kurt9 wrote: paulmarch wrote:
kurt9 wrote:I have a question about the dielectric material necessary for the Mach experiments. Is this the major engineering hurtle right now? Is the material cited in the powerpoints, BaTiO3, sufficient for realizing a demonstration device? Or do you need a better material? What about grain size?
The current M-E experiments use COTS Vishay/Cera-Mite Y5U barium titanate alloy ceramics as the dielectric in their 500pF at 15kV cap size. It's good enough for proof of principle tests, but for a working M-E thruster, much better materials are needed with their optimized parameters dependent on the type of M-E thruster built. If it’s a rotor based UFG, then we need to extend the lifetime of the material and decrease its internal losses while keeping the e-r=5,000 or greater. For MLT's we would also need to add higher magnetic permeability to the dielectric mix as well. Smaller grain size or just going to single crystal versions like quartz crystals needs to be investigated. That's a luxury we've not been able to afford to date due to the very small resources available for this M-E research.
Please let me know the specification for the desired dielectric for both examples of M-E thrusters. Presumably these would either have to be single crystal or, if multi-crystaline, nanosized grains. If multi-crystaline, internal stress is going to be a problem. Presumably these have to be fabricated in large sizes for a working thruster.
First off, is there any way to append jpg, doc, and/or pdf files to this Polywell forum? It’s a real pain in the posterior not being able to point to documents or slides that I’ve already authored for other folks who have asked similar questions, like I can at the “Next Big Future” or “NASASpaceflight.com” forums.
Now, in any M-E device, per Andrew Palfreyman’s STAIF-2006 M-E math model and a later unpublished “constrained input power” math model we created together in 2008, which are both based on Jim Woodward’s M-E derivation, the magnitude of the generated M-E derived mass/energy fluctuation signal in the energy storing dielectric is proportional to the available active dielectric mass, but inversely proportional to the density and volume of this active dielectric mass. What these three requirements translates out to is that the magnitude of the M-E delta mass/energy signal is proportional to the peak electrical and mechanical stresses applied to a given volume of the dielectric until it breaks at least. This high dielectric stress requirement limits the maximum lifetime of the dielectric so in any M-E device, a tradeoff between performance verses lifetime will have to be made. Also of note is that since the M-E signal is expressed in a cyclic manner that is in counter-(180 deg)-phase to the cap’s self-generated electrostrictive signal, using a dielectric material with a small electrostrictive constant is a big plus. Otherwise the M-E signal is cancelled out by the electrostrictive signal (E-S) until the M-E signal is driven large enough to overwhelm the E-S signal. This can happen because the M-E signal’s expression is much more nonlinear with input power than the E-S signal.
Operationally, the controlling M-E parameters of interest are the following. The dielectric’s M-E signal is proportional to the summation of the applied ac & dc bulk (relative to the distant stars) accelerations and the square of the da/dt “Jerk” accelerations. Desired peak bulk accelerations should be measured in thousands of gees or higher. Next, the M-E signal is proportional to the capacitance of the accelerated M-E cap dielectric, the cube of the applied operating voltage, the cube of the operating frequency, the square of the active dielectric constant, but varies inversely with the dielectric’s loss factor (i.e., lower ac Equivalent Resistance (E-R) is better) which controls the dissipated power and temp rise of the caps for a given input power. If making a solid state Mach Lorentz thruster (MLT), the magnitude of the rectified unidirectional force is proportional to the volumetric crossed B-field in the dielectric, and the thickness of the dielectric in the direction of the applied E-field which increases the leverage arm of the applied crossed B-field. MLTs also require the use of a single cap dielectric layer to preclude Lorentz force cancellation issues that arise by using standard multilayer capacitors were the applied E-field reverses direction in each layer at a given point in time.
Given the above M-E output signal’s optimization parameter space, the desired characteristics of operational M-E energy storage devices, AKA capacitors, is as follows:
1. Relative dielectric constant (e-r)= 1,000 or greater but depends on operating voltage.
2. Dielectric density should be less than 5.6 grams/cc (BaTiO3) and preferably much less.
3. Operating frequency should be optimized for the 10-to-50 MHz range.
4. Dielectric Loss Tangent should be less than 0.5% at the operating frequency.
5. Operating voltage should be up to 100.0 kV-p (See EEStor process), but depends on obtained e-r. Higher e-r allows lower peak voltage for a given energy storage value.
6. Operating times should be measured in thousands to tens of thousands of hours. This will require using low-k plastic film caps or higher-k single crystal or nano-crystal caps.
7. For MLTs the dielectric magnetic permeability should be 10 or greater in a single layer arrangement.