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| TU5PFP075 | Observation and Numerical Calculation of Lorentz-Detuning for the Cryomodule Test of STF Baseline Cavities at KEK-STF | 999 |
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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. |
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| TU5PFP086 | Status of RF Sources in Super-Conducting RF Test Facility (STF) at KEK | 1032 |
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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. |
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| WE5PFP077 | Analysis of DESY-FLASH LLRF Measurements for the ILC Heavy Beam Loading Test | 2189 |
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Funding: *Work supported by Fermi Research Alliance, LLC. under ContractNo. DE-AC02-07CH11359 with the United States Department of Energy. In September 2008 the DESY-FLASH accelerator was run with up to 550, 3 nano-coulomb bunches at 5 Hz repetition rate. This test is part of a longer term study aimed at validating ILC parameters by operation as close as possible to ILC beam currents and RF gradients. The present paper reports on the analysis that has been done in order to understand the RF control system performance during this test. Actual klystron power requirements and beam stability are evaluated with heavy beam loading conditions. Results include suggested improvements for upcoming tests in 2009 |
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| WE5PFP081 | Digital Low-Level RF Control System with Four Intermediate Frequencies at STF | 2198 |
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Digital low-level rf (LLRF) control system has been installed in many linear accelerators to stabilize the accelerating field. In the digital LLRF system, the rf signal is down-converted into intermediate frequency for sampling at analog-to-digital converter (ADC) and the number of ADC required for vector sum feedback operation is equal to the number of cavity. In order to decrease the number of the ADCs required, a digital LLRF control system using different four intermediate frequencies has been developed at STF (Superconducting RF Test Facility) in KEK. This digital LLRF control system was operated with four superconducting cavities and the rf field stability under feedback operation was estimated. The result of the performance will be reported. |
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| WE5PFP082 | Digital Feedback Control for 972 MHz RF System of J-PARC Linac | 2201 |
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Upgrade of J-PARC linac has been planed using 972 MHz rf system. The rf field regulation is required to be less than ±1% in amplitude and ±1deg. in phase. The basic digital llrf concept is same as the present 324 MHz llrf system using a compact PCI crate. The main alterations are rf and clock generator (RF&CLK), mixer and IQ modulator (IQ&Mixer) and digital llrf algorithm. Since the typical decay time is faster (due to higher operational frequency than present 324 MHz cavity), chopped beam compensation is one of the main concerns. Performance of the digital feedback system using a cavity simulator is summarized. |
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| WE5PFP083 | Vector-Sum Control of Superconducting RF Cavities at STF | 2204 |
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Vector-sum control of 4 superconducting cavities is examined at STF in KEK. The digital llrf control is carried out and the stabilities of rf fields are obtained. Various studies such as feedback margin necessary for enough field regulation, effects of perturbations of cavity detuning or klystron HV and so on. Performance degradation by elimination of circulators is also studied from the viewpoint of llrf system. |
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| WE5PFP084 | Evaluation of LLRF Stabilities at STF | 2207 |
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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. |
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| WE5PFP087 | Automatic Frequency Matching for Cavity Warming-up in J-PARC Linac Digital LLRF Control | 2213 |
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In the J-PARC Linac LLRF, for the cavity warming-up, the cavity resonance is automatically tuned to be the accelerating frequency (324MHz and 972MHz) with a mechanical tuner installed on the cavity. Now we are planning to introduce a new method of the cavity-input frequency matching into the digital LLRF control system instead of the cavity resonance tuning for the cavity worming-up. For the frequency matching with the detuned cavity, the RF frequency is modulated by way of phase rotation with the I/Q modulator, while the source oscillator frequency is still fixed. The phase rotation is automatically controlled by the FPGA. The detuned frequency of the cavity is obtained from phase gradient of the cavity field decay at the RF-pulse end. No hardware modification is necessary for this frequency modulation method. The cost reduction or the high durability for the mechanical tuner is expected in the future. The results of the frequency modulation test will be reported in this presentation. |
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| WE5PFP088 | Direct Sampling of RF Signal for 1.3 GHz Cavity | 2216 |
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Intermediate-frequency conversion technique has been widely used for rf signal detection. However, this technique has disadvantages such as temperature dependence higher order modes of downconverters. One of our recent attractive developments is the high-speed data acquisition system that combines commercial FPGA board ML555 and fast ADC (ADS5474 14bit, maximum 400MS/s and bandwidth of 1.4 GHz). Direct measurements of 1.3 GHz rf signals are carried out with 270 MHz sampling. The direct sampling method can eliminate a down-converter and avoid calibration of non-linearity of the down-converter. These results are analyzed and compared with conventional measurement system. |
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| WE6PFP109 | Operation of the FLASH Linac with Long Bunch Trains and High Average Current | 2766 |
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Funding: Work at Argonne supported by U.S. Department of Energy, Office of Science, office of Basic Energy, Sciences, under Contract No. DE-AC02-06CH11357 XFEL and ILC both intend to accelerate long beam pulses of a few thousand bunches and high average current. It is expected that the superconducting accelerating cavities will eventually be operated close to their respective gradient limits as they are pushed to higher energies. In addition, a relative energy stability of <10-4 must be maintained across all bunches. These parameters will ultimately push the limits of several sub systems including the low-level rf control, which must properly compensate for the heavy beam loading while avoiding problems from running the cavities close to their quench limits. An international collaboration led by DESY has begun a program of study to demonstrate such ILC-like conditions at FLASH, which serves as a prototype for both XFEL and ILC. The objective is to achieve reliable operation with pulses of 2400 3-nC bunches spaced by 330 ns (a current of 9 mA) while meeting the required energy stability and while operating accelerating cavities close to their quench limits. Other goals include measurement of cryoload from HOM heating and evaluation of rf power overhead for the ILC. The paper will describe the program and report recent results. |
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| TU5RFP081 | Status of the Energy Recovery Linac Project in Japan | 1278 |
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Future synchrotron light source project using an energy recovery linac (ERL) is under proposal at the High Energy Accelerator Research Organization (KEK) in collaboration with several Japanese institutes such as the JAEA and the ISSP. We are on the way to develop such key technologies as the super-brilliant DC photo-injector and superconducting cavities that are suitable for both CW and high-current operations. We are also promoting the construction of the Compact ERL for demonstrating such key technologies. We report the latest status of our project, including update results from our photo-injector and from both superconducting cavities for the injector and the main linac, as well as the progress in the design and preparations for constructing the Compact ERL. |