Figure 3

Boosted loop advection. Force-free magnetic loop with diagonal boost velocity \(\vert v\vert =0.5c\). Top: No shift, the loop is advected for one period. Bottom: The shift vector just opposes the (diagonal) advection velocity, \(\vert v\vert =0.5\), hence the loop remains stationary with respect to the grid. Base resolution is 64² cells with a total of three grid levels. The color shows the strength of the out-of-plane field component \(B^{z}\) and white lines are in-plane field lines of \((B^{x},B^{z})\). Blocks containing 8² cells are indicated.