Speaker
Description
Modern radiofrequency (RF) photoinjectors that are widely spread as $e^{-}$ sources for FEL, colliders and synchrotron radiation facilities, use semiconductor photocathodes quite often. Such photocathodes, as a rule, consist of a semiconductor layer (units-tens of $\text{nm}$) and a metal substrate.
The use of such structures along with well-known benefits is associated with a number of challenges and features. One phenomenon is as follows. Due to the laser pulse inducing photoemission process and the strong electric field $\textbf{E}$ existing in RF cavity semiconductor layer turns out to be depleted of electrons. The resulting positive dynamic charge of the semiconductor film $q(t)>0$, in turn, affects the photoemission process and the photoinjector operation regime as a whole.
In this paper, the diffusion problem for the conduction electrons in semiconductor layer $z\in[0,a]$ of the photocathode is solved. The generation rate of the electrons inside the semiconductor is considered to be propotional to laser pulse profile $S(t)$ (back front of trapezoidal-like laser pulse is not considered):
\begin{equation}
S(t)=\frac{1}{\tau}\left[ t\theta(t)-(t-\tau)\theta(t-\tau) \right]
\end{equation}
where $\theta(t)$ is a Heaviside function and $\tau$ is risetime. Obtained expression for electrons distribution along the semiconductor layer $n(z,t)$ allows to find the uncompensated charge $q(t)$, which is consistent with experimental one got at PITZ photoinjector at DESY.
| Young scientist paper | Yes |
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