Preparation of Experiment

Posted by Admin on Feb 22, 2009 at 12:42 PM
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Laboratory and office set up

The set-up of our initial office space within our lab is nearly completed and we expect to occupy the office starting February 24.

Getting to work

Krupakar Murali Subramanian has been working for LPP in preparing the experiment since Feb.1.

Unfortunately, the preparation of immigration papers for XinPei Lu is taking longer than anticipated and he will not be joining the work until around March 15.

Equipment Ordered

X-ray lens
We have ordered the first piece of diagnostic equipment, an x-ray lens capable of focusing x-rays up to around 80keV, which will be arriving shortly.

Dense Plasma Focus (DPF) Custom Design

Inner Buswork and “header”:  John Thompson has nearly completed the design of the inner buswork (metal conducting plates and insulators) and the “header” of the DPF, which attaches the electrodes to the buswork. 

Outer buswork and switching system:  At the same time, R.E. Beverly is advancing quickly in their design of the switching system and outer buswork.

The key aim in this work is to minimize the inductance of the system.

• The inductance is a measure of how much energy will be stored in the magnetic field between the conductors, which is generated when the current flows.
• The bigger the inductance, the greater this stored energy.  Since only a given amount of energy is available from the capacitors, the bigger the inductance, the smaller the peak current delivered to the DPF.
• To minimize the inductance, the conductors have to be as close to each other as possible. However, there has to be enough insulation to prevent a breakdown and a short at peak voltage. 
• This requirement is made more severe by the fact that when the DPF pinches—transfers energy to the tiny plasmoid,—there is a big spike in the voltage, 4 or 5 times above the maximum charging voltage of 45 kV.

Despite these challenges, Thompson and R.E. Beverly are completing a design that will have only 12 nH (nano-Henrys) inductance outside of the electrodes themselves.  This is far lower than that for other DPFs.  The machine we used at Texas A&M for example, had an inductance of 27nH. 

As a result, we anticipate that the DPF we build will be able to reach the 2.8 MA current we believe to be optimum when operating with decaborane fuel, but it will do this only at full 45kV capacitor charge.  Using Sing Lee’s 1-D simulation of the DPF, with a 10-torr fill of decaborane gas and 7-cm long anode, the pinch will occur at 1.6 microseconds.

Of course all these estimates, both the design parameters and the optimum operating currents, are not exact, and will be subject to refinement as the experiment progresses.

Plate Motion
We performed a preliminary mechanical analysis of the motion of the plates during the pulse, due to the repulsion created by the opposing current running through them. With suitable weighting, motion of the plates will be limited to 50 microns or so.  With silicon gaskets that can absorb up to 400 microns of motion, there should be very little stress put on the alumina insulators, so we should not be breaking them.  A similar stress analysis of the pinch forces compressing the anode indicates that a copper electrode should be able to withstand the full 2.8 MA current with no failures.

Capacitor ETA:  May

With this part of the design work essentially done, we will be contracting with a machine shop to actually produce the parts. Our plan is still to have the switching system, capacitors and power supply ready for assembly in May.

Goal this month:  Shielding

The main work we intend to do in the coming month is to design the shielding for the device, which will have to be built by a contractor.