LHC Dipole Rotating Coil System

Researchers at CERN have developed a unique system to measure the 15-meter-long LHC dipoles and their corrector magnets. The system consists of 13 ceramic segments, all together forming a 16-meter-long rotating shaft. Each segment contains two tangential and one radial coil. The modular design allows for easy switching-out of each unit with spares.

 

Since the LHC dipoles have a slight curvature, the ceramic segments of the measuring system are connected with titanium alloy bellows which allow curving while maintaining torsional rigidity.  The figure below shows a cross-section and side view of the rotating unit.

 

 

 

 

 

 

The rotating coil measuring unit: a) ball bearing, b) bronze cage with roller, c) Ti-bellow, d) tangential coil, e) central coil, f) dowel pin, g) ceramic support, h) SiN flange, i) cable connector, j) anticryostat, k) cold bore.

 

Two such units are used to simultaneously measure both dipole bores. With the current system, a dipole measurement takes about 10 seconds.  The main limitation of the system is the cabling which transmits the measured signal from the search coil to the data acquisition system. This cable permits only one full rotation of the search coil in either direction and a rotation rate of only about 0.1 Hz. Because the LHC will consist of 1232 main dipoles, it is necessary to increase the measurement rate of the rotating coil system. Rotation at 10 Hz and continuous operation are desired.

 

Harmonic Coil Method       

Slip Ring       

 

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