High energy efficiency demonstrated by first ion beam measurement

Posted by Rezwan on Feb 09, 2011 at 10:58 PM
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Note:  This evidence comes from the Rogowski Coils. 

This month, we produced strong evidence that we have succeed in transferring a large part (at least 15%) of total input energy into the plasmoid and from there into the beams. The first part of the evidence came from our first observation yet of the ion beam with the upper and lower Rogowski coils (URC and LRC). Like our main Rogowski coils, the URC and LRC produce a signal by induction when a current passes inside their loop. Both are located in a drift tube that extends downward from the main vacuum chamber, with the URC being 31 cm and the LRC 115 cm from the end of the anode, where the plasmoid forms.

On January 12, with shot 01121103, we saw a clear and very large signal from the URC, which records the rate of change of the current. Integrating this signal, we got a measurement of the current in the ion beam (Figure 1), which peaked at 20 kA and lasted (full-width at half maximum) 36 ns. This signal had an excellent signal-to-noise ratio and was far larger than we had seen before.

We used the delay between the ion beam and the electron beam to estimate the average energy of the ions in the beam, which turns out to be extremely high—5.5 Mev, about five times as high as predicted by our theory. The energy contained in the beam is therefore also quite high—4.6 kJ. Since equal energy must be transferred to the e-beam, at least before it exits the plasmoid, the total energy in the beams would then be around 9 kJ.

To see how efficient this energy transfer into the beam is, we consider that in this shot, 10 capacitors were charged to 33 kV, so they released a total of 51 kJ. By the time of the pinch, 63% of this energy, 32 kJ, had been transferred into the plasma, about half into the magnetic field and half into the kinetic energy of the plasma. So, about 28% of the available energy at the time of the pinch was transferred into the beam. We have some confirmation of this from the current trace itself, (Figure 2), since by the time the beam was over, the current had declined by 17%. This works out to a 30% decline in energy. (More confirmation of this energy transfer is below in the next section.)

This beam shot, while only one shot, tells us some other important things. First, it reveals that the bump into the current is actually an early electron beam arriving at the anode. A later beam, as in the short-pinch-time shots (SPTs), would get buried either in the very sharp decline of the current later in the pinch or in the rebound after that. So, we now know this is a beam, not a shock. Such an early powerful beam will also drain the plasmoid of most of its energy, preventing further contraction and the achievement of the expected density.

Second, it shows that, at least at 30 cm from the plasmoid, the ion beam has not been neutralized by an electron current. This is important for our plans to get energy out of the beam by an inductive coil.

Third, it shows that the beam can be relatively narrow. For the beam to fit entirely within the URC, which is only 3 cm in radius, it can have a half-opening angle of no more than about 6 degrees, about what other researchers have reported for a non-collimated beam. The beam, we believe, did not hit the LRC, but rather the side of the drift tube. The LRC signal was also larger than what we have seen in the past, but it started with a negative electron current, and was only 8% of the current of the LRC signal. The signal there also arrived only 19 ns after the LRC signal, which, if it was an ion beam, implies energy of 21 MeV, which is just too much energy. Electrons accelerated by collisions with the ions could travel much faster, however, with far less energy.

Finally, if the electron beam leaves the plasmoid with a substantial part of its energy, then the beam that strikes the anode will generate a very intense pulse of X-rays. If only one third of the energy is not absorbed by the plasmoid, a 1.5 kJ beam with an average energy of 1.8 MeV would generate more than 100 J of extremely hard X-ray energy, sufficient for our X-Scan spin-off technology.

See also:  More evidence for high energy efficiency—a high resolution plasmoid image