Collaboration with University of Ferrara
Note: Collaboration with the University of Ferrara has not progressed as they are still awaiting funding from the European Union. This endeavor is on hold.
[This news is from November 2003.] A new experimental collaboration has begun with the University of Ferrara, Italy. Their existing dense plasma focus device will be used for experiments to further confirm the theory behind focus fusion while a larger device is being designed. Detailed analysis of the mechanical and thermal considerations for the device’s electrode has also begun.
Lawrenceville Plasma Physics and the plasma focus group at the University of Ferrara, Italy have begun a collaboration to test theoretical predictions of focus models. These experiments, which will begin in November, will use the University of Ferrara’s existing medium-sized plasma focus device.
The initial aim of the experiments is to maximize the efficiency of energy transfer into the tiny plasmoids where the fusion energy is produced. Since the plasmoids emit their energy in the form of ion and electron beams, measurement of the ion beam will allow a calculation of the plasmoid energy, which must be at least twice the energy of the ion beam.
[From January, 2004]: At the University of Ferrara the start of data collection has been delayed because the an error was made in producing the vacuum chamber. It contained aluminum, which for several reasons is very bad for DPF functioning. For one thing aluminum atoms get into the plasma and cool it with strong x-ray radiation. So a new stainless steel vessel is being made. On the plus side, we learned that the Ferrara device has capacitors rated for 60kV although the switch used is only rated for 17kV, which is therefore the top voltage used. The switch we are intending to buy for the expanded machine is rated at 45kV. So simply getting this switch, without even getting new capacitors, should increase peak current on this DPF by a factor of about 2.6. Since this switch costs only $37,000, a relatively small amount of money will be able to get us quite a large machine. The capacitors we had been planning to buy will then be added to the existing capacitors, making possible the achievement of perhaps 3 MA rather than the 1.5MA originally planned.
The ion beam will be measured with two Rogowski coils, set at different distance along the axis of the plasma focus. A Rogowski coil is a circular coil of wire attached to a voltmeter. When a pulse of current—the ion beam—passes through the coil, the changing magnetic field generated by the current produces a changing electric potential in the coil. By measuring the potential produced in the coil, researchers can calculate the rate of change of the current, and thus the total current and the total amount of charge passing though the coil.
Fast digital oscilloscopes, taking data every 2 nano-seconds, will record the shape of the ion beam pulses and the time of arrival at each of the two coils. By measuring the time it takes the ion beams to travel between the two coils, the velocity of the beam ions can be calculated. This in turn gives the average energy of the ions. The ion energy multiplied by the total charge in the beam gives total beam energy.
Theoretical models indicate that the efficiency of energy transfer into the plasmoid may be increased by increasing the velocity that the plasma sheath runs down the electrodes. This in turn can be increased by making the inner electrode, the anode, smaller in diameter, with a stronger magnetic field. The experiments will test whether this model is valid.
The experimental end of the work will be carried out by Agostino Tartari and Federico Rocchi of the Universities of Ferrara and Bologna, while data analysis and comparison with theory will be done by FFS Executive Director Eric J. Lerner, who is also President of Lawrenceville Plasma Physics. Money raised by the Focus Fusion Society will help to finance this effort.
The collaborators hope that these experiments, performed at peak currents of 400-600 kA, will pave the way for future experiments with a larger DPF, of 1.5-3MA peak current. LPP is continuing to seek private funding for half of the larger machine and the Italian researchers have applied for European Union financing.