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Global particle balance in non-inductive long-duration plasma on QUEST has been investigated. Approximately 70% of the fuel hydrogen (H) was retained in the wall and then was almost exhausted just after the discharge. The global recycling ratio (Rg), defined as the ratio of the evacuated H2 flux to that injected, was found to gradually increase during discharges and subsequently rose rapidly. To study the growth of Rg, the thermal desorption spectra after deuterium implantation in a specimen exposed to QUEST plasma was analyzed with a model which includes reflection, diffusion, solution, recombination, trapping, and plasma-induced desorption in the re-deposition layer. The model reconstructs the growth of Rg during a long-duration plasma and indicates solution plays a dominant role in the growth.

In the middle of 1980th, the VpxB concept for accelerating electrons are found by Nishida et al, with the use of plasma wave excited by high power microwave in the interaction with weakly magnetized plasma. This acceleration concept was called “Surfatron effect” in the relativistic regime. However, there is no experimental evidence so far in the relativistic regime, although the acceleration efficiency is highest in all of the concepts based on the plasma wave acceleration scheme, and we are now under experiments. In order to make longer the acceleration distances, there are several ideas including 1)ducting of the electromagnetic waves (EM wave) in the preformed plasma, 2)self‐channeling of the EM waves, and others. In this paper, the experimental results are shown on the ducting phenomena by using strong microwave for simulating the laser ducting, and on the capillary plasma scheme.

The radiation from the interaction between the ultra‐short andultra‐high power laser(0.5 TW, 100 fs)and the weakly magnetized plasmais studied. We observed the short pulse radiation (200 ps) in themicrowave region(up to 100 GHz). Two kind of radiations whose frequenciesare much lower than the plasma frequency, are observed. One isin the higer frequency region and polarized in parallel to theexternal B field(up to 6 kG). The frequency doesnt depend on the thestrength of the B field. On the other hand, other componets of theemitted radiation is vertically polarized and its frequency depends onthe strength of the B field. The experimental results suggest that theformer radiation is generated by the electron oscillation along the Bfield and the latter is by the electron Bernstein mode.

The peak power of 30 TW and the pulse width of 1 ps produced by the Nd:glass laser system is capable of creating a highly-ionized plasma of a moderate density gas on an ultrafast time scale and generating a large amplitude plasma wave with an accelerating gradient of the order of GeV/m. We are going to demonstrate particle acceleration, injecting electrons of a few MeV emitted from a solid target by intense laser irradiation. >

A collinear wakefield test facility using two linacs with a common test section is constructed. Beams from one linac excite wakefields in a test medium such as a plasma, while beams from the other linac witness the wakefields. The time interval between the two beams is controllable with an accuracy of /spl sim/1 psec. Plasma wakefield acceleration and plasma lens experiments were conducted using this facility. >

Electron acceleration by plasma wakefields driven by multiple bunches was experimentally studied. It is expected that a wakefield driven by each bunch builds up to result in a large acceleration gradient. However, the build-up of wakefields was not ideal, due to the peaked plasma-density distribution in a small plasma chamber. Two puzzles were encountered. First, the amplitude of the wakefield observed was larger than that calculated based on a linear model. The observed wake structure was not sinusoidal. These results suggest that the plasma wave was nonlinear in spite of the fact that the perturbation of a plasma by the wave should be far smaller than unity. Second, a quadratic deformation was found in the shape of test beams; when it was focused transversely, it was defocused longitudinally, and vice versa. This contradicts the theory that the plasma-lens effect is uniform.

A frequency up‐shift is observed in the interaction of a high power microwave with an unmagnetic inhomogeneous argon plasma. The induced frequency up‐shift is considered to be related to a rapid expanding plasma which is created by the ponderomotive of a strong standing wave.