3C - RF Power Sources and Power Couplers

Paper Title Page
TU204 Design and Performance of L-Band and S-Band Multi-Beam Klystrons 369
  • Y.H. Chin
    KEK, Ibaraki

In the last couple of years, great achievements have been realized through world-wide developments of multi-beam klystrons (MBK) in the L-band and S-band. These MBKs are developed by industries such as Toshiba, Thales and CPI for the European X-FEL project or at the Naval Research Lab or by the Chinese Academy of Sciences for high-power, low-voltage radar systems. Some of them are already in operation at full specifications and are commercially available. The MBKs are superior to conventional single-beam klystrons through their ability to increase the output power dramatically while the operating voltage can be kept at a similar level. This talk will review the performances of these multi-beam klystrons, their design features, and future development plans.


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THP048 RF Power Amplifiers for the SPIRAL2 Driver: Requirements and Status 897
  • M. Di Giacomo, B. Ducoudret
    GANIL, Caen

The SPIRAL2 project uses an RFQ, normal conducting rebunchers and a superconducting linac to accelerate high intensity beams of protons, deuterons and heavier ions. All cavities work at 88 MHz, are independently phased and powered by amplifiers whose power ranges from a few kW to 250 kW. The paper describes the amplifier requirements, the proposed solutions and their status.

THP054 Status of RF Sources in Super-Conducting RF Test Facility (STF) at KEK 909
  • S. Fukuda, M. Akemoto, H. Hayano, H. Honma, H. Katagiri, S. Kazakov, S. Matsumoto, T. Matsumoto, S. Michizono, H. Nakajima, K. Nakao, T. Shidara, T. Takenaka, Y. Yano, M. Yoshida
    KEK, Ibaraki

Phase 0.5 and Phase 1.0 of the Superconducting RF Test Facility (STF) have been developed since 2005 in KEK. We have completed the two rf-sources and they have been used for the evaluation for the components of power distribution system (PDS) and couplers which were installed in the 5m-cryomodules. We have developed some rf components which is used in the power distribution system(PDS). Phase 1.0 have been conducted now and we attempt the R&D of PDS required in ILC project. This report describes the recent status of the rf source of STF in KEK including the modulator, PDS and LLRF.

THP076 Last SPIRAL 2 10 kW CW RF Coupler Design 969
  • Y. Gómez-Martínez, T. Cabanel, J. Giraud, D. Marchand, R. Micoud, F. Vezzu
    LPSC, Grenoble

The first tests of the SPIRAL 2 coupler have been done successfully in the B-cryomodule of the SPIRAL2 linac. It led to an updated design. We present the new design as well as the results of the last test and conditioning.


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THP077 Studies on Input Couplers for Superconducting Cavities 972
  • H. Jenhani, S. Cavalier, T. Garvey, W. Kaabi, M. Lacroix, B.M. Mercier, C. Prevost, A. Variola
    LAL, Orsay
  • L. Grandsire
    IN2P3-CNRS, Orsay

Drastic conditioning time reduction was successfully achieved for the TTF-III couplers at LAL. This was carried out by a systematic study of the different parameters that play a role in the conditioning process. Moreover, many investigations were made in order to have a better understanding of the couplers behaviour. These activities represent some aspects of a larger technology program that is being developed at LAL to study power couplers and multipacting. This paper will give an overview of some of these studies, the future experiments on couplers at LAL and the development of the associated technology program.

THP078 High Power RF Supplies for the FAIR Injector Linacs 975
  • W. Vinzenz, W. Barth, H.-L. Dambowy, L. Groening, M. Hoerr, G. Schreiber
    GSI, Darmstadt

During the LINAC conference in Knoxville 2006 the operating frequency of the FAIR proton linac was fixed at 325.224 MHz. Even though the six CH-Structures need slightly different rf levels, the proton linac will be equipped with identical rf power sources. That applies although for the RFQ structure. To supply the FAIR accelerators with a good beam quality by the UNILAC as the high current heavy ion injector for FAIR, as well as an high duty factor accelerator for nuclear physics experiments, different upgrades and modifications have to be made at the rf components. In addition there has to be an upgrade for a planned 50% duty cycle mode, higher beam load within the post-stripper section as well as the provision of an excellent rf operation for the next 30 years. Discussions on possible collaborations with CERN in terms of LLRF and the combining of the procurement for tube amplifiers for bunching cavities are on the way. This paper describes the actual status of the proton linac rf system and the future requirements for the existing UNILAC rf systems.

THP079 Operation Experience with the FLASH RF Waveguide Distribution System at DESY 978
  • S. Choroba, F. Eints, T. Frölich, A. Gamp, T. Grevsmühl, V.V. Katalev
    DESY, Hamburg

The rf stations for the FLASH linear accelerator at DESY provide rf power up to more than 5 MW, 1.3 ms and 10 Hz at 1.3 GHz for forty-eight superconducting cavities grouped into six cryogenic modules and for one normal conducting rf gun. A WR650 waveguide distribution system distributes the power generated by five active rf stations using 5 MW single beam and a 10 MW multibeam klystron to the cavities and the gun. Since FLASH is based on the Tesla Test Facility, TTF, a number of different distribution layouts for the different modules and the gun have been developed and used over the years in terms of type of components and distribution scheme. This paper presents the layout and summarizes the experience with the existing waveguide distribution system.


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THP080 Elimination of Parasitic Oscillations in RF Tube Amplifier for High Power Application 981
  • E. Feldmeier
    HIT, Heidelberg
  • G. Hutter, B. Schlitt, W. Vinzenz
    GSI, Darmstadt

For the heavy ion therapy center HIT in Heidelberg a 1.6 MW power amplifier for 217 MHz was built to supply the 7 MeV/u IH cavity. The inherent parasitic oscillations of the RF tube increases rapidly the anode current until the system switches off. For the elimination of those parasitic oscillations ferrite material is used. The electro magnetic fields are simulated to find an optimal positioning of the ferrite material in the anode cavity such that only the parasitic oscillations are attenuated without affecting the fundamental mode.

THP081 Development of All Solid State Bouncer Compensated Long Pulse Modulators for LEP 1MW Klystrons to be Used for LINAC4 Project at CERN 984
  • P. Shrivastava, J. Mulchandani, V.C. Sahni
    RRCAT, Indore (M.P.)
  • F. Bordry, C. De Almeida Martins, C. Rossi
    CERN, Geneva

Funding: Department of Atomic Energy, India.
CERN is building a 352.2 MHz, 3 MeV RFQ based Test Stand as first part of LINAC 4. Extending its collaboration with DAE of India, CERN approached us to design and develop a high voltage pulsed modulator for 1 MW LEP klystrons (planning their reuse). Three design schemes were proposed out of which an all solid state bouncer compensated modulator was chosen for follow up development. The main features of the modulator are: no gas tube crow-bar, all solid state construction low rise/fall times and high stability of the flat top. The major specifications are output voltage upto 110 kV, output current upto 24 Amp, pulse duration 800 μs, PRR 2Hz, pulse droop <1% and ripple on pulse top <0.1%. The energy in klystron arc is restricted to 10J. Based on these principles, a modulator has been developed and constructed at CERN and is currently undergoing tests with a klystron while another one with similar development is in the final stages of integration/evaluation at RRCAT. The present paper describes the topology, simulation results, protection strategy and integration aspects of the pulse modulator and would briefly summarize the results.

The work is done under DAE CERN Collaboration under NAT Protocol.

THP085 Cooling System Design of Compact Klystron Modulator Power Supply in the XFEL Project at SPring-8 987
  • C. Kondo
    RIKEN Spring-8 Harima, Hyogo
  • T. Inagaki, T. Sakurai, T. Shintake, K. Shirasawa
    RIKEN/SPring-8, Hyogo

A klystron modulator power supply for XFEL project at SPring-8 has been developed, which concepts are a compact body, a low noise, and a good stability. The cooling system of the power supply is one of the most important key for the stable modulator. For example, temperature change of insulation oil in the tank caused drift of the klystron voltage, and higher oil temperature deteriorates insulation oil and electric components. We adopted simple and compact cooling systems utilizing natural conviction cooling, because of low costs, limited space, and maintenance free. In order to estimate the requisite cooling ability, we designed four types of cooling panels and measured the natural conviction heat transfer coefficient between the oil and each cooling panels. Using the results, we designed cooling systems composed of water cooling panels placed on the side walls and a water pipe hanged from the ceiling panel. The temperature of the inner oil of the power supply in the rated operation was suppressed below 43 degree C, which is agreed with our expectation. In this paper we present the design and ability of the power supply, and the key point of oil cooling.

THP086 Cold Cathode Electron Tube Toward Plenty Multi Beam Tube 990
  • M. Yoshida
    KEK, Ibaraki
  • H. Hioka, S. Someya
    SUT, Noda-shi, Chiba
  • U. Utsunomiya
    University of Tokyo, Tokyo

The multi beam electron tube with a lot of beam pipes is required for the low applied voltage and the high frequency because the efficiency has a limit according to the perveance. However, the total heater power becomes too high if many thermal cathodes are used. Thus the cold cathode such as the carbon nano tube (CNT) is suitable for such a multi beam electron tube. Further the cold cathode has the advantage to work as a switching device since the metal grid close to the cathode can be used. The design and the fundamental test of the partial model will be presented.

THP087 Quarter-Wave-Stub Resonant Coupler 993
  • D.A. Swenson
    Linac Systems, LLC, Albuquerque, New Mexico

Most small proton and other ion linacs involve two different linac structures, namely an RFQ linac section and some other, more efficient, linac structure, such as the Drift Tube Linac (DTL), the interdigital (Wideroe) linac, or the Rf Focused Interdigital (RFI) linac. Such linacs can benefit a lot by being resonantly coupled into a single resonant unit. The resonantly coupled structures can be driven by a single rf power system, through single rf drive loop, at a single rf frequency. The relative phase and relative amplitude of the fields in the two structures are locked by the resonant coupler. Such systems require no control of phase of the rf power. By designing the rf power system to track the resonant frequency of the combined structures, the control of the resonant frequencies of the two structures is greatly simplified. A simple, compact, resonant coupler, based on a quarter-wave-stub, will be described. Models of this resonant couple have been tuned and adjusted, and are scheduled to be tested at operating powers in the early fall (2008).

THP088 High Power 325 MHz Vector Modulators for the Fermilab High Intensity Neutrino Source (HINS) 996
  • R.L. Madrak, D. Wildman
    Fermilab, Batavia

One of the goals of the low energy 60 MeV section of the Fermilab HINS H- linac is to demonstrate that a total of 40 rf cavities can be powered by a single 2.5 MW, 325 MHz klystron. This requires individual vector modulators at the input of each rf cavity to independently adjust the amplitude and phase of the rf input signal during the 3.5 ms rf pulse. Two versions of vector modulators have been developed; a 500 kW device for the RFQ and a 75 kW modulator for the remaining rf cavities. High power test results showing the vector modulator phase and amplitude responses will be presented.

THP089 High Power L-Band Fast Phase Shifter 999
  • I. Terechkine, T.N. Khabiboulline, N. Solyak
    Fermilab, Batavia

Following development and testing a prototype waveguide-based high power phase shifter, a design concept of a high power fast phase shifter has been developed. The shifter uses ferrite blocks positioned in a rectangular waveguide. The waveguide cross-section is chosen to suppress most of resonances that could otherwise be a limiting factor for the phase shifter high power performance. Base bias field is created with the use of permanent magnets. Low inductance coils in the same magnetic circuit excite fast (pulsed) bias field component. The waveguide is designed in a way to ensure that the pulsed magnetic field penetrates inside the waveguide with minimum delay while allowing effective heat extraction from the ferrite blocks. This report provides details of the system design, including expected rf behavior and frequency range.

THP090 Marx Bank Technology for Accelerators and Colliders 1002
  • J.A. Casey, F.O. Arntz, R. Ciprian, M.P.J. Gaudreau, M.K. Kempkes, I. Roth
    Diversified Technologies, Inc., Bedford, Massachusetts

Funding: U.S. Department of Energy SBIR Program
Diversified Technologies, Inc. (DTI) has developed high power, solid-state Marx Bank designs for a range of accelerator and collider designs. We estimate the Marx topology can deliver equivalent performance to conventional designs, while reducing acquisition costs by 25-50%. In this paper DTI will describe the application of Marx based technology to two different designs: a long-pulse ILC focused design (140 kV, 160 A, 1.5 ms), and a short-pulse design (500 kV, 265 A, 3 us). These designs span the known requirements for future accelerator modulators. For the ILC design, the primary challenge is minimizing the overall size and cost of the storage capacitors in the modulator. For the short-pulse design, the primary challenge is high speed operation, to limit the energy lost in the pulse rise-time while providing a very tight (± 3%) voltage flattop. Each design demands unique choices in components and controls, including the use of electrolytic capacitors in the ILC Marx design. This paper will review recent progress in the development and testing of both of these prototype Marx designs, being built under two separate DOE Phase II SBIR grants.

THP093 Power Coupler and Tuner Development for Superconducting Quarter-Wave Resonators 1005
  • J. Wlodarczak, P. Glennon, W. Hartung, M. Hodek, M.J. Johnson, D. Norton, J. Popielarski
    NSCL, East Lansing, Michigan

The construction of a reaccelerator for secondary ion beams is currently underway at the National Superconducting Cyclotron Laboratory (NSCL). The reaccelerator linac will use superconducting quarter-wave resonators (QWR) operating at 80.5 MHz with beta = 0.041 and beta = 0.085. A coaxial probe-type rf fundamental power coupler (FPC) will be used for both QWR types. The power coupler makes use of a commercially-available feedthrough to minimize the cost. The FPC has been simulated and optimized for operation at 80.5 MHz using a finite element electromagnetics code. Prototype FPC have been fabricated and conditioned with traveling wave and standing wave power using a 1 kW amplifier. A niobium tuning plate is incorporated into the bottom flange of the QWR. The tuner is actuated by a stepping motor for slow (coarse) tuning and a stacked piezoelectric element in series for fast (fine) tuning. A prototype tuner for the beta = 0.041 QWR has been tested on the cavity at room temperature. This paper will cover the design, fabrication, and testing of the prototype coupler and tuner.

THP094 Leveraging the LEDA High Voltage Power Supply Systems for the LANSCE Refurbishment Project 1008
  • J.T. Bradley III, D. Rees, W. Roybal, K.A. Young
    LANL, Los Alamos, New Mexico

Funding: Work supported by the NNSA, U. S. Department of Energy under contract DE-AC52-06NA25396.
The LANSCE Refurbishment Project (LANSCE-R) will revitalize the LANSCE accelerator infrastructure. Much of the equipment has been in use for over 36 years and is approaching the end of its design lifetime. As obsolescence issues make like-for-like replacements increasingly more expensive, modern systems with lower costs become a reasonable alternative. As part of the LANSCE-R project, four of the seven HV power supplies for the 805 MHz rf klystrons will be replaced. The present and future requirements for these power supplies influence the selection of replacement options. Details of the HV power supply replacement requirements and the different replacement options will be discussed. One option is to use four 95 kV, 21 A dc power supplies originally installed nearby as part of the Low Energy Demonstration Accelerator (LEDA) project. Significant material and labor cost savings can be achieved by leaving these supplies installed where they are and building a HV transport system to bring high voltage power from the existing LEDA facility to the LANSCE facility. The different replacement options will be compared based on material and labor costs as offset by long-term energy savings.

THP095 Progress Towards the LANSCE RF System Refurbishment 1011
  • D. Rees, J.T. Bradley III, S. Kwon, J.T.M. Lyles, M.T. Lynch, M.S. Prokop, W. Reass, K.A. Young
    LANL, Los Alamos, New Mexico

The Los Alamos Neutron Science Center (LANSCE) is in the conceptual design phase of a refurbishment project that will sustain reliable facility operations well into the next decade. The LANSCE accelerator was constructed in the late 1960s and early 1970s and is a national user facility that provides pulsed protons and spallation neutrons for defense and civilian research and applications. The refurbishment will focus on systems that are approaching "end of life" and systems where modern upgrades hold the promise for significant operating cost savings. The current baseline consist of replacing all the 201 MHz rf amplifiers, replacing greater than 75% of the 805 MHz rf systems with a combination of high efficiency klystrons and new klystrons of the existing style, replacing four high voltage systems, and replacing all the low level rf cavity field control systems along the accelerator. System designs and requirements will be presented and the project plan will be discussed.

THP096 Next Generation IGBT Switch Plate Development for the SNS High Voltage Converter Modulator 1012
  • M.A. Kemp, C. Burkhart, M.N. Nguyen
    SLAC, Menlo Park, California
  • D.E. Anderson
    ORNL, Oak Ridge, Tennessee

Funding: Work supported by the U.S. Department of Energy under contract DE-AC05-00OR22725
The rf source High Voltage Converter Modulator systems installed on the Spallation Neutron Source have operated well in excess of 200,000 hours, during which time numerous failures have occurred. An improved IGBT switch plate is under development to help mitigate these failures. The new design incorporates three significant improvements. The IGBTs are upgraded to 4.5 kV, 1200 A, press-pack devices, which increase the voltage margin, facilitate better cooling, and eliminate explosive disassembly of the package in the event of device failure. The upgrade to an advanced IGBT gate drive circuit decreases switching losses and improves fault-condition response. A common-mode choke is incorporated into the H-bridge to decrease dI/dt during a shoot-through condition, to further improve the circuit response to this fault condition. The upgrade design and development status will be presented.

THP097 ILC Marx Modulator Development Program Status 1015
  • C. Burkhart, T.G. Beukers, R.S. Larsen, K.J.P. Macken, M.N. Nguyen, J.J. Olsen, T. Tang
    SLAC, Menlo Park, California

Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515
A Marx-topology klystron modulator is under development as an 'Alternative Conceptual Design' for the International Linear Collider project. It is envisioned as a smaller, lower cost, and higher reliability alternative to the present, bouncer-topology, 'Baseline Conceptual 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. The developmental testing of a first generation prototype, P1, is nearing completion. Development of a second generation prototype, P2, is underway. Status updates for both prototypes will be presented.

THP098 RF Vector Control for Efficient Fan-Out Power Distribution 1018
  • Y.W. Kang
    ORNL, Oak Ridge, Tennessee

Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE.
An algorithm for direct high power rf vector control of fan-out rf distribution using reactive circuit elements is presented. In this approach, rf control is performed for the entire fan-out system with many cavities as one system to maximize the rf power efficiency. Control parameters for a set of required rf voltage vectors in the accelerating cavities are determined and maintained for the whole system. Maximizing rf power efficiency with fan-out power distribution can be valuable for large scale SRF accelerators since construction and operation costs can be saved significantly. If a fan-out system employs a fixed power splitter with high power vector modulators in cavity inputs, the optimum power efficiency especially for a SRF system can not be provided since certain rf power headroom is needed for the vector control at each cavity. In the new fan-out vector control approach, a set of required cavity rf voltages is delivered by adjusting the phase delays between the cavities and the reactive loadings at the cavity inputs. The phase shifts and the reactive loadings are realized with high power rf phase shifters.

THP099 Spallation Neutron Source Superconducting Linac Klystron to Cavity Mismatch Effects and Compensation 1021
  • M.P. McCarthy, M.T. Crofford, S.-H. Kim
    ORNL, Oak Ridge, Tennessee

Funding: Oak Ridge National Laboratory, P.O. Box 2008 Oak Ridge, Tennessee 37831-6285 managed by UT-BATTELLE, LLC for the U.S. Department of Energy Under Contract DE-AC05-00OR22725
Observations of several of the 81 klytron output waveforms into their respective superconducting cavities do not correspond with their rectangular klystron inputs in open loop mode. This can't be completely explained by a drooping high voltage power supply especially when the waveform is parabolic. Some possible causes and effects of these anomalies are presented.


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