Owing to the high critical temperature (Tc) of 40 K, intrinsically "weak-link" free grain boundaries, and low fabrication cost, MgB2 is believed to be promising for replacing conventional low Tc superconductors in many cryogen- free applications. Nevertheless, its rapid drop in critical current under applied magnetic field and low critical field exclude it from many industrial applications where a high critical current density (Jc) under high magnetic field is required. Many studies have shown that carbon containing dopants are effective means to enhance the field dependence of Jc and the...