Improvements have been made in the performance of the ETA-II accelerator that allow a nominal 2 kA, 6 MeV beam to be focused to a spot size less that 1 mm in diameter. The improvements include reducing the energy sweep to less than /spl plusmn/0.5% over 40 ns of the pulse using a real time energy diagnostic and improving the magnetic tune of the accelerator to reduce the emittance to 8 cm-mrad. Finally, an automated tuning system (MAESTRO) was run to minimize the time dependent centroid motion (corkscrew) by adjusting the steering dipoles over the focusing solenoids. The corkscrew motion was reduced to less than /spl plusmn/0.5 mm at the output of the accelerator.

On agricultural lands, animal waste disposal as fertilizer has been practiced since the beginning of agriculture. However, the practice has been an environmental concern in recent years due to over disposal of animal waste in some instances. This study evaluated soil NO3 response to beef-manure application on a corn (Zea mays L.) field and tested the Root Zone Water Quality Model (RZWQM) for manure management. The experiment site was located in Northeastern Colorado on a silage-corn field with a history of fertilization with beef manure every fall after corn harvest. To study the residual effect of lung-term manure application, 582 kg ha(-1) of manure-N was applied to the east side of the field in the Fall of 1993, 1993, and 1995, while the west side received manure in 1993 only. Average silage-corn yields from the west site were 25.4, 31.9, and 22.5 Mg ha(-1) for 1994, 1995, and 1996, respectively, which were not significantly different from that harvested from the east site (25.1, 30.9, and 24.3 Mg ha(-1), respectively). Average soil NO3 concentrations decreased significantly from 14.9 to 8.5 mg N kg(-1) in the top 30 cm of soil, and from 5.4 to 3.7 mg N kg(-1) in the 30- to 60-cm soil profile after stopping manure application, No significant difference in soil NO3 concentrations between the manured and not-manured sites was found below 60 cm. Average plant N uptake ranged from 140 to 362 kg N ha(-1) and was not significantly different between the two sites. The RZWQM was calibrated on the basis of the measured silage-corn yield and plant N uptake, and was then used to predict soil NO3 concentration and total water storage in the soil profile. Generally, the calibrated model provided adequate predictions for both NO3 and soil water content with r(2) > 0.83. The model was further used to evaluate alternative scenarios of manure and water management.

The challenge of tuning an induction accelerator in real time has been addressed with the new TUNE GUIDE code. The code initializes a beam at a particular position using a tracer particle representation of the phase space. The particles are transported using a matrix formulation, element by element along the beamline assuming that the field of a solenoid, or steering element is constant over its length. The other allowed elements are gaps and drift sections. A great deal of effort has been spent programming TUNE GUIDE to operate under the IBMPC Windows 3.1 system. This system features an intuitive, menu driven interface, which provides an ability to rapidly change beamline component parameter values. Consequently various accelerator setups can be explored and new values determined in real time while the accelerator is operating. In addition the code has the capability of varying a component value over a range and then plotting the resulting beam properties, such as radius or centroid position, at a down stream position. Element parameter editing is also included along with an on-line hyper text oriented help package

Emittance can be measured by intercepting an electron beam on a range thick plate and then observing the expansion of beamlets transmitted through small holes. The hole size is selected to minimize space charge effects. In the presence of a magnetic field the beamlets have a spiral trajectory and the usual field free formulation must be modified. To interpret emittance in the presence of a magnetic field an envelope equation is derived in the appropriate rotating frame.<>

An acceptable beam initial condition is most easily generated for propagation experiments when the beam energy variation is as flat as possible. Small energy variation helps to suppress instabilities and minimize transport problems. The ATA injector determines the beginning beam energy variation from the stalk resistance and specification of the time dependence of the applied voltage. The injector emits a beam from a diode configured with two re-entrant stalks, driven by 10 gaps. Ideally the gaps are triggered with a time of flight delay. In order to study the injector behavior when ideal gap triggering is not realized or stalk resistance is varied, an electromagnetic PIC computer model has been used. 5 figs.

Experimental work is being performed by collaborators at LLNL, SLAC, and LBL to investigate relativistic klystrons as a possible rf power source for future high-gradient accelerators. We have learned how to overcome or previously reported problem of high power rf pulse shortening and have achieved peak rf power levels of 330 MW using an 11.4-GHz high-gain tube with multiple output structures. In these experiments the rf pulse is of the same duration as the beam current pulse. In addition, experiments have been performed on two short sections of a high-gradient accelerator using the rf power from a relativistic klystron. An average accelerating gradient of 84 MV/m has been achieved with 80-MW of rf power.

Recent developments in the application of damped time advance methods to plasma simulations include the synthesis of implicit and explicit adjustably damped'' second order accurate methods for particle motion and electromagnetic field propagation. This paper discusses this method.

The next generation of linear colliders requires peak power sources of over 200 MW per meter at frequencies above 10 GHz at pulse widths of less than 100 nsec. Several power sources are under active development, including a conventional klystron with rf pulse compression, a relativistic klystron (RK) and a crossed-field amplifier. Power from one of these has energized a 0.5 meter two- section High Gradient Accelerator (HGA) and accelerated a beam at over 80 MeV meter. Results of tests with these experimental devices are presented here.

A two-aperture collimator has been used to measure the brightness of the electron beam produced by the injector and the first 20 acceleration cells of the ETA-II (Experimental Test Accelerator II) linear induction accelerator. Osmium alloy dispenser cathodes produce the electron beam. For accelerated currents up to 1.5 kA with 2.0- and 2.7-MeV beam energies, the measured brightness is 4*10/sup 9/ A/(rad-m)/sup 2/, exceeding the design goal by a factor of 2. At the highest current, 2.0 kA, a beam brightness of 2.6*10/sup 9/ A/(rad-m)/sup 2/ has been measured.<>

Laser-guided transport has been simulated in axisymmetry for intense electron beams at energies ranging from 3 to 45 MeV for currents of 2 to 5 kA. The simulation includes time variation of guiding channel formation and the time evolution of channel ion oscillations. Expressions are derived which determine when electrons are captured in a simple z independent model. In the same approximation, ignoring the spectrum of ion masses, the ion collapse time is calculated. For typical ATA (Advanced Test Accelerator) currents of 2 to 5 kA, the collapse occurs near the end of the pulse. Thus, any adverse emittance growth effects caused by ion collapse would be expected near the end of the pulse. The occurrence of unstable radial oscillations was demonstrated for extreme ion channel λi variation. The DPC code has been used to simulate laser guided transport for a complete pulse the entire length of ATA. The variation of channel radius throughout the beam pulse has been confirmed and emittance growth has been demonstrated at the end of the ATA accelerator

Detailed measurements of the time-dependent beam quality of an ATA (Advanced Test Accelerator) pulse transported on a KrF laser-photoionized benzene channel were performed. It was found that the tail portion (τ⩾20-30 ns) of the pulse becomes severely degraded both at high currents (I>3 kA) and at long transport distances. Nonaxisymmetric channel ion motion is suspected as the predominant source of the problem. The authors discuss various experiments which varied laser properties (timing, fluence, profiles), background ion pressure, and electron beam current in order to study the physics behind this degradation

Experimental work is now under way by collaborators at LLNL, SLAC, and LBL to investigate relativistic klystrons as a possible rf power source for future high- gradient accelerators. We have learned how to overcome our previously reported problem of high-power rf pulse shortening and have achieved peak rf power levels of 290 MW. We have used the rf from a relativistic klystron to power a short, 11.4- GHz high-gradient accelerator. The measured momentum spectrum of the accelerated electron beam corresponds to an accelerating gradient of 84 MVIm.

A two-aperture collimator has been used to measure brightness of the electron beam produced by the injector and the first 20 acceleration cells of the ETA-II linear induction accelerator. Osmium alloy dispenser cathodes produce the electron beam. For accelerated currents up to 1.5 kA with 2.0- to 2.7-MeV beam energies the measured brightness is 5 {times} 10{sup 9} A/(rad-m){sup 2}, exceeding our design goal by a factor of 2. At the highest current, 2.0 kA, a beam brightness of 2.6 {times} 10{sup 9} A/(rad-m){sup 2} has been measured. 6 refs., 5 figs., 2 tabs.

Experimental work is underway to investigate the feasibility of using relativistic klystrons as a power source for future high-gradient accelerators. The aim is to develop a high-power (500-MW) short-wavelength (2.6-cm) relativistic klystron with beam kinetic energy greater than 1 MeV. Two different relativistic klystron configurations have been built and tested: a high-gain multicavity klystron at 11.4 GHz and a low-gain two-cavity subharmonic buncher driven at 5.7 GHz. In both configurations power is extracted at 11.4 GHz. In order to understand the basic physics issues involved in extracting RF from a high power beam, both a single resonant cavity and a multicell traveling-wave structure were used for energy extraction. A previously reported problem of high-power RF pulse shortening was overcome, and peak RF power levels of 170 MW have been achieved with the RF pulse of the same duration as the beam current pulse.<>

A common element to most of the ATA transport experiments was a measurement of the beam's phase space properties. In general, we wanted a diagnostic that would quickly give us the time-resolved information that would quantitatively tell us how much of an effect a given ''knob'' or new machine element had on the beam's brightness. As explained below, it is extremely difficult to make quantitative measurements of the brightness of an ion-focused beam while it is still on the channel, nor is simple, unimpeded vacuum expansion much better. Instead, we designed and installed a simple set of three range-thick apertures beyond the fusible link which allowed us to use beam bugs to measure J over a useful range of nearly two orders of magnitude. Our results showed that the peak brightness of the beam core is a 10-15 ns spike whose temporal position follows the timing of the laser pulse and whose magnitude and duration is relatively insensitive to beam current, benzene pressure, laser intensity, profile, or timing. 2 figs., 1 tab.