Electron temperature relaxation and emittance conservation in active plasma lenses

Active plasma lenses (APLs) provide strong azimuthally-symmetric focusing fields in an extremely compact size, and may be a key component in future plasma-wakefield-based particle accelerators. However, the effect of an APL on the beam parameters of transiting electron beams must first be evaluated, and potentially mitigated. 

Within the capillary a non-uniform radial temperature profile develops via Joule-heating and heat loss to the capillary wall [1], resulting in a non-linear magnetic field profile and contributing to emittance growth. This non-linearity is most significant at large time-scales, i.e., in the quasi-steady-state, and is much less significant early in the relaxation process.

Here we investigate the relaxation process of the electron temperature in APLs via a magnetohydrodynamic (MHD) simulation. Our results indicate that the differences in emittance growth and radial magnetic field gradients measured in a series of recent experiments [2,3] are primarily due to sampling different parts of the relaxation process. We discuss the implications of our results to the development of emittance-preserving APLs.

[1] N. A. Bobrova et al., Phys. Rev. E, 65, 016407 (2001)

[2] J.-H. Roeckemann et al., submitted to PRAB

[3] C. Lindstrøm et al., in preparation.