Fermilab, Batavia
Funding: Fermi Research Alliance under contract with the US Department of Energy
In response to increasing beam intensity demands, the Fermilab 400 MeV Linac is operating at high intensity and higher repetition rates than were imagined when it was designed. This is happening at a time when maintenance time is at a premium. This has had an effect on Linac operation, tuning and reliability. Changes in tuning and equipment being made to accommodate the current running scenario along with reliability data will be presented.
CLASSE, Ithaca, New York
Funding: Work is supported by the National Science Foundation grant PHY 0131508.
Two high power 1300 MHz rf systems have been developed for the Cornell University ERL Injector. The first system, based on a 16 kWCW IOT transmitter, is to provide rf power to a buncher cavity. The second system employs five 120 kWCW klystrons to feed 2-cell superconducting cavities of the injector cryomodule. The sixth, spare klystron is used to power a deflecting cavity in a pulsed mode for beam diagnostics. A digital LLRF control stem was designed and implemented for precise regulation of the cavities' field amplitudes and phases. All components of these systems have been recently installed and commissioned. The first operational experience with the systems is discussed.
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.
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.
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.
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.
DESY, Hamburg
For the LLRF system of superconducting linacs, precision measurements of the rf phase and amplitude are critical for the achievable field stability. In this paper, a fast ADC (ADS5474) has been evaluated for the measurement of a 1.3 GHz rf signal directly without frequency down conversion. The ADC clock frequency is synchronized with the rf frequency and chosen for non-IQ demodulation. In the laboratory, the Signal to Noise Ratio (SNR) of the ADC was studied for different clock and rf input levels, and the temperature sensitivity of the ADC has been determined. A full bandwidth phase jitter of 0.2 degree (RMS) and amplitude jitter of 0.32% (RMS) was measured. For field control of superconducting cavities with a closed loop bandwidth up to 100 KHz, one can expect to achieve a phase stability close to 0.01 degree. The main limitation will be the jitter of the external clock. We present a measurements at the cavities at FLASH and compare the result with the existing system.
DESY, Hamburg
CRE, Wuppertal
The LLRF system of the European XFEL must fulfill the requirements of various stakeholders: Photon beam users, accelerator operators, rf experts, controls system, beam diagnostics and many others. Besides stabilizing the accelerating fields the system must be easy to operate, to maintain, and to upgrade. Furthermore it must guarantee high availability and it must be well understood. The development, construction, commissioning and operation with an international team requires excellent documentation of the requirements, designs and acceptance test. For the rf control system of the XFEL the new system modeling language SySML has been chosen to facilitate the system engineering and to document the system. SysML uses 9 diagram types to describe the structure and behavior of the system. The hierarchy of the diagrams allows individual task managers to develop detailed subsystem descriptions in a consistent framework. We present the description of functional and non-functional requirements, the system design and the test cases. An attempt of costing the software effort based on the use case point analysis is also presented.
KEK, Ibaraki
Recently, FPGA technology is widely used for the accelerator control owing to its fast digital processing. We have been developing several applications for LLRF control and measurement using commercial and custom-made FPGA board. XtremeDSP(the commercial FPGA board equipped two ADCs and two DACs) is mainly used for the performance evaluation of STF(Superconducting RF Test Facility) LLRF. Installing the custom-made FPGA board equipped with ten ADCs and two DACs is considering for up-grade of the rf driver and rf monitoring system in the injector linac. Development of the high-speed data acquisition system that combines commercial FPGA board ML555 and FastADC(ADS5474 14bit, 400MS/s) is carried out. Result of those data acquisition systems will be summarized.
KEK, Ibaraki
In a superconducting accelerator, an FPGA/DSP-based low-level rf (LLRF) system with feedback control is adopted to satisfy the requirement of stability in the accelerating field. An rf probe signal picked up from cavity is down-converted to an intermediate frequency and sampled by an analog-to-digital converter (ADC) in the digital LLRF control system. In order to decrease the number of the ADCs required for vector sum feedback operation, a digital LLRF control system using different intermediate frequencies has been developed. At STF (Superconducting RF Test Facility) in KEK, the digital LLRF system with four intermediate frequencies was operated and the rf field stability under the feedback operation was estimated using a superconducting cavity. The result of the performance will be reported.
KEK, Ibaraki
RF operation has started at the STF (Superconducting RF Test Facility) in KEK. The digital feedback system, which consists of one FPGA, ten 16-bit ADCs and two 14-bit DACs, was installed in order to satisfy the rf-field regulation requirements of 0.3% rms and 0.3 deg.rms in phase. The rf field stability under various feedback parameters are presented. Various studies were also carried out such as cavity detuning measurements (microphonics, quench detection, etc.). These results will also be summarized.
KEK, Ibaraki
In the superconducting rf test facility (STF) at KEK, high power tests of the nine-cell superconducting cavity for the international linear collider (ILC) have been performed. Although the cavity was operated in π-mode, the feedback instability due to 8/9π and 7/9π modes was observed in the STF. The intensities of 8/9π and 7/9π modes were measured by changing the feedback loop-delay and stable/unstable region appeared periodically as expected.
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
KEK, Ibaraki
JAEA, Ibaraki-ken
For the J-PARC linac low level rf system, in order to compensate beam-loading change by pulses in the operation of 25 Hz repetition, a function that switches the feed-forward control parameters in every pulse were installed into the digital accelerating-field control system. The linac provides a 50 mA peak current proton beam to a 3 GeV rapid-cycling synchrotron (RCS). Then the RCS distributes the 3-GeV beam into a following 50 GeV synchrotron (main ring, MR) and the Materials and Life Science Facility (MLF), which is one of the experimental facilities in the J-PARC. The 500-us long macro pulses from the ion source of the linac should be chopped into medium pulses for injection into the RCS. The duty (width or repetition) of the medium pulse depends on which facility the RCS provides the beam to the MR or MLF. Therefore the beam loading compensation needs to be corrected for the change of the medium pulse duty in the 25 Hz operation.
KAERI, Daejon
The requirements for the field amplitude and phase stability of the PEFP linac are 1% and 1 degree, respectively. To achieve the requirements, a digital LLRF control system has been developed using a commercial digital board for general purpose(FPGA). The feedback with PI control and feedforward are implemented in the FPGA. The LLRF control systems are currently used for the linac test. In this paper, test results and discussion on the advantage and disadvantage of the LLRF system based on a commercial board are presented.
Fermilab, Batavia
Funding: FRA
In this paper we present a model for the rf power distribution to multiple super-conductive cavities from a single klystron. The goal of this model is to find a distribution scheme in which the cavities are operated as close to their quench limit as possible. The approach presented in this work consists of setting all cavities to the same QL value by adjusting the power coupler, and optimizing the power (Pk) distribution individually to each cavity to maximize the vector sum voltage. The proposed approach yields an operating gradient very close to the theoretical limit and offers a great operational benefit as the gradient stability is conserved for any beam current.
C. Nantista, K.L.F. Bane, C. Adolphsen, RF Distribution Optimization in
the Main Linacs of the ILC. Proceedings of PAC07, Albuquerque,
New Mexico, USA.
Fermilab, Batavia
The Fermilab Proton Plan, tasked to increase the intensity and reliability of the Proton Source, has identified the Low Level RF (LLRF) system as the critical component to be upgraded in the Linac. The current 201.25 MHz Drift Tube Linac LLRF system was designed and built over 35 years ago and does not meet the higher beam quality requirements under the new Proton Plan. A new VXI based LLRF system has been designed to improve cavity vector regulation and reduce beam losses. The upgrade includes an adaptive feedforward system for beam loading compensation, a new phase feedback system, and a digital phase comparator for cavity tuning. The new LLRF system is phase locked to a temperature stabilized 805 MHz reference line, currently used as frequency standard in the higher energy accelerating section of the Linac. This paper will address the current status of the project, present the advancements in both amplitude and phase stability over the old LLRF system, and discuss commissioning plans.
Fermilab, Batavia
University of Pisa and INFN, Pisa
A multi cavity real time rf simulator and PID control has been implemented on a Xilinx Virtex-4 FPGA. The rf simulator simulates an entire rf unit with up to 4 cavities connected to a single simulated klystron. Each cavity is allowed to have its own set of parameters, set point gradients, synchronous phases, and beam loadings. The simulator is built based on an interdependent electrical and mechanical model of a cavity. The electrical model is a 1st order differential equation in the complex phase space. The mechanical model is a 2nd order differential equation of the Lorentz force detuning on the cavities. Other spurious effects as microphonics and noises can be added using an external source or a memory table. The simulator has been optimized for size and utilizes only one Xilinx DSP block per cavity. A typical Virtex-4 has of the order of 100 DSP blocks. The simulator bandwidth is 1MHz which is plenty for niobium type superconducting cavities which have a loaded Q of about 3 million and a half bandwidth of about 250 Hz. The Real Time simulator is currently running on hardware comprised by an ESECON LLRF controller* and a Linux based VME processor.
*ESECON, 14 channel LLRF controller, Low Level Radio Frequency Workshop (LLRF07), Knoxville, Tennessee, October 22-25, 2007, presentation 031.
Fermilab, Batavia
Funding: Work supported by Fermi Research Alliance LLC. Under DE-AC02- 07CH11359 with the U.S. DOE
The proposed 30 km long ILC electron/positron collider is pushing the limits not only in basic physics research but also in engineering. For the two main Linacs, the pulsed rf power that is feeding the high number of SCRF cavities (~17,000) must to be regulated to app. 0.1% for amplitude and 0.2 deg for phase. The regulation of phase and amplitude is carried out by the analog/digital electronics also denoted as the low-level rf control system. Besides meeting the regulation specifications, the low-level rf must be reliable, robust and low cost. In the paper we present a possible hardware solution that addresses these issues. We also reveal the main design strategies that allowed us meeting the conflicting demands of the system. The system is evaluated on a cavity emulator implemented on the FPGA, which shows that system performance is within the specifications. Finally, we discuss the obtained results and give some suggestions for future work.