Function Of Heater Power Research Articles

Near Contact Thermal Flying Height Control in Hard Disk Drives

A modeling and optimization approach is proposed and implemented for minimizing variations in flying height of thermal flying height control (TFC) sliders. The method utilizes the resistive heater element of TFC sliders for adjustment of spacing and the embedded thermal contact sensor (TCS) as a relative measurement for changes in flying height. In the modeling approach, the static and dynamic behavior of the TCS as a function of heater power is characterized. A model of the system is identified from experimental step excitation data using a realization algorithm. In the optimization approach, the optimal feedforward heater input profile is calculated via convex optimization techniques based on the static and dynamic behavior of the system. The modeling and optimization approach was verified experimentally, showing that the proposed approach reduces the difference between the maximum and the minimum value of the TCS measurements by a factor of two, indication a twofold reduction of flying height variations.

Hollow cathode conditioning and discharge initiation

In the framework of developing a fast-starting hollow cathode, one must understand how a cathode is conditioned for operation. The desorption of known contaminates as a function of heater power was measured to quantify cathode conditioning characteristics. In addition to conditioning, a study of hollow cathode emission characteristics under vacuum conditions was performed. Results of these two studies are described herein along with measurements of the temperature of the cathode as a function of time and heater power. The data are used to validate a transient surface diffusion model that describes the migration and surface coverage fraction of low-work-function material from the interior of the hollow cathode to the orifice barrel and to the exterior surface of the orifice plate of the cathode. A sufficiency condition is presented for our cathode geometry of vacuum emission current level and the ability to start a hollow cathode discharge once gas flow is initiated.

Noise Performance of Frequency- and Phase-Locked CW Magnetrons Operated as Current-Controlled Oscillators

Low-power continuous wave cooker magnetrons driven from industrial-quality switch-mode power supplies have been frequency locked by driving them as current-controlled oscillators in a phase-lock loop (PLL). The noise performance of these frequency-locked oscillators is reported as a function of heater power. The injection of -30- to -40dB signals derived from the reference oscillator of the PLL into the magnetron's output waveguide while the anode current is controlled by the PLL is shown to phase lock the magnetron's output. Results for locking performance are presented.

Impact of vibrational excitation on ionospheric parameters and artificial airglow during HF heating in the F region

Vibrational excitation by the impact of electrons on molecular nitrogen in the energy range of 1.8–3.2 eV is well known. Electrons heated by high‐power HF radio waves can effectively lose energy due to this vibrational excitation, which, in turn, creates a sharp energy barrier. Electrons must overcome this barrier in order to reach higher energies. A model for this vibrational barrier has been developed, and deviations of the electron energy distribution from a Maxwellian distribution have been estimated under different conditions. The depletion of electrons with energy higher than 2 eV decreases the excitation rate of the optical emissions (for example, 630.0 nm airglow) observed during HF heating. We show that the vibrational barrier can explain why the 630 nm airglow reported by Gustavsson et al. [2001] was only slightly enhanced during HF heating, in spite of the measured electron temperature being higher than 3000 K. In some cases, vibrationally excited molecules can accumulate in the ionosphere due to slow deactivation. These species increase the recombination coefficient, which, in turn, may result in the decrease of electron density. This effect can also contribute to the saturation of the optical emission strength as a function of heater power, as reported by Pedersen et al. [2003].

Thermal Characteristics of Back Cooled Impingement Cooler for Packaging of High Power Semiconductor Laser Diode Arrays

A simple impingement type of water cooled heat sink has been fabricated and characterized for packaging of high power semiconductor laser diode arrays. A single chilled water jet impinging normally on the back plane of copper submount is used to achieve enhanced heat transfer coefficient for convective cooling. The cooler is fabricated out of copper (OFHC), which consists of a chamber (3x9x12 mm3) with one pair of inlet and outlet tubes for chilled water flow at one end and 3 mm thick copper submount at the other end. The thermal characteristics of the cooler is measured as a function of heater power, heater temperature and chilled water pressure of up to 30PSI. The minimum thermal resistance obtained is 0.6°C/Watt for submount surface area of 3.2 x 10mm2. Experimental thermal resistance values closely match with theoretical calculations. The heat sink fabrication and characterization are discussed.

Crystalline to amorphous phase transition in very low temperature molecular beam epitaxy

For the first time, we use in situ time resolved reflectivity (TRR) measurement to determine the thickness for crystalline–amorphous transition. The use of TRR measurements to study the breakdown of the single crystalline growth and the following deposition of amorphous silicon ( α-Si) is based on the higher refraction index of α-Si at the wavelengths used (950 and 670 nm). An increasing α-film thickness causes cycles of constructive and destructive interference and leads to a time-dependent reflectivity. Final amorphous film thicknesses have been confirmed by ex situ spectroscopic ellipsometry. Samples were prepared by the deposition of electron-beam evaporated Si in an MBE equipment. The temperature, as a function of heater power, was carefully calibrated for highly doped substrates, with a thermocouple mounted into a test substrate. Substrates were kept at constant growth temperatures between 100 and 250 °C. From an Arrhenius-type expression, we can deduce an activation energy of 0.36±0.05 eV. The growth rate dependence was investigated between 0.013 and 0.7 nm s −1 at a constant temperature of 200 °C. Rate dependent data can be fitted by a power law. A variation of the deposition rate by a factor of 100 causes a variation in epi thickness by a factor 5. Similar experiments were also performed on low doped substrates and with non-linear temperature ramp. The obtained substrate temperature depends strongly on doping because of free carrier absorption (differences up to ≈50 °C).

Characterization of the nuisance heat load in a thermoacoustic refrigeration demonstration device

The heat load in a thermoacoustic refrigeration demonstration device is studied. In the demo, which acts only to create a low temperature at the position of a thermocouple, the only heat load is nuisance heat, which is not well known. The method described here for estimating experimentally the size of this heat load assumes that heat transport associated with acoustics depends on acoustic amplitude p and on the magnitude of the deviation from ambient temperature |ΔT|, but is independent of the sign of ΔT. That is, the heat load due to acoustics-induced transport is taken to have the form Q̇transport=-F(p)ΔT, where F(p) is some function of p only, and ΔT can be either positive (refrigerator) or negative (heater). Direct thermoviscous heating at the site of the thermocouple Q̇tv(p) is also a function of p only. At steady state, Q̇heater=F(p)ΔT-Q̇tv(p). In the experiment, the refrigeration stack is replaced by an electric heater, the power of which is easily measured. The steady−state temperature rise above ambient ΔT is measured as a function of heater power and acoustic amplitude. The experiment generates a family of straight lines, the slopes of which determine the function F(p), and the intercepts give Q̇tv. [Work supported by ONR and NSF.]

Second sound very near T?

The results of an experimental investigation of the evolution of planar, non-linear, second-sound pulses in superfluid4He, to within 650 nK of the λ-transition, are presented. A new method for extracting the second-sound velocity and damping is demonstrated. As predicted from two-fluid hydrodynamics, the pulses are well modeled by the solutions of Burgers' equation. The second-sound velocity (u 20) and damping (D 2) are extracted from fits of the model to the data. Damping data are obtained in this fashion to 3×10−7 in reduced temperature at saturated vapor pressure; nearly two decades closer to Tλ then any previous measurements. The superfluid density is extracted from theu 20 measurements and the critical exponent, ζ, is determined. A study of very large amplitude pulses near Tλ is also presented. These pulses extend well beyond the range of validity of Burgers' equation. The amplitude of the shock that forms at the trailing edge of the pulse is observed to saturate as a function of heater power and then decrease suddenly, as has been previously observed away from Tλ. However, the pulse shapes are quite different from any previously observed.

Phase slippage in thin superfluid films

We have extended the Ambegaokar, Halperin, Nelson and Siggia theory of vortex de-pairing in two-dimensional superfluids to describe how the current of free vortices varies with superfluid velocity, v s, in the steady state, for temperatures just above the Kosterlitz-Thouless transition. To do so we have solved exactly the Fokker-Planck equation which describes the current of vortices produced at one edge of the film. We are able to calculate how a persistent current decays, and the thermal resistance of a film as a function of heater power. Superconducting films are considered as a charged, two-dimensional superfluid, and the theory is applied to them.

Evidence for a low dimension strange attractor for temperature variations inside helium-II counter-flow jets

Time series measurements of the temperature of liquid helium inside the chamber of thermal counterflow jets driven by a constant heat source show four distinct regions of fluid flow as a function of heater power. Detailed analysis suggests that the temperature variations for the lowest power oscillatory region may be characterized by a strange attractor of fractal dimension, ∼4.

Theoretical analysis for low-noise beam transducers

Analytical expressions for the noise figure of a traveling-wave amplifier (TWA) preceded by a nonuniform drift space are derived. Numerical results show that the noise figure for an accelerated beam has a minimum at a specific drift length. Also, when the noise figure is plotted as a function of heater power, it shows a minimum value.