Techniques for intense-proton-beam profile measurements

In a collaborative effort with industry and several national laboratories, the Accelerator Production of Tritium (APT) facility and the Spallation Neutron Source (SNS) linac are presently being designed and developed at Los Alamos National Laboratory (LANL). The APT facility is planned to accelerate a 100-mA H{sup +} cw beam to 1.7 GeV and the SNS linac is planned to accelerate a 1- to 4-mA-average, H{sup {minus}}, pulsed-beam to 1 GeV. With typical rms beam widths of 1- to 3-mm throughout much of these accelerators, the maximum average-power densities of these beams are expected to be approximately 30- and 1-MW-per-square millimeter, respectively. Such power densities are too large to use standard interceptive techniques typically used for acquisition of beam profile information. This paper summarizes the specific requirements for the beam profile measurements to be used in the APT, SNS, and the Low Energy Development Accelerator (LEDA)--a facility to verify the operation of the first 20-MeV section of APT. This paper also discusses the variety of profile measurement choices discussed at a recent high-average-current beam profile workshop held in Santa Fe, NM, and will present the present state of the design for the beam profile measurements planned for APT, SNS, and LEDA

Comparison of beam-position-transfer functions using circular beam-position monitors

A cylindrical beam-position monitor (BPM) used in many accelerator facilities has four electrodes on which beam-image currents induce bunched-beam signals. These probe-electrode signals are geometrically configured to provide beam-position information about two orthogonal axes. An electronic processor performs a mathematical transfer function (TF) on these BPM-electrode signals to produce output signals whose time-varying amplitude is proportional to the beam`s vertical and horizontal position. This paper will compare various beam-position TFs using both pencil beams and will further discuss how diffuse beams interact with some of these TFs

Phase and synchronous detector theory as applied to beam position and intensity measurements

A popular signal processing technique for beam position measurements uses the principle of amplitude-to-phase (AM/PM) conversion and phase detection. This technique processes position-sensitive beam-image-current probe-signals into output signals that are proportional to the beam`s position. These same probe signals may be summed and processed in a different fashion to provide output signals that are proportional to the peak beam current which is typically referred to as beam intensity. This paper derives the transfer functions for the AM/PM beam position and peak beam current processors

FMIT diagnostic instrumentation

The Fusion Materials Irradiation Test facility (FMIT) cw prototype accelerator has noninterceptive beamline instrumentation to measure beam parameters. The transverse emittances and beam profiles are measured with an array of photodiode sensors viewing light emitted from the beam region. Tomographic reconstructions of both spatial-density distributions and of transverse-emittance distributions are performed throughout a quadrupole focusing section. Beam bunches passing through capacitive probes produce bipolar waveforms whose zero crossing corresponds to the bunch's longitudinal centroid. By measuring the time required for a bunch to travel the known distance between two probes, velocity and energy are determined. A toroidal transformer measures the average ac beam current. Beam spill is measured by a set of movable jaws that intercept the beam edges. Each jaw contains a water flow channel whose flow rate and differential temperature are measured to derive a transverse power distribution. Beam centroid position is measured by a four-lobe, magnetic-loop pickup. 5 refs., 6 figs

ANALOG FRONT-END ELECTRONICS FOR BEAM POSITION MEASUREMENT ON THE BEAM HALO MEASUREMENT

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

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

AUTOMATED CONTROL AND REAL-TIME DATA PROCESSING OF WIRE SCANNER/HALO SCRAPER MEASUREMENTS

The Low-Energy Demonstration Accelerator (LEDA), assembled and operating at Los Alamos National Laboratory, provides the platform for obtaining measurements of high-power proton beam-halo formation. Control system software and hardware have been integrated and customized to enable the production of real-time beam-halo profiles. The Experimental Physics and Industrial Control System (EPICS) hosted on a VXI platform, Interactive Data Language (IDL) programs hosted on UNIX platforms, and LabVIEW (LV) Virtual Instruments hosted on a PC platform have been integrated and customized to provide real-time, synchronous motor control, data acquisition, and data analysis of data acquired through specialized DSP instrumentation. These modules communicate through EPICS Channel Access (CA) communication protocol extensions to control and manage execution flow ensuring synchronous data acquisition and real-time processing of measurement data. This paper describes the software integration and management scheme implemented to produce these real-time beam profiles

A state variable approach to the BESSY II local beam-position-feedback system

At the BESSY II facility, stability of the electron beam position and angle near insertion devices (IDs) is of utmost importance. Disturbances due to ground motion could result in unwanted broad-bandwidth beam-jitter which decreases the electron (and resultant photon) beam`s effective brightness. Therefore, feedback techniques must be used. Operating over a frequency range of 100-Hz, a local feedback system will correct these beam-trajectory errors using the four bumps around IDs. This paper reviews how the state-variable feedback approach can be applied to real-time correction of these beam position and angle errors. A frequency-domain solution showing beam jitter reduction is presented. Finally, this paper reports results of a beam-feedback test at BESSY I

Noninterceptive transverse beam diagnostics

The transverse emittance properties of a high-current linear accelerator may be measured by using TV cameras sensitive to the visible radiation emitted following beam interactions with residual gas. This paper describes the TV system being used to measure emittances for the Fusion Materials Irradiation Test (FMIT) project