University of Cassino, Cassino
INFN-Pisa, Pisa
The possible issues related to the use of last-generations Insulated Gate Bipolar Transistors (IGBTs) switches into a Marx-topology klystron modulator are discussed. Experimental results obtained from two cells Marx prototypes using two different solutions, including single device and series connected devices both hard-switched, are presented. The use of single high voltage device per cell allowed us to obtain lower on-state voltage drop but much slower switching times. On the other side the series connection of lower voltage IGBTs results in much faster commutations and lower devices costs accompanied by a larger on state voltage drop.
RIKEN/SPring-8, Hyogo
XFEL/SPring-8 will use 72 line type modulator pulse-power supply for 66 C-band klystrons, 4 S-band, one L-band and pulsed 500 kV electron gun. In order to make the size smaller to fit the space available in the high gradient C-band accelerator, we have developed all in one box design of modulator. Using metal monocok design, filled with oil, it becomes possible to fit all circuitry: PFN, thyratron, pulse transformer, klyston socket, and protection circuit into a metal box of W 1m x L 1.7m x H 1m, which provides strong support for massive klystron and solenoide with lead shield and functions as superior EM shiled. We developed high precission HV charger for PFN, which has stability better than 100 ppm.pp. Modulator and PFN chargers are under mass prodution.
KEK, Ibaraki
This paper describes a long-pulse 1.3 GHz klystron modulator that was recently developed for the Superconducting RF Test Facility (STF) at High Energy Accelerator Research Organization (KEK). The modulators is a direct-switched-type design with a 1:15 step-up transformer and a bouncer circuit to compensate for the output pulse droop within ±0.5%; it can drive a klystron with up to 10 MW peak power, 1.5 ms rf pulse width, and up to 5 pps repetition rate. The main features of this modulator are the use of four 50 kW switching power supplies in parallel to charge the storage capacitors to 10 kV, self-healing-type capacitor to realize a compact storage capacitor bank, and a highly reliable IGBT switch which enables elimination of a crowbar circuit. Design considerations and its performance are presented. An IEGT (Injection Enhanced Gate Transistor) switch, composed of six series devices with a rating of 4.5 kV and 2100 A-DC, has been also developed and tested for R&D to realize a compact modulator.
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
J-PARC, KEK & JAEA, Ibaraki-ken
KEK, Ibaraki
At the J-PARC 3-GeV injection, the injection painting area is designed to be different for supplying the MLF (Material Life Science Facility) and MR (50GeV Main Ring) beams. Along with the injection system in the ring, pulsed switching magnets which are installed in the injection beam-line should also have a function to control the beam orbit at 25Hz. The deflection angle ranges from 3 to 38 mrad to meet the user operation as well as the beam physics run.
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
3 GeV rapid cycling synchrotron (RCS) of J-PARC accelerates proton beams from the 181 MeV up to 3 GeV. The RCS injects the beam to the Main Ring and transports it to the muon production target and neutron production target in the Materials and Life Science Experimental Hall. Proton beams in the RCS are fast extracted by kicker magnets at the repetition rate of 25 Hz. The rise time of the magnetic field is approximately 260 ns due to the propagation time through the coaxial cable and the kicker magnet itself. The flat-top length of it is required to 840 ns in order to extract two beam bunches. Pulse forming lines (PFL) and thyratrons are used to make the rise time and the flat-top, at the maximum charging voltage of 80 kV. Two thyratrons, which is a CX1193C made by e2V Ltd., are used for a power supply. 16 thyratrons are used in the eight power supplies of the kicker system. Since thyratrons are gaseous discharge switching devices, they often make misfire or self-breakdown in several hours. In this paper, present status of operation and voltage adjustment method of the reservoir and cathode heater power supply of the thyratrons in the kicker system are described.
CIEMAT, Madrid
CERN, Geneva
The goal of the present CLIC Test Facility (CTF3) is to demonstrate the technical feasibility of specific key issues of the CLIC scheme. The extracted drive beam from the combiner ring (CR), a pulse of 35 A magnitude and 140 ns duration, is sent to the new CLic EXperimental area (CLEX). A Tail Clipper (TC) kicker is required, in the CR to CLEX transfer line, to allow the duration of the beam pulse to be adjusted: the unwanted bunches are kicked into a collimator. The TC must have a fast field rise-time, of not more than 5 ns, in order to minimize uncontrolled beam loss. Striplines are used for the TC: to establish the required fields, the applied pulse wave front must fully propagate along the striplines. To reduce the wave front propagation time, the overall length of the stripline assembly is sub-divided into 4 sections. The TC has been designed with the aid of detailed numerical modelling: the stripline cross-section and coaxial-to-stripline transitions were carefully optimized using a 3D code. The results of simulations and the measured behaviour of the striplines are presented; in addition measured current pulses are shown.
CERN, Geneva
Proton and ion beams will be injected into LHC at 450 GeV by two kicker magnet systems, producing magnetic field pulses of up to 7.8 μs flat top duration with rise and fall times of not more than 900 ns and 3 μs, respectively. Both systems are composed of four traveling wave kicker magnets, powered by pulse forming networks. One of the stringent design requirements of these systems is a field flat top and post pulse ripple of less than ±0.5 %. A carefully matched high bandwidth system is required to obtain the stringent pulse response. Screen conductors are placed in the aperture of the kicker magnet to provide a path for the image current of the, high intensity, LHC beam and screen the ferrite against Wake fields: these conductors affect the field pulse response. Recent injection tests provided the opportunity to directly measure the shape of the kick field pulse with high accuracy using a pilot beam. This paper details the measurements and compares the results with predictions and laboratory measurements.
CERN, Geneva
The Compact Linear Collider (CLIC) study is exploring the scheme for an electron-positron collider with high luminosity (1034 - 1035 cm2/s) 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. In order to limit the beam emittance blow-up due to oscillations the combined flat-top ripple and droop of the field pulse, for the DR extraction kickers, must be less than 0.015%. In addition, the allowed beam coupling impedance for the kicker systems is also very low: a few Ohms longitudinally and a few MΩ/m transversally. This paper discusses initial ideas for achieving the extremely demanding requirements for the PDR and DR kickers.
CERN, Geneva
University of Applied Sciences Karlsruhe, Karlsruhe
In many particle accelerators considerable amounts of RF power reaching the megawatt level are converted into heat in dummy loads. After an overview of RF power in the range 200 MHz to 1 GHz dissipated at CERN we discuss several developments that had come up in the past using vacuum tube technology for RF-DC conversion. Amongst those the developments the cyclotron wave converter CWC appears most suitable. With the availability of powerful Schottky diodes the solid state converter aspect has to be addressed as well. One of the biggest problems of Schottky diode based structures is the junction capacity. GaAs and GaN Schottky diodes show a significant reduction of this junction capacity as compared to silicon. Small rectenna type converter units which had been already developed for microwave powered helicopters can be used in waveguides or with coaxial power dividers.
CERN, Geneva
A five-turn continuous extraction is currently used to transfer the proton beam from the CERN PS to the SPS. This extraction uses an electrostatic septum to cut the filament beam into five slices, causing losses of about 15 %. These losses would be an even greater drawback when the beam intensity is further increased for the CERN Neutrinos to Gran Sasso facility. To overcome this, a Multi-Turn Extraction (MTE) has been implemented, in which the beam is separated, prior to extraction, into a central beam core and four islands. Each beamlet is extracted using a set of kickers and a magnetic septum. For the kickers two new pulse generators have been built, each containing a lumped element Pulse Forming Network (PFN) of 12.5 Ohms, 80 kV and 10.5 μs. For cost reasons existing 15 Ω transmission line kicker magnets are reused. The PFN characteristic impedance deliberately mismatches that of the magnets to allow a higher maximum kick. The PFN design has been optimised such that undesirable side-effects of the impedance mismatch on kick rise-time and flat-top remain within acceptable limits. The kicker systems put in place for the current first phase of MTE are presented.
CERN, Geneva
The vertical beam dump system of the CERN Super Proton Synchrotron (SPS) uses two matched magnets with an impedance of 2 Ω and combined kick strength of 1.152 Tm at 60 kV supply voltage. For historical reasons the two magnets are powered from three 3 Ω pulse forming networks (PFN) through three thyratron-ignitron switches. Recently flashovers were observed at the entry of one of the magnets, which lead, because of the electrical coupling between the kickers, to a simultaneous breakdown of the pulse in both magnets. To improve the reliability an upgrade of the system was started. In a first step the radii of surfaces at the entry of the weak magnet were increased, and the PFN voltage was reduced by 4 %; the kick strength could be preserved by reducing the magnet termination resistance by 10 %. The PFNs were protected against negative voltage reflections and their last cells were optimised. In a second step the two magnets will be electrically separated and powered individually by new 2 Ω PFNs with semiconductor switches.
NSRRC, Hsinchu
National Tsing-Hua University, Hsinchu
A test unit of a pulse-forming-network (PFN) kicker power supply has been designed and fabricated for Taiwan Photon Source (TPS) beam injection/extraction of the booster ring. In order to fulfill the requirements, the performance of the designed unit has been bench tested and the results are examined for evaluation purpose. The pulse-to-pulse stability and the flattop specifications are specified according to the beam injection/extraction requirements. Effort has been made to enhance the rise/fall time of the delivered pulse current. The engineering evaluation and its possible application for beam diagnostics purpose are briefly discussed.
STFC/RAL/ISIS, Chilton, Didcot, Oxon
A description is given of the development of slow-wave chopper structures for the 3.0 MeV, 60 mA, H‾ MEBT on the RAL Front-End Test Stand (FETS) [1]. 'Helical' and 'Planar' electrode designs [2] have been developed by simulating their high frequency (HF) electromagnetic properties in a commercial 3D code [3], and the manufacture of prototypes has helped to validate the predictive accuracy of the design code, and the selection of suitable machine-able ceramics and alloys of copper and aluminium. A description is also given of a novel abrasive brushing process that enables fine tuning of stripline characteristic impedance by facilitating control of stripline edge radius. The transmission line properties of the previously described 'Helical' test assembly [4] are compared with those of the recently completed 'Planar' test assembly. Finally, the development status of a related prototype high voltage pulse generator is presented.
Diversified Technologies, Inc., Bedford, Massachusetts
Diversified Technologies, Inc. (DTI) recently delivered a 500 kW CW, 33 kV solid-state test stand for the evaluation and conditioning of high power tetrodes employed in accelerator and radar systems. The test system consists of DTI-manufactured and commercially-sourced power supplies, a DTI high voltage opening switch, and DTI controls. Combining an opening switch and fast responding power supplies allows the hi-potting and high power burn-in to be consolidated in one test stand. Faulty tubes, which would not operate in a crowbar-equipped modulator, and could not be processed to health on a high potter, can be revived to health with this fast opening switch circuitry. By limiting peak fault current and follow-on-current, the total energy in an arc event is greatly minimized, reducing damage inside the tube. If greater energy (or action) is required for initial tube processing, additional load capacitance downstream of the switch can be added into the circuit for 'spot knocking' purposes. This test stand is capable of operation in pulsed mode as well as CW. This paper will address the design and construction of the test stand and discuss results since its installation.
Diversified Technologies, Inc., Bedford, Massachusetts
Diversified Technologies, Inc.(DTI) has delivered a fully solid state Klystron Power Supply for the ISIS Front End Test Stand to Rutherford Appleton Laboratory in the UK. The new pulsed power supply drives a Toshiba E3740A klystron in preparation for construction of a system to demonstrate high quality intense chopped beams. DTI's system represents a significant advance in solid-state high power accelerator technology based upon a hard switch developed for the US Department of Energy (DOE) to meet similar requirements for the International Linear Collider(ILC). The system includes two 220 kW switching power supplies, a 110 kV solid state hard switch pulse modulator, mod anode and filament power supplies, klystron fault protection, and interfaces to the ISIS controls. This paper will address the design and construction of the KPS system, as well as test results from the installation at RAL in May 2009.
LBNL, Berkeley, California
The Next Generation Light Source (NGLS) at Lawrence Berkeley Laboratory is a 2.4 GeV linear accelerator with up to ten FELs. Each of the FELs require a fast kicker, with the exception of the final one which can use a normal bend magnet. The requirements for the kickers are to deflect the linac beam by an angle of 3 mrad with a magnetic length of 2 m, and an aperture size of 17 by 17 mm. A strip line magnet with an impedance of 50 Ohms being feed from the opposite direction as the beam has been selected for prototyping. The modulator requirements to drive such a magnet are ±15 kV and ±300 A, with rise and fall times of 5 ns and a flat top of 10 ns. The pulse to pulse stability must be better than 0.01% of the peak value. The design of the modulator is an inductive adder with 20 cells, each driven by 12 power MOSFETs. This paper describes details of the design as well as present preliminary test data.
LLNL, Livermore, California
Vacuum insulators composed of alternating layers of metal and dielectric, known as high-gradient insulators (HGIs), have been shown to withstand higher electric fields than conventional insulators. Generally, vacuum insulator failure is due to surface flashover, initiated by electrons emitted from the triple junction. These electrons strike the insulator surface and produce secondary electrons, which also strike the insulator surface to create more secondary electrons and lead to avalanche. Magnetic field from the external sources, the high-current electron beam, the conduction current in the transmission line or the displacement current in the insulator can deflect primary and secondary electrons' trajectories either toward to or away from the insulator surface, and hence affect the performance of the high-voltage vacuum insulator. The displacement current effects are particularly interesting for short pulse applications. This paper presents the displacement current effects with various short applied voltage pulses on performance of high-gradient insulators. Optimal HGI configurations will also be discussed.
SLAC, Menlo Park, California
SLAC National Accelerator Laboratory has built and is currently operating a first generation prototype Marx klystron modulator to meet ILC specifications. Under development is a second generation prototype, aimed at improving overall performance, serviceability, and manufacturability as compared to its predecessor. It is designed around 32 cells, each operating at 3.75 kV and correcting for its own capacitor droop. Due to the uniqueness of this application, high voltage gate drivers needed to be developed for the main 6.5 kV and droop correction 1.7 kV IGBTs. The gate driver provides vital functions such as protection of the IGBT from over-voltage and over-current, detection of gate-emitter open and short circuit conditions, and monitoring of IGBT degradation (based on collector-emitter saturation voltage). Gate drive control, diagnostic processing capabilities, and communication are digitally implemented using an FPGA. This paper details the design of the gate driver circuitry, component selection, and construction layout. In addition, experimental results are included to illustrate the effectiveness of the protection circuit.
SLAC, Menlo Park, California
A Marx-topology klystron modulator is under development for the International Linear Collider (ILC) project*. It is envisioned as a lower cost, smaller footprint, and higher reliability alternative to the present, bouncer-topology, baseline design. The application requires 120 kV (±0.5%), 140 A, 1.6 ms pulses at a rate of 5 Hz. The Marx constructs the high voltage pulse by combining, in series, a number of lower voltage cells. The Marx employs solid state elements; IGBTs and diodes, to control the charge, discharge and isolation of the cells. Active compensation of the output is used to achieve the voltage regulation while minimizing the stored energy. The developmental testing of a first generation prototype, P1, has been completed. This modulator has been integrated into a test stand with a 10 MW L-band klystron, where each is undergoing life testing. Development of a second generation prototype, P2, is underway. The P2 is based on the P1 topology but incorporates an alternative cell configuration to increase redundancy and improve availability. Status updates for both prototypes are presented.
* ILC Reference Design Report, http://www.linearcollider.org/cms/?pid=1000437
