Field Emission in SRF Cavity Cryomodule

Muons, Inc. Innovation in Research

Particle Trajectories in String of Cavities

The figure shows field-emitted electron trajectories in a string of two JLab upgrade SRF cavities. The electrons are seeded at one iris (left) and can travel either down- or upstream.

Particle Trajectories in String of Cavities

Animated figure showing the evolution of field-emitted electrons, when seeded on the leftmost iris.

FEA Meshing

Field-emitted electron are seeded within surface mesh cells. The surface mesh is refined to allow improved seeding for numerical analyses.

surface mesh

volume mesh

refine surface mesh

Complete Cavity Cryomodule String

Field emission studies have been performed for a complete string of cryomodules

slice model has 509k elements 9.2 M elements for full structure

refined surface mesh original mesh

full CEBAF upgrade cavity string meshed

Field Emission Analysis using

Supercomputing (ACE3P/Track3P) {cavity 2, iris 1} {cavity 2, iris 2} {cavity 2, iris 3} {cavity 2, iris 4}

{cavity 2, iris 5} {cavity 2, iris 6} {cavity 2, iris 7} {cavity 2, iris 8}

Data analysis for a complete cavity cryomodule: One can identify similarities and discrepancies depending on seeding sites

Impact Probability

Overall probability of field-emitted electrons hitting anywhere within the cryomodule. Cavities are operating at 19.2 MV/m totaling 108 MeV energy gain for the main beam.

{cavities: all, irises: all}

Impact Energies along Cryomodule

Possible impact energy in a CEBAF upgrade cryomodule covering all cavity irises as probable field emission sites. Cavities are operating at 19.2 MV/m totaling 108 MeV energy gain for the main beam. Field-emitted electrons captured by the RF may accumulate energies close to 100 MeV.

{cavities: all, irises: all}

Field Emission Consequences

A significant amount of high energy field-emitted electrons may hit cryomodule components causing radioactivation.

Impact Energies along Cryomodule

Impact energies along the cryomodule allow analysis of measured radiation dose rates and topology along the cryomodule to identify dominant field emitters and potentially track back to dominant site of field emission within a cavity or even iris region

accelerating field (MV/m)

measured γ (mrad/h) and n (mrem/h) dose rates

Impact Energies along Cryomodule

Impact energies along the cryomodule allow analysis of measured radiation dose rates and topology along the cryomodule to identify dominant field emitters and potentially track back to dominant site of field emission within a cavity or even iris region

accelerating field (MV/m)

measured γ (mrad/h) and n (mrem/h) dose rates

Impact Energies along Cryomodule

Impact energies along the cryomodule allow analysis of measured radiation dose rates and topology along the cryomodule to identify dominant field emitters and potentially track back to dominant site of field emission within a cavity or even iris region

{cavity 2, iris 2}