Residual phase noise measurements of the input section in a receiver

If not designed properly, the input section of an analog down-converter can introduce phase noise that can prevail over other noise sources in the system. In the paper we present residual phase noise measurements of a simplified input section of a classical receiver that is composed of various commercially available mixers and driven by an LO amplifier

Design and evaluation of a low-level RF control system analog/digital receiver for the ILC main Linacs

The proposed RF distribution scheme for the two 15 km long ILC LINACs, uses one klystron to feed 26 superconducting RF cavities operating at 1.3 GHz. For a precise control of the vector sum of the signals coming from the SC cavities, the control system needs a high performance, low cost, reliable and modular multichannel receiver. At Fermilab we developed a 96 channel, 1.3 GHz analog/digital receiver for the ILC LINAC LLRF control system. In the paper we present a balanced design approach to the specifications of each receiver section, the design choices made to fulfill the goals and a description of the prototyped system. The design is tested by measuring standard performance parameters, such as noise figure, linearity and temperature sensitivity. Measurements show that the design meets the specifications and it is comparable to other similar systems developed at other laboratories, in terms of performance

A 96 channel receiver for the ILCTA LLRF system at Fermilab

The present configuration of an ILC main LINAC RF station has 26 nine cell cavities driven from one klystron. With the addition of waveguide power coupler monitors, 96 RF signals will be down-converted and processed. A down-converter chassis is being developed that contains 12 eight channel analog modules and a single upconverter module. This chassis will first be deployed for testing a cryomodule composed of eight cavities located at New Muon Laboratory (NML) - Fermilab. Critical parts of the design for LLRF applications are identified and a detailed description of the circuit with various characteristic measurements is presented. The board is composed of an input band-pass filter centered at 1.3GHz, followed by a mixer, which down-converts the cavity probe signal to a proposed 13 MHz intermediate frequency. Cables with 8 channels per connector and good isolation between channels are being used to interconnect each down-converter module with a digital board. As mixers, amplifiers and power splitters are the most sensitive parts for noise, nonlinearities and crosstalk issues, special attention is given to these parts in the design of the LO port multiplication and distribution

Operational Experience with the MicroTCA Based LLRF System at FLASH

The Free–Electron Laser in Hamburg (FLASH) at Deutsches Elektronen–Synchrotron (DESY), Hamburg Germany is a user facility providing ultra–short, femtosecond laser pulses down to the soft X–ray wavelength range. For the precise regulation of the radio frequency (RF)fields within the 60 superconducting cavities, which are organized in 5 RF stations, digital low level RF (LLRF) control systems based on the novel MicroTCA.4 standard were implemented in 2013.Within the last two years of operation the outstanding LLRF regulation performance and reliability of the system has contributed to the successful operation of the whole user facility. Furthermore continuous development and upgrades on this system stepwise improvedthe field regulation in terms of short and long term stability. In addition to the LLRF system upgrade in FLASH, experiences during installation, commissioning and maintenance are directly transferred to the European XFEL. Using the same system layout for both facilities is highly beneficial for future upgrades and maintenance

Field Detection and Drift Calibration for the European XFEL

For a reliable and robust operation of free-electron lasers with bunch-arrival time variations on the sub 10fs scale, the short-term and long-term stability of the cavity field is an important factor. For the European XFEL we used the established non-IQ field detection scheme in the MicroTCA.4 crate standard. We achieved for a single channel cavity field detection an accumulated short-term time jitter of <6.7fs (<3.4mdeg), respectively amplitude stability of <5.5E-5 within the noise bandwidth of 1MHz operating at 1.3GHz. To achieve this we present the detectors spurious free signal spectra, its channel scaling behavior, sub-components, signal integrity, EMC zone concepts and the packaging. To achieve the required long-term stability, we present a 2U 19" drift calibration module with a phase stability of <+-0.01deg_pp over several days by injecting the reference. Furthermore component variants and options to improve the stabilityare discussed

Upgrade of the Read-out Electronics for the Energy Beam Position Monitors at FLASH and European XFEL

The dispersive sections of magnetic bunch compressor chicanes at free-electron lasers are excellent candidates for beam energy measurements. In the rectangular beamline sections of the bunch compressors at FLASH, energy beam position monitors (EBPM) with transversely mounted stripline pickups are installed. In this paper, we present the upgrade of the read-out electronics for signal detection of the EBPM installed at FLASH. The system is based on the MTCA.4 standard and reuses already available MTCA.4 compliant modules. This is also true for gateware and software development which fits into standard MTCA.4 framework development. The performance of the instrument was studied at FLASH during user operation and the results are presented

Temperature and Humidity Drift Characterization of Passive RF Components for a Two-Tone Calibration Method

Femtosecond-level synchronization is required for various systems in modern accelerators especially in fourth generation light sources. In those high precision synchronization systems the phase detection accuracy is crucial. However, synchronization to a low noise electrical source is corrupted by a phase detection error originating in the electrical components and connections due to thermal and humidity-related drifts. In future, we plan to implement calibration methods to mitigate these drifts. Those methods require a calibration signal injection, called second tone, into the system. Intrinsically, the injection circuit remains uncalibrated therefore it needs to be drift-free. We performed drift characterization of a set of RF components, which could serve for implementation of a signal injection circuit, namely selected types of couplers and splitters. We describe the measurement setup and discuss the challenges associated with this kind of measurement. Finally, we provide a qualitative and quantitative evaluation of the measurements results

Mitigating Noise Sources in MTCA.4 Electronics for High Precision Measurements

The RF field detection instrumentation plays a crucial role in modern accelerator performance. The most critical section is the transition from the analog signal processing to the digitalization. In this paper we present state of the art performance of COTS components and limitations imposed by crate-oriented solutions. We give recipes on how to optimize performance and present some of the recent results