Status and Prospects of $N\nu DEx$, a Se TPC detector for $0\nu21\beta$ decays

N$\nu$DEx (No Neutrino Double beta decay Experiment) is a Se TPC detector that will be located in China Jinping Underground Laboratory (CJPL), looking for neutrinoless double beta decays. In this talk, I will present the current status of the experiment and the prospects for future developments. The first phase of the experiment will be N$\nu$DEx-100, using 100 kg of SeF$_6$: due to the large overburden (2,400 m rock) and the high Q-value of $^{82}$Se (2.996 MeV) the background rate will be very low, which ensures excellent prospects for scalability. On the other hand, since SeF$_6$ is an electronegative gas, any free electron will be captured almost immediately, and negative ions will be drifting in the chamber, which prohibits the use of traditional electron-sensing TPC detectors. For this reason, a new kind of chip has been developed: it will allow us to observe the negative ions and reconstruct the energy of the events with great precision, even without electron avalanche multiplication. A third tape-out of the chip (V2) has been produced and it's currently being tested using a prototype TPC on the surface. The tracks of alpha particles were successfully detected during the test and the equivalent noise charge was measured to be about 58e$^-$, approaching the requirement of 45e$^-$.