A 52 quadrupole-magnet FODO lattice has been assembled and operated at the Los Alamos National Laboratory. The purpose of this lattice is to provide a platform to measure the resulting beam halo as the first four magnets of the lattice produce various mismatch conditions. These data are then compared with particle simulations so that halo formation mechanisms may be better understood. The lattice is appended to the LEDA 6.7-MeV radiofrequency quadrupole (RFQ) and is followed by a short high-energy beam transport (HEBT) that safely dumps the beam into a 670-kW beam stop. Beam diagnostic instruments are interspersed within the lattice and HEBT. The primary instruments for measuring the beam halo are nine interceptive devices that acquire the beam's horizontal and vertical projected particle density distributions out to an approximate 10/sup 5/:1 dynamic range. These distributions are acquired using both traditional wire scanners and water-cooled graphite scraping devices. The lattice and HEBT instrumentation set also includes position, bunched-beam current, pulsed current, and beam loss measurements. This paper briefly describes and details the operation of each instrument compares measured data from the different types of instruments, and refers to other detailed papers.

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Experience with the low energy demonstration accelerator (LEDA) halo experiment beam instrumentation

The Low-Energy Demonstration Accelerator (LEDA), designed and built at the Los Alamos National Laboratory, is part of the Accelerator Production of Tritium (APT) program and provides a platform for measuring high-power proton beam-halo formation. Beam Position Monitors (BPMs) are placed along the FODO lattice and the HEBT. The BPM systems employing log-ratio processor electronics have recently been upgraded for all fifteen BPMs along the accelerator. Two types of calibration are now used. The first corrects for errors within the electronics module and the log-amp transfer function non-conformity. The second is a single-point routine used to correct for cable plant attenuation differences. This paper also covers the new switching systems used for various system calibration modes as well as various results from LEDA beam runs. New switching algorithms were implemented in order to remove sensitive electronic switches from within the beam tunnel radiation environment. Attention will be paid to the calibration algorithms and switching system interactions, and how well they work in practice.

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Upgrade to initial BPM electronics module and beamline components for calibration of the LEDA beam position measurements

A versatile and configurable system has been developed in order to monitorize the beam position and to meet all the requirements of the future ESS-Bilbao Linac. At the same time the design has been conceived to be open and configurable so that it could eventually be used in different kinds of accelerators, independent of the charged particle, with minimal change. The design of the Beam Position Monitors (BPMs) system includes a test bench both for button-type pick-ups (PU) and striplines (SL), the electronic units and the control system. The electronic units consist of two main parts. The first part is an Analog Front-End (AFE) unit where the RF signals are filtered, conditioned and converted to base-band. The second part is a Digital Front-End (DFE) unit which is based on an FPGA board where the base-band signals are sampled in order to calculate the beam position, the amplitude and the phase. To manage the system a Multipurpose Controller (MC) developed at ESSB has been used. It includes the FPGA management, the EPICS integration and Archiver Instances. A description of the system and a comparison between the performance of both PU and SL BPM designs measured with this electronics system are fully described and discussed.

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A configurable electronics system for the ESS-Bilbao beam position monitors

The Los Alamos Neutron Science Center (LANSCE) is installing two beam lines to both improve operational tuning and provide new capabilities. The Isotope Production Facility (IFF) will provide isotopes for medical purposes by using the H/sup +/ beam spur at 100 MeV and the Switchyard Kicker Upgrade (SYK) will allow the LANSCE 800-MeV H/sup -/ beam to be rapidly switched between various beam lines within the facility. The beam position instrumentation for both of these beam lines uses a microstripline beam position monitor (BPM) with a 50-mm or 75-mm radius. The cable plant is unique in that it unambiguously verifies the operation of the complete position instrumentation. The processing electronics use a log ratio technique with error correction such that it has a dynamic range of -12 dBm to -85 dBm with errors less than 0.15 dB within this range. This paper will describe the primary components of these measurement systems and provide initial data of their operation.

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Beam position measurements at Los Alamos: Isotope Production Facility and Switchyard Kicker Upgrade

En esta tesis se describen diversas soluciones analogicas y digitales para realizar sistemas de control LLRF (Radio Frecuencia de Bajo Nivel) para cavidades resonantes de radiofrecuencia de aceleradores de particulas. Para analizar dichas cavidades, se desarrolla un modelo generico que representa la respuesta dinamica de la cavidad bajo la influencia del haz de particulas. Despues, se usa este modelo para desarrollar y analizar un sistema analogico de LLRF para el booster' del sincrotron ALBA, asi como un sistema LLRF digital para el linac de la futura Fuente Europea de Protones y Neutrones de Bilbao (ESS-Bilbao). A continuacion, se presentan los detalles del diseno e implementacion de los dos sistemas LLRF aludidos, asi como los resultados experimentales obtenidos en distintas cavidades de radiofrecuencia, asi verificando la validez de los dos disenos propuestos. Tambien, se presenta el diseno basico de la electronica de RF de un sistema de Monitorizacion de la Posicion del Haz de Particulas (BPM) y los resultados preliminares obtenidos con un haz simulado en un banco de ensayos desarrollado al efecto. Hay dos consideraciones importantes a la hora de desarrollar un modelo electrico de cavidades radiofrecuencia util para analizar el sistema o disenar un lazo de LLRF: la respuesta transitoria y los desajustes de impedancia. Sin embargo, en la literatura raramente se consideran estas cuestiones de manera conjunta, y una suele prevalecer sobre la otra, dependiendo de si la cavidad de radiofrecuencia se mira desde una perspectiva de alta potencia o de LLRF. En esta tesis, en primer lugar, se desarrolla un modelo para representar los aspectos mas importantes de la cavidad, incluyendo desajustes de impedancia, potencia reflejada y la respuesta transitoria, por ejemplo en el arranque del sistema o en los instantes de llegada del haz de particulas que carga la cavidad. Como un caso especial, se aplica el modelo a las cavidades RF del anillo de almacenamiento (storage ring) de ALBA, estudiando asi los efectos de carga del haz (beam loading), el arranque del sistema y los retardos en la respuesta de los lazos de regulacion. Para simular estos lazos, se emplea una tecnica matematica para hacer corresponder la frecuencia resonante de la cavidad a banda base, obteniendo de esta manera un modelo equivalente en banda base de la cavidad, con una respuesta aproximadamente igual al modelo convencional RF, pero con una velocidad de simulacion mucho mayor. A continuacion, se presenta el diseno y la implementacion del sistema de LLRF analogico del booster' de ALBA, basado en lazos de realimentacion de las senales IQ del sistema. Se miden los parametros importantes del LLRF operando la cavidad tanto a baja como a alta potencia de RF, verificando asi el diseno propuesto. Finalmente, se presenta el diseno, implementacion y diversos resultados experimentales del sistema LLRF digital pulsado que hemos desarrollado para el Cuadrupolo de Radio Frecuencia (RFQ) del Rutherford Appleton Laboratory - Front End Test Stand (Oxfordshire, Inglaterra) y para el futuro linac de ESS-Bilbao. En lugar de emplear un front-end' analogico estandar que convierta las senales medidas en la cavidad a una Frecuencia Intermedia (IF) para a continuacion submuestrear este senal, en este diseno usamos un demodulador IQ analogico, que transforma directamente las senales RF medidas en sus componentes En-fase (I) y Cuadratura (Q) en banda base. La ventaja principal de usar este metodo es eliminar la necesidad para un sistema preciso y complejo de sincronizacion y timing', lo cual da lugar a un sistema LLRF simple y versatil que puede servir para un rango grande de frecuencias y virtualmente para cualquier aplicacion LLRF, sean pulsadas, en rampa o de onda continua (CW). Los errores asociados al uso de demoduladores de IQ analogicos han sido identificados y corregidos mediante algoritmos implementados en la FPGA y por medio del ajuste apropiado de los parametros del lazo de control. Ademas, se ha desarrollado un modelo equivalente en banda base del RFQ en MATLAB-Simulink para estudiar su respuesta transitoria en condiciones de carga del haz y en presencia de errores de fase y retardos. Los resultados experimentales obtenidos con una cavidad de prueba y un modelo en cobre del RFQ verifican que en lazo cerrado pueden obtenerse campos acelerantes con niveles de estabilidad de amplitud y fase superiores al 1 por ciento y un grado respectivamente, ademas de un margen de fase mayor de +/- 50 grados que confiere robustez al sistema, conservando al mismo tiempo la linealidad y el ancho de banda de los lazos de regulacion, y cumpliendo por tanto sobradamente las especificaciones requeridas para el acelerador.

Design, analysis and implementation of a versatile low level radio frequency system for accelerating cavities

Enhancements have been made to the log-ratio analog front-end electronics based on the Analog Devices 8307 logarithmic amplifier as used on the LEDA accelerator. The dynamic range of greater than 85 dB, has been extended to nearly the full capability of the AD8307 from the previous design of approximately 65 dB through the addition of a 350 MHz band-pass filter, careful use of ground and power plane placement, signal routing, and power supply bypassing. Additionally, selection of high-isolation RF switches (55dB) has been an integral part of a new calibration technique, which is fully described in another paper submitted to this conference. Provision has also been made for insertion of a first-stage low-noise amplifier for using the circuit under low-signal conditions.

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J.D. Gilpatrick

Papers

Analog front-end electronics for beam position measurement on the beam halo measurement