Technology, Components, and Subsystems

RF Power, Pulsed Power, and Components

Paper Title Page
MO2003 High-Power RF Sources 17
 
  • E. L. Wright
    CPI, Palo Alto, California
  
  Vacuum electron devices continue to play a major role in most high-power RF accelerator systems. They provide continuous wave power to megawatt levels and pulsed power to hundreds of megawatts, at frequencies ranging from HF to millimeter wave. Power grid tubes, Tetrodes, are used for high-power accelerators operating in the HF and VHF frequency bands. Klystrons, multiple-beam klystrons (MBKs) and inductive output tubes (IOTs) take over as the amplifier-of-choice above 300 MHz, while a number of low-power systems utilize magnetron oscillators. A shift in technology, from klystrons to IOTs, has begun for many systems in the 300 MHz to 1500 MHz frequency range due to the IOTs improved efficiency and linearity. In the frequency range from 2.8 GHz to 18 GHz the klystron is king. In the millimeter frequency range gyro-klystrons are available. These technologies will be described, and developments and future trends discussed.  
WE2003 LLRF Systems for Modern Linacs: Design and Performance 498
 
  • A. Brandt
    DESY, Hamburg
  
  Near-future linac projects put yet unreached requirements on the LLRF control hardware in both performance and manageability. Meeting their field stability targets requires a clear identification of all critical items along the LLRF control loop as well as knowledge of fundamental limitations. Large-scale systems demand for extended automation concepts. The experience gained with present systems as well as dedicated experiments deliver the basis for a design of future systems. Digital hardware has evolved quickly over the past years and FPGAs became common not only in LLRF control. A high degree of digitization in various fields, as for example beam diagnostics, suggests to aim for a convergence of the digital platform designs. Channeling of efforts of different research laboratories may be the key to an affordable solution that meets all requirements and has a broad range of applications.  
TH2003 Recent Developments in Pulsed High-Power Systems 541
 
  • D. E. Anderson
    ORNL, Oak Ridge, Tennessee
  
  Pulsed power systems are inherent in any high power accelerator system. Applications include, among others, modulators for powering high power klystrons, pulsed power systems to drive linear induction accelerating cells, kicker magnet drivers for storage rings, and a wide variety of beam deflection and pulsed focusing systems. As with many enabling technologies, component limitations and materials properties dominate the engineering tradeoffs that must be made during the system design. An overview of the state-of-the-art in major components of pulsed power systems will be presented. An examination of how those components are being integrated into linac systems will also be performed and an overview of these systems shall be given. The relatively recent shift toward solid-state power electronics solutions to pulsed power engineering problems will be emphasized. Finally, some future trends in the field will be examined.  
THP021 Study of Vacuum Insulator Flashover for Pulse Lengths of Multi-Microseconds 610
 
  • T. L. Houck, D. A. Goerz, J. B. Javedani, E. J. Lauer, L. K. Tully, G. E. Vogtlin
    LLNL, Livermore, California
  
  We have studied the flashover of vacuum insulators for applications where high voltage conditioning of the insulator and electrodes is not practical and for pulse lengths on the order of several microseconds. The study was centered about experiments performed with a 100-kV, 10-μs pulsed power system and supported by a combination of theoretical and computational modeling. The base line geometry for the experiments was a cylindrically symmetric, +45° insulator between flat electrodes. In the experiments, flashovers or breakdowns were localized by operating at field stresses slightly below the level needed for explosive emissions with the base line geometry. The electrodes and/or insulator were then seeded with an emission source, e.g. a tuff of velvet, or a known mechanical defect. Our study differs from most vacuum insulator studies in that our emphasis was on flashovers originating at the anode triple junction as well as bulk breakdowns within the insulator. Various standard techniques were employed to suppress cathode-originating flashovers/breakdowns. We present the results of our experiments and discuss the capabilities of modeling insulator flashover.  
THP022 Status of RF Sources in Super-Conducting RF Test Facility (STF) at KEK 613
 
  • S. Fukuda, M. Akemoto, H. Hayano, H. Katagiri, S. Kazakov, S. Matsumoto, T. Matsumoto, S. Michizono, H. Nakajima, K. Nakao, T. Shidara, T. Takenaka, Y. Yano, M. Yoshida
    KEK, Ibaraki
  
  Super-conducting rf test facility (STF) has been progessing in KEK since 2005. In this paper, we describe the current status of rf sources in STF. STF rf sources comprise of a long pulse modulator with bouncer circuit, a pulse transformer, an L-band 5MW klystron, power distribution system and low level rf system. We have completed the construction of the first rf system and have been testing for the system evaluation and for the coupler test of the super-conducting cavity. We have a schedule to feed a power to the cryomodule with 8 super-conducting cavities in December of 2006. We also describe the plan of the second rf sources of STF.  
THP023 Status of and Future Plan for the NSRL Microwave Power System 616
 
  • L. Shang
    USTC/NSRL, Hefei, Anhui
  
  In this paper, 20MW microwave power system for NSRL (National synchrotron radiation Laboratory) Linac is introduced. The power system includes five s-band 20MW klystrons and their modulators. In 2002, the klystron modulators and the control system were upgraded. Constant-current, switching power supplies were employed to replace the old conventional LC resonant charging facilities. The new system has run for four years and played an important role in the operation of the 200MeV LINAC. A new soft x-ray FEL project (HTF) is now proposed in NSRL, the energy of electron beam will be increase from 200MeV to 800MeV. Seven s-band 80 MW klystrons and modulators will be employed as the new microwave power sources. The low energy spread specification of the Linac sets a stringent requirement to the stability of the klystron modulators. The paper also presents the technical considerations and preliminary design of the new system  
THP024 Development of Ultra-fast Silicon Switches and their Applications on Active X-Band, High-Power RF Compression Systems 619
 
  • J. Guo, S. G. Tantawi
    SLAC, Menlo Park, California
  
  In this paper, we present the recent results of our research on the ultra-high power fast silicon RF switch and its application on active X-Band RF pulse compression systems. This switch is composed of a group of PIN diodes on a high purity silicon wafer inserted into a cylindrical waveguide operating in the TE 01 mode. Switching is performed by injecting carriers into the bulk silicon through a high current pulse. A switch module is composed of the silicon switch, a circular waveguide T with the silicon switch at the center port and a movable short at the other end of silicon switch. The module can tune the S-matrix of on and off states to desired value. Our current design uses a CMOS compatible process and the fabrication is accomplished at SNF (Stanford Nanofabrication Facility). The switch has achieved <300ns on time with ~3% loss on the wafer. The RF energy is stored in a room-temperature, high-Q 400 ns delay line; it is then extracted out of the line in a short time using the switch. The pulse compression system has a achieved a gain of 7, which is the ratio between output and input power. Power handling capability of the switch is estimated at the level of 10MW.  
THP025 R&D of the Long-Life Thyratron Tube 622
 
  • H. Matsumoto
    KEK, Ibaraki
  • J.-S. Oh
    PAL, Pohang, Kyungbuk
  
  Long lifetime over 50k hours for the thyratron is essential to provide the reasonable availability of the accelerator such as X-FEL and future e+e- linear collider. The lifetime and reliability of a solid-state device are not well confirmed yet. There are some examples that show long life of a thyratron. Many thyratrons were dead due to several common causes related to circuits and operation environment rather than intrinsic problems of a device itself. Several valuable feedback systems are easily adopted to enhance the lifetime. There are still unidentified questions to be verified in the thyratron. Close collaboration between laboratories and companies is strongly requested in order to improve the lifetime and performance of a thyratron.  
THP027 Study of PPM-Focused X-band Pulse Klystron 628
 
  • S. Matsumoto, M. Akemoto, S. Fukuda, T. Higo, H. Honma, S. Kazakov, N. K. Kudo, H. Nakajima, T. Shidara, M. Yoshida
    KEK, Ibaraki
  
  The R&D of PPM (Periodic Permanent Magnet)-focused X-band pulse klystrons has been conducted since 1999, originally for Global Linear Collider (GLC) project. So far six prototype tubes have been tested. Some of them successfully produce the power required in GLC (75MW, 1.6μsec pulse width). However their performance was not perfect as a GLC tube. The problems are the stability of RF output and the gun performance. Since GLC programs were terminated in 2004, some limited work on the improvement of the PPM tubes continues at X-Band Test Facility (XTF) in KEK. The work includes the test to evaluate the performance of revised (rebuilt) tubes as well as disassembling these tubes after the test for further inspection. Recent results are reported.  
THP028 Master Oscillator for Fermilab ILC Test Accelerator 631
 
  • J. Branlard, B. Chase, E. Cullerton
    Fermilab, Batavia, Illinois
  
  The low phase-noise master oscillator generates and distributes the various frequencies required for the LLRF system controlling ILCTA cavities. Two chassis have been developed for this design, generating the programmable frequencies and performing the distribution and amplification, respectively. It has been successfully used with the SNS and the DESY-SIMCON LLRF systems, driving two different superconducting cavities. The design approach and a full characterization of the master oscillator are presented in this paper. The measurement results include the frequency stability and the phase and amplitude noise spectrums of the multiple frequency outputs.  
THP029 Development of an RFQ Input Power Coupling System 634
 
  • Y. W. Kang, A. V. Aleksandrov, M. M. Champion, M. S. Champion, M. T. Crofford, P. E. Gibson, T. W. Hardek, P. Ladd, M. P. McCarthy, D. Stout, A. V. Vassioutchenko
    ORNL, Oak Ridge, Tennessee
  • H. L. Haenichen
    TU Darmstadt, Darmstadt
  
  An RF input coupler system is designed, manufactured, and tested for future upgrade of the coupling system of the RFQ in the SNS linac. The design employs two coaxial loops in vacuum side of two coaxial ceramic windows through coaxial transmission lines that are connected to a magic-T waveguide power splitter for 402.5 MHz operation. The couplers will be used with up to total 800 kW peak power at 8% duty cycle. RF properties of the system and fabricated structure along with vacuum and thermal properties are discussed. Two couplers are joined together through an evacuated bridge waveguide for high power RF processing. Result of the high power conditioning that is performed in the RF test facility of the SNS is presented.  
THP030 Investigation of Ferroelectrics for High-Power RF Phase Shifters in Accelerator Systems 637
 
  • Y. W. Kang, J. L. Wilson
    ORNL, Oak Ridge, Tennessee
  • A. E. Fathy
    University of Tennessee, Knoxville, Tennessee
  
  High power vector modulators enable independent control of RF power to each accelerating cavity, allowing a fan-out configuration to be used to power many cavities from a single high-power klystron. Previously, ferrite materials have been used in high-power phase shifters and vector modulators. It is shown that ferroelectric materials such as barium-strontium titanate (BST) can also be used in such tunable structures. Since ferroelectrics are controlled by an electric, rather than magnetic field, tuning can be faster than tuning a ferrite-loaded device. A BST-loaded coaxial structure is investigated theoretically and experimentally. Good high voltage performance is critical since DC biasing voltages of up to 80 kV can be impressed on the BST sections for tuning. It can also be seen that matching structures around the BST can improve performance over a wider range of amplitudes and phases.  
THP031 Pulse Cables For XFEL Modulators 640
 
  • H.-J. Eckoldt
    DESY, Hamburg
  
  For the XFEL, housed in a single tunnel, most of the modulators will be placed in a central modulator building outside of the tunnel. The pulse transformers and the klystrons will be positioned inside the tunnel near the superconducting linac. Therefore the energy has to be transported via pulse cables. These cables have lengths between 350m and 1.7 km. The power is up to 16.8 MW per pulse with a repetition rate of 10 Hz. In order to keep the rise time short and match the klystron impedance four 25Ohm cables will be put in parallel. A tri-axial design was chosen to prevent magnetic field outside of the cables in order not to disturb electronics or electron beam. A prototype of the cable was produced in industry and delivered to DESY. A set of four 1.5km long parallel cables is in test at present at one of the modulators of the TTF/VUV-FEL at DESY. The cable design criteria and test results are presented in this paper.  
THP032 A Variable Directional Coupler for an Alternate ILC High-Power RF Distribution Scheme 643
 
  • C. D. Nantista, C. Adolphsen
    SLAC, Menlo Park, California
  
  We describe the design and functionality of an RF directional coupler for which the power division between the output ports is mechanically variable. In an alternate power distribution scheme for the ILC, power is delivered to cavities in pairs, through hybrids. Four pairs, or eight cavities, are fed from one waveguide feed, from which one fourth, one third, and one half of the power is coupled out at consecutive directional couplers. Three such feeds are powered by a single 10 MW klystron. Experience suggests that cavities considered useable will display some variation in the operational accelerating gradient they can sustain. With fixed distribution, the klystron power must be kept below the level at which the weakest cavity out of 24 receives its power limit. This problem can be solved by installing variable attenuators, but that means wasting precious power. With adjustable coupling, distribution can be optimized for more efficient use both of available power and of the accelerating cavities. This novel device, feeding cavities paired by similar performance, can provide such benefit to the ILC.  
THP033 Pulsed RF Heating Particularities in Normal-Conducting L-band Cavities 646
 
  • V. V. Paramonov, A. K. Skasyrskaya
    RAS/INR, Moscow
  • K. Floettmann
    DESY, Hamburg
  • F. Stephan
    DESY Zeuthen, Zeuthen
  
  For present projects, such as X-FEL and ILC, the SC technology is chosen for the main linacs. However, in some special parts, NC cavities are applied, operating with high electric and magnetic fields. RF gun cavities with an electric field up to 60 MV/m at the photo cathode are now under development. Capture cavities in the ILC positron source should operate with an accelerating gradient of up to 15 MV/m, practically the same value (14 MV/m), as for the CDS booster cavity in the Photo Injector Test Facility at DESY in Zeuthen (PITZ). High field strength leads to high specific RF heat loading. In combination with long RF pulses (~ 1ms) it results in substantial surface temperature rise, small cavity shape deformations and measurable frequency shifts. In this report we discuss both particularities and some general regularities related to long pulse operation of L-band cavities. Results of 3D numerical simulations for cavity surface temperature, displacements distributions and corresponding frequency shifts for different cavities are presented and compared with existing experimental data. The presented results will give the input for cavities optimization and sub-systems improvements.  
THP035 Design on Accelerating Tube of High-Power Electron Linac for Irradiation Processing 652
 
  • H. Liu, X. Wang
    CIAE, Beijing
  • S. Fu
    IHEP Beijing, Beijing
  
  There is an unstable phenomenon for high-power electron linacs for irradiation processing. The main source of the instability of this type of linac comes from the thermal effect of the accelerator tube under an intense heat load. If a lot of injected electrons are lost in the tube, they can cause an intense and uneven heat load on the tube that may deform the cavities of the accelerator tube and deviate the correct acceleration phase relationship. In this paper, a constant gradient accelerating structure is chosen to accelerate the electron beam, and the designed phase velocity is gradually increased along the tube. By adjusting the size of the accelerating cavities and the phase velocity function, a high capture-efficiency is reached. After a series of simulations studies, we obtained a 90% capture-efficiency, which minimizes the probability of the unstable phenomenon in the high power electron linac.  
THP036 Long-Pulse Modulator for the Superconducting RF Test Facility at KEK 655
 
  • M. Akemoto, S. Fukuda, H. Honma, H. Nakajima, T. Shidara
    KEK, Ibaraki
  
  A long-pulse modulator for the Superconducting RF Test Facility(STF) at KEK is under development now. The modulator is a direct-switched type design with a bouncer circuit to compensate the output pulse droop, and operates the klystron up to 5 MW peak power, 1.5 ms rf pulse width and up to 5 pps repetition rate. The modulator is built by improving a klystron modulator system inherited from Power Reactor and Nuclear Fuel Corp. The design and specifications of the modulator as well as R&D status for ILC modulator are described.  
THP037 Wide-Range Frequency Compensation by Coaxial Ball-Screw Tuner 658
 
  • T. Higo, Y. Higashi, Y. Morozumi, K. Saito, K. Ueno, H. Yamaoka
    KEK, Ibaraki
  
  Low-loss 9-cell 1.3GHz cavities are studied at KEK aiming at a high-gradient operation for the International Linear Collider. One of the most important issues to realize such a high gradient in a pulsed operation of super-conducting cavities is the issue of how to compensate the Lorentz detuning. The Lorentz detuning of the cavity amounts to 3kHz at 45MV/m acceleration field. None of the tuners to date have achieved this range. A coaxial ball-screw tuner was designed and proved to reach this level in the room temperature operation. The performance at liquid Nitrogen temperature is also studied. From these results, we try to evaluate the feasibility of the operation at 2K.  
THP039 Status of the RF Systems for the SPIRAL2 Linac at the Beginning of the Construction Phase 664
 
  • M. Di Giacomo, B. Ducoudret, M. Tripon
    GANIL, Caen
  • P. De Antoni, P. Galdemard, M. Luong, O. Piquet
    CEA, Gif-sur-Yvette
  
  The Spiral 2 project uses an RFQ and a superconductiong linac to accelerate high intensity beams of deuterons and heavier ions. The accelatoror frequency is 88 MHz. The construction phase was approved in Mai 2005 and the project organization was recently finalized. The RF Systems activity includes power amplifiers and control electronics for all the accelerator and some of the RF devices on the beam line: the slow and fast chopper and the rebunchers. The paper describes the status of the amplifiers prototypes, the architecture chosen for the digital LLRF and the preliminary studies on the other RF devices.  
THP040 New Concept of Small Delay Line Type RF Pulse Compressor Using Coupled Cavities 667
 
  • M. Yoshida
    KEK, Ibaraki
  
  I propose a new concept for the RF pulse compressor using the coupled cavities to make a small delay line. This new concept is a hybrid scheme of a cavity type and a delay line type of the RF pulse compressor. The delay line produces the pulse compression outputs through resultant RF beat between two inputs connected both ports of the coupled cavities. The time constant of the beat is matched to the time constant of the power flow of the coupled cavities. Further the special test stand for the coupled cavities was developed to easily adjust the resonant frequency of such high-Q coupled cavities.  
THP041 400-kW RF Amplifier for a 201.5-MHz Deuteron RFQ Accelerator 670
 
  • Y. R. Lu, J.-E. Chen, J. X. Fang, Z. Y. Guo, W. G. Li, X. B. Wang, X. Q. Yan, K. Zhu
    PKU/IHIP, Beijing
  • W. Li, M. Qian
    New Affiliation Request Pending, -TBS-
  
  The dedicated 400kW RF amplifier with hypervaportron TH781 tetrode for a 201.5MHz Deuteron RFQ accelerator has been manufactured and tested successfully. It can deliver 400kW pulse power over RF frequency range from 199MHz to 203MHz with maximum pulse duration of 1ms and 10% duty cycle. The exciter with solid state transistors can output 1kW at both CW and pulse modes. The driver stage can output maximum 20kW. The dummy load with CW 50kW and peak to average ratio of 10 has been modified to fit the requirements of amplifier test measurements.  
FR2003 New Materials and Designs for High-Power, Fast-Phase Shifters 829
 
  • R. L. Madrak, D. Sun, D. Wildman
    Fermilab, Batavia, Illinois
  • E. E. Cherbak, D. Horan
    ANL, Argonne, Illinois
  
  In the 100 MeV H- Linac to be constructed at Fermilab, the use of fast ferrite high power phase shifters will allow all accelerating RF cavities to be driven by a single 2.5 MW, 325 MHz klystron. This results in substantial cost savings. The tuners are coaxial with aluminum doped Yttrium Iron Garnet (YIG) ferrite. In combination with a branch line couplers, they will provide independent phase and amplitude control for each cavity. This is achieved by adjusting the solenoidal magnetic field applied to the ferrite. We report on our results in both low power (timing) and high power tests, for both 3'' and 1-5/8'' OD phase shifters. The low power measurements demonstrate that the rate of phase shift is well within the spec of 1 degree/us. The high power tests were performed at the Advanced Photon Source at Argonne National Lab. We measured phase shifts and the failure point (applied power) for tuners in various configurations. In addition, we performed phase and amplitude measurements for a setup consisting of a 1-5/8'' OD phase shifter along with a prototype branch line coupler.