Internship for young academic teachers (CAS/36/POKL) CERN X-XII 2014 Zuzanna Krawczyk This work has been supported by the European Union in the framework of European Social Fund through the Warsaw University of Technology Development Programme.

Agenda Simulations of a new Short Waveguide Coupler The need of a new coupler design The ShoCo design process ShoCo prototype Estimation of the coupling coefficient and internal cell resonant frequencies of multicell cavities on the basis of the equivalent circuit model Parallel equivalent circuit model Corresponding field simulations 2 cells case

Short waveguide coupler

The current solution T-type Coupler The weight: 111kg The dimensions: 811x584.2x146.05[mm] Adjustable part: short circuit The T-type coupler connected to a PIMS cavity

Need for more compact design

ShoCo – Short Coupler Weight: 4.12kg Sizes: 160x50x310mm Adjustable parts: Big plungers – diameter of 36mm Small tuners – diameter of 20 mm The antenna

Types of simulation – ShoCo with connected cavity Eigenmode solution Symmetry Simulation time: 20 min Number of elements: Estimation of β parameter cavity vaacum cavity iris ShoCo The antenna

Types of simulation – ShoCo with T-coupler Solution type: driven modal, Network Analysis (S-parameters) Simulation time: 1-2 min Number of elements: 7500 Estimation of S parameters T-coupler ShoCo coupler Short circuit Port 1 Port 2

Position of the elements

Big plungers

Small tuners Just for the case when the initial coupling (big plungers fully out) is not sufficient.

The prototype The prototype of the ShoCo connected to the PIMS cavity

Results + cavity-to-waveguide coupling adjustable as desired - resonant frequency of the center cell strongly modified (~1MHz) => strong change of the field distribution inside the cavity (+/- 12% flatness error) => modification of the coupler is needed

Equivalent circuit for Resonant Coupled Structures

Equivalent circuit model We described resonant coupled structure with an equivalent circuit model, where each structure is represented by a parallel RLC circuit. k1 – first order coupling k2 – second order coupling R,L,C – lumped parameters: resistance, inductance, capacitance In – current which goes through the inductor n

Equations for the circuit in terms of k,Q, ZL and modes frequencies

Equations transformed to eigensystem form – A matrix

2 - cells model k 1 -? f 01 -? f 02 -? f M01,f M02, voltages Unknowns: internal frequencies of cells and coupling coefficient:

HFSS – field simulations Model of two cells in the eigenmode solution type was set up. To speed up the simulation 30% of the cavities rings was modelled Both cavities were modelled with tuning rings Obtained: mode frequencies

The procedure Detune the first cell (0- 50mm, step 1mm) with second tuner in the position: 0mm 10mm 20mm Observation: The minimal difference between the two mode frequencies – when both tuners are at the same position (both cavities are the same)

Comparison of the changes in mode frequency by detuning the first cell in HFSS simulation and by changing the internal frequency of the first cell in internal circuit simulation

Setup of the parameters

Relation between two mode frequencies for different coupling coefficient : - measurements from HFSS simulation (change of the first tuner from 0 to 50mm) Solid lines – RLC simulation, with change of internal frequency of first cavity from to 390 MHz

Results For 2 cells cavities procedure has been established Precision: ~1% of coupling factor For 3 cells investigation is ongoing