A sheet production apparatus, comprising: a vessel configured to hold a melt of a material, said vessel having a channel corresponding to a freezing area; a cooling plate disposed proximate said melt, said cooling plate configured to form a sheet of said material on said melt in said freezing area; a return configured to hold said melt, wherein a first end of said return is connected downstream of said channel and a second end of said return is connected upstream of said channel; a pump, comprising either a first gas source and a first conduit and a second conduit in fluid communication with said first gas source, one end of said first conduit being connected to said gas first source and another end of said first conduit being disposed inside said second conduit, one end of said second conduit being connected to said return and another end of said second conduit being connected to said channel, wherein at least part of said first conduit is disposed above a surface of said melt and wherein said gas first source is configured to raise said melt from said return to said freezing area; or a second gas source, said second gas source having an outlet configured to inject a gas into said melt in a direction parallel to a surface of said melt whereby said gas causes motion of said melt in said direction; a first baffle disposed partially in said melt and partially out of said melt downstream of said pump and upstream of said cooling plate; and a second baffle disposed in said melt on a top surface of said channel, said second baffle disposed downstream of said pump and upstream of said cooling plate, proximate said first baffle, wherein the first baffle and the second baffle affect the flow of the melt. a vessel configured to hold a melt of a material, said vessel having a channel corresponding to a freezing area; a cooling plate disposed proximate said melt, said cooling plate configured to form a sheet of said material on said melt in said freezing area; a return configured to hold said melt, wherein a first end of said return is connected downstream of said channel and a second end of said return is connected upstream of said channel; a pump, comprising either a first gas source and a first conduit and a second conduit in fluid communication with said first gas source, one end of said first conduit being connected to said gas first source and another end of said first conduit being disposed inside said second conduit, one end of said second conduit being connected to said return and another end of said second conduit being connected to said channel, wherein at least part of said first conduit is disposed above a surface of said melt and wherein said gas first source is configured to raise said melt from said return to said freezing area; or a second gas source, said second gas source having an outlet configured to inject a gas into said melt in a direction parallel to a surface of said melt whereby said gas causes motion of said melt in said direction; a first baffle disposed partially in said melt and partially out of said melt downstream of said pump and upstream of said cooling plate; and a second baffle disposed in said melt on a top surface of said channel, said second baffle disposed downstream of said pump and upstream of said cooling plate, proximate said first baffle, wherein the first baffle and the second baffle affect the flow of the melt.