H-mode accelerating structures with permanent-magnet quadrupole beam focusing

Abstract

We have developed high-efficiency normal-conducting rf accelerating structures by combining H-mode resonator cavities and a transverse beam focusing by permanent-magnet quadrupoles (PMQ), for beam velocities in the range of a few percent of the speed of light. The shunt impedance of interdigital H-mode (IH-PMQ) structures is 10-20 times higher than that of a conventional drift-tube linac, while the transverse size is 4-5 times smaller. Results of the combined 3D modeling-electromagnetic computations, multiparticle beam-dynamics simulations with high currents, and thermal-stress analysis-for an IH-PMQ accelerator tank are presented. The accelerating-field profile in the tank is tuned to provide the best propagation of a 50-mA deuteron beam using coupled iterations of electromagnetic and beamdynamics modeling. Measurements of a cold model of the IH-PMQ tank show a good agreement with the calculations. Examples of cross-bar H-mode structures with PMQ focusing for higher beam velocities are also presented. H-PMQ accelerating structures following a short radio-frequency quadrupole accelerator can be used both in the front end of ion linacs or in stand-alone applications.

High gradient linac for proton therapy

“…So, traveling through cells, the particle shows a linear displacement with energy, and zero integrated kick. Solutions proposed in previous works [30] were based on the modification of the drift tube shape and relative position with respect to the x axis, to reduce the dipole component. For the IH cavity under study, this presents the disadvantage of reducing the ZTT with respect to the nominal solution.…”

InterdigitalH-mode drift-tube linac design with alternative phase focusing for muon linac

“…The vertical trajectory is dominated by the finite value of the vertical electric field. In order to reduce the additional growth, some conventional solutions, such as the use of drift tube bulges [23], have been considered. However, this approach only reduces the vertical field by a small number of percentage points because the cell length is relatively large (because of the application of the IH structure to yield a higher β region).…”

“…However, insertion of the focusing sections increased the accelerator length and, hence, caused additional decay loss. One solution involves the use of an H-mode accelerating structure with permanent-magnet quadrupole (PMQ) magnets in the drift tubes [23]. However, although this setup provides sufficient transverse focusing, the production cost is increased.…”

Design of an alternating phase focusing Interdigital H-mode Drift-Tube-Linac with low injection energy

“…The high shunt impedance is attributed to the compact drift tubes and the enhanced transit-time factor from π-mode operation. With the APF (Alternating Phase Focusing) method or KONUS (Kombinierte Null Grad Struktur) applied, the dimension of the drift tubes decreases significantly, and the shunt impedance increases notably [4,5].…”