以磁性波電漿尾隨場加速為極高能宇宙射線之產生機制

Abstract

近幾十年來極高能宇宙射線的來源一直是個未解的謎團。目前一些現有的機制，如震波擴散加速與其他，在解釋這些粒子上仍存在問題。所以根據電漿加速器的概念，我們提出了新的機制—磁性波電漿尾隨場加速—來解釋極高能宇宙射線的產生。這篇論文中，我們以哨波作為電漿尾隨場的驅動脈衝來建立磁性波電漿尾隨場加速的理論及模擬，電漿模擬的結果證實磁性波電漿尾隨場的存在，同時它的場強符合我們新推導的相對論性理論預測；在適當的條件下，我們也證明磁性波電漿尾隨場經過幾百個電漿肌膚深度後仍可以維持高度同調性及高度加速梯度，這樣的特性使磁性波電漿尾隨場可以應用在加速器實驗。在天文環境中，粒子與尾隨場的隨機交互作用讓加速粒子能譜遵守指數律，我們最後說明活躍星系核加速粒子到1021 電子伏特的可能性。

The origin of ultrahigh energy cosmic rays has been puzzled over several decades. So far, the existing mechanisms, such as diffusive shock acceleration (DSA) and others, still present problems in explaining these particles. Based on the concept of plasma wakefield accelerator, we proposed a novel mechanism, the so-called magnetowave induced plasma wakefield acceleration (MPWA) to elucidate the production of ultrahigh energy cosmic rays. In this thesis we establish the general MPWA theory and perform a particle-in-cell simulation that provides the evidence of the generation of magnetowave induced plasma wakefield. Here we invoke the high frequency and high speed whistler mode for the driving pulse. The plasma wakefield obtained in the simulation compares favorably with our newly developed relativistic theory of MPWA. We show that under appropriate conditions, the plasma wakefield maintains very high coherence and sustains high-gradient acceleration over hundreds of plasma skin depths. In astrophysical setting, the power-law spectrum and accelerating gradient are given in the theory. Invoking AGNs as the acceleration site, we will show that the particle accelerated to 1021eV is possible.