Patent ID: 8336337

Claim:
A method of producing a preform of synthetic quartz glass, said method comprising: supplying a gaseous hydrogen-free media flow-comprising a glass starting material that contains silicon tetrachloride (SiCl 4 ) and nitrogen as a carrier gas to a media nozzle of a multi-nozzle deposition burner, said media nozzle comprising a wall defining a passage therein communicating with a nozzle opening so that the gaseous media flow passes through the passage and through the nozzle opening, said wall having a tapered portion wherein the passage tapers inwardly up to the nozzle opening; enveloping the media flow when exiting from the media nozzle with an oxygen-containing working gas flow flowing through a working gas nozzle, and enveloping the working gas flow when exiting from the working gas nozzle with at least one oxygen-containing separating gas flow exiting from an annular gap nozzle coaxially surrounding the working gas nozzle; the gaseous media flow from the media nozzle being focused into a plasma zone; oxidizing the glass starting material in the plasma zone so as to form SiO 2 particles; and depositing the SiO 2 particles on a deposition surface while being directly vitrified; wherein the tapered portion has a length of at least 5 mm; and wherein the nozzle opening ranges between 4.5 mm and 6.5 mm in diameter.