Competition between self-modulation and hosing instability in self-modulated wakefield acceleration
As conventional particle acceleration techniques are hitting technological limits, plasma based acceleration is emerging as a leading technology in future generations of higher energy, compact particle accelerators. Although initially proposed more than 30 years ago by Prof. T. Tajima and Prof. J. Dawson at the University of California in Los Angeles (UCLA), the first ground breaking plasma acceleration experimental results appeared in 2005. Plasma acceleration is presently an active field of research, being pursuit by several leading laboratories (e.g. SLAC, DESY, RAL, LOA, LBNL).
Electron or positron acceleration in plasma waves is similar to sea wave surfing. Plasma accelerators use an intense laser pulse or particle bunch (boats on water) as driver to excite relativistic plasma waves (sea waves for surfing). Accelerating structures are sustained by plasma electrons and are not affected by physical boundary effects as in conventional accelerators. The plasma accelerator only lasts for the driver transit time through the plasma. The resulting plasma wavelength is only a few microns long (<10 m for sea waves), and support accelerating electric fields up to 3 orders of magnitude higher conventional particle accelerators. These accelerating fields can accelerate electrons or positrons (as surfers in sea waves) to high energy in short distances (<1 m). A plasma based acceleration experiment using proton bunches from the Super Proton Synchrotron (SPS) at CERN has been recently proposed. The beam dynamics will be dominated by competing instabilities such as self-modulation and hosing or beam break-up instabilities (SMI and HI respectively). The first part of the animation illustrates the growth and saturation of the desired instability, the SMI. It leads to the production of several particle beamlets (colored yellow and orange) that generate large amplitude plasma waves (colored blue and gray), which can then accelerate externally injected particle bunches to high energies. The second part of the movie shows SMI and HI competition. The HI wins in this case and leads to beam break up. The aim of the work is to identify conditions where SMI is enhanced and HI mitigated in the conditions of the CERN experiment. More information here.