TWIICE 2014: Topical Workshop on Instabilities, Impedances, and Collective Effects

1. TWIICE 2014: Topical Workshop on Instabilities, Impedances, and Collective Effects BEAM COUPLING IMPEDANCE STUDIES OF THE CLIC DAMPING RING EXTRACTION KICKER C. Belver-Aguilar (IFIC) Onbehalf of: A. Faus-Golfe (IFIC), F. Toral (CIEMAT), M.J. Barnes (CERN) http://gap.ific.uv.es

2. KICKER PARAMETERS FOR CLIC DAMPING RINGS 16th January 2014 TWIICE workshop 1/12

3. KICKER TECHNOLOGY AND PARAMETER CHOICES PARAMETERS FOR THE STRIPLINES OF THE EXTRACTION KICKER OF THE DAMPING RINGS • Striplines have a significantly lower longitudinal beam coupling impedance, than a screened MKI magnet, at frequencies above 400 MHz . • The imaginary component of the longitudinal beam impedance is known to be significant, for the MKI magnet above 600 MHz. • The use of striplines rather than a screened ferrite loaded magnet is supported by experience at KEK/ATF, where metallized ceramic tubes were used to reduce the beam coupling impedance of ferrite loaded kickers: the thickness of the metallization was difficult to accurately control and, as a result, two kickers had very different pulsed magnetic characteristics. 16th January 2014 TWIICE workshop 2/12

4. STRIPLINE KICKER OPERATION COUPLED LINES → TWO OPERATION MODES: ODD AND EVEN MODE • ODD MODE: • The electric field lines have an odd symmetry about the centre line, and a voltage null exists between the two electrodes. • There is a virtual ground plane midway between the electrodes (capacitance = 2C12) • The effective capacitance between an electrode and ground is . • EVEN MODE: • The two electrodes are at the same potential, so there is no charge stored in the capacitance between them. • The resulting capacitance of either electrode to ground is . Eachmode has itsownelectromagneticfieldpattern and itsowncharacteristicimpedance: 16th January 2014 TWIICE workshop 3/12

5. CHARACTERISTIC IMPEDANCE CALCULATION: ANALYTICAL APPROXIMATION Thegeometriccross-section of thestriplines defines thecharacteristicimpedance and thehomogeneity of theelectromagneticfield in theaperture. FIRST-ORDER ANALYTICAL APPROXIMATION: plate-typeelectrode : parallelplatecapacitance, whereedgeeffects and fringefields are neglected. : capacitancebetween a strip conductor and aninfinitegroundplane. • isthepermittivity of free-space • isthesurfacearea of oneplate 16th January 2014 TWIICE workshop 4/12

6. CHARACTERISTIC IMPEDANCE CALCULATION: ANALYTICAL APPROXIMATION versus HFSS SIMULATION ANALYTICAL EQUATION HFSS SIMULATION • It is confirmed that a small stripline beam pipe radius results in closer values of even and odd mode characteristic impedance. • The even mode characteristic impedance of striplines is always higher than the odd mode. • For half-moon electrodes (simulation), the odd mode impedances are all equal. For a 50 Ω even mode characteristic impedance, an odd mode characteristic impedance of 40.9 Ω is achieved with a stripline beam pipe radius of 20 mm. • R = 20 mm • Higher odd mode characteristic impedance • Good field homogeneity HFSS SIMULATION 16th January 2014 TWIICE workshop 5/12

7. BEAM COUPLING IMPEDANCE: ANALYTICAL EQUATIONS FOR UNTAPERED STRIPLINE BEAM POSITION MONITORS • istheevenmodecharacteristicimpedance • isthecoverageangle of a single electrode • isthe angular frequency • isthestriplineslength • isthestriplinebeam pipe radius • At low frequencies: • Longitudinal impedance per harmonic: • where is the DR radius. • Transverse impedance: High frequency beam coupling impedance is an open question to be studied. 16th January 2014 TWIICE workshop 6/12

8. BEAM COUPLING IMPEDANCE: CST SIMULATIONS • Geometric parameters: • = 1,8 rad • = 1,7 m • = 20 mm 16th January 2014 TWIICE workshop 7/12

9. FIRST RESULTS IN TAPERING STUDIES • Advantages of taperingthetransitionbetweentheelectrode and theadjacentbeam pipe: • Minimimizethe non uniformity of transversedeflection as a function of thetransverse position; • Minimizethecontribution of thekickertothe machine impedance; • Minimizethereflectioncoefficient at highfrequency Thanks to S. Smith 16th January 2014 TWIICE workshop 8/12

10. MANUFACTURING PROCESS: Trinos VacuumProjects 16th January 2014 TWIICE workshop 9/12

11. FIRST LABORATORY TESTS AT CERN S11 PARAMETER • The frequencybetweenpeaksis ≈95 MHz, whichcorresponds to thetwo-waydelay of theelectrodes. • Theelectrodesupports (Macor rings) increasethemagnitude of thereflectionparameterstartingfrom 300 MHz, of everythirdpeak. • Theseparationbetweenthesemaximacorresponds to thedistance, there and back, betweentheequally-spaced Macor rings. 16th January 2014 TWIICE workshop 10/12

12. FUTURE TESTS WITHOUT BEAM • Verification of thestriplinedimensions. • Vacuumcompatibility. • High voltage performance. • Longitudinal and transversebeamcouplingimpedancemeasurements.. FUTURE BEAM TESTS • Striplinesnotused as a extraction device andwithoutinductive adder • Longitudinal and transverse beam coupling impedance • Striplines not used as extraction device and withinductive adder • Field inhomogeneity • Pulse shape and repeatability • Long term reliability of the system • Once long-term reliability is demonstrated: possible use as extraction device 16th January 2014 TWIICE workshop 11/12

13. SUMMARY • The stripline design provides the performancespecified for the extraction kicker of the CLIC DRs: excellent field homogeneity, good power transmission and reasonable broadband beam coupling impedance. • The stripline design has been carried out by using analytical approximations and simulations to optimize the stripline geometry. • Beam coupling impedance has been studied both analitically and with CST simulations, only for a low frequencies. The behavior of the kicker at high frequencies is an open question to be studied. • A prototype of the extraction stripline kicker for the CLIC DR has been manufactured by Trinos Vacuum Projects (Valencia, Spain). • Laboratory tests have commenced at CERN labs. Results for the reflection parameter S11 match quite well with the results predicted by the simulations. Other laboratory tests will be done in the next months. • The stripline and the inductive adder will be finally tested separately and jointly with beam. 16th January 2014 TWIICE workshop 12/12