One aspect relates to a process for the preparation of a quartz glass body, including providing a silicon dioxide granulate composed of a pyrogenic silicon dioxide powder, making a glass melt out of the silicon dioxide granulate and making a quartz glass body out of at least part of the glass melt. The quartz glass body has an OH content of less than 10 ppm, a chlorine content of less than 60 ppm and an aluminium content of less than 200 ppb. One aspect also relates to a quartz glass body which is obtainable by this process. Furthermore, one aspect relates to a formed body and a structure, each of which is obtainable by further processing of the quartz glass body.

One aspect relates to a process for the preparation of a quartz glass grain, including providing a silicon dioxide granulate from a pyrogenically produced silicon dioxide powder, making a glass melt out of silicon dioxide granulate, making a quartz glass body out of at least part of the glass melt and reducing the size of the quartz glass body to obtain the quartz glass grain. One aspect further relates to a quartz glass grain which is obtainable by this process. One aspect further relates to opaque quartz glass bodies, which are obtainable by further processing of the quartz glass grain.

A coupled-core multi-core fiber in which an inter-core distance is stabilized is manufactured. A method of manufacturing a coupled-core multi-core fiber includes forming a second cladding base material by depositing glass particulates on an outer periphery of a first cladding base material and sintering the glass particulates. The first cladding base material has a hydroxyl group concentration that is less than or equal to 10 ppb; obtaining a ground rod by grinding an outer periphery of the second cladding base material; and forming holes in the first cladding base material in the ground rod, inserting a core base material into each of the holes, and obtaining an assembly.

Common solar radiation receivers are equipped with a chamber for transmission of an operating gas which is directed along to an absorber for solar radiation for thermal absorption. The absorber has a dome-shaped entry window made of quartz glass, wherein the inner side facing the absorber assumes a nominal interior temperature Ti of at least 950 C. during proper use, preferably at least 1000 C., whereas the outer side facing away from the absorber is exposed to the environment and subject to risk of devitrification. The invention relates to modifying the known solar radiation receiver so that a high absorber temperature can be set and thus a high efficiency of the solar thermal heating is enabled, without increasing the risk of devitrification in the region of the outer side of the entry window.

A perforated quartz glass tube includes a jacket tube containing a quartz glass material, a plurality of cylindrical glass tubes which are inserted into a pore region of the jacket tube along an axial direction of the jacket tube, and contain a quartz glass material having a softening point higher than a softening point of the jacket tube, and a gap member which is inserted into a gap between the cylindrical glass tubes and a gap between the jacket tube and the cylindrical glass tube, and contains a quartz glass material having a softening point lower than a softening point of the cylindrical glass tube.

The present invention relates to a method (300) for drawing an optical fiber (101) having step of stacking (302) at least two glass sub-preforms of a plurality of glass sub-preforms (114a-114n) inside a hollow cylindrical glass tube (108) to form a master glass preform (130) and melting (304) the bottom end (134) of the master glass preform (130) in a furnace (110) to continuously draw an optical fiber (101). In particular, the at least two glass sub-preforms are stacked in such that the master glass preform has a top end (132) and a bottom end (134) and each of the glass sub-preforms is defined by a first end (126) and a second end (128). Further, the first end (126) of a successive glass sub-preform is stacked on the second end (128) of a previous glass sub-perform such that the successive glass sub-preform rests on the previous glass sub-preform.

Hollow ingots of transparent synthetic vitreous silica glass of external diameter greater than 400 mm and internal diameter greater than 300 mm are disclosed. The ingots are substantially free from bubbles or inclusions greater than 100 m in diameter, have no more than 100 ppB of any individual metallic impurity, and have chlorine concentration less than 5 ppM. Also disclosed are methods for producing such ingots, in which a porous soot body of density greater than 0.4 g/cm.sup.3 is deposited on an oxidation resistant mandrel. The soot body is dehydrated on a mandrel comprising graphite, carbon fiber reinforced carbon, silicon carbide, silicon impregnated silicon carbide, silicon carbide-coated graphite or vitreous silica, either under vacuum or in the presence of a reducing gas, and then sintered to transparent pore-free glass under vacuum or in an atmosphere of helium.

A method for producing a tubular quartz glass composite body in an outside deposition method comprising the following method steps: providing a substrate tube, rotating the substrate tube about a rotation axis, depositing SiO.sub.2 particles on the outer lateral surface of the substrate tube to form a composite consisting of the substrate tube and an SiO.sub.2 soot body, and sintering the composite by heating at a sintering temperature to form the tubular quartz glass composite body. A substrate tube is provided which consists at least partially of quartz glass of a first quartz glass quality, and that the soot body consist of quartz glass of a second quartz glass quality, wherein the first quartz glass quality has a material-specific viscosity at the sintering temperature that is higher than the material-specific viscosity of the second quartz glass quality.