[en] The results of recent neutron scattering measurements of the energies and linewidths of long-wavelength acoustic-phonon modes in PbF₂ at temperatures between 10 and 898 K are described, and then interpreted in terms of theoretical expressions for the effects of anharmonicity, the hopping motion of the anions, and the time-averaged defect structure. The dynamical properties of PbF₂ are of particular interest, since this compound exhibits a diffuse specific heat anomaly and a rapid increase in ionic conductivity due to a dynamic disorder of the anion sublattice at a temperature Tsub(c) approximately 700 K, which is well below its melting point Tsub(m) = 1100 K. The neutron data show that the elastic constants decrease linearly with temperature as Tsub(c) is approached from below, but decrease more rapidly in the vicinity of Tsub(c). This is particularly marked for C₁₁ which halves in value between 600 K and 800 K. At 570 K and above, the linewidths of transverse acoustic phonons increase as the square of the phonon wavevector, approximately independently of direction, implying that the measurements are in the hydrodynamic regime. The widths vary linearly with temperature below Tsub(c) but increase rapidly in the region of Tsub(c). Theoretical considerations show that the low-temperature behaviour is consistent with the effects of anharmonicity and that the rapid change in linewidth near Tsub(c) is attributable to the effects of defects in the lattice. Anion hopping contributes only slightly to the linewidth. (author)

[en] Free-electron laser (FEL) amplifiers have demonstrated high efficiencies and high output power at microwave wavelengths. However, measurements and simulations have indicated that the present level of phase stability for these devices is not sufficient for driving linear accelerators. Fluctuations in the diode voltage, which is needed to accelerate the electron beam, are the largest cause of the shifts in the phase of the output power. Pulse-power technology cannot keep the voltage fluctuations less than 1/4%. However, we have found a scheme that will make the output phase much less sensitive to these fluctuations by exploiting the traveling wave nature of the FEL interaction. In this paper we study the phase stability issue by analyzing the dispersion relation for an axial FEL, in which the rf field is transversely wiggled and the electron trajectories are purely longitudinal. The advantage of using the axial FEL interaction instead of the common transverse FEL interaction is that (1) the dispersion relation is not additionally complicated by how the transverse electron motion depends on the diode voltage and (2) such a device is simpler and less expensive to construct than a transverse-coupling FEL because there is no wiggler. The axial FEL interaction is with a fast wave and does involve axial bunching of the electron beam, so the results found for this device also apply to transverse-coupling FELs. By examination of the dispersion relation it is found that the effect of the phase dependency on the beam's velocity can be cancelled by the effect of the phase dependency on the beam's plasma wave, for an annular electron beam. By changing the annulus radius, exact cancellation can be found for a variety of beam voltages and currents in the ranges of 0.5-1.0 MV and 1-5 kA. This cancellation leads to first-order phase stability, which is not possible for standing-wave devices, such as klystrons

[en] The Central Detector of the UA1 experiment at the CERN pp Collider underwent a first physics run at the end of 1981. The detector consists of a large drift chamber assembly (25 m³, about 6000 sense wires). An electronics readout with multi-hit capability simultaneously digitizes the time and the analog information used for charge division and energy measurement. The initial performance of the readout and control system will also be presented. The detector was tested in two cosmic ray runs, and is now fully operational for the second physics run; this started at the beginning of October 1982

[en] A 1 μs pulse-length, high-current relativistic klystron is being developed with a desired peak output power of 1 GW at 1.3 GHz. The tube consists of an input cavity, a single idler cavity, and an output cavity. Power levels as high as 475 MW have been experimentally observed. Current experimental results are presented. Physics and engineering issues affecting klystron performance are discussed

[en] The upgraded UA1 experiment utilizes twelve 3081/E emulators for its third-level trigger system. The system is interfaced to VME, and is controlled by 68000 microprocessor VME boards on the input and output. The output controller communicates with an IBM 9375 mainframe via the CERN-IBM developed VICI interface. The events selected by the emulators are output on IBM-3480 cassettes. The usder interface to this system is based on a series of Macintosh personal computers connected to the VME bus. These Macs are also used for developing software for the emulators and for monitoring the entire system. The same configuration has also been used for offline event reconstruction. A description of the system, together with details of both the online and offline modes of operation and an evaluation of its performance are presented. (orig.)

[en] Currently ongoing at Los Alamos National Laboratory is a program to develop high-power, planar 100-300 GHz traveling-wave tubes. An enabling technology for this effort is a sheet electron beam source and much of our effort has been geared toward understanding sheet beam generation and transport. Toward this end we have developed a robust, high resolution optical diagnostic for measuring the transverse density profiles of our electron beams. The diagnostic consists of a thin metal foil followed by an YAG:Ce or YAP:Ce scintillator crystal, both mounted on a vacuum actuator that allows us to position the foil/scintillator combination at arbitrary positions along the beam's longitudinal axis. The electron beam strikes the metal foil and is stopped, generating Bremsstrahlung x rays that are imaged by the scintillator crystal. This image is then captured by an optical system using a high-speed, intensified gated camera. Using this diagnostic, we have measured beam profiles with resolutions as low as 0.05 mm from a 0.51 μP electron gun operated between 20 and 120 kV

[en] As a new application of the Fermilab ECL-CAMAC logic modules, a fast trigger processor was developed for Fermilab experiment E-537, aiming to measure the high mass di-muon production by antiprotons. The processor matches the hit information received from drift chambers and scintillation counters, to find candidate muon tracks and determine their directions and momenta. The found tracks are then paired to compute and invariant mass: when the computed mass falls within the desired range, the event is accepted. The whole process is accomplished in times of the order of 5 to 10 microseconds, while achieving a trigger rate reduction of up to a factor of ten. (orig.)

[en] An upgrade of the Beam Position Monitor (BPM) signal processing and data acquisition system for the Fermilab Main Injector is described. The Main Injector is a fast cycling synchrotron that accelerates protons or antiprotons from 8 to 150 GeV. Each Main Injector cycle can have a totally different magnet ramp, RF frequency configuration, beam bunch structure, and injection/extraction pattern from the previous cycle. The new BPM system provides the capabilities and flexibility required by the dynamic and complex machine operations. The system offers measurement capability in the 2.5 MHz and 53 MHz channels to detect the range of bunch structures for protons and antiprotons in both wideband (turn-by-turn) and narrowband (closed-orbit) modes. The new BPM read-out system is based on the digital receiver concept and is highly configurable, allowing the signal processing of nearly all Main Injector beam conditions, including the detection of individual batches. An overview of the BPM system in the Main Injector operating environment, some technology details and first beam measurements are presented

[en] An upgrade of the Beam Position Monitor (BPM) signal processing and data acquisition system for the Fermilab Main Injector is described. The Main Injector is a fast cycling synchrotron that accelerates protons or antiprotons from 8 to 150 GeV, Each Main Injector cycle can have a totally different magnet ramp, RF frequency configuration, beam bunch structure, and injection/extraction pattern from the previous cycle. The new BPM system provides the capabilities and flexibility required by the dynamic and complex machine operations. The system offers measurement capability in the 2.5 MHz and 53 MHz channels to detect the range of bunch structures for protons and antiprotons in both wideband (turn-by-turn) and narrowband (closed-orbit) modes. The new BPM read-out system is based on the digital receiver concept and is highly configurable, allowing the signal processing of nearly all Main Injector beam conditions, including the detection of individual batches. An overview of the BPM system in the Main Injector operating environment, some technology details and first beam measurements are presented

[en] We report results from recent 2.1 GHz superconducting radio frequency (SRF) photonic band gap (PBG) resonator experiments at Los Alamos. Two 2.1 GHz PBG cells with elliptical rods were fabricated and tested at high power in a liquid helium bath at the temperatures of 4 K and below 2 K. The described SRF PBG cells were designed with a particular emphasis on changing the shape of the PBG rods to reduce peak surface magnetic fields and at the same time to preserve its effectiveness at damping higher-order-modes. The superconducting PBG cavities have great potential for damping long-range wakefields in SRF accelerator structures without affecting the fundamental accelerating mode. The cells performed in accordance with simulation's predictions and the maximum achieved accelerating gradient was 18.3 MV/m. This represents a 30% increase over gradients previously demonstrated in superconducting PBG cavities with round rods.