8 Accelerator Engineering and Technology: Accelerator Technology
465
Topologies such as the inductive adder [181–183] and Marx generator [184,
185], utilizing fast and high-voltage semiconductor switches such as MOSFETs, are
being actively pursued by CERN as possible alternatives to both thyratron and PFL
technologies. The inductive adder and Marx generator use the series and parallel
connection of power semiconductor switches to achieve high pulse power designs.
The required energy is stored in capacitors. The MOSFET semiconductor switches
have the ability to both turn on and turn off the current pulse.
Other types of switches for particular applications include so called “pseudo
spark gaps”, fast high-voltage MOSFETS and Fast Ionisation Dynistors (FID, also
called Fast ionization Devices) [162]. With advances in semiconductor technology
new, interesting, types of devices or switches with improved characteristics are
expected to become commercially available.
8.7.1.5 Other Types of Circuits
In applications where only a few bunches need to be injected or extracted (e.g.
LEP), fast deflection is most economically achieved by an oscillation system using
half-sine wave pulses, where a capacitor is discharged into a purely inductive
magnet terminated in a short circuit [186]. In this case no particular PFN is needed
and the magnet does not need to be fitted with matching capacitors, permitting
important economies. The charging voltage is half that for a travelling wave kicker
system, with the same magnetic parameters, which often allows working with more
economic air insulation in the pulse generator.
Capacitive discharge systems complemented by free-wheel circuits are mainly
used for applications such as beam abort systems where a fast rise of the magnet
pulse is required which can be followed by a long exponential decay (since all beam
has been dumped after one turn), while the requirements of the flat-top are not very
stringent. This is the case for instance for the LHC extraction kickers [174]. Here a
capacitor is discharged into an inductive magnet with a stack of diodes in parallel.
During the sinusoidal rise of the current the diodes are non-conducting, but when
the magnet current pulse starts to reduce in magnitude the diodes conduct and the
magnet current free-wheels in the low impedance circuit.
Where very fast rise times are required (order of few ns) stripline kickers are
used [166, 167, 187]. These consist essentially of electrodes parallel to the beam
direction, and contain no magnetic material. The deflection is provided by the
electric and magnetic field between the plates. Generators with fast semiconductor
(MOSFET) switches are typically used and sub-nanosecond jitter can be achieved.
For an ultra-relativistic beam, the beam is deflected only if it is travelling from the
terminated to the driven end of the striplines [188]. A schematic view of a stripline
kicker system, for the tail clipper of the CTF3 facility, is given in Fig. 8.73.
465
Topologies such as the inductive adder [181–183] and Marx generator [184,
185], utilizing fast and high-voltage semiconductor switches such as MOSFETs, are
being actively pursued by CERN as possible alternatives to both thyratron and PFL
technologies. The inductive adder and Marx generator use the series and parallel
connection of power semiconductor switches to achieve high pulse power designs.
The required energy is stored in capacitors. The MOSFET semiconductor switches
have the ability to both turn on and turn off the current pulse.
Other types of switches for particular applications include so called “pseudo
spark gaps”, fast high-voltage MOSFETS and Fast Ionisation Dynistors (FID, also
called Fast ionization Devices) [162]. With advances in semiconductor technology
new, interesting, types of devices or switches with improved characteristics are
expected to become commercially available.
8.7.1.5 Other Types of Circuits
In applications where only a few bunches need to be injected or extracted (e.g.
LEP), fast deflection is most economically achieved by an oscillation system using
half-sine wave pulses, where a capacitor is discharged into a purely inductive
magnet terminated in a short circuit [186]. In this case no particular PFN is needed
and the magnet does not need to be fitted with matching capacitors, permitting
important economies. The charging voltage is half that for a travelling wave kicker
system, with the same magnetic parameters, which often allows working with more
economic air insulation in the pulse generator.
Capacitive discharge systems complemented by free-wheel circuits are mainly
used for applications such as beam abort systems where a fast rise of the magnet
pulse is required which can be followed by a long exponential decay (since all beam
has been dumped after one turn), while the requirements of the flat-top are not very
stringent. This is the case for instance for the LHC extraction kickers [174]. Here a
capacitor is discharged into an inductive magnet with a stack of diodes in parallel.
During the sinusoidal rise of the current the diodes are non-conducting, but when
the magnet current pulse starts to reduce in magnitude the diodes conduct and the
magnet current free-wheels in the low impedance circuit.
Where very fast rise times are required (order of few ns) stripline kickers are
used [166, 167, 187]. These consist essentially of electrodes parallel to the beam
direction, and contain no magnetic material. The deflection is provided by the
electric and magnetic field between the plates. Generators with fast semiconductor
(MOSFET) switches are typically used and sub-nanosecond jitter can be achieved.
For an ultra-relativistic beam, the beam is deflected only if it is travelling from the
terminated to the driven end of the striplines [188]. A schematic view of a stripline
kicker system, for the tail clipper of the CTF3 facility, is given in Fig. 8.73.