K. W. Wenzel

Measurement and analysis of neutron and gamma-ray emission rates, other fusion products, and power in electrochemical cells having Pd cathodes

Results of experiments intended to reproduce cold fusion phenomena originally reported by Fleischmann, Pons, and Hawkins are presented. These experiments were performed on a pair of matched electrochemical cells containing 0.1×9 cm Pd rods that were operated for 10 days. The cells were analyzed by the following means: (1) constant temperature calorimetry, (2) neutron counting and γ-ray spectroscopy, (3) mass spectral analysis of4He in effluent gases, and4He and3He within the Pd metal, (4) tritium analysis of the electrolyte solution, and (5) x-ray photoelectron spectroscopy of the Pd cathode surface. Within estimated levels of accuracy, no excess power output or any other evidence of fusion products was detected.

X‐ray response of silicon surface‐barrier diodes at 8 and 17.5 keV: Evidence that the x‐ray sensitive depth is not generally the depletion depth

The absolute x‐ray response of 18 EGG thus the depletion depth, proportional to the square root of the bias voltage, does not play a critical role in determining the x‐ray sensitive d...

X‐ray imaging arrays for impurity transport studies on the Texas Experimental Tokamak

Three multichannel soft x‐ray imaging arrays are used for impurity transport studies on the Texas Experimental Tokamak. The entire system has a total of 92 broadband x‐ray detectors that view the plasma at the same toroidal location from three different poloidal angles: Array A is a 40‐channel vertically viewing set of silicon surface barrier diodes (SBDs); array B is a 40‐channel horizontally viewing set of SBDs; and array C is a 12‐channel set of p‐intrinsic‐n (p‐i‐n) detectors viewing the plasma from 45° above the horizontal plane. Array B is absolutely calibrated; array A is relatively calibrated in situ; and array C is cross‐calibrated relative to array B. In this article we describe the primary components of the system: (1) the specific x‐ray diodes used for the arrays and their spectral sensitivities; (2) the corresponding electronics necessary for data acquisition; and (3) the vacuum system for the arrays. Furthermore, we describe a novel krypton edge absorption filter which discriminates between ...

Response of X-UV photodiodes to 1. 5--17. 5 keV x rays and MeV alpha particles

The absolute x‐ray response of three X‐UV photodiodes was measured over an energy range of 1.5–17.5 keV so that they could be used to calibrate x‐ray imaging systems for the ASCA satellite mission. An intense electron‐beam x‐ray generator was used to test both the dc and ac x‐ray response at 1.5, 4.5, 8.0, and 17.5 keV, and an 55Fe source was used to examine one of the photodiodes at 5.9 keV. The x‐ray response was determined by comparing the X‐UV diode signal to that of a previously calibrated silicon surface barrier diode (SBD). The X‐UV detector response was similar to the SBD response at low energies (1.5 and 4.5 keV). At 8 keV, the X‐UV detectors exhibited about 70% of the SBD response, and at 17.5 keV, about 50%. This result is surprising, because the X‐UV diodes actually have a greater silicon thickness than the SBD. In contrast to our findings for SBDs in the past, this implies that not the entire physical volume of these detectors comprises the active volume. The X‐UV detector x‐ray response was ...

Transport with pellet fuelling in the Texas Experimental Tokamak

In the Texas Experimental Tokamak, a discharge regime characterized by persistent peaked profiles was observed to be induced by pellet fuelling, and its transport properties were studied. The hallmark of the regime is the suppression of sawteeth, and the regime was attained by injecting hydrogen pellets to promptly double the plasma density. In each of several pairs of experiments, a pellet fuelled discharge was compared with an edge fuelled discharge with similar averaged electron density, plasma current and toroidal magnetic field in order to characterize the transport change and to look for causal changes in the plasma turbulence. The impurity, radiation and working gas particle profiles were more peaked for the pellet fuelled case. The values of rjt derived from measured ion temperature and density profiles for high density edge fuelled and pellet fuelled discharges indicate that ion pressure gradient driven turbulence should be reduced in the pellet fuelled case. The macroscopic effects were accompanied by microscopic changes. Measurements of turbulent density fluctuations in high density edge fuelled discharges give strong evidence that a component of the turbulence propagates in the ion diamagnetic direction and that this particular mode is reduced in pellet fuelled discharges. The effects of the reduction of an ion mode turbulence were sought in the energy confinement of the discharges, but it was found that for these experiments (tailored for the turbulence diagnostics) the energy flowing in the ion channel was not large enough to affect the energy confinement. Simulations were used to interpret some of the results. Discharge simulations which include the pellet injection can reproduce the sawtooth suppression. This result and known properties of discharges in which sawteeth are suppressed suggest that some of the profile effects (including peaking of the working gas particles) induced by pellet injection are due to sawtooth suppression. The particle peaking may cause the observed reduction in the turbulence which follows pellet injection.

Response of SBDs to MeV protons, tritons, and alphas: Evidence that the charged‐particle sensitive depth is not generally the depletion depth

As part of an on‐going effort to develop diagnostics for energetic charged particles from laboratory and space experiments, we examined the possibility that particle identification could be expedited by varying the applied bias voltage on silicon surface barrier detectors (SBDs). Using MeV protons, tritons, and alphas, we performed spectroscopy experiments whereby we observed changes of the energy spectrum as a function of the bias voltage. These particles were either generated via a Cockcroft–Walton linac as fusion products, or emitted from radioisotopes. The results indicate that, contrary to commonly held belief, the detector sensitive depth is not generally the depletion depth. Indeed for partially depleted SBDs the performance is not greatly degraded even for zero bias.

A fusion‐product source

A Texas Nuclear Cockcroft–Walton neutron generator was refurbished for use as a general fusion‐product source. This well‐calibrated source is now used routinely for characterizing energetic charged‐particle detectors, for the development of nuclear fusion diagnostics, for studying radiation damage, and for calibrating x‐ray detectors for laboratory and space plasmas. This paper is an overview of the facility. We describe the main accelerator operating systems, the primary fusion reactions studied, and several diagnostics used to characterize the fusion‐product source.

14 MeV neutron yields from D-T operation of the MIT Cockcroft-Walton accelerator

As part of our fusion-product diagnostic development program, we have begun a series of experiments with 14 MeV neutrons generated in a Cockcroft-Walton accelerator. Two different detectors have been used to measure the neutron yield: a silicon SBD and a Cu foil. The energy of the emitted neutrons has been determined by using two spectrometers: the SBD and a3He proportional counter. The reaction rate is monitored, with about ±5% accuracy, by detecting the α particles from D + T →n +α. The neutron yields obtained from the Si detector and the Cu activation had associated uncertainties of about ±15% and agreed well with the predicted values from α measurements.

PIXE x rays: From Z=4 to Z=92

A high‐intensity, charged‐particle‐induced x‐ray (PIXE) source has been developed for the purpose of characterizing x‐ray detectors and optics, and measuring filter transmissions. With energetic proton beams up to 165 keV, intense line x radiations (0.5 A≤λ≤111 A) have been generated from the K, L, M, and N shells of elements 4≤Z≤92. The PIXE spectrum has orders‐of‐magnitude lower background continuum than a conventional electron beam or radioactive α‐fluorescence source [C. K. Li, R. D. Petrasso, K. W. Wenzel et al. (to be published)].

Thermal transport during electron cyclotron heating in the TEXT tokamak

Electron Cyclotron Heating experiments have been performed on the TEXT tokamak using Varian gyrotron. Some degradation of electron energy confinement is observed for sawtoothing and non‐sawtoothing discharges. Sharp electron temperature profiles are produced in high‐q discharges by extremely localized ECH power deposition. (AIP)