This article discusses small molecule elimination from group IVB (Ti, Zr, Hf) amido complexes. An ab initio quantum chemical analysis of HX (X = H, CH₃, Cl, NH₂, SiH₃) elimination by group IVB (Ti, Zr, Hf) amidos (H₂(X)M - NH₂ → H₂M = NH + HX), of interest in the context of CVD precursor design, is reported.

Article on an investigation of the gas-phase kinetics of the reaction K + SO₂ + Ar.

We are developing CMOS circuits for readout of interpolating cathode strip and pad chambers for the GEM experiment at the SSC. Because these detectors require position resolution of about 1% of the strip pitch, the electronic noise level must be less than 2000 electrons. Several test chips have been fabricated to demonstrate the feasibility of achieving the combination of low noise, speed, and wide dynamic range in CMOS. Results to date show satisfactory noise and linearity performance. Future development will concentrate on radiation-hardening the central tracker ASIC design, optimizing the shaper peaking time and noise contribution, providing more user-configurable output options, and packaging and test issues.

With statistical analysis of global data from one, two and four stellarators, it is possible to draw limited conclusions whether Gyro- Bohm or Bohm scaling prevails. Either scaling may be favored, depending on whether corrections are included for possible {Beta} and v{sub *} corrections and whether all data are taken, or selected cases with low collisionality, or low net toroidal current, or with ECH heating applied, and so on. Monte Carlo-like simulations are used to test reliability of inferences about power-law scaling exponents made from data having substantial statistical variance and collinearity of control parameters. These show that for reliable conclusions, statistical studies should be augmented; more directed experimental studies are needed, with well controlled discharges and radially resolved data - such as those already begun on ATF and W7-AS.

We analyze some consequences of grand unification of the third-generation Yukawa couplings, in the context of the minimal supersymmetric standard model. We address two issues: the prediction of the top quark mass, and the generation of the top-bottom mass hierarchy through a hierarchy of Higgs vacuum expectation values. The top mass is strongly dependent on a certain ratio of superpartner masses. And the VEV hierarchy always entails some tuning of the GUT-scale parameters. We study the RG equations and their semi-analytic solutions, which exhibit several interesting features, such as a focusing effect for a large Yukawa coupling in the limit of certain symmetries and a correlation between the A terms (which contribute to b {yields} s{gamma}) and the gaugino masses. This study shows that non-universal soft-SUSY-breaking masses are favored (in particular for splitting the Higgs-doublets via D-terms and for allowing more natural scenarios of symmetry breaking), and hints at features desired in Yukawa-unified models. Several phenomenological implications are also revealed.

After the achievement of the SSCL`s Congressionally Mandated milestone, the Accelerator System String Test (ASST) half cell under went a series of power tests. These tests involved quenches induced in various configurations and in power levels up to the maximum operation point. These tests have produced data which has defined various parameters and requirements for the individual elements and system.

The Accelerator Systems String Test (ASST) R&D Testing Facility has been established at the SSC Laboratory to test Collider and High Energy Booster (HEB) superconducting magnet strings. The facility is operational and has had two testing periods utilizing a half cell of collider prototypical magnets with the associated spool pieces and support systems. This paper presents a description of the testing capabilities of the facility with respect to components and supporting subsystems (cryogenic, power, quench protection, controls and instrumentation), the planned testing program for the collider magnets.

The SSCL collider arc and high energy booster corrector magnets are 50 mm bore cryogenic magnets. The integral strength and harmonics will be measured by industry at full current at 4.2 K and at plus and minus 400 mA at room temperature. Dipoles, quadrupoles, and sextupoles have error tolerances of a few tens of units. A prototype harmonic analysis system for magnetic measurements of production and prototype dipole, quadrupole and sextupole magnets has been designed and is being fabricated. We describe the criteria for search coil designs, data acquisition system hardware and software. Radial search coil arrays are being fabricated utilizing multifilar wire. Two digital integrators will allow simultaneous accumulation of unbucked and bucked configurations.

In order to achieve the required injection momentum, the Superconducting Super Collider (SSC) has an accelerator chain comprised of a Linear Accelerator and three synchrotrons. The Low Energy Booster (LEB) is the first synchrotron in this chain. The LEB project has made significant progress in the development of major subsystems and conventional construction. This paper briefly reviews the performance requirements of the LEB and describes significant achievements in each of the major subsystem areas. Highlighted among these achievements are the LEB foreign collaborations with the Budker Institute of Nuclear Physics (BINP) located in Novosibirsk, Russia.

The CEBAF accelerator requires accurate phasing of the 338 superconducting cavities to achieve the design rms energy spread of 2.5 X 10{sup {minus}5}. The rms phase error along each linac, with 160 cavities over a length of 200 m, may not exceed 2.6 degrees, assuming that the whole linac is operated on crest. The common procedure is to maximize the energy gain with a spectrometer. At CEBAF, however, phase-dependent cavity steering effects cause deflections of the beam of several mrad, requiring steering corrections in the linac, which makes this method very time consuming. Beam-induced transients can also be used in pulsed operation to determine the zero-energy-gain phase with high accuracy. Better than 2 degrees accuracy is achieved when the signal-to-noise ratio is improved by signal averaging. These and other approaches for the phasing of cavities are compared and accuracy and feasibility are discussed.

The quench in a magnet describes a process which occurs while the superconductivity state goes to the normal resistive state. The consequence of a quench is the conversion of the stored electromagnetic energy into heat. During this process the initiating point will reach a high temperature, which will char the insulation or melt the conductor and thereby destroy the magnet. To prevent the magnet from being lost, it is standard practice to observe several resistance and/or inductance voltages across the magnet as quench signatures -- detection. When a quench symptom is detected, protection operations are initiated: proper shutdown of the magnet excitation systems and treatment to dilute the heat energy at a spot -- protection. The temperature rise is diluted by firing heaters along the length of the magnet to insure that the dissipated energy is spread. To develop a reliable quench detection system, two distinct approaches have been tried in the past: (i) Understanding of the Noise Mechanism and Sub-system Optimization, and (ii) Escaping from the Known Electromagnetic Noises by Observing Optical Waves or Acoustic Waves. The MTL of SSCL confronts a mass-measurement of about 10,000 production magnets. To meet the testing schedule, the false quench detection rate needs …

The CEBAF beam can burn through the vacuum wall in approximately 100 {mu}s. The authors have developed an inexpensive beam loss sensor that will unambiguously detect a true beam loss and shut off the beam within this time without tripping on moderate interference from other sources. They have incorporated a full system test into the system, with provision for direct replacement of faulty sensors without adjustment. They describe the sensors, the signal processing design, system test results, and characterization procedures.

Industrial Computerized Tomography has been applied to magnet components in various stages of the manufacturing process. These Computerized Tomographic images can be analyzed to infer detailed dimensional information about magnet component positions (conductor, wedges, collars, etc.) throughout the magnet manufacturing process (cable winding, collaring, yoked/skinned). An analysis technique will be presented and measurement accuracies will be discussed.

Results of the initial beam tests and early operation of the CEBAF recirculation beam transport system are presented.

The first three quarters of the first CEBAF arc have been instrumented with beam position monitors. Thirty-seven monitors (of 450) have been installed and their noise measured. Resolution of 100 mu-m was obtained at the lowest operating current of 1 mu-A. The update time of the system is 1 sec, limited by computer interfacing with a potential bandwidth of greater than 10 kHz.

Data analysis for the TTR requires integrating a large number of muon chamber technologies, each with different requirements, into a single analysis chain. Many of these technologies come with their own software, which have different conventions; these packages are grafted on. Data are stored on a tape robot with essential information stored in a database where it may be queried. Operation is done from special-purpose X{trademark} windows designed to facilitate data selection and its subsequent analysis. Program development was done using the Hewlett-Packard Softbench{trademark} product.

This report gives a brief description of the major electrical technical equipment used in the Superconducting Super Collider accelerators systems and the present laboratory plans for the acquisition of the equipment.

At CEBAF, 676 Higher-Order-Mode (HOM) loads are being installed, within the beam vacuum at 2 K, to damp HOM's that affect the stability of the recirculating electron beam. In this paper, the requirements imposed on the loads and the microwave absorbing material comprising them are discussed together with an analysis of their performance and effect on some relevant modes.

The CEBAF injector chopping system must generate three interleaved 499 MHz pulse trains of independently variable current from a DC input beam prior to axial compression. The chopper consists of two deflection cavities with an aperture midway between them. Lenses flanking the aperture focus the beam from the first cavity into the center of the second, where the RF deflection from the first cavity is removed. The symmetry of the RF energy spread across any time-slice of the beam is dominantly odd. The inverting optics used to focus the beam into the second cavity causes near cancellation of the energy spread from the two cavities. We present experimental measurements of the energy spread effects from a fundamental frequency (1497 MHz) chopper prototype producing a beam of suitable transverse emittance and energy spread, and discuss the expected performance of the subharmonic chopper system to be used for commissioning starting in January 1994.

CEBAF has recently performed automated beam orbit control in real time. This effort was achieved by exploiting the capabilities of the TACL control system, using the newly implemented STAR network, which easily yielded the required data transfer density needed. Also involved in this effort was the On-Line Envelope code OLE, which provided first-order transfer matrices that reflected the current machine optics. These tools made the implementation of the specific orbit-correction algorithms easier and increased reliability. The implemented algorithms include beamthreading, orbit-locks with 2 correctors/2 monitors, most-effective corrector, and eta-corrector/eta-monitor correction.

When complete, the Continuous Electron Beam Accelerator Facility will house a 4 GeV recirculating linear accelerator containing 42 1/4 cryomodules arrayed in two antiparallel linacs and an injector. Currently, over half of the cryomodules have been installed. Each cryomodule contains eight superconducting niobium 5-cell rf cavities that operate at 1.497 GHz [1]. A cryomodule must provide an energy gain of 20 MeV to the 200 mu-A beam [2]. The resultant dynamic heat load must be less than 45 W. The cavity parameters that are measured during the commissioning process include the external Q's of the cavity ports, the unloaded Q (Q{sub 0}) of the cavity as a function of accelerating gradient, and the maximum operating gradient of the cavity. The sensitivity of the resonant frequency to changes in pressure and gradient is also measured. Finally, the mechanical tuners are cycled and characterized. In all cases, the performance of CEBAF cryomodules has exceeded the design requirements. A portable test stand allows local control of the rf system and provides automated data acquisition. This paper describes the cryomodule commissioning hardware, software, and measurements.

The superconducting RF, CW CEBAF accelerator will use a pair of antiparallel 400 MeV linacs connected by recirculation arcs for nominal 4 GeV in five passes. Single-pass, high power testing of the first linac has been conducted during the months preceding the conference. The RF control system [1] has been designed to control cavity gradient and phase under a wide range of gradients and significant beam loading. At full beam current, accelerating gradient is approximately equal to accelerating voltage in the superconducting RF cavities. Even though the beam current during the high power testing is one-fifth of the full current, beam loading is substantial. Operational experience of the response of the RF system is presented. A tuning algorithm which compensates for beam loading effects has been developed and tested. Heavy beam loading, corresponding to five-pass operation, was studied by increasing the loaded Q of the cavities. A current modulation experiment addressed the issue of energy spread increase due to current fluctuations, and the effect of by-passed cavities on beam properties was investigated.

The CEBAF accelerator is designed in a multipass racetrack configuration, with two 1497 MHz linear accelerator sections joined by independent magnetic transport arcs. Room temperature subharmonic rf separator cavities will be used on each independent arc to extract a portion of the recirculating beam, and one additional cavity will be used to divide the final full-energy beam between CEBAF's three experimental end stations. A single-cell prototype cavity has already been built and tested a low power levels. The next stage of the design process is the construction of a cavity capable of operation at full power, i.e. at a gradient sufficient to provide the required mu-rad bend to a 6 GeV beam. The paper will discuss both the electrical and mechanical design of the cavity, construction techniques employed, and preliminary test results.

This paper discusses the various software used in the analysis of beam viewer images at CEBAF. This software, developed at CEBAF, includes a three-dimensional viewscreen calibration code which takes into account such factors as multiple camera/viewscreen rotations and perspective imaging, and maintaining a calibration database for each unit. Additional software allows single button beam spot detection, with determination of beam location, width, and quality, in less than three seconds. Software has also been implemented to assist in the determination of proper chopper RF control parameters from digitized chopper circles, providing excellent results.