Upper bore tube

Magnet bore tube. Syn. bore, bore tube. The hollow, cylindrical tube that runs vertically (for an NMR magnet, horizontally for an MRI magnet) through the interior of a cryomagnet. The magnetic field maximum occurs within the interior of the bore tube. The room temperature (RT) shims are a hollow cylinder that is inserted inside the bore tube, and the probe is inserted inside the RT shims. Samples are lowered pneumatically down the upper bore tube, which is a smaller tube that rests on top of the RT shims and probe assembly. 

A portion of the magnet bore tube space is occupied by a sleeve of insulated wires called a room temperature (RT) shim set. The RT shim set should never be removed from a magnet s bore tube unless it is defective. On the other hand, the NMR probe fits inside the RT shim set in the bore and can be more or less freely exchanged with other NMR probes, depending on need. Both the RT shim set and the NMR probe are inserted into the NMR magnet s bore tube from the bottom. In most cases there will be an upper magnet bore assembly (also called the upper bore tube) through which the spinner/tube assembly will travel as the spinner/tube assembly is raised and lowered pneumatically. 

The apparatus consists of a tube T (Fig. 76) usually of total height about 75 cm. the upper portion of the tube has an internal diameter of about I cm., whilst the lower portion is blown out as shown into a bulb of about 100 ml. capacity. Near the top of T is the delivery-tube D of coarse-bored capillary, bent as shown. The tube T is suspended in an outer glass jacket J which contains the heating liquid this jacket is fitted around T by a split cork F which has a vertical groove cut or filed m the side to allow the subsequent expansion of the air in J. The open end of the side-arm D can be placed in a trough W containing water, end a tube C, calibrated in ml. from the top downwards, can be secured ts shown over the open end of D. 

A distilling flask ( litre) is fitted with a double-bored cork. Through one hole a thermometer is inserted, the bulb of which must be covered by the liquid in the flask and through the other a tap-funnel passes. The side-tube of the distilling flask is fixed by a coik into the upper end of a long condenser. An adapter is fitted to the lower end and passes through the neck of a flask, which is surrounded by ice. The apparatus is shown... 

C, is a cylindrical glass vessel with a volume of 450 cm. The piezometer contains the solution and 330 gms of Hg. The top of the piezometer is fitted with a Taper joint for filling. A precision bore capillary, E, (2mm in diameter) is fitted to the bottom of the piezometer. The piezometer is suspended (6) in a brass or stainless steel pressure vessel, H. A glass boiler tube, J, encloses the upper portion of the capillary. The pressure vessel is filled with ethylene glycol which serves as a thermal and pressure medium. The entire apparatus is submerged in a constant temperature bath controlled to 0.001 C. The temperature inside the pressure vessel is monitored with a Hewlett-Packard quartz crystal thermometer (to determine when thermal equilibrium is reached after compression and decompression). 

Brass top plate machined upper surface and bore to push fit on tube... 

The diameter of the capillary tube must be known with accuracy and the cross-section must be truly circular. It is not as a rule easy to obtain tubing of uniform circular bore, but in default of time for the tedious process of calibrating tubing the difficulty may be overcome by the following method due to Ferguson Proc. Phys. Soc. XXXVI. 37, 1923) Lengths of capillary tube are examined under a micrometer until one is found whose end cross-section is circular. This tube is then used so that the measured end dips downwards into the liquid the upper end, instead of being open to the atmosphere is connected to a source of pressure and a manometer, and the meniscus is forced down until its lowest point is level with the end of the tube, so as to be observed at the only point where its curvature is accurately known. If then p be the pressure in dynes/cm. recorded by the manometer we have... 

Equipment. At the time of publication of Ref 1 (1931), there were two Bichel Closed Bombs at BurMines, each of them made of strong cast steel. The No 1 apparatus had an interior capacity of 15 liters,. while the No 2 was of 20 liters. Their walls were 12.5cm thick. The heads of their cylinders were provided with lead gaskets, which were secured in pLace by 12 heavy stud bolts and aa iron yoke. For exhausting the air there was a tube inserted in a hole bored in an upper segment of each cylinder (See Fig on p C332-L of Vol 3 of Encycl), near one end. Exhaust tuhe of each cylinder was connected with a rotary, vacuum-air pump, driven by a 2-HP motor and provided with a valve which excluded the outside air after the desired vacuum was reached (usually 50li5ram of Hg). 

The diffusion tube was designed and constructed such that the length L of the upper section is equal to the length of the lower section plusihe length of the bore of stopcock A. Hence the stopcock bore and the lower section of the tube are both filled with CO2. 

Close stopcock 1 and fill the system with CO2 to a pressure between 750 and 770 Torr. Close stopcock B and read the COj pressure exactly. After closing stopcock A, pump away the remaining CO2. Fill the upper portion of the tube with He to a pressure as close as possible to the CO2 pressure (the difference should be less than 1 Torr). Close stopcock C and evacuate the remaining portion of the apparatus. Begin the diffusion by carefully opening stopcock A and simultaneously starting a stopwatch or timer (be sure to align the stopcock bore with the vertical axis of the upper and lower tubes). After the estimated optimum time, close stopcock A and record the elapsed time. 

Fig. 8 Design features of a wide bore probe head for HPNMR (400 MHz) measurements. 1 O-ring 2 probe jacket 3 thermal insulation 4 polyvinyl chloride 5 O-ring 6 O-ring 7 semi-rigid coaxial cable 8 connection to thermostat 9 titanium tube 10 lid 11 screw 12 capacitor 13 capacitor holder 14 aluminium tube 15 upper plug 16 sample tube 17 saddle coil 18 -Macor 19 TiA16V4 vessel 20 lower plug 21 lower pressure screw 22 capacitor 23 coaxial cable and 24 capacitor holder.

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