C. Powell

X-ray emission above 10 keV from focused discharges (calorimetry and time-resolved monitoring)

Summary form only given, as follows. Two issues are addressed: [1] The location of the source of hard X-rays (/spl ges/10 keV) in MA focused discharges. [2] The debated correlation of the deuterium-plasma reaction yield with the absolute intensity in different spectral region of the X-ray emission. Correlation, or the lack of it, can be observed when (a) different spectral regions, and/or (b) different source locations in the discharge vessel, are monitored. The hard component emission up to /spl sime/100 keV is recorded by using differential filters. Energy per pulse (kJ) and emitted power (TW) are monitored with filter-fitted calorimeters and with fast scintillation detectors (NE-102). Emission scaling tests utilized two plasma focus machines with Mathers type electrodes hollow anode (APE-10, W/spl sime/7 kJ, an APF-50, W/spl ges/20 kJ). Different emission levels from a series of discharges with D/sub 2/ filling and with D/sub 2/+Ar fillings (Ar partial pressure from 2% to 16%) contribute to discriminating plasma pinch emission from anode emission. X-ray collimators designed for the same purpose establish the cogency of data analysis and of conclusions.

Relation between /sup 16/O(d,n) reaction yield and the fine structure of D(d,n) neutron emission in the Dense Plasma Focus

Summary form only given. When DPF is fired with the vessel filled by a mixture of HZ (C,N,O) and LZ (D/sub 2/,/sup 3/He) elements, a strong yield Y(HZ+LZ) of HZ+LZ reactions is observed. These reactions differ strongly in energy of the involved ions: E/sub i//spl ges/1 MeV for HZ+LZ and E/sub i//spl les/0.3 MeV for LZ+LZ. Even though, HZ+LZ and LZ+LZ reactions do not necessary occur in the same space location, the corresponding yields are correlated as Y(HZ+LZ)-Y/sup 2/(LZ+LZ). To understand this phenomenon the time structure of D(d,n)-neutrons and hard X-ray emission have been correlated with the time integrated Y(HZ+LZ). The plasma focus (7 kJ; 17 kV) was fired with the vessel filled by D/sub 2/+O/sub 2/ mixture. The dP/sub n//dt signal was unfolded to the real time resolved neutron emission signal dY/sub n//dt with a novel method accounting precisely for the signal distortion due to effects such as neutron scattering, radiation detection and signal formation/transmission/recording process. An example of measured unfolded signals for a shot with strong radioactivity and hard X-ray spikes, is shown. Implications of this type of data on the plasma domain of the enhanced nuclear reactivity model are discussed.

Inductance modulation effects on the PF reaction yield

Summary form only given. A variation of the interelectrode spacing as a function of the axial coordinate z is used to assess the bearing on the D+D neutron yield per pulse, Y, of the inductance [L(z) dl/dt] and of the resistivity [ldL/dt] term amplitude during the axial propagation of the plasma current sheet in the interelectrode gap of plasma focus discharges. Two funnel-shaped electrodes were assembled coaxially in a PF machine to replace the two Y-optimizing cylindrical electrodes. Two configurations (A), (B) were used, both with the same center electrode (anode) of 30/spl deg/ conic aperture. In configuration (A) the outer electrode (cathode) had the same conic aperture /spl theta/=30/spl deg/ of the anode. In configuration (B), the cathode aperture was /spl theta//sub c/>30/spl deg/. It was found that, systematically, Y(B)>Y(A), under identical operation conditions of capacitor charging voltage and filling pressure. The current-sheet propelling force j_(r)/spl times/B_(r) near the anode surface is essentially the same in (A) and (B). The electrode current variations dl/dt were monitored by a Rogowski coil at the electrode breech. The velocity of the current sheet v(z) measured via magnetic probes in the interelectrode gap determines dL/dt/spl equiv/(dl/dz)v for the assigned dl/dz. Reaction yield Y and emission of ion and ion cluster beams from the PF pinch depend critically on the current distribution between pinch region and breech region.

Fusion-reaction-yield scaling with PF plasma current density

Summary form only given, as follows. The scaling of the neutron yield Y from D+D reactions and, specifically, of its fluctuations /spl Delta/Y from discharge to discharge was experimentally determined with four plasma focus machines, as a function of the peak plasma-current density J. The powering energy levels were W=6 kJ for one PF machine (PF/sub 1/), 20 kJ for two identical PF machines [but one (PF/sub 2/) with, the other (PF/sub 3/) without, field distortion element at the electrode breech to sharpen the plasma current distribution], 35 kJ and 50 kJ for a fourth machine (PF/sub 4/). The comparative tests at 20 kJ and 35 kJ had the same peak electrode current I=1 MA the same charging voltage of the capacitor bank 25 kV, the same ratio inductance/capacitance (L/C), but with C(PF/sub 4/)=2C(PF/sub 2/) and L(PF/sub 4/)/spl equiv/[T(PF/sub 4/)/2/spl pi/]/sup 2//C(PF/sub 4/)=2L(PF/sub 2/). T(PF/sub 4/)/spl sime/1.4 T(PF/sub 4/), is the measured period of the complete PF electric circuit, including the propagating current sheet between coaxial electrodes. The bearing on Y, /spl Delta/Y of the breech overvoltage during the pinch collapse and of the variations of J is experimentally determined. The data indicate that MaxY(PF/sub 4/)/spl sime/mean value Y/sub Av/(PF/sub 2/) of Y, Y/sub Av/(PF/sub 2/)/spl sime/3Y/sub Av/(PF/sub 3/). The neural network analysis connecting Y and the current sheet multiplicity in the same discharge, was carried out as in earlier experiments.

Energy scaling of focused discharges with enhanced reactivity

Summary form only given. The neutron yield per pulse (Y/sub n/) from D+D reactions, the thickness and speed of the leading plasma current sheath in the electrode gap, and the multiplicity (/spl upsi/) of current sheaths in one discharge have been monitored in two plasma focus machines operating at different levels of the capacitor bank energy, 5 kJ /spl les/ W /spl les/ 10 kJ and 12 kJ /spl les/ W /spl les/ 30 kJ. The time spacing (/spl Delta/ t) between the leading (CS/sub 1/) and trailing (CS/sub 2/) current sheath is also recorded up to a CS distance 4 = 1.7 cm from the center electrode (anode) axis. The scaling of Y/sub n/ /spl sim/ A W/sup 2/ is tested for PF-Mather-geometry machines with a field distortion element (FDE) inserted at the breech side of the electrode gap, which increases Y/sub n/ (i.e., the constant A) by a factor /spl ges/ 5 above the Y/sub n/ value of the same machines operating under identical conditions, but without FDE.

Ion clusters, REB, and current sheath characteristics in focused discharges

Summary form only given. Small fluctuations in current sheath characteristics (peak current density, FWHM of leading sheath, and control parameters of sheath internal structure) are linked to wide fluctuations of ion and ion cluster emission from the pinch. Magnetic probe data were used to correlate variations of current sheath parameters with particle emission intensity, Z/M composition, and particle energy spectrum. The emission of ions and ion clusters at 90° from the axis of a plasma focus discharge was monitored simultaneously with the 0° emission. The cross-sectional structure of the REB (relativistic electron beam) at 180° along the discharge axis was monitored via the deposition of collective-field accelerated ions on a target in the REB direction. Sharp peaks of the D+-ion spectrum at 90° were found for E>200 keV/unit charge in all focused discharges. These peaks are due to ion crossing of the azimuthal magnetic field of the pinch region in a predominant ion cluster structure