## 4 Database of JET with the ITER-Like Wall  
In building the database, the intentional disruptions and those in which the control system had activated the massive gas injection have been excluded from the training. Only times when the plasma current exceeds 750 kA have been considered. All the signals used as input features have been resampled at 1 kH frequency. Since on JET 10, ms is the shortest interval to implement reliable mitigation strategies, alarms, launched less than the10 ms from the beginning of the current quench, are considered tardy. Early alarms are those triggered more than 2.5 s before the beginning of the current quench; this is a conservative assumption because on JET with the ILW the main cause of disruptions is impurity accumulation, which takes place on time scales even longer that the 3 s.  
In more detail, campaigns C29 to C31 have been analysed. Various considerations have motivated this choice. First, the investigated campaigns are at the beginning of the operation of JET with the ITER-like Wall. The results are therefore more relevant for the next generation of devices and also simulate the beginning of the operation of a new machine. Moreover, in these first campaigns with the ILW, very little use was made of the fast valve to mitigate the effects of the disruptions with massive gas injection. The JET control system therefore did not interfere much with the natural evolution of the discharges, which is the situation of interest for the subject of analyses of the present work.  
The database has been divided into two parts. The data of C29 and C30 have been analysed with the aim of providing interpretable models. The examples of the campaign C31 have then been kept in reserve to form a test set; so the models have been derived from the examples of C29-C30 and have then been used to classify the completely new data of C31.  
After suitable cleaning and validation of the database, campaigns C29-C30 provided overall 187 disruptive and 1020 non-disruptive shots, unless differently specified (in some analyses at the end of the paper, the need to consider additional variables, which are not always available, will require a slight reduction in the statistical basis). Campaign C31 provided a total of 590 examples: 154 disruptions and 436 safe discharges. The operational space covered by the database is summarised graphically in Figure 4. As can be seen from the reported plots, the set of discharges considered is representative of JET operation with the ILW; therefore, the same quality of the results is to be expected also if the methodology is applied to future campaigns.  
The set of signals, considered as potential inputs to the predictors, includes: the vacuum toroidal magnetic field B, the plasma current I, the edge density n, the amplitude of the locked mode LM, the safety factor at 95% of the plasma radius q95 and the amplitude of the internal inductance li. The locked mode amplitude is estimated from the measurements of the s inductance is obtained from the Shafranov integrals calculated on the plasma last closed magnetic surface. The safety factor q95 is an output of EFIT, the main equilibrium reconstruction code used at JET.