At CERN, one of the most advanced High Energy Physics laboratories, the latest technologies for magnetic measurements are available. On this page you can find a brief introduction to them.
There are three main types of magnets categorized by the working principle:
- Resistive Magnets. They are not magnetic unless a certain current flows into their coils. The field can be increased and concentrated by means of a ferromagnetic yoke. The resistance of the windings dissipates some energy and the resulting heat has to be removed with a water circuit or air flow. Normally, they are measured in building 311.
- Superconducting Magnets. They work only at very low temperatures (liquid or superfluid helium). The high current density possible in their special cables produces a high magnetic field not possible with resistive magnets. Special benches and instruments are needed for measurements on such magnets.They take place in building SM18.
- Permanent Magnets. No current flows into these magnets. The field is produced by means of the permanent residual magnetization of special materials. This technology allows the construction of compact magnets with a relatively strong field. No cooling is required.
Some of these magnets might be radioactive. In this case they are measured in building 867, where the appropriate instrumentation is available.
The type of cycling mode is an important characteristic together with the converters that allow it.
Three different types of power cycling can be identified.
- DC: the current in the magnet is not changed once it is at the 
required level.
- AC: the current changes at a certain defined frequency. Dynamic and loss effects have to be assessed.
- Pulsed: the magnet is operated with fast ramps of the field. Transient effects have to be studied.
We also can distinguish different characteristics of a magnet that can be measured:
- Transfer function.
- Magnetic axis.
- Field quality and harmonics.
- Dynamic effects and transients.
Our measurements techniques
We have many different techniques for measuring the field produced in the magnet aperture. Depending on the characteristic we want to evaluate, the type of magnet, its geometry, the field level, etc., we choose one of the following techniques:
- Rotating coils: the analysis of the flux intercepted by rotating a coil inside the magnet aperture provides information about the strength, the direction and the quality of the field.
- Stretched wire: a conducting wire is inserted along the magnet aperture. The voltage induced by a displacement of the wire or the oscillations induced by an AC current flowing into the wire can be analysed in order to retrieve a measurement of some characteristics of the integral field.
- 3D scanner: by means of a hall sensor precisely driven into the magnet aperture, we can draw a map of the field.
- Fluxmeters: one or more coils are positioned in the magnet aperture and the voltage induced by a field change is measured.
- Nuclear Magnetic Resonance (NMR): sensors based on this principle are used only on dipoles. It is the most accurate technique for measuring the absolute field. It is often used for the calibration of other sensors.
- 3D survey: by using a laser interferometer, we can precisely measure the position of a geometrical point surrounding the magnet with respect to some reference points.
