Direction of electron flow in X-ray Tube in X-ray Crystallography

In X-ray crystallography, X-ray tube may be used to generate X-ray. The set-up is the following:


[![X-ray tube](https://i.stack.imgur.com/ccmMK.png)](https://i.stack.imgur.com/ccmMK.png)


Here it shows the electron beam goes from cathode to anode. If anode is the negative electrode, why will electron travel towards it? Why don't electrons travel from anode to cathode?


Thanks!




For one, the question potentially displays confusion about *electric current* as either *flow of positive charge* (and *by convention*, the direction of electric current among e.g., electricians from $+ \rightarrow{} -$), or *flow of electrons*. See e.g., Wikipedia's [article](https://en.wikipedia.org/wiki/Electric_current#Conventions) about this:


[![enter image description here](https://i.stack.imgur.com/l17t4.png)](https://i.stack.imgur.com/l17t4.png)


For two, the anode of X-ray tubes not only is where the electrons travel to, but often literally is called the *target* they hit, because its composition has a great influence on the [brightness](https://dictionary.iucr.org/Brightness), [brilliance](https://dictionary.iucr.org/Brilliance), the position of the [characteristic emissions](https://en.wikipedia.org/wiki/Characteristic_X-ray) (in first approximation e.g., $\ce{Mo} K\alpha \approx \pu{0.71 Å}$, $\ce{Cu} K \alpha \approx \pu{1.54 Å}$), and underlying bremsstrahlung of such a source. As they carry much energy to a small spot, largely released as heat, you need good cooling (water on the backside of the anode, the Coolidge X-ray tube), use a *rotating disc* as target (a frequently used design in protein crystallography), or switch to a liquid jet altogether (one form of a microfocus source).


[![enter image description here](https://i.stack.imgur.com/lO200.jpg)](https://i.stack.imgur.com/lO200.jpg)


(image credit English Wikipedia, [X-ray tube](https://en.wikipedia.org/wiki/X-ray_tube)).




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In case the next question is where the X-ray photons travel to: the spatial distribution of their paths is not uniform (an [earlier question](https://chemistry.stackexchange.com/questions/151859/how-to-find-the-angle-of-emission-of-an-x-ray-during-impact-of-accelerated-catho/152113#152113)).


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