SLAC, Menlo Park, California
SAIC, Billerica, Massachusetts
Funding: Work supported by Department of Energy contract DE-AC02-76SF00515
SLAC is developing a 10 MW, 5 Hz, 1.6 ms, L-band (1.3 GHz) Sheet-Beam Klystron as a less expensive and more compact alternative to the ILC baseline Multiple-Beam Klystron. The Klystron is intended as a plug-compatible device of the same beam current and operating voltage as existing Multiple-Beam Klystrons. At this time, a beam tester has been constructed and currently is in test. The beam tester includes an intercepting cup for making beam quality measurements of the 130 A, 40-to-1 aspect ratio beam. Measurements will be made of the electrostatic beam and of the beam after transporting through a drift tube and magnetic focusing system. General theory of operation, design trade-offs, and manufacturing considerations of both the beam tester and klystron will be discussed.
ANL, Argonne
Funding: Work supported by U.S.Department of Energy, Office of Science, Office of Basic Energy Science, under Contract No. DE-AC02-06CH 11357
Recently, a new SLED test stand located in the Advanced Phone Source linac klystron gallery was developed using a spare modulator-klystron system and a recently developed prototype water station. The new test stand will be used to condition, tune and perform rf measurements on spare SLEDs without interfering with normal daily linac operations. This will allow technical groups to replace a low-performance SLED from one of the operational linac sectors with a fully conditioned SLED. The pre-conditioned SLED is expected to require less conditioning time after being put into operation compared to an unconditioned SLED. As an additional benefit, the prototype water station system developed to replace aging linac water systems can be tested under realistic conditions. In this paper, we describe the test stand design, prototype water station system, and first results using it to condition SLEDs and perform SLED rf measurements.
Far-Tech, Inc., San Diego, California
We describe the design and construction status of a compact, 830 kW multi-beam klystron (MBK) for driving 1300 MHz cryomodules. The applications for this tube range from ILC and ILC test facilites to Project X. The use of low gun voltage (36 kV) simplifies the modulator and gun socket requirements. A high efficiency, predicted to be > 65%, will allow the klystron to be used in applications requiring low overall site power and high wallplug efficiency.
CLASSE, Ithaca, New York
The superheating magnetic field of a superconducting niobium 1.3 GHz reentrant cavity was measured at several points in the temperature range from (1.7 to 4.4) K. This experimental data is used to discriminate between two competing theoretical s for the temperature dependent behavior of the RF superheating field. Measurements were made with <250 us high power pulses (HPP, ~1MW) to avoid defect initiated thermal breakdown from contaminating the data. Our test incorporated oscillating superleak transducers to determine the cavity quench locations and characterize changes and the migrations of the quench locations during processing. This information provides insight into the factors which limit the ultimate achievable RF surface magnetic field.
KEK, Ibaraki
TIPC, BeiJing
A pulsed RF operation of four units of 9-cell L-band (1.3 GHz) cavities in a horizontal cryostat (cryo-module) was conducted in 2008 as part of R&D efforts at STF at KEK for ILC. A series of compensation experiments were conducted for Lorentz-detuning effects, which are critically important for pulsed RF operation of high-gradient linacs based on superconducting cavity technologies. The experiments were done at a repetition rate of 5 Hz with RF pulses of a width of 1.5 msec, and the typical accelerating gradient within the cavities was 20 32 MV/m. Two types of compensation techniques have been tested. In a “feed-forward” method, piezo actuators on individual cavity tuners are activated to mechanically control the tuning of the cavity in synchronization with the RF pulses. In a “feed-back” method, the low-level RF system is driven so as to maintain the average of “I” and “Q” components of the cavities as constant. This paper reports the experimental results using the various parameters of the piezo control to compensate the effect of Lorentz-detuning. These results are consistent with the numerical calculation postulating that two mechanical modes mainly contribute to the effect.
ANL, Argonne
Funding: U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357
Work is underway to improve the reilability and power handling capability of input couplers used in the Advanced Photon Source single-cell and five-cell cavities. Coupler performance during conditioning in a test cavity suggests that ceramic material defects and field enhancement caused by a mechanical gap in the coupler design may be responsible for past coupler failures at high power. Simulation results and high-power test data will be discussed.
ANL, Argonne
Funding: U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
An investigation into development of a 200-kW CW solid state rf power system design to replace the existing klystron-based 352-MHz rf systems at the Advanced Photon Source has been started. The baseline 352-MHz solid state system design will consist of multiple 1-kW CW modules combined to produce a total output capability of 200-kW CW, sufficient to drive one single-cell storage ring cavity. A description of the 1-kW CW module building block of the solid state power sistem will be presented, along with results from hardware evaluation tests at the 1-kW CW level.
ANL, Argonne
Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
The redesign, construction, and high-power testing of a 95-kV DC, 2MW water-cooled resistive load has been completed. This load was built and installed to test and troubleshoot the Advanced Photon Source (APS) 352-MHz high voltage klystron power supplies. The original resistive load*,** was modified to enhance and improve the load performance .In this paper, we describe the redesign of the DC load, report on the recent test results, and discuss it’s performance improvements.
*D. Horan et al., “A 2-Megawatt Load for Testing High Voltage DC Power Supplies”.
** D. Horan et al., “Performance of a 2-Megawatt High Voltage test Load”.
BNL, Upton, Long Island, New York
Continental Electronics Corp., Dallas, Texas
CPI, Palo Alto, California
Funding: DoE Contract No. DE-AC02-98CH10886
Brookhaven’s ERL (Energy Recovery LINAC) requires a 1 MW CW RF system for the superconducting electron gun cavity. The system consists primarily of klystron tube, transmitter, and High-Voltage Power Supply (HVPS). The 703.75 MHz klystron made by CPI, Inc. provides RF power of 1 MW CW with efficiency of 65%. It has a single output window, diode-type electron gun, and collector capable of dissipating the entire beam power. It was fully factory tested including 24-hour heat run at 1.1 MW CW. The solid state HVPS designed by Continental Electronics provides up to 100 kV at low ripple and 2.1 MW CW with over 95% efficiency. With minimal stored energy and a fast shut down mode no crowbar circuit is needed. Continental’s transmitter includes PLC based user interface and monitoring, RF pre-amplifier, magnet and Vac-Ion pump supplies, cooling water instrumentation, and integral safety interlock system. BNL installed the klystron, HVPS, and transmitter along with other items, such as circulator, water load, and waveguide components. The collaboration of BNL, CPI, and Continental in the design, installation, and testing was essential to the successful operation of the 1 MW system.
DESY Zeuthen, Zeuthen
DESY, Hamburg
The European XFEL, an X-ray free electron laser, is planned as an European project with a strong connection to the DESY research center in Hamburg. The LINAC of the XFEL incorporates 27 RF stations, which supply the RF power required by the superconducting cavities. In order to generate the RF power (1.3 GHz, 10MW pulses) HV pulse modulators are required. Each modulator has to supply 12kV pulses at 1.6kA for 1.5ms pulse duration and at 10Hz nominal repetition rate. The repetition rate can be increased to 30Hz at shorter pulse duration. Although extensive experience exists from the test facilities FLASH and PITZ (DESY Hamburg and Zeuthen sites) a dedicated modulator test stand has been setup to test and investigate additional new modulator prototypes developed by different companies. The results of these tests and the experience gained with the RF-stations at PITZ and FLASH will be an important criterium for the decision on the final layout and choice of vendor. An overview of the Modulator Test Facility at DESY will be presented. The first of two prototypes was delivered in July 2008 and started its operation in October. First test results of this prototype will be presented.
KEK, Ibaraki
The super-conducting RF test facility (STF) at KEK has been functional since 2005, and the STF phase-I, which involves the testing of a cryomodule with four superconducting cavities, was performed at the end of 2008. In this test, intense study of the power distribution system for the possible linear collider scheme was performed. Linear power distribution and tree-like distribution were compared and also the effects of eliminating circulator are studied. Current status of RF source of KEK STF are reported.
KEK, Ibaraki
Four klystron power supplies that can provide a typical voltage of 40kV (current 8A) are used for the PF storage ring at High Energy Accelerator Research Organization (KEK). The original power suplies were fabricated during 1979-1987. Although the power supplies have been operated well, we anticipate some difficulty in maintaining them in future. Then, we planned to renew them by stages. As the first step, we renewed one of the power supplies in 2003. The renewed power suplly have been operated well without any trouble. As the second step, we updated another power supply in the summer of 2008. The renewed power supply is equipped with a solid-state high-voltage (HV) switch that is made of insulated gate bipolar transistors (IGBT) for klystron protection. The renewed power supply have been operated well from September, 2008. We report the performance of the new power supply.
Nano, Moscow
RAS/INR, Moscow
Solid State High Power RF System is proposed for XFEL and ILC. It includes individual RF power supply for each SC cavity and common control system. Each RF power supply includes Solid State Generator, circulator and Q-tuner. Triggering, synchronization, output power and phase of each Solid State Generator are controlled from the common control system through fiber-optic lines. Main parameters of Solid State Generator are: frequency 1.3 GHz, peak power 128 kW, pulse length 1.4 msec, repetition rate 10 Hz, average power 1.8 kW, CW power 2.5 kW. Advantages of Solid State High Power RF System are: simple triggering, synchronization, output power and phase adjustment for all cavities separately, operation both in pulse and in CW modes, unlimited lifetime, no high voltage, no oil-tank, compactness.
ORNL, Oak Ridge, Tennessee
ORNL RAD, Oak Ridge, Tennessee
Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.
The SNS has been operational and delivering beam to the target for 3 years. Over this time period we have increased the beam power delivered to the target to 700 kW, 50% of the design goal. The RF Group has acquired a fair amount of experience in the operation and maintenance of our RF systems during the power ramp up process. This paper reviews the design and layout of the various SNS RF systems, documents the present state and performance of the systems and covers, in a broad sense, issues raised during operation and improvements we have undertaken as well as future RF system requirements.
PAL, Pohang, Kyungbuk
Funding: Supported by the Korea Ministry of Science and Technology mhchun@postech.ac.kr
The RF system for the Pohang Light Source (PLS) storage ring is operating at total maximum RF power of 300kW with four 75kW klystron amplifiers and four PF-type normal conductivity(NC) RF cavities for 190mA at 2.5GeV. The PLS will be upgraded from 2.5GeV/200mA to 3.0GeV/400mA in the near future. Therefore the RF system should be greatly upgraded to supply total 627kW beam power. We are investigated the some upgrade ways with adding NC cavities or new super conductivity(SC) RF cavities. According to the cavity type, the high power RF system will be adjusted the total RF power, and source type and quantity such as klystron or IOT. This paper describes the present operation status and several optional ways of high power RF system for the upgrade project of PLS storage ring
BINP SB RAS, Novosibirsk
Yale University, Physics Department, New Haven, CT
KEK, Ibaraki
Fermilab, Batavia
Funding: Sponsored in part by US Department of Energy, Office of High Energy Physics.
Conceptual design of a multi-beam klystron (MBK) for ILC and Project X application is presented. The chief distinction between the MBK design and existing 10-MW MBK’s is the low operating voltage of 60 kV. There are at least four compelling reasons that justify development of a low-voltage MBK, namely (i) no pulse transformer would be required; (ii) no oil tank would be required for the tube socket; (iii) modulator would be a compact 60-kV IGBT switching circuit. The proposed klystron consists of four clusters that contain six beams each. The tube has common input and output cavities for all 24 beams, and individual gain cavities for each cluster. A closely related optional configuration for a 10 MW tube would involve a design having four totally independent cavity clusters and four 2.5 MW output ports, all within a common magnetic circuit. This option has appeal because the output waveguides would not require a controlled atmosphere and because it would be easier to achieve phase and amplitude stability as required in individual SC cavities.
ELETTRA, Basovizza
Funding: The work was supported in part by the Italian Ministry of University and Research under grant FIRB-RBAP045JF2
The former linac sections used in the injector system of the Elettra Laboratory storage ring will be upgraded for use on the FERMI@elettra project, a free-electron laser user facility operating down to 3 nm. These seven accelerating sections are 3π/4 mode backward-travelling wave (BTW) constant-impedance structures, powered by 45 MW TH2132A klystrons couple to what was called a PEN – power enhancement network, or more commonly referred to as a SLED system. Due to breakdown problems inside the sections, that was the result of high peak fields generated during conventional SLED operation, the sections experienced difficulties in reaching the design gradients. To lower the peak field and make the compressed pulse “flatter”, phase-modulation of the SLED drive power option is investigated. This paper presents the results of this investigations and includes a detailed mathematically analysis.
RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
We report the high power rf test results of C-band accelerator system for X-ray free electron laser (XFEL) in SPring-8. The C-band accelerator system is composed of two C-band accelerator of Choke-mode-type HOM damping structure, the rf pulse compressor, the 50 MW klystron, oil-filled modulator and solid state switching high voltage charger. It is designed to operate at rather high accelerating gradient as high as 35 MV/m, therefore it is crucial to evaluate high gradient performance and reject some component with defect or poor performance. In the 8 GeV main accelerator, 64 C-band systems will be used in total, whose components are under mass production at several industries in Japan. Some of these systems have been installed and tested in high-power test bunker since July 2008. We report on statistics of the high voltage breakdown, and related measurement; such as power calibration of klystron 50 MW, gain measurement on rf pulse compressor.
Thomson Broadcast & Multimedia AG, Turgi
DESY, Hamburg
DESY Zeuthen, Zeuthen
The European XFEL project at DESY in Germany requires 27 RF stations capable of 10 MW RF power each. Each RF station needs one high voltage modulator that generates pulses up to 12 kV and 2 kA with a duration of 1.7 ms and a nominal repetition rate of 10 Hz. DESY decided to investigate new modulator prototypes and Thomson has been awarded to design and build one of these prototype modulators. The Thomson modulator is based on the pulse step modulator (PSM) principle. This technology allows the regulation of the pulse voltage during the pulses and by this achieving a good flatness. In addition to the common PSM technology this modulator design includes additional features. The first one is a constant power regulation system in order to prevent a 10 Hz loading of the mains. The second one is the extension of a part of the system to allow 2-quadrant mode in order to demagnetise the core of the pulse transformer between the pulses. The modulator has been delivered to DESY in July 2008 and is under testing at the modulator test facility in Zeuthen. The paper will give a detailed overview on the system and shows the results of the factory testing and of the testing at DESY.
ASCo, Clayton, Victoria
Argonne National Laboratory, Office of Naval Research Project, Argonne
Monash University, Faculty of Science, Victoria
SLAC, Menlo Park, California
This paper describes the implementation of a neural network hybrid controller for energy stabilization at the Australian Synchrotron Linac. The structure of the controller consists of a neural network (NNET) feed forward control, augmented by a conventional Proportional-Integral (PI) feedback controller to ensure stability of the system. The system is provided with past states of the machine in order to predict its future state, and therefore apply appropriate feed forward control. The NNET is able to cancel multiple frequency jitter in real-time. When it is not performing optimally due to jitter changes, the system can successfully be augmented by the PI controller to attenuate the remaining perturbations.
FEL/Duke University, Durham, North Carolina
PKU/IHIP, Beijing
Funding: This work was supported by US Air Force Office of Scientific Research medical FEL grant FA9550-04-01-0086.
The Madey theorem is a valuable research tool for studying Free-Electron Lasers (FELs). The theorem relates the shape of the on-axis spontaneous radiation spectrum of FEL wigglers to the FEL gain. The theorem predicts that degradation of the spontaneous spectrum, for example as a result of the increase of the electron beam energy spread, provides a direct measure of the reduction of the FEL gain. Extensive experiments have been performed to study the validity of the Madey theorem for a storage ring base optical klystron FEL. The experimental data show that the lasing wavelength of the FEL is very close to the maximum slope of spontaneous spectra as predicted by the Madey theorem with a relative wavelength discrepancy less than 0.2%. Further analysis is underway to understand this wavelength difference. In addition, we have performed direct measurements of the start up gain of the FEL and compared it with the changing slope of the spontaneous spectra. The preliminary results show a good agreement between the measured FEL gain and the prediction by Madey theorem.
FEL/Duke University, Durham, North Carolina
Funding: This work was supported by US Department of Defense Medical FEL Program as administered by the AROSR under contract number FA9550- 04-01-0086 and US Department of Energy grant DE-FG05-91ER40665.
Accurate simultaneous measurements of storage ring free-electron laser (SRFEL) average power output and electron beam energy spread has been achieved at the Duke FEL Laboratory. It is well known that the SRFEL power is limited by the electron beam synchrotron radiation power and the induced energy spread of the electron beam. The two-wiggler spectrum of an optical klystron can be used to determine the energy spread of the electron beam. Measuring the interference pattern of the modulated spontaneous spectrum with the FEL turned on, we are able to study the FEL power output as a function of electron beam energy spread. As the energy spread increases, the modulation in the two-wiggler spectrum reduces, resulting in a smaller FEL gain. During this process, the operation of an optical klystron degrades back to that of a conventional FEL. This paper reports our recent experiment study of transition of the FEL operation from an optical klystron to a conventional FEL.
TRIUMF, Vancouver
The medical isotope Molybdenum-99 is presently used for 80-85% of all nuclear medicine procedures and is produced by irradiating highly enriched uranium U-235 targets in nuclear reactors. It has been proposed* that an electron linac be used for the production of 99Mo via photo-fission of a natural uranium target. The nominal linac parameters are 50 MeV electron energy, 100 mA beam current and 100% duty factor. This paper describes two possible superconducting RF accelerator design concepts based on the frequencies of 704 MHz and 1.3 GHz. We present design parameters, efficiency and reliability estimates, and comparisons between the two options. Finally, we describe how the proposed e-linac project at TRIUMF can be used for proof-of-principle demonstration and critical validation tests of the accelerator-based production of 99Mo.
*Making Medical Isotopes: Report of the Task Force on Alternatives for
Medical-Isotope Production (2008)
KEK, Ibaraki
JAEA/LINAC, Ibaraki-ken
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
The output energy of J-PARC linac is planned to be upgraded from 190 MeV to 400 MeV by adding an ACS (Annular Coupled Structure linac) section. The ACS is a variety of coupled-cavity structure linac newly devised for former JHP (Japan Hadron Project), and its original beam dynamics design for J-PARC was presented in LINAC02 [M. Ikegami et. al., in Procs. of LINAC02, p. 629]. Extensive R&D studies have been conducted since then to establish the feasibility of ACS, where four ACS modules have been fabricated and successfully high-power tested. In parallel, the beam dynamics design of the ACS has been further optimized to reflect the experience obtained in the R&D studies and reduce the cost for mass production. In this paper, the revised beam dynamics design of the J-PARC ACS is presented with some simulation results with a particle simulation code.
BINP SB RAS, Novosibirsk
DESY, Hamburg
Funding: This work was performed within the framework of the agreement between Deutsches Elektronen-Synchrotron (DESY, Hamburg) and BINP SB RAS (Russia, Novosibirsk), "Attachment N 18".
Power system for the klystron cathode heater power supply has been developed to transfer 800 Watts up to 130 kV potential based on the high-voltage gap transformer. Power transfer has been implemented resonant way on the frequency of 19.5 kHz using coupled LC-loops with further transformation to DC. Transformer coupling factor is of 0.58, high-voltage gap is 49 mm, and maximum calculated electric field intensity is 35 kV/cm. Primary winding is powered by the full bridge inverter using phase shifted pulse modulation. This inverter topology provides soft switching of the transistors in a wide range of power regulation (from 18 up to 800 Watts) without an auxiliary active resonant snubber circuits. High stability (0.3%) of the output power has been reached using proportional regulation in the feedback circuit. The achieved power conversion efficiency of inverter is more than 0.95 in the regulation range; efficiency of the whole power system is more than 0.88. The reliable operation of the power system is guaranteed on three types of klystrons (Toshiba E3736; Thales TH1801; CPI VKL8301). The work has been performed within the European XFEL project.
DULY Research Inc., Rancho Palos Verdes, California
Marx modulators, operated by the solid-state switches of Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) or Insulated Gate Bipolar Transistors (IGBTs), offer an alternative to conventional high voltage modulators for rf power sources. They have the advantages of compact size, high-energy efficiency, high reliability, pulse width control and cost reduction. However, Marx modulators need a complex voltage compensation circuit if they are employed in long pulse applications such as the ILC project. We describe novel schemes to compensate the voltage droop of the Marx modulator and minimize the flattop fluctuation of the voltage pulse output through the utilization of inductances and the fast switching properties of solid-state switches. The feasibility of the schemes has been analyzed and relevant data will be presented.
LBNL, Berkeley, California
Funding: *Work supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Science and Engineering Division, of the Department of Energy under contract No. DE-AC02-05CH11231.
ALS is the 1.9GeV third generation synchrotron light source which has been operating since 1993 at Berkeley National Lab. Our team is now working on the design of a new RF power source (replacement of the existing 320kW klystron with 4 IOT’s). In the new design the existing conventional crow-bar klystron protection system will be replaced with a fast disconnect switch. The switch will be constructed out of 16 high-voltage IGBT’s connected in series equipped with static and dynamic balancing system. The main advantage of using this new technology is faster action and virtually no stress for the components of the high voltage power supply. This paper will describe the hardware design process and the test results of the prototype switch unit.
SLAC, Menlo Park, California
Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515
A program is underway at SLAC to develop a Marx-topology klystron modulator for the International Linear Collider* project. It is envisioned as a smaller, lower cost, and higher reliability alternative to the 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 without an output transformer, large at these parameters, by instead combining a number of lower voltage cells in series. The modularity of the Marx topology is further exploited to achieve a redundant, high-availability design. The ILC Marx employs solid state elements; IGBTs and diodes, to control the charge, discharge and isolation of the cells. The SLAC designs are oil-free; air is used for high voltage insulation and cooling. The first generation prototype, P1, is undergoing life testing. Development of a second generation prototype, P2, is underway. Status updates for both prototypes will be presented.
*ILC Reference Design Report, http://www.linearcollider.org/cms/?pid=1000437
SLAC, Menlo Park, California
Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515
Introduced by the U.S. Navy more than a decade ago*, the concept of Power Electronic Building Blocks (PEBBs) has been successfully applied in various applications. It is well accepted within the power electronics arena that this concept offers the potential to achieve increased levels of modularity and compactness. This approach is thus ideally suited for applications where easy serviceability and high availability are key, such as the ILC. This paper presents a building block approach for designing Marx modulators. First the concept of "bricks and buses" is briefly discussed. Then a PEBB-oriented design is presented for the basic Marx cell of a 32-cell Marx modulator to power an ILC klystron; 120 kV, 140 A, 1.6 ms pulses at a repetition rate of 5 Hz. Each basic Marx cell is composed of a main cell and a correction cell that compensates the main cell droop. The main cell has a stored energy of 2.1 kJ per Marx cell and the correction cell an additional 0.5 kJ. This design allows over 30% of the total stored energy in the Marx modulator, 84 kJ, to be delivered in the output pulse, 26.9 kJ, while keeping the droop within a ±0.5% range.
*T. Ericsen. 'Power Electronics Building Blocks - A systematic approach to power electronics.' In: Proceedings of Power Engineering Society Summer Meeting, Seattle, WA, 16-20 July 2000.
CPI, Palo Alto, California
Funding: The authors would like to thank DESY for their support. In addition, we appreciate SLAC helping us out with test equipment.
CPI has designed and is currently in the process of building a prototype of a horizontally oriented multiple beam klystron (MBK) required to provide at least 10 MW peak rf output and 65% efficiency at 1300 MHz and 1.5% rf duty. The klystron was ordered by DESY for the European XFEL. In our design six off-axis electron beams go through seven ring resonators operating in the fundamental-mode. This ensures sufficient beam separation for longer cathode life while keeping the overall diameter of the device small. The MBK was designed using sate-of-the-art multi-dimensional design codes which showed that it was exceeding all performance requirements. First rf hot test data at reduced duty produced 11.2 MW peak saturated rf output and 74% efficiency, which was however accompanied by high beam interception. Initial optimization of the electromagnet resulted in a 70% reduction of the rf body current, but at the expense of rf output power, efficiency (down to 67%) and gain. The magnetic field balance has to be further optimized for low body current and high efficiency at all required operating conditions. Complete test data after optimization and tuning will be presented at the conference.
Fermilab, Batavia
Funding: FRA
Fermilab’s High Intensity Neutrino Source (HINS), the 325 MHz low energy section of Project X consists of an RFQ, 18 copper cavities and a section of superconducting spoke resonator cavities, all driven by a single 2.5 MW klystron. Each cavity has a high power ferrite vector modulator which provides individual RF power control. This paper proposes a scheme that optimizes RF drive and vector modulator control. The different gradients, acceleration phase angles, unloaded Q’s and beam loading are taken into account to optimize the cavities detuning angles, forward power, and loaded Q’s. This scheme makes an efficient use of the klystron’s high bandwidth ability to modulate the forward power, hence minimizing the burden on the high power vector modulator during the RF pulse. The proposed method is explained in details, a parameter sensitivity analysis is performed and the impact on the total power consumption for the RF station is calculated.
SLAC, Menlo Park, California
Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515.
We present a concept for powering the main linacs of the International Linear Collider (ILC) by delivering high power RF from the surface via overmoded, low-loss waveguides at widely spaced intervals. The baseline design employs a two-tunnel layout, with klystrons and modulators evenly distributed along a service tunnel running parallel to the accelerator tunnel. This new idea eliminates the need for the service tunnel. It also brings most of the warm heat load to the surface, dramatically reducing the tunnel water cooling and HVAC requirements. In the envisioned configuration, groups of 70 klystrons and modulators are clustered in surface buildings every 2.4 km. Their outputs are combined into two half-meter diameter circular TE01 mode evacuated waveguides. These are directed via special bends through a deep shaft and along the tunnel, one upstream and one downstream. Each feeds approximately 1.2 km of linac with power tapped off in 10 MW portions at 38 m intervals. The power is extracted through a novel coaxial tapoff (CATO), after which the local distribution is as it would be from a klystron. This tapoff design is also employed in reverse for the initial combining.
ELETTRA, Basovizza
Funding: The work was supported in part by the Italian Ministry of University and Research under grants FIRB-RBAP045JF2 and FIRB-RBAP06AWK3
FERMI@Elettra is a seeded FEL user facility under construction at Sincrotrone Trieste, Italy. The linac is based on S-band normal conducting technology. It will use the accelerating sections of the original Elettra linac injector, seven sections received from CERN after LIL decommissioning and two additional sections to be constructed for a total number of 18 S-band accelerating structures. Installation of the machine is presently being carried on. This paper will provide a summary of the requirements of the different parts of the S-band RF system and of the options for a possible upgrade path both in energy and reliability. The ongoing activities on the main subassemblies, in particular regarding the tests and the installation work, are also presented.
ELETTRA, Basovizza
Funding: The work was supported in part by the Italian Ministry of University and Research under grant FIRB-RBAP045JF2 or grant FIRB-RBAP06AWK3 or grants FIRB-RBAP045JF2 and FIRB-RBAP06AWK3
The FERMI@ELETTRA project will use the existing ELETTRA linac. The linac includes seven accelerating sections, each section is a backward traveling (BTW) structure comprised of 162 nose re-entrant cavities coupled magnetically. Furthermore, there are specialized input and output cavities specifically designed to match the structure to the RF source and load. These BTW accelerating structures work on the 3pi/4 mode which was chosen to optimize the structure efficiency and to achieve a simple RF tuning setup. These accelerating sections are powered by a TH2132A 45 MW klystron providing a 4.5 microsecond rf pulse and are coupled to a Thomson CIDR. In this paper the 3pi/4 backward BTW structures are investigated and the results of the electromagnetic simulations are presented.
BNL, Upton, Long Island, New York
Funding: Work performed under contract number 126615 for Brookhaven Science Associates, LLC.
NSLS-II is a new ultra-bright 3GeV 3rd generation synchrotron radiation light source. The performance goals require operation with a beam current of 500mA and a bunch current of at least 0.5mA. The position and timing specifications of the photon beam place tolerances on the phase stability of the RF cavity fields of less than 0.15 degrees jitter. This study develops computational methods for the construction of LQG controllers for discrete-time models of single-cavity rf systems coupled to rigid-bunch beams able to meet this tolerance. It uses Matlab’s control-systems toolbox and Simulink to synthesize the LQG controller; establish resolutions of state variables, ADCs, DACs, and matrix coefficients that, in a fixed-point controller provide essentially undiminished performance; simulate closed-loop performance; and assess sensitivity to variations of the model. This machinery is applied to NSLS-II-, CLS-, and NSLS VUV-ring models showing exceptional noise suppression and bandwidth. Thoughts are given on the validation and tuning of the rf model by machine measurements, DSP implementations, and future work.
DESY, Hamburg
Warsaw University of Technology, Institute of Electronic Systems, Warsaw
TUL-DMCS, Łódź
Future RF Control systems will require simultaneuous data acquisition of up to 100 fast ADC channels at sampling rates of around 100 MHz and real time signal processing within a few hundred nanoseconds. At the same time the standardization of low-level systems are common objectives for all laboratories for cost reduction, performance optimization and machine reliability. Also desirable are modularity and scalability of the design as well as compatibility with accelerator instrumentation needs including the control system. All these requirements can be fulfilled with the new telecommunication standard ATCA when adopted to the domain of instrumentation. We describe the architecture and design of an ATCA based LLRF system for the European XFEL. Initial results of the demonstration of such a system at the FLASH user facility will be presented.
KEK, Ibaraki
NETS, Fuchu-shi
In STF phass-1, four-cavities are operated with vector-sum feedback (FB) control. The FB control instabilities arising from passband of TM010 mode other than π mode with FB loop-delays were measured. Further, a feedforward (FF) table was used in combination with FB control, which improved the flatness of the flat-top region. A method for reduction of overshoot in FB + FF operation is also proposed. By electrically developing a quasi-beam, the response for quasi-beam injection was also measured, and the correction on beam-loading was performed.
NSRRC, Hsinchu
The quasi-constant current operation is achieved in the NSRRC by periodically injecting electrons from the booster to the storage ring. It means the booster RF system keeps running during operation period, even the injection period occupies only a small portion of the total operation time. To benefit both the energy saving and klystron life, an energy saving controller has been developed and integrated into the TLS booster RF system. The cathode current of the klystron is decreased during the top-injection period. The energy consumption is thus dramatically reduced. A continuous record since the beginning of 2009 shows this controller can save about 78 percent of energy consumption of the booster RF system during normal operation. An overview of the control architecture and its functionality is presented herein.
PAL, Pohang, Kyungbuk
SLAC, Menlo Park, California
In PAL, We are preparing the 3GeV Linac by upgrading the present 2.5GeV Linac and new 10GeV PxFEL project. The specification of the beam energy spread and rf phase is tighter than PLS Linac. In present PLS 2.5 GeV Linac, the specifications of the beam energy spread and rf phase are 0.6%(peak) and 3.5 degrees(peak) respectively. And the output power of klystron is 80 MW at the pulse width of 4 microseconds and the repetition rate of 10 Hz. In PxFEL, the specifications of the beam energy spread and rf phase are 0.1%(rms) and 0.1 degrees(rms) respectively. We developed the modulator DeQing system for 3GeV linac and PxFEL. And the phase amplitude detection system(PAD) and phase amplitude control(PAC) system is needed to improve the rf stability. This paper describes the microwave system for the PxFEL and the PAD and PAC system.
SLAC, Menlo Park, California
Funding: Work supported by the U.S. Department of Energy under contract # DE-AC02-76SF00515 and the US-LARP program
A non-linear time-domain simulation has been developed that can determine technical limitations, effects of non-linearities and imperfections, and impact of additive noise on the interaction of the beam with the Impedance Control Radio Frequency (RF) systems [1]. We present a formalism for the extraction of parameters from the time-domain simulation to determine the sensitivity of the beam longitudinal emittance and dilution on the RF system characteristics. Previous studies [2], [3] have estimated the effect of a noise source on the beam characteristics assuming an independent perturbation source of the RF voltage and a simplified beam model with no coupling. We present the methodology for the time-domain simulation study of the dependence of the accelerating voltage noise spectrum on the various RF parameters and the technical properties (such as non-linearities, thermal noise, frequency response etc.) of the Low Level RF (LLRF) system components. Future plans to expand this formalism to coupled bunch studies of longitudinal emittance growth in the LHC at nominal and upgraded beam currents are briefly summarized.
SLAC, Menlo Park, California
ANL, Argonne
DESY, Hamburg
Funding: *Work supported by the DOE under contract DE-AC02-76SF00515
The FLASH L-Band superconducting (SC) accelerator facility at DESY has a LLRF system that is similar to that envisioned for ILC. This system has extensive monitoring capability and was used to gather performance data relevant to ILC. In particular, waveform data were recorded with beam off for three, 8-cavity cryomodules to evaluate the input rf stability, perturbations to the SC cavity frequencies and the rf overhead required to achieve constant gradient during the 800 μs pulses. In this paper, we discuss the measurements made in September 2008 and the data analysis procedures, and present key findings on the pulse-to-pulse input rf and cavity field stability.
SLAC, Menlo Park, California
CERN, Geneva
Funding: Work supported through SLAC/DOE Contract DE-AC02-76-SF00515 and US LARP CERN collaboration.
The LHC Low Level RF System (LLRF) is a complex multi-VME crate system which is used to regulate the superconductive cavity gap voltage as well as to lower the impedance as seen by the beam through low latency feedback. This system contains multiple loops with several parameters which must be set before the loops can be closed. In this paper, we present a suite of matlab based tools developed to perform the preliminary alignment of the RF stations and the beginnings of the closed loop model based alignment routines. We briefly introduce the RF system and in particular the base band (time domain noised based) network analyzer system built into the LHC LLRF. The main focus of this paper is the methodology of the algorithms used in the routines within the context of the overall system. Measured results are presented which validate the technique. Because the RF systems are located underground in a location which is relatively un-accessible even without beam and completely un-accessible when beam is present, these tools will allow CERN LLRF experts to maintain and tune their LLRF systems from a remote location similar to what was done very successfully in PEP-II at SLAC.
SLAC, Menlo Park, California
Funding: Work supported by Department of Energy contract DE-AC03-76SF00515.
The electron beam for the Linac Coherent Light Source (LCLS) at SLAC is accelerated by disk-loaded RF structures over a length of 1 km. The mainly longitudinal field can sometimes exhibit transverse components, which kick the beam in x and/or y. This is normally a stable situation, but when a klystron, which powers some of these structures, has to be switched off and another one switched on, different kicks can lead to quite a different orbit. Some klystrons, configured in an energy and bunch length feedback, caused orbit changes of up to 1 mm, which is about 20 times the σ beam size. The origins and measurements of these kicks and some efforts (orbit bumps) to reduce them will be discussed.
SLAC, Menlo Park, California
INFN/LNF, Frascati (Roma)
Funding: Work supported by the U.S. Department of Energy under contract number DE-AC03-76SF00515.
The use of normal conducting cavities and an ion-clearing gap will cause a significant RF accelerating voltage gap transient and longitudinal phase shift of the individual bunches along the bunch train in both rings of the SuperB accelerator. Small relative centroid position shifts between bunches of the colliding beams will have a large adverse impact on the luminosity due to the small beta y* at the interaction point (IP). We investigate the possibility of minimizing the relative longitudinal position shift between bunches by reducing the gap transient in each ring and matching the longitudinal bunch positions of the two rings at the IP using feedback/feedforward techniques in the LLRF. The analysis is conducted assuming maximum use of the klystron power installed in the system.
DESY, Hamburg
Funding: This work is supported by the Commission of the European Communities under the 6th Framework Programme "Structuring the European Research Area", contract number RIDS-011899.
The International Linear Collider (ILC) relies on very high beam powers and very small beam emittance to achieve the ambitious luminosity of 2·10+34 cm-2s-1. The potential for damage to the accelerator hardware in the event of some machine failure will require a sophisticated machine protection system. The small apertures in the Beam Delivery System (BDS) - specifically the collimators (by definition the smallest apertures in the machine) are particularly critical. Possible failures in the Main Linac of the ILC and their impact on the BDS are studied using the MERLIN C++ library*. We show that the machine is safe for at least one bunch in case of one of the described failures; a fast abort system is designed to safely extact the remainder of the bunches in the pulse to a dump. Investigated are phase and voltage shifts of the klystrons, quadrupole and corrector coil failures.
*Merlin - A C++ Class Library for Accelerator Simulations; http://www.desy.de/~merlin.
SLAC, Menlo Park, California
CERN, Geneva
Funding: Work supported by the DOE under contract DE-AC02-76SF00515.
Plasma Wake-Field Acceleration (PWFA) has demonstrated acceleration gradients above 50 GeV/m. Simulations have shown drive/witness bunch configurations that yield small energy spreads in the accelerated witness bunch and high energy transfer efficiency from the drive bunch to the witness bunch, ranging from 30% for a Gaussian drive bunch to 95% for bunch with triangular shaped longitudinal profile. These results open the opportunity for a linear collider that could be compact, efficient and more cost effective than the present microwave technologies. A concept of a PWFA-based Linear Collider (PWFA-LC) has been developed by the PWFA collaboration. Here we will describe the conceptual design and optimization of the drive beam, which includes the drive beam linac and distribution system. We apply experience of the CLIC drive beam design and demonstration in the CLIC Test Facility (CTF3) to this study. We discuss parameter optimization of the drive beam linac structure and evaluate the drive linac efficiency in terms of the drive beam distribution scheme and the klystron / modulator requirements.
MIT/PSFC, Cambridge, Massachusetts
Funding: This work was supported by the Department of Energy, Grant No. DE-FG02-95ER40919 and the Air Force Office of Scientific Research, Grant No. FA9550-06-1-0269.
Relativistic elliptic electron beams have applications in the research and development of a new class of elliptic- or sheet-beam klystrons which have the potential to outperform conventional klystrons in terms of power, efficiency, and operating voltage. This paper reports on results of a small-signal analysis of space-charge waves on a relativistic elliptic electron beam in a perfectly-conducting beam tunnel. A dispersion relation is derived. A computer code is developed and used in studies of the dispersion characteristics of various relativistic elliptic electron beams.
MIT/PSFC, Cambridge, Massachusetts
SLAC, Menlo Park, California
Funding: Work supported by DoE HEP, under contracts DE-FG02-91ER40648 and DE-AC02-76-SF00515
In order to understand the performance of photonic bandgap (PBG) structures under realistic high gradient operation, an X-band (11.424 GHz) PBG structure was designed for high power testing in a standing wave breakdown experiment at SLAC. The PBG structure was hot tested to gather breakdown statistics, and achieved an accelerating gradient of 65 MV/m at a breakdown rate of two breakdowns per hour at 60 Hz, and accelerating gradients above 110 MV/m at higher breakdown rates, for a total pulse length of 320 ns. High pulsed heating occurred in the PBG structure, with many shots above 270K, and an average of 170K for 35 x 106 shots. Damage was observed in scanning electron microscope imaging. No breakdown damage was observed on the iris surface, the location of peak electric field, but pulsed heating damage was observed on the inner rods, the location of magnetic fields as high as 1 MA/m. Breakdown in accelerator structures is generally understood in terms of electric field effects. PBG structure results highlight the unexpected role of magnetic fields on breakdown. We think that relatively low electric field in combination with high magnetic field on the rod surface may trigger breakdowns.
PAL, Pohang, Kyungbuk
The Pohang Accelerator Laboratory (PAL) celebrated its 20th anniversary this year. After the completion of the Pohang Light Source (PLS) construction in 1994, the PLS started user service with two beamlines in 1995. The PLS energy was 2.0 GeV. The first major upgrade of the PLS had been done from 2000 to 2002, in which operation energy of the PLS was increased from 2.0 GeV to 2.5 GeV. The number of beamlines has been steadily increased since the start of user service. The number of beamlines currently in service is 28. Three beamlines are under construction. Number of users and performed experiments in 2007 were respectively 2553 and 837. Average impact factor of published papers is over 3.0, which is one of the best among Korean research institutes. Based on such success, the PAL is pursuing the second upgrade plan, called the PLS-II. The PLS will be upgraded its energy from 2.5 GeV to 3.0 GeV. With the upgrade, it will be possible to construct ten more insertion devices. The brightness of the PLS-II will be more than a order higher compared to the current PLS. In this presentation, details of the PLS-II project will be introduced.
This work was supported by the MEST (Ministry of Education, Science and Technology) and the POSCO (POhang iron and Steel making COmpany) in Korea.
Cockcroft Institute, Warrington, Cheshire
STFC/DL, Daresbury, Warrington, Cheshire
Cockcroft Institute, Lancaster University, Lancaster
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
This work reports on the developments of a computational infrastructure framework that aids achievement of computational research objectives. Examples from a broad range of accelerator problems will be presented, along with ways in which the workflow can be modified.
IUCF, Bloomington, Indiana
Funding: This work is supported by AFOSR under grant FA9550-08-1-0160.
We present the theoretical and numerical results of a dispersion free time-dependent Green's function method which can be utilized for calculating electromagnetic space-charge fields due to arbitrary current in a conducting pipe. since the Green's function can be expanded in terms of solutions to the wave equation, the numerical solutions to the fields also satisfy the wave equation yielding a completely dispersion free numerical method. This technique is adequately suited for modeling bunched space-charge dominated beams, such as those found in high-power microwave sources, for which the effects of numerical grid dispersion and numerical Cherenkov radiation are typically found when using FDTD type methods.
DESY, Hamburg
Fermilab, Batavia
KEK, Ibaraki
With a now extended plan to 2012, the ILC Global Design Effort Technical Design Phase focuses on key R&D to verify performance goals and to reduce both technical risk and cost. This talk will review the progress during the last two years, and plans for the future.
SLAC, Menlo Park, California
Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515.
An L-band (1.3 GHz) sheet beam klystron that will nominally produce 10 MW, 1.6 ms pulses is being developed at SLAC for the ILC program. In recent particle-in-cell transport simulations of the 115 kV DC beam through the klystron buncher section without rf drive, a hose-type instability has been observed that is the result of beam noise excitation of transverse modes trapped between the rf cells. In this paper we describe analytical calculations and numerical simulations that were done to study the nature of this instability and explore the required mode damping and changes in the beam focusing to suppress it.
SLAC, Menlo Park, California
R.W. Downing Inc., Tucson
Funding: US Department of Energy Contract DE AC03 76SF00515.
The ILC R&D electronics program at SLAC includes development of key technologies aimed at improving reliability and availability and reducing cost. This paper discusses the development of high availability interlocks and controls for the L-Band high power RF stations. A new Fast Fault Finder (F3) VME module has been developed to process both slow interlocks using FPGA logic to detect the interlock trip excursions. This combination eliminates the need for separate PLC control of slow interlocks with modules chained together to accommodate as many inputs as needed. Next a high availability platform demonstration will port the F3’s via a specially designed VME adapter module into the new industry standard ATCA[1] crate (shelf). This high-availability platform features an Intelligent Platform Management (IPMI) system to control and monitor the health of the entire system, provide redundancy as needed for the application, and demonstrate auto-failover and hot-swap to minimize MTTR. The goal is to demonstrate “five nines” (0.99999) system availability at the shelf level. A new international initiative, the xTCA for Physics Standards Working Group, will be briefly mentioned.
[1] Advanced Telecom Computing Architecture
CERN, Geneva
The civil engineering works of the Linac4 linear accelerator at CERN started in October 2008 and regular machine operation is foreseen for 2013. Linac4 will accelerate H- ions to an energy of 160 MeV for injection into the PS Booster (PSB). It will thus replace the ageing Linac2, which presently injects at 50 MeV into the PSB, and it will also represents the first step in the injector upgrade for the LHC aiming at increasing its luminosity. This paper reports on the status of the design and construction of the main machine elements, which will be installed in the linac tunnel from the beginning of 2012 onwards, on the progress of the civil engineering and on the ongoing activities at the Linac4 test stand.
IUCF, Bloomington, Indiana
LANL, Los Alamos, New Mexico
Funding: LENS is supported by the National Science Foundation grants DMR-0220560 and DMR-0320627, the 21st Century Science and Technology fund of Indiana, Indiana University, and the Department of Defense.
The Indiana University Cyclotron Facility is operating a Low Energy Neutron Source which provides cold neutrons for material research and neutron physics as well as neutrons in the MeV energy range for neutron radiation effects studies. Neutrons are being produced by a 13 MeV proton beam incident on a Beryllium target. The LENS Proton Delivery System (PDS) is routinely operating at 13 MeV and 25 mA at 1.8% duty factor. The RF system, consisting of three Litton 5773 klystron RF tubes at 425 MHz and 1 MW each, power the AccSys Technology PL-13 Linac. The proton beam delivers 6 kilowatts of power to the Beryllium target. Details of the beam spreading system, target cooling system, and accelerator operations will be discussed.
POSTECH, Pohang, Kyungbuk
PAL, Pohang, Kyungbuk
NFRI, Daejon
Funding: This work is supported by KAPRA and POSTECH Physics BK21 Program.
An intense L-band electron linac is now being commissioned at ACEP (Advanced Center for Electron-beam Processing in Cheorwon, Korea) for irradiation applications. It is capable of producing 10-MeV electron beams with the 30-kW average beam power. For a high-power capability, we adopted the traveling-wave structure operated with the 2π/3-mode at 1.3 GHz. The structure is powered by a 25-MW pulsed klystron with 60-kW average RF power. The RF pulse length is 8 μs while the beam pulse length is 7 μs due to the filling time in the accelerating structure. The accelerating gradient is 4.2 MV/m at the beam current of 1.45 A which is the fully beam-loaded condition. In this paper, we present details of the accelerator system and commissioning status.
USP/LAL, Sao Paulo
Funding: FAPESP, CNPq
The Instituto de Física da Universidade de São Paulo (IFUSP) is building a two-stage 38 MeV continuous wave racetrack microtron. This accelerator consists of a linac injector that delivers a 1.7 MeV beam to a microtron (booster) with 5 MeV exit energy. A transport line guides the beam to the main microtron to be accelerated to energies up to 38 MeV in steps of 0.9 MeV. This work describes the commissioning of the linac injector that comprises the first two accelerating structures of the IFUSP Microtron. A provisional beam line was built at the end of the linac to provide energy and current measurements. We also present results concerning RF power, RF phase, and temperature control of the accelerating structures. The first results of the chopper and buncher systems are also presented.