Space-charge compensation is routinely used in linacs and rf photoinjectors. In rings, it would enable higher intensities.
It is a challenging subject: is it possible to mitigate a global effect (space-charge repulsion) with a local correction?
Issues include the need for high charge densities, unwanted lattice distortions, and beam-plasma instabilities.
Implementation with an electron lens has advantage of magnetic confinement for stability. Two concepts were developed:
- generating a given current profile (transverse and possibly longitudinal) from the electron gun or
- trapping electrons from residual-gas ionization in a Penning-Malmberg configuration (electron column).
Numerical simulation studies are necessary to guide experiments in IOTA.
Physics of space-charge compensation in rings¶
Early experimental studies demonstrated higher intensities or desired tune shift, but
- Dimov and Chupriyanov, Part. Accel. 14, 155 (1984) (BINP PSR, no confinement)
- Shiltsev et al., PAC09 (Tevatron, limited parameters and diagnostics)
Simulations with rigid e-columns show benefits on emittances and lifetimes, but
also lattice distortions and resonances, depending on the number of devices:
- Burov et al., FERMILAB-TM-2125 (2000) [Fermilab Booster]
- Alexahin and Kapin, Fermilab Beam-docs 3108 (2008) [Fermilab Booster]
- Aiba et al., PAC07 [LHC injectors]
- Boine-Frankenheim and Stem, NIM A 896, 122 (2018) [GSI SIS]
- Stern et al., Beams-doc-6790 (2018) [Fermilab RCS model]
A campaign of self-consistent simulations was started for IOTA:
- Single pass, with gas ionization: Park et al., NAPAC16
- Two passes, no lattice: Freemire et al., HB18
- Multi-pass integration Synergia+Warp: Freemire et al., IPAC19
Next steps include:
- linear and nonlinear lattices between passes
- electron-ion recombination
- plasma collisions and thermalization
Previous work by Chong Shik Park, Diletta Milana and others: https://cdcvs.fnal.gov/redmine/projects/ecolumns