[en] Work on fueling by pellets is proceeding on several fronts: (1) experimental studies of interactions between beams of keV electrons and light ions and solid hydrogen and deuterium; (2) theoretical studies of pellet ablation; (3) injection of deuterium pellets into the tokamak Dante; and (4) experimental work on pellet handling and acceleration. A design exists of a versatile pneumatic pellet injector. The design will be used for an injector for small, slow pellets, 0.4 mm diam. and 100 m/s, for the reverse pinch Eta-Beta in Padova in Italy. This design was used for large, fast pellets, 3.2 mm diam. and 1400 m/s, in a contract work for JET

[en] Thin films of N₂ on a substrate of solid Xe were bombarded with 1-2 keV/amu H₁⁺, H₂⁺, and H₃⁺ ions, and the energy spectra for those positive ions backscattered through 135⁰ were measured. The minimum energy loss of particles scattered from the Xe-surface was found to vary linearly with film thickness up to typically approx. equal to 150 A, where multiple collision effects become important. It is argued that stopping powers for solid N₂ may be extracted from these measurements. Existing stopping powers for gaseous N₂ are about twice as large as our results. (orig.)

[en] The secondary electron emission (SEE) coefficient delta was measured for solid hydrogen and deuterium resulting from the normal incidence of 0.5--3-keV electrons and 4--10-keV H⁺, H₂⁺, H₃⁺, and D₃⁺ ions. The SEE coefficients for solid hydrogen are 60--70% of those for solid deuterium, and the coefficients are small, in contrast to what is expected for insulating materials. One explanation is that the secondary electrons lose energy inside the target material by exciting vibrational and rotational states of the molecules, so that the number of electrons that may escape as secondary electrons is rather small. The losses to molecular states will be largest for hydrogen, so that the SEE coefficients are smallest for solid hydrogen, as was observed. For the incidence of ions, the values of delta for the different molecular ions agree when the number of secondary electrons per incident atom is plotted versus the velocity or the stopping power of the incident particles. Measurements were also made for oblique incidence of H⁺ ions on solid deuterium for angles of incidence up to 75degree. A correction could be made for the emission of secondary ions by also measuring the current calorimetrically. At largest energies, the angular dependence corresponds to delta (theta) =delta (theta)(costheta)^-1

[en] A deuterium pellet injector built for the reversed field pinch Eta Beta II is described. The pellet gun is the versatile type developed at Risphi. Pellets are small, 0.38 or 0.72 mm diam., and rather slow, 100 m/s. They are transported to Eta Beta II through a guide tube system, which they leave with an angular spread below 1⁰ and are then injected through a long radial tube. The pellets are detected by optical pellet detectors the signals from which are used to trigger the firing of Eta Beta II. The injector is operated automatically by means of a PLC

[en] The mirror-substrate method was used for measuring the penetration depth of 0.5-3-keV electrons in solid hydrogen and deuterium. The penetration depth was found to be 0.53 x 10¹⁸E/sup 1.72/ molecules/cm² with the energy given in keV. There was satisfactory agreement with other data. The measurements also showed that the escape depth for true secondary electrons from solid deuterium is less than 50 A, which agrees well with the small values for the secondary-electron-emission coefficient found for solid deuterium. Results were furthermore obtained for the electron-reflection coefficient for the gold substrate, i.e., the number of electrons that are reflected with high energies. The electron-reflection coefficient agrees well with other results, both with respect to magnitude and energy dependence

[en] Measurements have been made of the emission of both positive and negative particles from solid hydrogen and deuterium for normal incidence of H⁺, H⁺₂, H⁺₃, D₂H⁺, D⁺₃ and He⁺ ions up to 10 keV. For positive particles the emission coefficient increased with increasing energy of incidence to reach a value of 0.08 per atom for 10 keV H⁺ onto hydrogen. Apparently the positive particles are sputtered ones. The negative particles emitted are predominantly electrons. The emission coefficient per incident atom as a function of the velocity of the incident particle agress fairly well with results published earlier for incidence of hydrogen and deuterium ions. However, systematic differences of up to 10% are now observed between the coefficients for the different types of ions. (orig.)

[en] Experimental studies were made of the interaction between solid nitrogen and beams of 1--3-keV electrons. The projected range for the electrons was measured by means of the mirror-substrate method (gold substrate), giving the result 9.02 x 10¹⁶ E/sup 1.75/ molecules/cm² with the energy given in keV. The escape depth for secondary electrons was studied by means of the equivalent-substrate method (carbon substrate). The results varied from 280 A at 1 keV to 400 A at 3 keV. Measurements were also made of the secondary-electron-emission coefficient, which varied from 2.3 el/el at 1 keV to 1.2 el/el at 3 keV. At 3 keV, the SEE coefficient is 12 times that for solid deuterium. This is attributed partly to the larger production rate for low-energy electrons in nitrogen and partly to the larger escape probability for these electrons. Moreover, measurements were made of the electron-reflection coefficient, both for solid nitrogen and for the carbon substrate. For nitrogen, it varied from 0.17 el/el at 1 keV to 0.13 el/el at 3 keV, and for carbon it varied from 0.13 to 0.12. The observations are discussed and comparisons made with other theoretical and experimental results. The agreement ranges from good to fair

[en] The calorimetric deuterium film method operating at liquid-helium temperature was used for measuring the energy reflection coefficient γ for 1--10-keV protons incident on gold at angles of incidence up to 75degree. H⁺₂ and H⁺₃ ions were used to obtain the lowest velocities. The growth with angle increases with energy. There is fair agreement with the theoretical results of Robinson and of Oen and Robinson

[en] A flow cryostat allowing independent cooling of eight pipe guns in a multishot deuterium pellet injector is described. The pipe guns are placed symmetrically around the flow cryostat and with a liquid helium consumption of 4--5 l/h the cooling is sufficient for simultaneous formation of eight pellets at 8--9 K with a diameter of 2.1 mm containing up to 8x10²⁰ atoms/pellet. The thermal interaction between the eight pipe guns is sufficiently low to allow successive firing of the guns with time intervals of up to 1 s

[en] In the studies of pellet-plasma interactions made at Riso National Laboratory, 0.13-mg pellets of solid D² are accelerated to velocities up to 200 m/s and injected into a small tokamak, named Dante. The pellets are accelerated in a light-gas gun by means of a propeller gas pressure created by pulse evaporation of solid H². The pellets are injected into the tokamak through a 2.8-m long curved guide tube with 4-mm bore. At the moderate velocities used, injection through a 20-m guide tube proved possible without a serious loss of pellet material. A pellet gun can thus be placed in nearly any position with respect to a tokamak. Another gun is being tested where 0.01-mg pellets are accelerated to velocities above 300 m/s. (author)