Prediction and suppression of beam breakup instability in multicell superconducting cavities

Abstract

Beam breakup instability in superconducting cavities is a serious problem. In this work, a four-cell LEP cavity installed in the KAERI linear accelerator is considered as an example. Dependence of the breakup instability threshold currents on the characteristics of a dipole mode was determined both analytically and numerically. An efficient technique to suppress breakup instability using rf beam focusing within a cavity is suggested. The technique involves applying TE-type monopole higher-order modes and is useful for multicell superconducting cavities with many trapped high-Q dipole modes.

Correcting the beam centroid motion in an induction accelerator and reducing the beam breakup instability

“…The BBU instability, a transverse magnetic coupling which destroys the beam quality, was discovered by the authors of Refs. [8,9] and has been studied extensively in both rf and induction accelerators [5,6,[10][11][12][13][14][15][16][17][18][19][20]. The Advanced Test Accelerator demonstrated the highest intensity transport in an induction accelerator to date with a 10 kA, 50 MeV electron beam utilizing phase mix damping through a laser ionized channel to suppress the BBU [12,13,21].…”

Monopole passband excitation by field emitters in 9-cell TESLA-type cavities

“…Both the modification of the electron trajectory as well as the emission current modulation plays an important role in determining the level of mode excitation. The latter mechanism is new when compared to the excitation of dipole modes during beam break-up instabilities [8]. Still, spontaneous excitation of the monopole mode has the same instabilitylike process with the threshold current being dependent on the mode quality factor.…”

Beam breakup instability suppression in multicell superconducting rf guns

“…We can assume without a loss of generality that the focusing (10), even if the averaging of ÁE over all phases of the TE mode is applied. This is proved analytically and numerically in [4].…”

“…3, Table I) is numerically calculated according to the algorithm described in Ref. [4]. The calculated values fit the analytical dependence of Eq.…”