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We conducted a Ka-band (26.1--35 GHz) line survey towards Orion KL using theTianMa 65-m Radio Telescope (TMRT). It is the first blind line survey in the Kaband, and achieves a sensitivity of mK level (1--3 mK at a spectral resolutionof $\sim$1 km s$^{-1}$). In total, 592 Gaussian features are extracted. Amongthem, 257 radio recombination lines (RRLs) are identified. The maximum $\Deltan$ of RRLs of H, He and C are 20, 15, and 5, respectively. Through stacking, wehave detected the $\beta$ lines of ion RRLs (RRLs of C$^+$ with possiblecontribution of other ions like O$^+$) for the first time, and tentative signalof the $\gamma$ lines of ion RRLs can also be seen on the stacked spectrum.Besides, 318 other line features were assigned to 37 molecular species, and tenof these species were not detected in the Q-band survey of TMRT. Thevibrationally excited states of nine species were also detected. Emission ofmost species can be modeled under LTE. A number of transitions of E-CH3OH($J_2-J_1$) display maser effects, which are confirmed by our modeling, andbesides the bumping peak at $J\sim 6$ there is another peak at $J\sim 13$.Methylcyanoacetylene (CH$_3$C$_3$N) is detected in Orion KL for the first time.This work emphasizes that the Ka band, which was long-ignored for spectral linesurveys, is very useful for surveying RRLs and molecular lines simultaneously.

The first Ka-band (26.1-35 GHz) blind line survey towards Orion KL