  The global linear behaviors of 2/1 DTM in the collisional regime are
investigated based on a concisely resistive drift-MHD model. Besides DTM, extra
normal modes including EDW and SAW are coupled together and destabilized in
different parameter regimes by considering resistivity in this system. The EVP
approach is applied for solving the eigenstate spectra with the distribution of
all unstable solutions. It is found that in the small EDD frequency (omega_*e)
regime, DTM growth rate agrees well with local theory that is reduced with
increasing omega_*e. However, when omega_*e exceeds a critical threshold
omega_*crit, the strongly linear coupling between DTM and other discretized EDW
instabilities happens so that the free energies from current and pressure
channels can be released together and thus enhance the DTM, of which growth
rate increases with increasing omega_*e and deviates from local theory results
qualitatively. Correspondingly, a cross-scale mode structure forms with mixed
polarization, namely, phi perturbation is dominated by electrostatic polarized
short-wavelength oscillation as EDW instability character, and A_para
perturbation remains typical tearing mode solution of Alfvenic polarized
macroscopic structure. Within omega_*e > omega_*crit, the additional IDD causes
phi oscillating structure to shift towards small density gradient domain, which
cancels the extra drive from ion channel and thus DTM growth rate is
insensitive to IDD frequency. Compared to EDD effects, the IDD effect alone
with zero-omega_*e only leads to the stabilization of RTM that shows agreements
between global simulation and local theory, which is no longer the condition
for DTM regime. These results are useful for clarifying the DTM global
properties with underlying physics mechanisms, which occurs in the regime of
omega_*e >> gamma_c that is relevant to nowadays tokamak discharges with hot
plasmas.
