Pressurized H2 RF cavities in ionizing beams and magnetic fields

Area of Science:

• Particle Accelerators
• Plasma Physics
• RF Engineering

Background:

• Operating radio frequency (RF) cavities within intense multitesla magnetic fields presents a significant technological challenge for muon cooling channels.
• Beam-induced plasma in RF cavities can lead to substantial RF power consumption, hindering efficiency.

Purpose of the Study:

• To experimentally validate the feasibility of a high-pressure gas-filled RF cavity for intense ionizing beams in strong magnetic fields.
• To investigate RF power consumption by beam-induced plasma and explore methods for its reduction.

Main Methods:

• Conducted proof-of-principle experiments using hydrogen and deuterium gases at pressures from 20 to 100 atm and RF gradients of 5-50 MV/m.
• Investigated the impact of varying oxygen concentrations on electron removal and RF power consumption.
• Measured electron attachment and ion-ion recombination rates.
• Tested cavity operation in a 3 Tesla solenoidal magnetic field.

Main Results:

• RF power consumption by beam-induced plasma was quantified.
• Analytical models for low-pressure scenarios showed good agreement with experimental data.
• Oxygen addition effectively reduced RF power consumption by removing free electrons.
• The gas-filled RF cavity operated effectively up to 3 T with no significant magnetic field dependence.

Conclusions:

• High-pressure gas-filled RF cavities are a viable technology for muon ionization cooling.
• The demonstrated performance in strong magnetic fields addresses a critical challenge in accelerator design.