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Electron Acceleration in an Ultra-intense Laser Illuminated Capillary and Its Application
https://repo.qst.go.jp/records/61239
https://repo.qst.go.jp/records/61239a7c934e7-c14f-4260-b715-8ed9c9f3bce1
Item type | 会議発表用資料 / Presentation(1) | |||||
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公開日 | 2005-12-20 | |||||
タイトル | ||||||
タイトル | Electron Acceleration in an Ultra-intense Laser Illuminated Capillary and Its Application | |||||
言語 | ||||||
言語 | eng | |||||
資源タイプ | ||||||
資源タイプ識別子 | http://purl.org/coar/resource_type/c_c94f | |||||
資源タイプ | conference object | |||||
アクセス権 | ||||||
アクセス権 | metadata only access | |||||
アクセス権URI | http://purl.org/coar/access_right/c_14cb | |||||
著者 |
Kitagawa, Yoneyoshi
× Kitagawa, Yoneyoshi× 北川 米喜 |
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抄録 | ||||||
内容記述タイプ | Abstract | |||||
内容記述 | A gas jet is mainly used for the plasma source, limiting the acceleration length to 2 mm or less. This is only a few times larger than the Rayleigh range, in which the laser spot size increases by $\sqrt{2}$ and is written as ${z_R} = \pi r_0^2/\lambda_0$, where $r_0$ is a laser spot radius and $\lambda_0$ is the laser wavelength. Even though the ultra-intense lasers have dramatically increased the acceleration gradient from one GV/m of the above-mentioned CO$_2$ laser beatwave to hundreds GV/m of a self-modulated wakefield or other scheme, nevertheless, nothing makes the plasma length longer. The acceleration gain is, therefore, limited to a few hundreds MeV level. Suppose an plasma, whose size is much longer than ${z_R}$ and close to the dephasing limit, given by $\lambda_p\gamma_\phi^2/\pi$, where $\lambda_p$ is the plasma wave length and square of a relativistic factor $\gamma_\phi^2$ is a ratio of the cutoff plasma density $n_c$ to the electron density $n_e$. The dephasing limit is typically 30 cm for $10^{17}$cm$^{-3}$. In the relativistic laser regime, the maximum acceleration field is approximated by $E_{max} \sim E_{wb}a_0 = m\omega_pca_0/e \sim E_L/{\gamma_\phi},$ where $E_{wb}$ is the classical wavebreaking field $\sim30\sqrt{n_e/10^{17}\rm{cm}^{-3}}$ [GV/m], and $a_0$ the normalized laser field $eE_L/{m\omega_0c}$. If, then, a laser of $a_0 = 2$ transmits 30 cm under a $10^{17}$cm$^{-3}$ plasma, electrons obtain the gain $eE_{max} \times 30$ cm $>18$ GeV. Many theoretical and experimental efforts, such as z-pinch, axicon channel and capillaries, are dedicated to make the acceleration length longer. On the other hand, the maximum energy gain $W_{max}$, which the electron can obtain within the dephasing limit, can be written as $2mc^2\gamma_\phi^2a_0^2/\sqrt{1+a_0^2/2}$. So if you want to have GeV electrons, since $a_0$ is $1 \sim 4$ for $2 \times 10^{18} \sim 2\times 10^{19}$ Wcm$^{-2}$, $\gamma_\phi$ must be larger than 15, which means that the electron density must be less than $10^{19}$ cm$^{-3}$. Then, we need a thin but cm -class plasma. Some have realized $2 \sim10$ cm plasma columns, but no electron acceleration has been yet reported. Here the 1-cm long or longer capillary accelerations of electrons are presented\cite{YK}. A 1-mm long cone, attached to the entrance edge, guides the laser beam into the capillary. The laser ablates plasmas in the order of $10^{16}$ cm$^{-3}$ from the capillary wall. We show a energy bump due to the trapping. Both the GMII laser of 15 J -1.053 $\mu$m pulse in $0.5 $ ps and the PW laser of 150 J -1.053 $\mu$m pulse in $0.6 $ ps were injected into the glass capillaries of 1 to 7 cm in length and 30 to 150 $\mu$m in bore size, which accelerated plasma electrons to 100 MeV via the laser wakefield inside the capillary. The plasma length was longer than any gas jet plasmas. The one and two-dimensional Particle-In-Cell simulations show the middle energy shoulder. The simulations describe that the capillary sustains a 10 GV/m laser wakefield. The particle trapping and the resulting bunch are explained by the simulation, which is the important steps to cool the accelerated beams. The PIC simulations well described the capillary acceleration, since the capillary confines the laser pulse as well as the plasma over a distance much longer than $z_R$. The application of the capillary accelerator will be discussed. {YK} Y. Kitagawa {\it et al.}, Phys. Rev. Lett. {\bf 92}, 205002(2004). | |||||
会議概要（会議名, 開催地, 会期, 主催者等） | ||||||
内容記述タイプ | Other | |||||
内容記述 | レーザーとビーム相互作用及びレーザーとプラズマの加速器に関するICFAワークショップ | |||||
発表年月日 | ||||||
日付 | 2005-12-16 | |||||
日付タイプ | Issued |