Julien Branlard

Multichannel vector field control module for LLRF control of superconducting cavities

The field control of multiple superconducting RF cavities with a single Klystron, such as the proposed RF scheme for the ILC, requires high density (number of RF channels) signal processing hardware so that vector control may be implemented with minimum group delay. The MFC (Multichannel Field Control) module is a 33- channel, FPGA based down-conversion and signal processing board in a single VXI slot, with 4 channels of high speed DAC outputs. A 32-bit, 400MHz floating point DSP provides additional computational and control capability for calibration and implementation of more complex control algorithms. Multiple high speed serial transceivers on the front panel and the backplane bus allow a flexible architecture for inter-module real time data exchanges. An interface CPLD supports the VXI bus protocol for communication to a SlotO CPU, with Ethernet connections for remote in system programming of the FPGA and DSP as well as data acquisition.

High-speed data processing module for LLRF

Linear accelerators, like the Free-electron LASer in Hamburg (FLASH) or the European X-Ray Free Electron Laser (E-XFEL) take advantage of the digital Low Level Radio Frequency (LLRF) system to control the phase and amplitude of an electromagnetic field inside superconducting cavities. The real-time control LLRF system, processing data within a few microseconds, has to fulfil performance requirements and provide comprehensive monitoring and diagnostics. The AMC-based controller (DAMC-TCK7) board was developed as a general purpose high-performance low-latency data processing unit designed according to the PICMG MTCA.4 spec. The module provides the processing power, data memory, communication links, reference clock, trigger and interlock signals that are required in modern LLRF control systems. The module was originally designed as a cavity field stabilizing controller for standing-wave linear accelerators. However, the application of the board is much wider because it is a general purpose data processing module suitable for systems requiring low latency and high-speed digital signal processing. According to authors knowledge this is the first MTCA.4 module offering 12.5 Gbps links, unified Zone 3 connectivity and advanced Module Management Controller proposed by DESY. The DAMC-TCK7 card was used as a hardware template for the development of the other AMC modules of the XFEL accelerators LLRF system. This paper discusses the requirements for the digital real-time data processing module, presents the laboratory performance evaluation and verification in Cryo-Module Test Bench (CMTB) at DESY.

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 up- converter 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 1.3 GHz, 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.

Technique for monitoring fast tuner piezoactuator preload forces for superconducting RF cavities

The technology for mechanically compensating Lorentz Force detuning in superconducting RF cavities has already been developed at DESY. One technique is based on commercial piezoelectric actuators and was successfully demonstrated on TESLA cavities [1]. Piezo actuators for fast tuners can operate in a frequency range up to several kHz; however, it is very important to maintain a constant static force (preload) on the piezo actuator in the range of 10 to 50% of its specified blocking force. Determining the preload force during cool-down, warm-up, or re-tuning of the cavity is difficult without instrumentation, and exceeding the specified range can permanently damage the piezo stack. A technique based on strain gauge technology for superconducting magnets has been applied to fast tuners for monitoring the preload on the piezoelectric assembly. The design and testing of piezo actuator preload sensor technology is discussed. Results from measurements of preload sensors installed on the tuner of the Capture Cavity II (CCII )[2] tested at FNAL are presented. These results include measurements during cool-down, warm- up, and cavity tuning along with dynamic Lorentz force compensation.

High Field Transport in GaN and AlGaN/GaN Heterojunction Field Effect Transistors

Here we report on high field transport in GaN and GaN field effect devices, based on the rigid-ion model of the electron-phonon interaction within the Cellular Monte Carlo (CMC) approach, including quantum- mechanical effects. The calculated velocity is compared with experimental data from pulsed I–V measurements, where good agreement with experiment is found. We have applied the CMC transport kernel above to the simulation of the DC and high frequency characteristics of GaN MESFETs and AlGaN/GaN HFET devices. Various effects are considered, such as thermal heating and nonequilibrium phonons, in comparing with the dc and high frequency behavior of these devices.

Comparative analysis of SOI and GOI MOSFETs

In this paper, the authors use a full-band particle-based simulator based on the cellular Monte Carlo method to investigate and compare the performance of silicon-on-insulator (SOI) and germanium-on-insulator (GOI) technologies. To this end, p-type GOI and SOI MOSFETs of effective gate lengths ranging from 30 to 110 nm are simulated, and their static and dynamic characteristics are analyzed through simulations. The transconductance, channel conductance, current-voltage (I-V) characteristics, and cutoff frequencies are extracted from the simulation results. The results indicate that drive currents are enhanced up to 25% by replacing Si with Ge. The enhancement is not as significant with respect to the unity gain frequency, which is only increased by 13% in the case of a 50-nm MOSFET. Additionally, the I-V characteristics indicate that GOI MOSFETs are more sensitive to impact ionization than their SOI counterparts, and that the channel conductance is degraded

Frequency analysis of semiconductor devices using full-band cellular Monte Carlo simulations

The goal of this work is to use a particle-based simulation tool to perform a comparative study of two techniques used to calculate the small-signal response of semiconductor devices. Several GaAs and Si devices have been simulated in the frequency domain to derive their frequency dependent complex output impedance. Conclusions are drawn regarding the applicability and advantages of both approaches.

Capture cavity II results at FNAL

As part of the research and development towards the International Linear Collider (ILC), several test facilities have been developed at Fermilab. This paper presents the latest Low Level RF (LLRF) results obtained with Capture Cavity II (CCII) at the ILC Test Accelerator (ILCTA) test facility. The main focus will be on controls and RF operations using the SIMCON based LLRF system developed in DESY. Details about hardware upgrades and future work will be discussed.

Experience with capture cavity II

Valuable experience in operating and maintaining superconducting RF cavities in a horizontal test module has been gained with Capture Cavity II. We report on all facets of our experience to date.

Cellular Monte Carlo Modeling of AlxIn1−xSb/InSb Quantum Well Transistors

In this work, an Indium Antimonide (InSb) quantum well transistor is investigated using full-band Monte Carlo simulations. The steady-state characteristic of the device is first analyzed, showing particle transport along the two-dimensional electron gas (2DEG). The small-signal behavior of the device is also investigated. Finally, the noise analysis is performed, allowing for a two-dimensional mapping of the noise within the device.