Lorentz relativistic gamma factor γ=E/(511 keV)˜(1+Iλ2/1.4×1018Wcm−2)1/2−1, where I is the laser intensity in Watts/cm2 and λ is the laser wavelength in μm,.
If the plasma is a slab of electron-positron (e+e−) pairs, in addition to the collisionless heating, the light pressure will also snowplow the e+e− pairs with a bulk velocity determined by momentum conservation, as described, for example, by W. L. Kruer, E. J. Valeo, K. G. Estabrook, Phys. Rev. Lett. 35, 1076 (1975). For λ=1 μm and I=1021W/cm2, particle-in-cell (PIC) simulations, which are described, for example, by S. C. Wilks, W. L. Kruer, M. Tabak, A. B. Langdon, Phys. Rev. Lett. 69, 1383 (1992), A. Pukhov, J. Meyer-ten-Vehn, Phys. Rev. Lett. 79, 2686 (1997), and E. P. Liang, S. C. Wilks, M. Tabak, Phys. Rev. Lett. 81, 4887 (1998), show that the electrons can be accelerated to greater than about 10MeV. This has been confirmed with experiments, as described, for example, by S. P. Hatchett et al. Phys. Plasmas 7, 2076 (2000), K. W. D. Ledingham et al. Phys. Rev. Lett. 84, 899 (2000). and T. E. Cowan et al., Phys. Rev. Lett. 84, 903 (2000).
In a conventional laser ponderomotive accelerator in which a single ultra-intense laser (UL) strikes an overdense e+e− plasma surface, as described, for example, by S. C. Wilks, W. L. Kruer, M. Tabak, A. B. Langdon, Phys. Rev. Lett. 69, 1383 (1992), all upstream particles share the momentum of the Poynting flux. For a laser wavelength λ=1 μm and an ultra-intense laser (UL) intensity I=1021W/cm2, in conventional laser ponderomotive heating, the Lorentz relativistic gamma factor γ may reach only γ˜Ωe/ωo˜30, where Ωe=eB/mec is equal to the electron gyrofrequency in the laser magnetic field B, me is the rest mass of an electron e− or a positron e+, e is the absolute value of the electric charge of an electron e− or a positron e+, c is the speed of light in a vacuum, and ωo is equal to the laser frequency. (See e.g., W. L. Kruer, K. G. Estabrook, Phys. Fluids 28, 430 (1985) and S. C. Wilks, W. L. Kruer, M. Tabak, A. B. Langdon, Phys. Rev. Lett. 69, 1383 (1992)). A Diamagnetic Relativistic Pulse Accelerator (DRPA) of an overdense plasma has been proposed, as described, for example, by E. Liang, K. Nishimura, H. Li, S. P. Gary, Phys. Rev. Lett. 90, 085001 (2003), E. Liang, K. Nishimura, Phys. Rev. Lett. 92, 175005 (2004), and K. Nishimura, E. Liang, Phys. Plasmas, 11 (10) (2004). However, the Diamagnetic Relativistic Pulse Accelerator (DRPA) is difficult and expensive to realize practically.
High-energy gamma-ray (γ-ray) beams are conventionally only produced by large conventional particle accelerators (e.g., synchrotron sources) at national research facilities. Both the intensity of the high-energy gamma-ray (γ-ray) beams produced by the large conventional particle accelerators, and the energy conversion efficiency, are relatively low. Consideration is now being given to the design of particle accelerators that can produce relativistic particles. In particular, attention is being directed to the production of relativistic particles by colliding a plasma with electromagnetic pulses.