Browsing by Author "Chen, Pisin"

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A new type of plasma wakefield accelerator driven by magnetowaves
(2009-02-01)
Chen, Pisin
;
Chang, Feng-Yin
;
Lin, Guey-Lin
;
Noble, Robert J.
;
Sydora, Richard
We present a new concept for a plasma wakefield accelerator driven by magnetowaves (MPWA). This concept was originally proposed as a viable mechanism for the 'cosmic accelerator' that would accelerate cosmic particles to ultra-high energies in the astrophysical setting. Unlike the more familiar plasma wakefield accelerator (PWFA) and the laser wakefield accelerator (LWFA) where the drivers, the charged-particle beam and the laser, are independently existing entities, MPWA invokes the high-frequency and highspeed whistler mode as the driver, which is a medium wave that cannot exist outside of the plasma. Aside from the difference in drivers, the underlying mechanism that excites the plasma wakefield via the ponderomotive potential is common. Our computer simulations show that under appropriate conditions, the plasma wakefield maintains very high coherence and can sustain high-gradient acceleration over many plasma wavelengths. We suggest that in addition to its celestial application, the MPWA concept can also be of terrestrial utility. A proof-of-principle experiment on MPWA would benefit both terrestrial and celestial accelerator concepts.
Influence of plasma collective effects on cosmological evolution
(2008-06-28)
Lai, Kwang-Chang
;
Chen, Pisin
;
物理研究所
;
Institute of Physics
It is well-known that the universe was in a plasma state both before decoupling and after reionization. However, the conventional wisdom has been that the plasma effects are largely Debye-shielded and can thus be safely ignored when considering large scale evolutions. Recently we showed that large scale structure formation in the universe may actually be suppressed by the plasma collective effect. Indeed, observational data indicate that the conventional theoretical formula tends to overestimate the matter power spectrum at scales k > 1hMpc(-1). In this paper, we further develop our theory through a more thorough and general derivation of the Maxwell-Einstein-Boltzmann equation. In addition to baryon density perturbation post reionization, we apply this general formulation to investigate the possible plasma effect on CMB anisotropy. As expected, while the plasma effect does render an observable effect to the former, its impact on the latter is totally negligible.
Magnetowave Induced Plasma Wakefield Acceleration for Ultrahigh Energy Cosmic Rays
(2009-03-20)
Chang, Feng-Yin
;
Chen, Pisin
;
Lin, Guey-Lin
;
Noble, Robert
;
Sydora, Richard
Magnetowave induced plasma wakefield acceleration (MPWA) in a relativistic astrophysical outflow has been proposed as a viable mechanism for the acceleration of cosmic particles to ultrahigh energies. Here we present simulation results that clearly demonstrate the viability of this mechanism for the first time. We invoke the high frequency and high speed whistler mode for the driving pulse. The plasma wakefield obtained in the simulations compares favorably with our newly developed relativistic theory of the MPWA. We show that, under appropriate conditions, the plasma wakefield maintains very high coherence and can sustain high-gradient acceleration over hundreds of plasma skin depths. Invoking active galactic nuclei as the site, we show that MPWA production of ultrahigh energy cosmic rays beyond ZeV (10(21) eV) is possible.
Plasma suppression of large scale structure formation in the universe
(2007-12-07)
Chen, Pisin
;
Lai, Kwang-Chang
;
物理研究所
;
Institute of Physics
We point out that during the reionization epoch of the cosmic history, the plasma collective effect among the ordinary matter would suppress the large scale structure formation. The imperfect Debye shielding at finite temperature would induce an electrostatic pressure which, working together with the thermal pressure, would counter the gravitational collapse. As a result, the effective Jeans length, (lambda) over tilde (J) is increased by a factor (lambda) over tilde (J)/(lambda) over tilde (J) = root 8/5, relative to the conventional one. For scales smaller than the effective Jeans scale the plasma would oscillate at the ion-acoustic frequency. The modes that would be influenced by this effect lie roughly in the range 0.5h Mpc(-1)< k, which corresponds to the Lyman-alpha forest from the intergalactic medium. We predict that in the linear regime of density-contrast growth, the plasma suppression of the matter power spectrum would approach 1 - (Omega(dm)/Omega(m))(2) similar to 1 - (5/6)(2) similar to 30%.