Should I take admissions to this phd programme? I get selected in Phd course. My area of interest is cloud security. There are two lectures whose area of interest is cloud security. I requested one of the supervisor,  who has good record and has good publications,  to take me as her phd student. She said that she doesn't have the vacant seat now but after 6 month she can have 1 vacant seat. She talked with another lecturer to be my supervisor and  said that in these, 6 month, she will evaluate my performance and based on that she will make decisions. So, after 6 months, if she likes my performance,  I can have two supervisor in which one is my original supervisor (which is mam to whom I requested) and another mam is my co-supervisor. If she doesn't like my performance,  I can have only  another lecturer as  my supervisor.

The problem is that she is not 100% percent sure and she will evaluate me during this 6 months.  I want that mam (to whom I requested) to be my supervisor as she has good knowledge and publications in good journals. Should I continue with this phd or quit?
Any guidance will surely help.
To me this arrangement is the greatest chance you could get to work under the supervision of whom you requested in the future. Since you have such strong orientation towards that particular supervisor (at least the way I see it), I think you should take the offer.

However, if all you want is to secure a good Ph.D. position, you should take into account whether you are ready to accept the worst case scenario, which is she refuse to take you in and you have to work under the supervision of the other supervisor. If this is the case, none of us here can help you in the decision making.