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Previous studies [Malara et al ApJ, 533, 523 (2000)] consideredsmall-amplitude Alfven wave (AW) packets in Arnold-Beltrami-Childress (ABC)magnetic field using WKB approximation. In this work linearly polarised Alfvenwave dynamics in ABC magnetic field via direct 3D MHD numerical simulation isstudied for the first time. Gaussian AW pulse with length-scale much shorterthan ABC domain length and harmonic AW with wavelength equal to ABC domainlength are studied for four different resistivities. While it is found that AWsdissipate quickly in the ABC field, surprisingly, AW perturbation energyincreases in time. In the case of the harmonic AW perturbation energy growth istransient in time, attaining peaks in both velocity and magnetic perturbationenergies within timescales much smaller than resistive time. In the case of theGaussian AW pulse velocity perturbation energy growth is still transient intime, attaining a peak within few resistive times, while magnetic perturbationenergy continues to grow. It is also shown that the total magnetic energydecreases in time and this is governed by the resistive evolution of thebackground ABC magnetic field rather than AW damping. On contrary, whenbackground magnetic field is uniform, the total magnetic energy decrease isprescribed by AW damping, because there is no resistive evolution of thebackground. By considering runs with different amplitudes and by analysingperturbation spectra, possible dynamo action by AW perturbation-inducedperistaltic flow and inverse cascade of magnetic energy have been excluded.Therefore, the perturbation energy growth is attributed to a new instability.The growth rate appears to be dependent on the value of the resistivity andspatial scale of the AW disturbance. Thus, when going beyond WKB approximation,AW damping, described by full MHD equations, does not guarantee decrease ofperturbation energy.

3D MHD simulation of linearly polarised Alfven wave dynamics in Arnold-Beltrami-Childress magnetic field