J. Power

LEDA and APT beam diagnostics instrumentation

A 20-MeV 100-mA-CW proton-accelerator, Low Energy Demonstration Accelerator (LEDA), is presently being developed, fabricated, and tested at Los Alamos National Laboratory (LANL). The beam diagnostic instrumentation for LEDA and the final 1700-GeV Accelerator Production of Tritium (APT) are classified into two categories: operation and characterization instrumentation. The operational instrumentation does not intercept or minimally-intercepts the beam and are sufficiently prompt and robust to provide accurate information to the operators and commissioners during full-current CW beam operation. The characterization instrumentation, primarily utilized during commissioning project-phases, operates under more traditional 100-mA-peak and approximately 0.1-mA-average beam-current conditions. This paper will review some of the LEDA and APT operational beam diagnostic instrumentation.

Beam position monitors for the SNS linac

The Spallation Neutron Source (SNS) linac accelerates 52-mA peak of pulsed H- particles to over 800 MeV. There are three types of accelerating structure in which the beam position must be measured: the drift-tube-linac (DTL); cavity-coupled-linac (CCL); and superconducting-linac (SCL)[1, 2]. Beam with a 402.5-MHz structure is injected into a 402.5 MHz DTL, followed by 805-MHz CCL and SCL structures. The position monitor pickups are all of the shorted-microstrip type with apertures of 2.5-cm, 3-cm and 7.3-cm-dia. In all cases, we down convert signals from the beam position pickups to a 50-MHz intermediate frequency (IF) for processing. We use the sampled in-phase and quadrature-phase (I&Q) processing technique to obtain the amplitude and phase information of the IF signals. All of the electronics are PCI-based hardware installed in PC computers employing standard technologies. LabVIEW/sup TM/ is used for all of the acquisition, processing, and serving of the data to ethernet, and hence, the control system. The design of this beam position system hardware is described herein.

Experience with the ground test accelerator beam‐measurement instrumentation

During the past two years, the Ground Test Accelerator (GTA) has used a variety of off‐ and on‐line beam diagnostic measurements to understand and verify the transverse and longitudinal phase space characteristics of a 35‐mA, low‐energy (2.5‐ to 3.2‐MeV) H−‐beam. For the transverse phase‐space characterization measurements, a slit and collector device samples of the x−x’ and y−y’ phase space, to determine the transverse emittance and Courant–Snyder parameters. The longitudinal phase‐space data are acquired by a laser neutralization technique developed at Los Alamos know as the laser induced neutralization diagnostics approach (LINDA). The transverse and longitudinal phase‐space centroids of the low‐energy, 425‐MHz‐bunched beam are directly measured using the microstrip probe systems. Beam current and transmission are measured by various toroid systems. Beam‐loss‐detection techniques have just been installed and a non‐interceptive beam‐profile measurement has been commissioned. All of these measurement sys...

Stability requirements of rf-linac-driven free-electron lasers

Abstract Fluctuations in the output power and wavelength have been observed in two high-power, rf-driven free-electron lasers (FELs): (1) the 10 μm FEL that has operted at the Los Alamos National Laboratory and (2) the visible FEL at the Boeing Physical Sciences Research Center. The fluctuations have been traced primarily to instabilities in the electron beam. Specifically, these are variations in the electron energy, the charge per micropulse and the time interval between micropulses. The effects of these instabilities on the performance of one of the FELs is demonstrated. Efforts made to minimize these instabilities are discussed and the subsequent improvements in the operation of each of the FELs are presented.

LEDA beam diagnostics instrumentation: Measurement comparisons and operational experience

The Low Energy Demonstration Accelerator (LEDA) facility has been used to characterize the pulsed- and cw-beam performance of a 6.7 MeV, 100 mA radio frequency quadrupole (RFQ). Diagnostic instrumentation, primarily located in a short beam transport downstream of the RFQ, allow facility commissioners and operators to measure and monitor the RFQ’s accelerated and total beam transmission, beam loss, bunched beam current, beam energy and output phase, and beam position. Transverse beam profile measurements are acquired under both low and high duty-factor pulsed beam conditions using a slow wire scanner and a camera that images beam-induced fluorescence. The wire scanner is also used to acquire transverse beam emittance information using a technique known as a “quad scan”. This paper reviews the measurement performance and discusses the resulting data.The present configuration of the Low-Energy Demonstration Accelerator (LEDA) consists of a 75-keV proton injector, a 6.7-MeV 350-MHz cw radio-frequency quadrupole (RFQ) with associated high-power and lowlevel rf systems, a 52-magnet periodic lattice followed by a short high-energy beam transport (HEBT) and highpower (670-kW cw) beam stop. The rms beam emittance was measured prior to the installation of the 52-magnet lattice, based on wire-scanner measurements of the beam profile at a single location in the HEBT. New measurements with additional diagnostic hardware have been performed to determine the rms transverse beam properties of the beam at the output of the 6.7-MeV LEDA RFQ. The 52-magnet periodic lattice also includes ten beam position monitors (BPMs) evenly spaced in pairs of two. The BPMs provide a measure of the bunched beam current that exhibits nulls at different locations in the lattice. Model predictions of the locations of the nulls and the strength of the bunched beam current are made to determine what information this data can provide regarding the longitudinal beam emittance.

Wire-scanner design for the SNS superconducting-RF linac

The requirement for profile measurements in the SNS superconducting-RF (SRF) linac has presented diagnostic designers with unusual challenges. In addition to making accurate measurements of a high-brightness H/sup -/ beam, the device must be compatible with 10/sup -10/ Torr vacuum requirements. Also, it cannot impact reliability of the nearby superconducting structures, either by failure modes, by introducing particulate matter, by vaporization, or by producing excessive radiation levels. We have designed a device to meet these stringent requirements by using a lever-action mechanism and a formed bellows that provide a clean interface and keep all moving joints outside the vacuum. Both tungsten and niobium wires are suitable, but thermal properties and charge collection are important issues that are considered. The prototype currently being fabricated will be used to verify vacuum and reliability performance.

BPM ANALOG FRONT-END ELECTRONICS BASED ON THE AD8307 LOG AMPLIFIER

Beam position monitor (BPM) signal-processing electronics utilizing the Analog Devices AD8307 logarithmic amplifier has been developed for the Low Energy Demonstration Accelerator (LEDA), part of the Accelerator Production of Tritium (APT) project at Los Alamos. The low-pass filtered 350 MHz fundamental signal from each of the four microstrip electrodes in a BPM is “detected” by an AD8307 log amp, amplified and scaled to accommodate the 0 to +5 V input of an analog-to-digital (A/D) converter. The resultant four digitized signals represent a linear power relationship to the electrode signals, which are in turn related to beam current and position. As the AD8307 has a potential dynamic range of approximately 92 dB, much attention must be given to noise reduction, sources of which can be digital signals on the same board, power supplies, inter-channel coupling, stray RF and others. This paper will describe the operational experience of this particular analog front-end electronic circuit design.

LEDA beam diagnostics instrumentation: Beam position monitors

The Low Energy Demonstration Accelerator (LEDA) facility located at Los Alamos National Laboratory (LANL) accelerates protons to an energy of 6.7-MeV and current of 100-mA operating in either a pulsed or cw mode. Of key importance to the commissioning and operations effort is the Beam Position Monitor system (BPM). The LEDA BPM system uses five micro-stripline beam position monitors processed by log ratio processing electronics with data acquisition via a series of custom TMS32OC40 Digital Signal Processing (DSP) boards. Of special interest to this paper is the operation of the system, the log ratio processing, and the system calibration technique. This paper will also cover the DSP system operations and their interaction with the main accelerator control system.

The los Alamos Proton Storage Ring Fast-Extraction Kicker System

We describe the kicker system used by the Los Alamos Proton Storage Ring1 (PSR) for fast extraction of accumulated 800-MeV proton beam. The system has several severe constraints in terms of rise time, field quality, and magnet dimensions. These are, in turn, defined by characteristics of the stored beam, ring lattice, and the allowable activation of ring components. Design methods to meet the constraints are outlined here and we describe the novel modulators that produce the fast pulses required.

Space-based FPGA radio receiver design, debug, and development of a radiation-tolerant computing system

Los Alamos has recently completed the latest in a series of Reconfigurable Software Radios, which incorporates several key innovations in both hardware design and algorithms. Due to our focus on satellite applications, each design must extract the best size, weight, and power performance possible from the ensemble of Commodity Off-the-Shelf (COTS) parts available at the time of design. A large component of our work lies in determining if a given part will survive in space and how it will fail under various space radiation conditions. Using two Xilinx Virtex 4 FPGAs, we have achieved 1 TeraOps/second signal processing on a 1920 Megabit/second datastream. This processing capability enables very advanced algorithms such as our wideband RF compression scheme to operate at the source, allowing bandwidth-constrained applications to deliver previously unattainable performance. This paper will discuss the design of the payload, making electronics survivable in the radiation of space, and techniques for debug.