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tokens: grid cell, and then integrate the total photon flux density as in the photon energy range. We use 0.01 keV as , meaning 90 bins in total in the energy range. This process leads to the images shown in Figure 1 , right column. 3. RESULTS AND DISCUSSION 3.1. Asymmetric Footpoint Heating Inducing KHI The temporal evolution of the number density (left column), temperature (middle column), and synthesized SXR photon fluxes (right column) are shown in Figure 1 , covering a timespan of about 4.15 minutes. As described in Section 2.2 , we use H 1 to mimic the flare energy deposited in the upper chromosphere, and the consequent overpressure resulting from H 1 drives upward mass flows at a speed up to 700 km s −1 . We also witness a rapid thermodynamic change (due to thermal conduction) in the loop, reaching an extremely hot temperature around 18 MK. These upward chromospheric evaporation flows have been detected directly in imaging sequences as SXR emission propagating toward the loop-top sources (Silva et al. 1997 ; Liu et al. 2006 ; Nitta et al. 2012 ). This is also seen in our simulation, as in panel (f) of Figure 1 (and in the time period before this image, for which we refer to the corresponding movie). In the last several decades, simulations of chromospheric evaporation have been mostly carried out with symmetric energy input assumptions on both loop footpoints and these focused mainly on the UV-SXR spectral lines produced by the evaporated plasma (Fisher et al. 1985 ; Mariska et al. 1989 ; Yokoyama Shibata 2001 ; Allred et al. 2005 ; Liu et al. 2009 ). However, asymmetric energy deposition at footpoints is a much more likely scenario, and could be intrinsic to the acceleration process as pursued by McClements Alexander ( 2005 ). So, in our simulation we assume that the deposition of flare energy at two footpoints is slightly asymmetric, with a ratio of 0.8 as described in Equation ( 5 ). As a result, the right evaporation flow rises quicker and is hotter than the left one as shown in panel (e). Asymmetric energy deposition guarantees that the two evaporation flows will not merely collide at the apex, a situation known to only generate reflected shocks. Panel (e) indeed shows that when our two evaporation flows run into each other asymmetrically, the right one has already crossed the loop apex. In addition, the hotter, right evaporation flow causes a bigger expansion of the loop cross-section in the right half of the loop. This configuration provides the conditions for the formation of shear flows, the trigger of KHI. As shown in panel (e), right after the collision of both flows, KHI begins to develop immediately, and the typical vortical structures of the KHI appear and grow up quickly from panels (e) to (g). The development of vortices in a magnetized plasma can further induce small-scale structure to develop, with a potential cascade of energy to establish a turbulent plasma state (Keppens et al. 1999 ; Baty et al. 2003 ; Elmegreen