414
F. Bordry et al.
the LHC main power converters is in the order of one ppm and that tracking between
different sectors is within a couple of ppm [78].
8.4.4.2 Current Measurement in Particle Accelerators
Traditionally, accurate current measurement devices for particle accelerators are
associated with beam current measurement. Magnetic transducers and in particular
current transformers have been for a long time the preferred transducers to measure
beam currents. The requirements for beam current measurement have driven
progress in transducer technology, culminating with the introduction of the DCCT
(Direct-Current Current Transformer) for beam current measurement at CERN
in late 1960s. The idea was to build a magnetic beam current transformer with
frequency response extended down to DC to measure beam current in the ISR
accelerator. The new transducer combined the zero flux detection principle used
in flux-gate magnetometers since the 1930s, with the active transformer circuit as
originally proposed by H.G. Hereward (and already used to measure the circulating
beam in the CERN PS accelerator) [81]. Although the new transducer was not
initially intended for power supply regulation applications, its advantages compared
with previous DC instrument transformers (e.g. Kramer and Hingorani [82]) soon
became obvious. The concept got picked up by industry and the new transducer was
soon being used at accelerators such as DESY in Hamburg. In late 1970s, DCCTs
were used for the first time in large quantities in the SPS project at CERN [83].
The use of DCCTs spread to other applications but it continued to be widely
used in particle accelerators. In particular, the beginning of the twenty-first century
saw important progress in DCCT technology with the development and deployment
of the DCCTs for the main dipole and quadrupole power supplies of the LHC, at
CERN [84]. Short term stability in the order of two part-per-million (ppm), yearly
drifts better than fifteen ppm and linearity better than two ppm have been achieved.
8.4.4.2.1 Current Measurement Technologies
The most common current measurement technologies used in electrical power
converters include resistive shunts and current sense resistors, Hall-Effect current
transducers (based on the polarization of charges in an electrical conductor in the
presence of an external magnetic field), Current Transformers, Rogowsky Coils
(high current, high bandwidth applications), Active CTs and DCCTs (both based
on the zero flux detection principle).
The choice of a current measuring device for a specific application depends on
factors such as current range, bandwidth, required accuracy, required output signal,
need for isolation, reliability, installation constraints, availability and cost. DCCTs
provide isolated measurements for different current ranges and can reach very high
accuracy, albeit with a higher cost.
F. Bordry et al.
the LHC main power converters is in the order of one ppm and that tracking between
different sectors is within a couple of ppm [78].
8.4.4.2 Current Measurement in Particle Accelerators
Traditionally, accurate current measurement devices for particle accelerators are
associated with beam current measurement. Magnetic transducers and in particular
current transformers have been for a long time the preferred transducers to measure
beam currents. The requirements for beam current measurement have driven
progress in transducer technology, culminating with the introduction of the DCCT
(Direct-Current Current Transformer) for beam current measurement at CERN
in late 1960s. The idea was to build a magnetic beam current transformer with
frequency response extended down to DC to measure beam current in the ISR
accelerator. The new transducer combined the zero flux detection principle used
in flux-gate magnetometers since the 1930s, with the active transformer circuit as
originally proposed by H.G. Hereward (and already used to measure the circulating
beam in the CERN PS accelerator) [81]. Although the new transducer was not
initially intended for power supply regulation applications, its advantages compared
with previous DC instrument transformers (e.g. Kramer and Hingorani [82]) soon
became obvious. The concept got picked up by industry and the new transducer was
soon being used at accelerators such as DESY in Hamburg. In late 1970s, DCCTs
were used for the first time in large quantities in the SPS project at CERN [83].
The use of DCCTs spread to other applications but it continued to be widely
used in particle accelerators. In particular, the beginning of the twenty-first century
saw important progress in DCCT technology with the development and deployment
of the DCCTs for the main dipole and quadrupole power supplies of the LHC, at
CERN [84]. Short term stability in the order of two part-per-million (ppm), yearly
drifts better than fifteen ppm and linearity better than two ppm have been achieved.
8.4.4.2.1 Current Measurement Technologies
The most common current measurement technologies used in electrical power
converters include resistive shunts and current sense resistors, Hall-Effect current
transducers (based on the polarization of charges in an electrical conductor in the
presence of an external magnetic field), Current Transformers, Rogowsky Coils
(high current, high bandwidth applications), Active CTs and DCCTs (both based
on the zero flux detection principle).
The choice of a current measuring device for a specific application depends on
factors such as current range, bandwidth, required accuracy, required output signal,
need for isolation, reliability, installation constraints, availability and cost. DCCTs
provide isolated measurements for different current ranges and can reach very high
accuracy, albeit with a higher cost.