BUT when a client disconnects immediately from access point and connects again the portal page doesnt appear. 

If the authentication does not timeout, the clients which reconnect to the EAP will pass the authentication directly. The authentication page will pop up only if you need to do the authentication.

So is there a way allways the  authentication page pop up no matter time limit?

Thanks for the help.

If the clients have already passed the authentication and the authentication status is not timeout, clients will not pop out the portal page, because the clients does not need to pass the authentication at this situation. Does this machanism will affect the normal using of clients?

I agree but we want this AP for a specific operation thats why i asked if there is this option availiable. Some other AP like Microtik  do the job  , i mean everytime the same client connects to the AP facing the portal page.

Got your demand. But I think the EAP does not support this specific function now.

Do you have some special notes in the portal authentication page, then you need the clients to read the notes every time it connect to the EAP? 

Yes the client must always see some notes before continue to net. I think this is very simple for tp-link to install a tik box in the captive portal session enabling or disabling ''always ask for authentication''. With this option covers any public demand as the whole interface is very well structured.