The transmission coefficient of a wavepacket traversing a potential barrier can be determined by steady state calculations carried out in imaginary time instead of by real time dynamical calculations. The general argument is verified for the Eckart barrier potential by a comparison of transmission coefficients calculated from real and imaginary time solutions of the Schroedinger equation. The correspondence demonstrated here allows a formulation for the reaction rate that avoids difficulties due to both rare events and explicitly time dependent calculations. 5 refs., 2 figs.

Magnetic drift pumping on TMX-U involves driving four antennae through high Q-resonant circuits. One of the key elements in the resonant circuit is a variable inductor able to carry the 3500 amperes through the circuit and maintain its shape and inductance. The eight resonant circuits can be combined to feed the four antennae with one or two frequencies on each antenna, or frequency shift keying between two frequencies. Each resonant circuit is fed by two 10 to 30 kHz exciters capable of delivering 80 kW each to the circuit. Each exciter receives its power from its own adjustable 0 to 400 volt power supply. The entire system is controlled by a CAMAC control system over a fiber-optic link. The control system checks interlock status, controls ''On'' and ''Off'' status, calculates and adjusts phasing of the exciters for addition or deletion of the proper beat frequencies, and monitors operation. 3 refs., 5 figs.

We have installed a new diagnostic instrument to investigate ions emanating along magnetic-field lines of the TMX-U tandem-mirror experiment. This analyzer contains parallel electric and magnetic fields, which yield ion mass and energy spatial separation. A dual array of 128 copper collector plates detects particles in the ion flux that is first collimated and then focused through the 180-degree bending magnetic field. An electric field applied transverse to the bending particle path then separates the ion masses in the direction perpendicular to the magnetic-pole faces while the magnetic field spreads out the different energies of each mass in a plane parallel to the magnetic-pole tips. The CAMAC-based data recorders are fiber-optically coupled to the system controller for data acquisition, analysis, and display. A commercial CAMAC data recorder was modified for current input. We expect to measure higher particle energies than the present gridded end-loss analyzers as well as to more accurately determine the energy spectra.

Low-energy ions trapped in the thermal barrier region of the TMX-U plasma cause a potential reduction which results in increased scattering and less thermal isolation between regions of the plasma. A method of removing these ions using magnetic field perturbations at the ion drift frequency has been developed. The concepts of ''drift pumping'' and hardware development are described in this paper. 5 refs., 7 figs.

Ion Cyclotron Resonant Heating (ICRH) is part of the plasma heating system used on the TMX-U experiment. Radio frequency (RF) energy is injected into the TMX-U plasma at a frequency near the fundamental ion resonance (2 to 5 MHz). The RF fields impart high velocities to the ions in a direction perpendicular to the TMX-U magnetic field. Particle collision then converts this perpendicular heating to uniform plasma heating. This paper describes the various aspects of the ICRH system: antennas, power supplies, computer control, and data acquisition. 4 refs., 10 figs.

A scheme to generate high accelerating gradients (approximately (approx.) a few gigaelectronvolts per meter) is described. The acceleration is nonresonant so that staging may be fairly easy, and the energy source is relativistic e-beams so that a relatively high over all efficiency may be achievable.

May 1983 marked the beginning of an intensive effort to both improve the operating reliability, and improve the performance of the TMX-U Diagnostic Computer System. At that time, the system was handling (acquiring, storing, processing, plotting, displaying, and archiving) about 3 million bytes (Mb) of data per shot, with a 15-minute cycle time between shots. In addition, the system was fairly fragile, with frequent (about 5 times/day) crashes, requiring re-booting. At the present time, the system reliably handles about 5 Mb of data per shot, with a 7-minute cycle time between shots. This improvement was accomplished by a combination of new hardware, rearranging existing hardware, and new or revised software. Hardware changes were made in two areas. First, the shared disks were rearranged into different domains to make more efficient use of locking features. Second, we purchased and installed a solid-state RAM disk emulator (8 megabytes) to provide extremely fast access to lists and files that must be accessed frequently. In the software area, we made improvements in several areas. Initial effort went into finding bugs and optimizing existing code. We developed a template so that we could produce efficient code from applications that had first been developed on a …

A numerical simulation has been constructed to obtain a detailed, quantitative estimate of the electromagnetic fields and currents existing in the Advanced Test Accelerator under conditions of laser guiding. The code treats the secondary electrons by particle simulation and the beam dynamics by a time-dependent envelope model. The simulation gives a fully relativistic description of secondary electrons moving in self-consistent electromagnetic fields. The calculations are made using coordinates t, x, y, z for the electrons and t, ct-z, r for the axisymmetric electromagnetic fields and currents. Code results, showing in particular current enhancement effects, will be given.

The PPD is an instrument used to indirectly measure the potential of the center-cell plasma of TMX-U. Thallium ions are injected at energies of about 60 keV from an ion gun capable of 80 kV operation. The singly charged ions collide with plasma electrons and generate double-charged ions. Ions in the higher charge state exit the plasma and are detected in an electrostatic energy analyzer. From measurements of the injected ion energy and the output ion energy one can determine the plasma potential in the ionization region. The absolute potential measurements required careful calibrations of the energy analyzer. Hardware and techniques for calibration of the energy analyzer are discussed. 2 refs., 4 figs.

This paper describes control of gyrotron microwave energy output by modulation of gyrotron anode voltage. At present, Electron Cyclotron Resonant Heating (ECRH) uses five gyrotrons on the Tandem Mirror Experiment-Upgrade (TMX-U) for plasma heating. One is in the 10 kG region of each end plug, one at the 5 kG region of each end plug, and one is used for central-cell heating. Also described are the design and operation of the anode modulation system. The operating advantages of gyrotron anode modulation include power balance, independent control of each gyrotron, an ability to modulate microwave output power up to 50 kHz, and gyrotron tuning. The performance results of anode modulation will be discussed. 9 figs.

A set of 18 separately controlled plates have been added to each end of the Tandem Mirror Experiment Upgrade (TMX-U) vessel to allow measurement of end-wall currents and to provide a means of plasma potential control (PPC). These plates are shaped to form elliptical rings separated into quadrants. Each plate can be individually grounded, float at plasma potentials, or be actively biased to control the plasma. Voltage and current monitoring are provided for each of the plates, and the control and monitoring functions are controlled by the PPC system computer. The details of the field line mapping and the plate shapes are discussed, and the control architecture and performance are presented. 1 ref., 5 figs.

The marriage of Induction Linac technology with Nonlinear Magnetic Modulators has produced some unique capabilities. It appears possible to produce electron beams with average currents measured in amperes, at gradients exceeding 1 MeV/meter, and with power efficiencies approaching 50%. A 2 MeV, 5 kA electron accelerator has been constructed at the Lawrence Livermore National Laboratory (LLNL) to demonstrate these concepts and to provide a test facility for high brightness sources. The pulse drive for the accelerator is based on state-of-the-art magnetic pulse compressors with very high peak power capability, repetition rates exceeding a kilohertz and excellent reliability.

This paper presents a brief history of the TMX-U Titanium Sublimation Pumping process (gettering). Titanium sublimation pumps offer an economical means of pumping chemically active gases (especially hydrogen) at high speeds, and serve as additional pumps, along with liquid nitrogen-cooled panels, to provide pumping during each physics experiment. The getter wires are 85% titanium and 15% tantalum alloy. The Ti-Ta alloy is heated by the passage of current until titanium begins to evaporate. This vapor condenses on the cold surfaces surrounding it and forms an absorption layer which binds the available chemically active gas particles. Saturated layers are covered by further depositions of Ti. Each getter delivers approximately 106 amperes of regulated power for a 60-second getter cycle. In the vacuum vessel, the wires are arranged in arrays of 6, 5, and 2, each cabled to the exterior of the vessel. This alloys for the advancement of the wires. We follow a current schedule allowing a proper deposition rate which extended our average shot, per wire, to exceed 250+. This allows quality gettering in the system effectively, without raising the vessel to atmospheric pressure because of deteriorated wires. Because of the size of the system, a complex computer program was …

The use of digital signal techniques for removal of noise components present in plasma diagnostic signals is discussed, particularly with reference to diamagnetic loop signals. These signals contain noise due to power supply ripple in addition to plasma characteristics. The application of noise canceling techniques, such as adaptive noise canceling and model-based estimation, will be discussed. The use of computer codes such as SIG is described. 19 refs., 5 figs.

Due to the complexity of the Tandem Mirror Experiment-Upgrade (TMX-U) and the importance of operating time, all the subsystems must be made as reliable as possible. ECRH is such a subsystem. In order to accomplish this task with ECRH, two things were needed: (1) training in proper operation and maintenance of the system; (2) a quality control assurance program. This paper will explain how these things were implemented.

The ECRH Control System was installed on the Tandem Mirror Experiment-Upgrade (TMX-U) in 1980. The system provides approximately 1 MW of 28 GHz microwave power to the TMX-U plasma. The subsystems of ECRH that must be controlled include high-voltage charging supplies, series pass tubes, and magnet supplies. In addition to the devices that must be controlled, many interlocks must be continuously monitored. The previous control system used relay logic and analog controls to operate the system. This approach has many drawbacks such as lack of system flexibility and maintainability. In order to address these problems, it was decided to go with a CAMAC and Modicon based system that uses a Hewlett-Packard 9836C personal computer to replace the previous analog controls. 2 figs.

Obtaining detailed knowledge of the condition of the electron beam delivered to the experimental tank is of prime importance in the attempt to correlate the propagation data with theory. There are many interesting and unique features of the beam delivered by Advanced Test Accelerator (ATA) to the experimental tank.

The Mirror Fusion Test Facility (MFTF-B), under construction at LLNL, requires measurement of the neutral gas density in high magnetic fields near the plasma at several axial regions. This Background Gas Pressure (BGP) diagnostic will help us understand the role of background neutrals in particle and power balance, particularly in the maintenance of the cold halo plasma that shields the hot core plasma from the returning neutrals. It consists of several cold-cathode, magnetron-type gauges stripped of their permanent magnets, and utilizes the MFTF-B ambient B-field in strengths of 5 to 25 kG. Similar gauges have operated in TMX-U in B-fields up to 3 kG. To determine how well the gauges will perform, we assembled a test stand which operated magnetron gauges in an external, uniform magnetic field of up to 30 kG, over a pressure range of 1E-8 T to 1E-5 T, at several cathode voltages. This paper describes the test stand and presents the results of the tests.