Kenneth Eppley

Differential effects of relaxation techniques on trait anxiety: A meta-analysis

Hand and computer searches located studies on the effects of relaxation techniques on trait anxiety. Effect sizes for the different treatments (e.g., Progressive Relaxation, EMG Biofeedback, various forms of meditation, etc.) were calculated. Most of the treatments produced similar effect sizes except that Transcendental Meditation had significantly larger effect size (p less than .005), and meditation that involved concentration had significantly smaller effect. Correlations with effect size were calculated for many variables, e.g., population, age, sex, experimental design, duration and hours of treatment, pretest anxiety, demand characteristics, experimenter attitude, type of publication, attrition, etc. Only a few variables (mainly population, duration, hours, and attrition) significantly influenced effect size. Controlling for possible confounding variables did not alter the overall conclusions. The difference in effect size between treatments was maintained both when only published studies were included and when only the studies with the strongest design were included. Possible explanations for the findings are examined.

Algorithms for the self‐consistent simulation of high power klystrons

We discuss an improvement to the algorithm developed by Yu1 for modelling rf cavities in klystrons using the port approximation. In this method, the cavity is simulated by imposing an rf voltage as a boundary condition across the outer wall. The voltage and phase are chosen to be consistent with the cavity impedance and with the rf current induced by the electron beam. In the original method, each cavity was calculated successively using either linear theory or an iterative method to achieve a self‐consistent voltage. The new method relaxes the voltage and phase of several cavities simultaneously during the simulation. The time dependence of the voltages are calculated from a relaxation equation. The new algorithm reduces the total computation time by about a factor of five for a complete klystron.

Design of a 50 MW klystron at X-band

This paper describes the design and performance of the XL-1 klystron; a 50 MW klystron operating at a frequency of 11.424 GHz for use on the SLAC Next Linear Collider Test Accelerator (NLCTA). Problems associated with the development of high-power rf sources for NLC, and the solutions implemented on XL-1 are discussed.

Development of multimegawatt klystrons for linear colliders

A number of experimental klystrons have been constructed and evaluated at SLAC, KEK and INP, aiming toward output power objectives of 100 and 120 MW at 11.4 GHz (SLAC and KEK respectively) or 150 MW at 14 GHz (INP), with pulse lengths of the order of 1 /spl mu/s. Since RF breakdown is considered to be the principal mechanism limiting power for such tubes, most of the effort has been concentrated on the design of output circuits that reduce RF gradients by distributing fields over a longer region of interaction. Another klystron component receiving emphasis has been the output window, where the approach for future tubes may be to use a circular TEO1-mode, half-wave window. Best results to date in this continuing international effort are: 50 MW with 1 /spl mu/s pulses, using a traveling-wave output circuit (SLAC and INP), and 85 MW with 200 ns. Pulses (SLAC), using two conventional reentrant, but uncoupled, output cavities. At KEK a klystron with a single, but not reentrant, cavity has produced 80 MW in 50 ns pulses. Finally, Haimson has demonstrated 100 MW at 50 ns with a traveling-wave output. This paper addresses primarily the work performed at SLAC during the last two years.<<ETX>>

High-energy high-efficiency phase-locked HPM magnetron for an array

We have developed a 60 MW, 60% efficient, 35 Joule/pulse secondary emission magnetron at S-band. We report on experimental results from this moderate voltage (120 kV), repetitively pulsed (10 Hz), injection locked (14 - 15 dB gain) magnetron. Results from particle-in-cell code computer simulations are presented which compare very well with the experiment when space-charge-limited emission is achieved. Experimental results from a proof-of-principle, low power (6 MW) two-magnetron array are also described.

Design of a 100 MW X-band klystron

Future linear colliders require klystrons with higher peak power at higher frequency than are currently in use. SLAC (Stanford Linear Accelerator Center) is designing a 100-MW klystron at 11.4 GHz as a prototype for such a tube. The gun has been designed for 440 kV and 510 A. Transporting this beam through a 5-mm radius X-band drift tube presents the major design problem. The area convergence ratio pf 190:1 is over ten times higher than that found in conventional klystrons. Even with high magnetic fields of 6 to 7 kG, careful matching is required to prevent excessive scalloping. Extensive EGUN and CONDOR simulations have been made to optimize the transmission and RF efficiency. The EGUN simulations indicate that better matching is possible by using resonant magnetic focusing. CONDOR calculations indicate efficiencies of 45% are possible with a double output cavity. The results of the simulations and the status of the experimental program are discussed.<<ETX>>

A high power cross-field amplifier at X-band

A high power cross-field amplifier (CFA) is under development at SLAC to provide sufficient peak power to feed a section of an X-band accelerator without the need for pulse compression. The CFA employs a conventional distributed secondary emission cathode and a novel anode structure which consists of an array of vane resonators alternatively coupled to a rectangular waveguide. The waveguide impedance is tapered linearly from input to output to provide a constant RF voltage at the vane tips, leading to uniform power generation along the structure. Nominal design for this tube calls for 300 MW output power, 20 dB gain, a DC voltage of 142 kV, a magnetic field of 5 kG, an anode-cathode gap of 3.6 mm, and a total interaction length of about 60 cm. The authors have used ARGUS to model the cold circuit properties and CONDOR to model the electronic power conversion. An efficiency of 60% is expected. The design effort is discussed.<<ETX>>

Modeling RF sources using 2D PIC codes

In recent years, many types of RF sources have been successfully modeled using 2‐D PIC codes. Both cross field devices (magnetrons, cross field amplifiers, etc.) and pencil beam devices (klystrons, gyrotrons, TWT’s, lasertrons, etc.) have been simulated. All these devices involve the interaction of an electron beam with an RF circuit. For many applications, the RF structure may be approximated by an equivalent circuit, which appears in the simulation as a boundary condition on the electric field (‘‘port approximation’’). The drive term for the circuit is calculated from the energy transfer between beam and field in the drift space. For some applications it may be necessary to model the actual geometry of the structure, although this is more expensive. One problem not entirely solved is how to accurately model in 2‐D the coupling to an external waveguide. Frequently this is approximated by a radial transmission line, but this sometimes yields incorrect results. We also discuss issues in modeling the cathod...

Design of a high-power cross-field amplifier at X-band with an internally coupled waveguide

30Cross field amplifiers (CFA) have been used in many applications where high power, high frequency microwaves are needed. Although these tubes have been manufactured for decades, theoretical analysis of their properties is not as highly developed as for other microwave devices such as klystrons. The authors have developed a simulation model for CFAs using the PIC code CONDOR. Their simulations indicate that there are limits to the maximum rf field strength that a CFA can sustain. When the fields become too high, efficiency becomes very poor, and the currents drawn may become so large that secondary emission cannot be maintained. It is therefore desirable to reduce the circuit impedance of a very high power tube. One method for doing this, proposed by Feinstein, involves periodically coupling a standard CFA circuit to an internal waveguide. Most of the power flows in the waveguide, so the overall impedance is much reduced. By adjusting the guide dimensions one can vary the impedance. Thus one can retain high impedance at the low power end but low impedance at the high power end. In principle one can maintain constant rf voltage throughout the tube. CONDOR simulations have identified a good operating point at X band, with power generation of over 5 MW/cm and total efficiency of over 60%. ARGUS simulations have modeled the cold test properties of the coupled structure. The nominal design specifications are 300 MW output, 17 db gain, frequency 11.4 GHz, DC voltage 142 kV, magnetic field 5 kG, anode cathode gap 3.6 mm, total interaction length about 60 cm. Results of code simulations are discussed and the status of the experimental effort is reported.