ORNL, Oak Ridge, Tennessee
The Spallation Neutron Source accelerator systems are designed to deliver a 1.0 GeV, 1.4 MW proton beam to a liquid mercury target for neutron scattering research. The accelerator complex consists of an H- injector, capable of producing one-ms-long pulses at 60 Hz repetition rate with 38 mA peak current; a 1 GeV linear accelerator; an accumulator ring; and associated transport lines. The accelerator systems are equipped with a variety of beam diagnostics, which played important roles during beam commissioning. They are used for accelerator tuning and monitoring beam status during production runs. This talk will give an overview of our experience with the major SNS beam diagnostics systems.
ORNL, Oak Ridge, Tennessee
A new Target Imaging System (TIS) has been installed to directly measure the size and position of the proton beam on the Spallation Neutron Source (SNS) mercury target. The proton beam passing through a luminescent coating on the target nose produces light that is transported via a radiation-tolerant optical system to an image acquisition system integrated with the accelerator controls network. This paper describes the software that acquires and analyzes the image, the integration of the system with the SNS control system, and a comparison of the TIS results with the indirect methods of calculating the peak densities of the proton beam.
NSTec, Los Alamos, New Mexico
LANL, Los Alamos, New Mexico
An optical diagnostic instrument developed for the acquisition of high-speed time-resolved images has been fielded at the Dual-Axis Radiographic Hydrodynamic Test (DARHT) Facility at Los Alamos National Laboratory. The instrument was developed for the creation of time histories of electron-beam cross-section through the collection of Cerenkov light. This is accomplished through four optical lines of sight that optically collapse an image, an optical fiber relay, recording instruments, and a tomographic reconstruction algorithm. The instrument may be operated, adjusted, and calibrated remotely due to potential adverse environmental conditions. The instrument was operated over the course of various activities during and after DARHT commissioning, and tomographic reconstructions reported verifiable beam characteristics. Results from the collected data and reconstructions and analysis of the data are discussed.
LANL, Los Alamos, New Mexico
The primary goal of this newly installed beam profile measurement is to provide the facility operators and physicists with a reliable horizontal and vertical projected beam distribution and location with respect to the proton beam target and beam aperture. During a 3000-hour annual run cycle, 5 microcoulombs of charge is delivered every 50 milliseconds through this harp to the downstream 1L target. The resulting radioactive annual dose near this harp is at least 600 MRads. Because of this harsh environment, the new harp design has been further optimized for robustness. For example, compared to an earlier design, this harp has half of the sensing wires and utilizes only a single bias plane. The sensing fibers consist of a 0.078-mm diameter SiC fiber. To hold these fibers to a rigid ceramic structure, a “collet” fiber-clamping device accomplishes the three goals of maintaining a mechanical fiber clamp, holding the sense fiber under a slight tensile force, and providing a sensing fiber electrical connection. This paper describes the harp analysis and design, and provides fabrication, assembly, and installation information, and shows how facility wiring was altered.
LANL, Los Alamos, New Mexico
This study evaluates a technique for the closed-loop position and velocity control of a wire scanner actuator. The focus of this technique is to drive a stepper motor-driven actuator through a 1-mm move using a combination of velocity feedback control and position feedback control. More specifically, the velocity feedback control will be utilized to provide a smooth motion as the controller drives the actuator through a pre-planned motion profile. Once the controller has positioned the actuator within a certain distance of the target position, the controller will transition to position-based feedback control, bringing the actuator to its target position and completing the move. Position and velocity data is presented detailing how the actuator performed relative to its commanded movement. Finally, the layout of, and algorithms employed by the wire scanner control system are presented.
GSI, Darmstadt
Technical University Darmstadt, Darmstadt
TU Darmstadt, Darmstadt
Scintillating screens are widely used for transverse beam profile monitoring and pepper-pot emittance measuring instruments at accelerator facilities. For high current beam operations at the GSI heavy ion UNILAC, several inorganic scintillators were investigated under different ion beam conditions in the energy range from 4.8 to 11.4 MeV/u and currents up to some mA. The imaging properties of various scintillating screens were studied with respect to light yield and imaged beam width, i.e. important parameters for precise beam profile measurements. The measured light yield and beam width show a strong dependence on the scintillating material and change significantly with screen temperature. The spectral response of the materials was mapped for different temperature levels, using a spectrometer in the visible and near UV range. The results clearly demonstrate that the scintillating properties of the materials, and their temperature, are critical issues for high current operations and have to be taken into account for correct beam profile reading.
ANL, Argonne
LBNL, Berkeley, California
Time-correlated single-photon counting (TCSPC) techniques have been used for bunch purity measurement since the Advanced Photon Source started operations. Over the past three years, improvements made in the monitor have increased the signal-to-noise ratio and dynamic range to above 10 billion. Recently, improvements of the timing resolution of TCSPC to < 50 ps FWHM allowed us to measure the longitudinal profile of individual bunches in the APS storage ring. The profile monitor uses a visible-light single-photon avalanche photodiode (SPAD) and a PicoHarp 300 TCSPC unit. Due to its robustness, the system operates continuously and measures the average longitudinal profile of the stored beam, updating the process variables for bunch phases and bunch lengths in intervals less than 30 seconds. In a third application, using a TCSPC x-ray detector with an x-ray wire scanner in the monochromatic beam of the diagnostics undulator, measurements of transverse profiles of individual bunches can be completed in less than 30 minutes. Since the beam sizes and phases are dependent on the bunch charge, these online tools will provide users with valuable information performing timing experiments.
CERN, Geneva
The LHC Beam Loss Monitoring (BLM) system is one of the most complex instrumentation systems deployed in the LHC. In addition to protecting the collider, the system also needs to provide a means of diagnosing machine faults and deliver feedback of losses to the control room as well as to several systems for their setup and analysis. It has to transmit and process signals from over 4,000 monitors, and has nearly 3 million configurable parameters. In a system of such complexity, firmware reliability is a critical issue. The integrity of the signal chain of the LHC BLM system and its ability to correctly detect unwanted scenarios and thus provide the required protection level must be ensured. In order to analyze the reliability and functionality, a test bench has been developed that emulates different types of loss signals and monitors the performance and response of the FPGA-based data analysis firmware. This paper will report on the numerous tests that have been performed and on how the results are used to quantify the reliability of the system.
LBNL, Berkeley, California
Laboratory high energy density experiments using ion beam drivers rely upon the delivery of high-current, high-brightness ion beams with high peak intensity onto planar targets. Solid-state optical scintillators are typically used to measure the ion beam spatial profile but they display dose-dependent degradation and aging effects. These effects produce uncertainties and limit the accuracy of measuring peak beam intensities delivered to the target. For beam tuning and benchmarking the incident beam intensity, we have developed a cross-calibrating diagnostic suite that both places a lower limit on intensity and extends the upper limit of measurable peak intensity dynamic range. Absolute intensity calibration is obtained with a 3 um thick tungsten foil calorimeter. We present experimental evidence for peak intensity measures in excess of 200 kW/cm2 using a 300 kV, 25 mA, 5-20 usec K+ beam driver. Radiative models and thermal diffusion effects are discussed as they affect temporal and spatial resolution of beam intensity profiles.
UMD, College Park, Maryland
MPI-K, Heidelberg
Cockcroft Institute, Warrington, Cheshire
We have developed a technique that employs a digital micro-mirror array to produce an image of the halo of an electron beam with enhanced dynamic range. Light produced by the beam intercepting a phosphor screen is first imaged onto the array; an adaptive mask is created and applied to filter out the beam core; and the result is reimaged onto an intensified CCD camera. We describe the optics used, the masking operation and preliminary results of experiments we have performed to study beam halo at the University of Maryland Electron Ring (UMER).