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We developed an experimental apparatus for the study of non-linear stopping of low-energy heavy ions in non-ideal plasmas. The target plasma was produced by an electromagnetically driven shock tube. A pair of 50- μ m -diameter beam apertures was attached to the shock tube wall. These apertures confined hydrogen gas of ≈ 5 Torr in the tube and sustained the pressure difference ( ∼ 10 5 – 10 6 ) between the tube and the beam line. In order to measure the energy loss in the plasma in the tube, we used a semiconductor charged-particle detector, which could directly measure the kinetic energy of single particles, since the beam transmission through these apertures was very small. To synchronize the plasma production in the shock tube and the injection of projectiles, a fast beam kicker was installed in front of the plasma target. Results of preliminary experiments using thin carbon foil targets showed that the measured energy loss of single projectiles after passing through the target was in agreement with other data. The time resolution of the energy-loss measurement system was ≈ 150 ns , which is enough to measure the projectile energy loss during the life time of the target plasma.

Stopping power of low-energy, highly charged projectiles in cold dense plasmas was numerically investigated to search realistic parameters for beam–plasma interaction experiments using ≈10–100 keV/u projectiles delivered by a 1.7 MV electrostatic accelerator. In order to evaluate the energy loss, a simple Molecular Dynamics (MD) computer code was applied. If the projectile velocity was as low as the thermal velocity of plasma electrons, and the projectile charge was sufficiently high, nonlinear stopping was observed even for weakly nonideal plasma targets with Γ ≈ 0.1 . According to a numerical analysis on the charge state distribution coupled with an energy loss calculation, projectiles with such a high charge state are rapidly lost by the strong recombination owing to electrons loosely trapped by the projectile, as well as the residual hydrogen atoms in the plasma.

In order to determine the Coulomb logarithm in the interaction between hot plasma and ion beams, the stopping power of 350 keV protons in a laser plasma target was measured by TOF method. The electron temperature and the electron density of the target plasma was 20 eV and 1018 cm−3, respectively. The Bethe’s Coulomb logarithm calculated using the measured stopping power of protons was 1.8 times as large as that in the beam–cold matter interaction. The mean charge state for 350 keV/u 16O after the interaction with the plasma was also measured by using a time-resolved magnetic spectrograph. The Coulomb logarithm of 350 keV/u 16O was estimated by using measured mean charge state and previously measured stopping power. The obtained Coulomb logarithm for both projectiles are compared.

Experimental investigations into the interaction of an ion beam with a plasma target showed increased stripping as compared to cold targets. Measurements were performed with a 900 keV ion beam of 7 Li 1+ . The plasma was created by irradiating the surface of a polyethylene disk with a 6 J TEA CO 2 laser. This produced a partially ionized surface blow-off plasma with electron densities between 10 18 and 10 16 cm −3 . As another plasma target a z -pinch discharge in helium gas has been prepared. This target yields electron densities of about 5×10 17 cm −3 . Interaction will be measured with a 6 MeV/u 40 Ar 18+ beam from the HIMAC accelerator. Concerning the detector signals, the beam line was designed to minimize any noise stemming from the pulsed discharge. The beam line allows acceptably good beam transmission for current densities in the plasma of up to 80 kA/cm 2 .

By means of a numerical method, beam dynamics was analyzed for an RFQ, where mixtures of positive and negative ions were injected into the quadrupole channel. In order to simulate simultaneous bunching of ions with opposite charges, the motion of particles injected into the cavity during two RF periods was traced under consideration of 3D Coulomb forces between particles. Effects of neighbor bunches were also taken into account. In the input region of the structure, the transverse beam divergence due to space charge forces was suppressed by the charge neutralization. However, it was found that the bunch formation in the cavity was disturbed by the attractive forces between positive and negative ions, leading to longitudinal beam loss. Dependence of the beam transmission efficiency on the input beam intensity as well as on the blend ratio of two ion species is reported. These results are compared with those obtained when injecting ions of single species.

Tape coil technique has been applied to a compact quadrupole magnet for Wideroe-linac drift tubes. Boiling heat transfer has been tested for effective heat removal from the coil. A simplified numerical analysis of the coil temperature has been made and qualitative agreement with the experimental results has been obtained. A magnetic field gradient of 4.1 kG/cm has been stably obtained for a drift tube size of 100 mm in outer diameter and 23 mm in bore tube inner diameter.