High power X-band RF test stand development and high power testing of the CLIC crab cavity

This thesis describes the development and operation of multiple high power X-band RF test facilities for high gradient acceleration and deflecting structures at CERN, as re-quired for the e+ e- collider research programme CLIC (Compact Linear Collider). Signif-icant improvements to the control system and operation of the first test stand, Xbox-1 are implemented. The development of the second X-band test stand at CERN, Xbox-2 is followed from inception to completion. The LLRF (Low Level Radio Frequency) system, interlock system and control algorithms are designed and validated. The third test stand at CERN, Xbox-3 is introduced and designs for the LLRF and control systems are pre-sented. The first of the modulator/klystron units from Toshiba and Scandinova is tested. CLIC will require crab cavities to align the bunches in order to provide effective head-on collisions. An X-band travelling wave cavity using a quasi-TM11 mode for deflection has been designed, manufactured and tested at the Xbox-2 high power test stand. The cavity reached an input power level in excess of 50 MW, at pulse widths of 150 ns with a measured breakdown rate (BDR) of better than 10-5 breakdowns per pulse (BDs/pulse). At the nominal pulse width of 200 ns, the cavity reached an input power level of 43 MW with a BDR of 10-6 BDs/pulse. These parameters are well above the nominal design pa-rameters of an input power of 13.35 MW with a 200 ns pulse length. This work also de-scribes surface field quantities which are important in assessing the expected BDR when designing high gradient structures.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

Lancaster University

Year dc:date.issued

2015

Authors dc:creator

• Woolley, Benjamin
• Dexter, Amos
• Syratchev, Igor
• Burt, Graeme