404
F. Bordry et al.
Large-capacity helium refrigerators and liquefiers operate under this principle,
however with many refinements aiming at meeting specific cooling duties and
improving efficiency and flexibility of operation, such as three- and sometimes
four-pressure cycles, liquid nitrogen pre-cooling of the helium stream, numerous
heat exchangers, many turbines in series or parallel arrangements, Joule-Thomson
expansion replaced by adiabatic expansion in a “wet” turbine, cold compressors to
lower the refrigeration temperature below 4.5 K.
The capital cost of these complex machines is high, but scales less than linearly
with refrigeration power, which favours large units. Operating costs are dominated
by that of electrical energy, typically amounting to about ten percent of the capital
cost per year in case of quasi-continuous operation. For overall economy, it is
therefore very important to seek high efficiency, which is also easier to achieve on
large units. For a review of these aspects, see [70].
8.4 High Precision Power Converters for Particle
Accelerators
F. Bordry · J. P. Burnet · M. Cerqueira Bastos
8.4.1 Introduction to Magnet Power Converters
The trend in power electronics is evolving rapidly, mainly due to progress in
power semiconductors. Since the nineties, the IGBT (Insulated Gate Bipolar
Transistor) took the leadership in medium and large power, with the development
of new converter topologies called switch-mode power converters [71, 72]. With
the progress of electronics (analogue and digital) and measurement systems, the
performance of the power converters made a step forward in precision and stability.
This chapter will give an overview of the state of the art for high precision power
converters for particle accelerators (conventional and superconducting magnet, RF
klystrons, solenoids, . . . ).
8.4.2 Main Parameters of Magnet Power Converters
The powering of particle accelerator magnets are mainly DC power converters and
in most cases, the feedback control system regulates the magnet current. The choice
of the power converter topology and thus the technology will be defined by the
required performance, translated into a precise specification. First of all, the peak
and the rms ratings of the current and voltage to power the magnet should be
F. Bordry et al.
Large-capacity helium refrigerators and liquefiers operate under this principle,
however with many refinements aiming at meeting specific cooling duties and
improving efficiency and flexibility of operation, such as three- and sometimes
four-pressure cycles, liquid nitrogen pre-cooling of the helium stream, numerous
heat exchangers, many turbines in series or parallel arrangements, Joule-Thomson
expansion replaced by adiabatic expansion in a “wet” turbine, cold compressors to
lower the refrigeration temperature below 4.5 K.
The capital cost of these complex machines is high, but scales less than linearly
with refrigeration power, which favours large units. Operating costs are dominated
by that of electrical energy, typically amounting to about ten percent of the capital
cost per year in case of quasi-continuous operation. For overall economy, it is
therefore very important to seek high efficiency, which is also easier to achieve on
large units. For a review of these aspects, see [70].
8.4 High Precision Power Converters for Particle
Accelerators
F. Bordry · J. P. Burnet · M. Cerqueira Bastos
8.4.1 Introduction to Magnet Power Converters
The trend in power electronics is evolving rapidly, mainly due to progress in
power semiconductors. Since the nineties, the IGBT (Insulated Gate Bipolar
Transistor) took the leadership in medium and large power, with the development
of new converter topologies called switch-mode power converters [71, 72]. With
the progress of electronics (analogue and digital) and measurement systems, the
performance of the power converters made a step forward in precision and stability.
This chapter will give an overview of the state of the art for high precision power
converters for particle accelerators (conventional and superconducting magnet, RF
klystrons, solenoids, . . . ).
8.4.2 Main Parameters of Magnet Power Converters
The powering of particle accelerator magnets are mainly DC power converters and
in most cases, the feedback control system regulates the magnet current. The choice
of the power converter topology and thus the technology will be defined by the
required performance, translated into a precise specification. First of all, the peak
and the rms ratings of the current and voltage to power the magnet should be