Experimental Observation of Proton Bunch Modulation in a Plasma at Varying Plasma Densities

We give direct experimental evidence for the observation of the full transverse self-modulation of a long, relativistic proton bunch propagating through a dense plasma. The bunch exits the plasma with a periodic density modulation resulting from radial wakefield effects. We show that the modulation is seeded by a relativistic ionization front created using an intense laser pulse copropagating with the proton bunch. The modulation extends over the length of the proton bunch following the seed point. By varying the plasma density over one order of magnitude, we show that the modulation frequency scales with the expected dependence on the plasma density, i.e., it is equal to the plasma frequency, as expected from theory.

Experimental Observation of Plasma Wakefield Growth Driven by the Seeded Self-Modulation of a Proton Bunch

We measure the effects of transverse wakefields driven by a relativistic proton bunch in plasma with densities of 2.1×10^{14} and 7.7×10^{14}  electrons/cm^{3}. We show that these wakefields periodically defocus the proton bunch itself, consistently with the development of the seeded self-modulation process. We show that the defocusing increases both along the bunch and along the plasma by using time resolved and time-integrated measurements of the proton bunch transverse distribution. We evaluate the transverse wakefield amplitudes and show that they exceed their seed value (<15  MV/m) and reach over 300  MV/m. All these results confirm the development of the seeded self-modulation process, a necessary condition for external injection of low energy and acceleration of electrons to multi-GeV energy levels.

Calcium release from InsP3-sensitive internal stores initiates action potential in Chara

Neomycin and U73122 are known to suppress inositol 1,4,5-trisphosphate (InsP3) production by inhibition of phospholipase C. We studied the effects of these inhibitors on the excitatory currents, Iex, in Chara corallina under voltage-clamp conditions. Computer simulations of the experimental effects by a minimum model for the excitatory reaction pathway allow the assignment of the inhibitory effects to one specific reaction step, i.e. the release of Ca2+ from InsP3-sensitive internal stores. In contrast, the inhibitory effect of La3+ on Iex suggests inactivation of Cl- channels. Furthermore, ryanodine-sensitive Ca2+ stores seem to be irrelevant for electrical excitation in Chara.