M.J. Barnes

Analysis of high power IGBT short circuit failures

The next linear collider (NLC) accelerator proposal at Stanford Linear Accelerator Center (SLAC, Menlo Park, CA), requires a highly efficient and reliable, low cost, pulsed-power modulator to drive the klystrons. A solid-state induction modulator has been developed at SLAC to power the klystrons; this modulator uses commercial high voltage and high current insulated gate bipolar transistor (IGBT) modules. Testing of these IGBT modules under pulsed conditions was very successful; however, the IGBTs failed when tests were performed into a low inductance short circuit. The internal electrical connections of a commercial IGBT module have been analyzed to extract self- and mutual partial inductances for the main current paths as well as for the gate structure. The IGBT module, together with the partial inductances, has been modeled using PSpice. Predictions for electrical paths that carry the highest current correlate with the sites of failed die under short circuit tests. A similar analysis has been carried out for a SLAC proposal for an IGBT module layout. This paper discusses the mathematical model of the IGBT module geometry and presents simulation results.

Design of the injection kicker magnet system for CERN's 14 TeV proton collider LHC

Two counter-rotating proton beams will be injected into the LHC at an energy of 450 GeV by two kicker magnet systems, producing magnetic field pulses of approximately 750 ns rise time and 6.6 /spl mu/s flat top duration. To avoid dilution of the beam emittance during injection, a stringent design requirement of the system is a flat top ripple of the magnetic field of less than /spl plusmn/0.5%. Both injection systems are composed of 4 travelling wave kicker magnets of 2.17 m length each, powered by pulse forming networks (PFNs) and matched to their characteristic impedance. To achieve the high required kick strength of 1.2 Tm, for a compact and cost efficient design, a comparably low characteristic impedance of 5 /spl Omega/ has been chosen. The electrical circuit of the system is being designed with the help of PSpice computer modelling. Most known parasitic elements are included in the model to obtain a realistic pulse response prediction. The present paper reports on design and modeling results of the LHC injection kicker magnet system that has several novel and demanding design requirements.

The LHC injection kicker magnet

Proton beams will be injected into LHC at 450 GeV by two kicker magnet systems, producing magnetic field pulses of approximately 900 ns rise time and up to 7.86 /spl mu/s flat top duration. One of the stringent design requirements of these systems is a flat top ripple of less than /spl plusmn/0.5%. Both injection systems are composed of 4 traveling wave kicker magnets of 2.7 m length each, powered by pulse forming networks (PFNs). To achieve the required kick strength of 1.2 Tm, a low characteristic impedance has been chosen and ceramic plate capacitors are used to obtain 5 /spl Omega/. Conductive stripes in the aperture of the magnets limit the beam impedance and screen the ferrite. The electrical circuit has been designed with the help of PSpice computer modeling. A full size magnet prototype has been built and tested up to 60 kV with the magnet under ultra high vacuum (UHV). The pulse shape has been precision measured at a voltage of 15 kV. After reviewing the performance requirements the paper presents the magnet design, emphasizing several novel design features, and discusses the test results.

A FET Based Frequency And Duty Factor Agile 6 kV Pulse Generator

A pulse generator has been developed which has many potential applications. The pulse generator consists of a high-voltage modulator incorporating two stacked Field-Effect Transistor switches operating in a “push-pull” mode. A continuous 1 kV to 6 kV pulse train has been obtained with a prototype pulse generator over a frequency range from 1 Hz to 20 kHz. Pulse widths in the range from 250 ns to 1 s have been achieved with rise and fall times of 30 ns into a capacitive load of 26 pF. A 3 kHz, 5 kV version of this pulse generat,or has been installed and t,ested in the 300 keV injection line for t,he 500 MeV TRIUMF cyclotron. The circuit performance was evaluated with the aid of PSpice in t,he design stage and confirmed by measurement,s in the prototype. Results of measurements and simulations are presented.

An improved beam screen for the lhc injection kickers

The two LHC injection kicker magnet systems must produce a kick of 1.3 T.m with a flattop duration variable up to 7860 ns, and rise and fall times of less than 900 ns and 3000 ns, respectively. Each system is composed of two resonant charging power supplies (RCPSs) and four 5 Omega transmission line kicker magnets with matched terminating resistors and pulse forming networks (PFNs). A beam screen is placed in the aperture of the magnets: the screen consists of a ceramic tube with conductors on the inner wall. The conductors provide a path for the image current of the, high intensity,LHC beam and screen the ferrite against Wake fields. The conductors initially used gave adequately low beam coupling impedance however inter-conductor discharges occurred during pulsing of the magnet: an alternative design was discharge free at the nominal operating voltage but the impedance was too high for the ultimate LHC beam. This paper presents the results of a new development undertaken to meet the often conflicting requirements for low beam coupling impedance, fast magnetic field rise- time and good high voltage behaviour. High voltage test results and thermal measurements are also presented.

The Prototype Inductive Adder With Droop Compensation for the CLIC Kicker Systems

The Compact Linear Collider (CLIC) study is exploring the scheme for an electron-positron collider with high luminosity and a nominal center-of-mass energy of 3 TeV. The CLIC predamping rings and damping rings (DRs) will produce, through synchrotron radiation, an ultralow emittance beam with high bunch charge. To avoid beam emittance increase, the DR kicker systems must provide extremely flat, high-voltage, pulses. The specifications for the extraction kickers of the DRs are particularly demanding: the flattops of the pulses must be ±12.5 kV with a combined ripple and droop of not more than ±0.02% (±2.5 V). An inductive adder is a very promising approach to meeting the specifications. Recently, a five-layer prototype has been built at CERN. Passive analog modulation has been applied to compensate the voltage droop, for example of the pulse capacitors. The output waveforms of the prototype inductive adder have been compared with predictions of the voltage droop and pulse shape. Conclusions are drawn concerning the design of the full-scale prototype inductive adder.

Preliminary design of the pulse generator for the CLIC DR extraction system

The Compact Linear Collider (CLIC) study is exploring the scheme for an electron-positron collider with high luminosity (1034 – 1035 cm−2s−1) and a nominal centre-of-mass energy of 3 TeV: CLIC would complement LHC physics in the multi-TeV range. The CLIC design relies on the presence of Pre-Damping Rings (PDR) and Damping Rings (DR) to achieve the very low emittance, through synchrotron radiation, needed for the luminosity requirements of CLIC. To limit the beam emittance blowup due to oscillations, the pulse power modulators for the DR kickers must provide extremely flat, high-voltage, pulses: specifications call for a 160 ns duration flattop of 12.5 kV, 250 A, with a combined ripple and droop of not more than ±0.02%. In order to meet these demanding specifications, a combination of broadband impedance matching, optimized electrical layout and advanced control techniques is required. A solid-state modulator, the inductive adder, is the most promising approach to meeting the specifications; this topology allows the use of both digital and analogue modulation. To effectively use modulation to achieve such low ripple and droop requires an in-depth knowledge of the behaviour of the solid-state switching components and their gate drivers, as well as a thorough understanding of the overall circuit dynamics. Hence, circuit simulation tools have been employed to study the proposed inductive adder and various control schemes. This paper describes the initial design of the inductive adder and the use of active-filtering control algorithms for achieving the required pulse waveform.

Injection and extraction magnets: septa

An accelerator has limited dynamic range: a chain of accelerators is required to reach high energy. A combination of septa and kicker magnets is frequently used to inject and extract beam from each stage. The kicker magnets typically produce rectangular field pulses with fast riseand/or falltimes, however the field strength is relatively low. To compensate for their relatively low field strength, the kicker magnets are generally combined with electromagnetic septa. The septa provide relatively strong field strength but are either DC or slow pulsed. This paper discusses injection and extraction systems with particular emphasis on the hardware required for the septa.

A High Frequency Mosfet Driver for the Titan Facility at TRIUMF

TRIUMFs Ion Trap for Atomic and Nuclear Science (TITAN) Radio Frequency Quadrupole (RFQ) Beam Cooler is a device that cools and collects short-lived isotopes, with half-lives as short as 10 ms, created by an Isotope Separator and Accelerator (ISAC). An RF square wave driver (RFSWD), that must have rise and fall times of less than 125 ns (10% to 90%), performs 2-dimensional focusing of the ion beam within the RFQ, along planes normal to the beams intended trajectory, to confine ion motion along a stable path; hence the ions can be trapped and collected for extraction. The RFSWD, which is based on previous kicker designs developed at TRIUMF, employs stacks of MOSFETs, operating in push-pull, to generate high voltage (HV) rectangular waveforms at a prescribed frequency and duty cycle. Currently a 500 V, 2 MHz drive system is undergoing tests, however, the system configuration allows for operation with higher voltage amplitudes and a repetition rate from 300 kHz up to 3 MHz, continuous. Technical details of the design, operation and performance of the RFQ system, in particular of the drive system, are presented.

High Voltage Measurements on Nine PFNS for the LHC Injection Kicker Systems

Each of the two LHC injection kicker magnet systems must produce a kick of 1.3 T. m with a flattop duration variable up to 7.86 ms, and rise and fall times of less than 900 ns and 3 ms, respectively. A kicker magnet system consists of four 5 W transmission line magnets with matched terminating resistors, four 5 W Pulse Forming Networks (PFNs) and two Resonant Charging Power Supplies (RCPSs). Six RCPSs and nine PFNs, together with associated switch tanks and dump switch terminating resistors, have been built at TRIUMF and all have been tested at up to 60 kV PFN voltage to ensure that the performance is within specification. This paper describes the HV measurements, compares these results with low voltage measurements and analyses the pulse performance of the PFNs. The measurements are compared with results from PSpice simulations.