Departmental Oral Examination (Thesis Title: The TRIUMF nine-cell SRF cavity for ARIEL)

Speaker: 
PHILIPP KOLB
Event Date and Time: 
Thu, 2016-01-07 14:00 - 16:00
Location: 
ISAC-II Conference Room, TRIUMF
Local Contact: 
Physics and Astronomy, UBC
Intended Audience: 
Public

ABSTRACT:
Modern physics research relies on particle accelerators and available beam time is a very limited resource. The ARIEL eLINAC will strengthen the rare isotope program at TRIUMF by providing alternative way to create rare isotope beams (RIB). A possible way to add additional use to this machine is to create a return beam line and use the beam to excite a free electron laser (FEL). The remaining beam can be used to drive fields in the SRF cavities.

One limitation of these energy recovery LINACs (ERL) is beam-break up.

Higher order modes (HOM), especially dipole modes, have a negative influence on the beam which can lead to beam loss. The design of the SRF cavity has to accommodate this to make sure a beam current of up to 10mA can be used for both RIB production and ERL operation.

This thesis will go through the design process of the ARIEL 1.3GHz nine-cell cavity. The design relies on simulations to calculate the fields inside the cavity and with it the shunt impedance of HOMs.

The investigations showed that resistive beam line absorbers can be used to reduce the shunt impedance of HOMs sufficiently without interfering with the accelerating mode. The performance of the absorber material has been verified in dedicated low temperature measurements, while the HOM field distribution been measured via beadpulling on a copper model of the cavity. These measurements showed good agreement with the simulations.

The power dissipation in the SRF cavities is of vital importance. The cryogenic system is a significant part of the capital investment for the accelerator and sets the power budget for each cavity to around 10W.

This corresponds to a Q0value of 1*1010 at a operational temperature of 2K. The gradient goal is 10MV/m to reach the design energy of 50MeV with five cavities. Both Q0 and Eacc specifications have been met in the first two cavities that are installed in cryomodules. Two more cavities have been built and are in their qualification phase.

 

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