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Minutes of the CLIC Meeting - 23 May 2003


Agenda: 
Local RF power switching in CLIC main linac
Speakers:
Igor Syratchev


Abstract:
After a short review of the CLIC PETS properties and configuration the different scenarios for switching off RF power locally in case of breakdown in PETS or accelerating structures will be discussed.

Igor gave a short introduction of the present Power Extraction and Transfer Structure (PETS) design.
copy of his transparencies (ppt format [including animations], or pdf format)
animation of the electric field in a PETS structure using steady state beam simulation with HFSS (avi format)
 
Then he discussed several mechanisms and scenarios for the local RF power production switching in a case of single CLIC PETS or accelerating structure failure. This is an important issue with R1 ranking in the ILC-TRC report.
For the case of accelerating structure failure, he proposed a local high RF power attenuator installation between single PETS and set of few structures in the form of a power splitter based on a rotating elliptic waveguide section and polarization sensitive RF power extractor in combination with a variable phase shifter to keep a constant output phase (see also CLIC Note 552). This could be also used to feed the PETS output back to the entry of the same or an adjacent structure to lower the fields.
Another possibility is the single PETS dephasing by splitting the PETS in two parts with an intermediate phase shifter.
Physical removal of a PETS could be one possible approach, as well.
Finally, he presented that detuning a PETS to 32.5 GHz would significantly reduce the output power. He showed to approaches:
- a modified PETS geometry with a pull/push option to increase the cavity size. This could reduce the power by a factor of six.
- a detuning by inserting 4 or 8 'knives' in the damping slots of the PETS which gives a reduction of about 1000.
Igor also showed a '8-petals' PETS with lower maximum surface field compared to the circularly symmetric PETS and a geometry nicely suited for the detuning knives installation.
Comparing the different solutions for power switch off, the PETS knife variant seems to be the most promising, due to its very good power suppression in the PETS and the accelerating structure together with a, at first look, good potential for mechanical feasibility.
copy of his transparencies (ppt format [including animations], or pdf format)
Ian Wilson proposed to initiate studies of a mechanical design for both the phase shifter and the 'knife'-PETS device.

In the discussion the question was raised if local phase shift capability is necessary or if global phase shifting of sectors together with a good pre-phasing during installation is sufficient. No final conclusion has been drawn and a follow-up is required.


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Frank Tecker  - Last updated  26-05-2003