XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Wakefields in Linacs Subjected to Detuning and Manifold Coupled Damping Roger M. Jones Cockcroft Institute and The University of Manchester

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Rationale for Wakefield Suppression  Charged particle beam excites parasitic modes  Why damp these modes?  Here we focus on linear collider applications in which a train of bunches is accelerated  In order to maintain Beam Quality and to ensure BBU (Beam Break Up) resonant instabilities do not occur the modes with particularly large kick factors must be damped

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Overview Two Main Parts: 1.Past experience in X-Band Linear Accelerating Structure Design: NLC /GLC (Next Linear Collider/Global Linear Collider). -Vast (more than 15 years) experience obtained in a collaborative (SLAC/KEK/FNL) design and fabrication of a host of test structures. -Principles of wakefield suppression and built-in structure diagnostic discussed 2.Alternate Design for Wakefield Suppression for CLIC: Initial studies at Cockcroft Inst./Univ. Manchester -Method described in 1 applied to CLIC

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Preservation of Luminosity

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Increased Energy Reach

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec SLAC NLCTA

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec  Why damp long range wakefields? BBU and Emittance dilution issues  Analysis of DDS (Damped and Detuned Structures Modal and spectral analysis  ASSET results: theoretical prediction (with no asposteri fittings) vs Experiment: DDS1, RDDS through to H60VG4A/B  Influence of fundamental coupler on wakefield  Stack measurements of RDDS  Built-in diagnostic properties of RDDS  Influence of fabrication errors on BBU and emittance dilution  New high phase advance structures (TW 5  /6 and SW  )  TW and SW designs and interleaving of frequencies  Limited local damping and manifold damping 1. Outline

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Features of Wakefields

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Wakefields Fundamentals

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Mode Multipoles

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec  Superconducting TESLA-style linacs have large cell apertures (~ 35 mm) => smaller wakes. ILC Choice!  NLC/GLC warm X-band linacs have small irises (~ 4 mm radius) =>larger wakefield.  CLIC has even smaller irises (~3 mm)! => larger wakes => needs heavy damping (Q~10) of dipole modes or can use moderate damping (Q~500) and detuning? ILC (1.3 GHz ) SLAC (2.8 GHZ) NLC/GLC (12GHz CLIC!) Spring8 (5.7 GHz ) CERN (30GHz Old!) 1. Comparison of Wakes in Various Accelerators

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec  Band partitioning of kick factors in 206 cell DDS1 X-band structure (f acc = GHz). Largest kick factors located in the first band. Third and sixth bands although, an order of magnitude smaller, must also be be detuned along with the 1 st band.  CLIC design f acc = GHz shifts the dipole bands up in frequency. 1. Band Partitioning Ref: Jones et. al, 2003, SLAC-PUB 9467  The partitioning of bands changes with phase advance. Choosing a phase advance close to pi per cell results in a diminution of the kick factor of the first band and and enhancement of the 2 nd and 3 rd bands. A similar effect occurs close to  /2.  Kick factors versus phase advance for cells with an iris radius of ~ 4.23 mm.

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Review of General Methods of Wake-Field Damping 1.Strong Damping (Q~10) => loss in the shunt impedance of the monopole mode. a)Magnetic coupling –azimithal slots (kidney slots) b)Electric coupling – longitudinal slots 2. Resonant suppression a)single frequency: f dipole = (n/2) f bunch (zero-mode crossing) b)multiple frequency, beat-note: f dipole1 – f dipole2 = n f bunch 3. Non-resonant suppression –Detuning a)Rectangular Kdn/df (kick factor weighted mode density) => sinc function wake b)Gaussian Kdn/df => Gaussian wake function c)Truncation of Gaussian necessitates light damping in addition to detuning d)Less sensitivity to frequency errors e)Less impact on fundamental mode shunt impedance

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec General Aspects of Detuning Gaussian density distributions  Kick factor weighted density function: Kdn/f ~ exp[-(  -  0 )2/ 2   2 ]  Ideally: W(t) ~ exp(-   2 t 2 /2)  Advantages over other methods 1.It is non-resonant and hence it does not freeze collider operation a bunch spacing other than the minimum bunch spacing. 2.Wakefield decreases rapidly and monotonically 3.It permits an error function interpolation with relatively sparse parameters  Disadvantages 1.Gaussian distribution is not limited and thus eventually it is truncated. This truncation gives rise to a sinc-like (=sin(x)/x) wake which curtails the rapid fall- off at a level dependent on the truncation point 2.The finite number of cells => finite number of modes => partial recoherence of wake-field starting at a time t ~ 1/  f max (where  f max is the maximum separation of modes). Also, with damping there is another coherence point, further out, at 1/  f min (where  f min is the minimum separation of modes, which lies in the centre of the Gaussian)

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec DDS Accelerators Installed in NLCTA at SLAC

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Tapering (Effects Detuning) of RDDS Accelerator

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Physics of Manifold Mode Coupling to Dipole Modes

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Coupling Along Complete Structure

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Circuit Model of DDS **Wakefield damping in a pair of X-band accelerators for linear colliders.R.M. Jones, et al, Phys.Rev.ST Accel.Beams 9:102001,2006.

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Circuit Model Equations

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Determination of Parameters

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Determination of Wakefunction

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Perturbation Analysis

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Spectral Function Method

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Spectral Function Regimes

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec (R)DDS HIGHLIGHTS: Features and Achievements/Lessons Many involved in the NLC/JLC programme (SLAC, KEK, FNAL, LLNL). Several major contributors here today: Roger Miller (see Friday plenary talk), Walter Wuensch (previous talk), Chris Adolphsen (see Thursday plenary on light source application), Sami Tantawi (this afternoon’s plenary).

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec DS Q cu RDDS1 ASSET Data Conspectus of GLC/NLC Wake Function Prediction and Exp. Measurement (ASSET dots) DDS3 (inc 10MHz rms errors) DDS1 RDDS1 H60VG4SL17A/B -2 structure interleaved Refs: 1. R.M. Jones,et al, New J.Phys.11:033013, R.M. Jones et al., Phys.Rev.ST Accel. Beams 9:102001, R.M. Jones, Phys.Rev.ST Accel. Beams, Oct., GLC/NLC Exp vs Cct Model Wake

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Meaurements lead by Chris Adolphsen, SLAC National Accelerator Lab..

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Determination of Modes in Structure via Stretched Wire Measurement

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec RDDS1 ASSET Measurement Contin.

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Multi-Functional Properties of Manifolds

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Determination of Cell Offset From Energy Radiated Through Manifolds

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Verification of Synchronous Frequencies from Measurement of Cell Stacks

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Summary of Manifold Suppression of Wakefields in Detuned Structures

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Fabrication Tolerances from a Beam Dynamics/Wakefield Suppression Perspective

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec RMS of Sum Wakefield as an Indicator of Beam Break (BBU) Instability

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Beam Dynamics Simulations Under the Influence of Frequency Errors

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Effect of Breakdown Observed in DDS

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Structure Breakdown and Group Velocity

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec New High Phase Advance Structures

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Interleaving of Cell Frequencies  The cells effectively sample the prescribed Gaussian distribution.  As there are a finite number of cells then eventually the modes add up constructively and the wake-field re-coheres at (t ~ 1/f min ).  We can fabricate structures such that neigbhouring structures are interleaved to reduce the magnitude of the re-coherence peak and to push it further out from the location of the first trailing bunch

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Wake-Field of Two-Fold Interleaved Structure  Spectral function and the inverse Fourier transform thereof for both individual and two-fold interleaved structures  The method of interleaving can be a straightforward positioning of each cell at the mid-point of the uncoupled single-cell of its neighbour or, the synchronous frequencies are chosen according to the location of the coupled frequencies. Clearly, the latter method is optimum.  The method display above used the mid-point of the separation of the cell synchronous frequencies. It was chosen in order to make a rapid experimental comparison with the predicted wake-field.  The amplitude of the re-coherence peak can be reduced with further optimisation. Spectral function and the wake-function for H60VG4SL17A

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Impact of Fabrication Errors on Wakefield Suppression in RDDS1 Frequency Errors Wakefield Experienced by Bunches Kdn/df and Mode Spacing

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Beam Dynamics and Relaxed Tolerances  Emittance dilution (illustrated by the red dashed curve) versus the percentage change in the bunch spacing.  Also shown is the corresponding rms of the sum wake-field (by the solid blue curve).  Emittance we incorporate random frequency errors into a set of 50 accelerating structures and randomly distribute them along the entire linac. In all cases the beam is injected into the linac with an offset of approximately one  y, with an energy of 5 GeV and the progress of the beam is monitored as it traverses the entire linac.  The final emittance dilution, together with the rms of the sum wake-field, is illustrated for small changes in the bunch spacing.  The particular simulation illustrated includes a cell-to-cell frequency error with an rms value of 20 MHz. We chose this rather large frequency error in order to gain an understanding of the impact of relaxed **Wakefield damping in a pair of X-band accelerators for linear colliders.R.M. Jones, et al, Phys.Rev.ST Accel.Beams 9:102001,2006.

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Summary of NLC/GLC Wakefield Damping  Detuning along with moderate damping has been shown to be well-predicted by the circuit model.  Interleaving of successive structures allows the detuning to be effective.  Manifold wakefield suppression has added benefits: 1.Serves as built-in beam diagnostic 2.Allows internal alignment of cells to be obtained from manifold radiation 3.Serves as vacuum pump-outs.

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Summary  Analytical truncated Gaussian is a useful design tool to predict wakefield suppression.  Initial design provides a well-damped wakefield.  Including the constraints imposed by breakdown forces a consideration of zero-point crossing.  Beam dynamics study including systematic and random errors in progress –will provide detailed answer.  Manifold damping provides useful characteristics of built-in BPM together with a direct indication of internal alignments

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec X-Band Wake-field Suppression for CLIC

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec  Roger M. Jones (Univ. of Manchester faculty)  Alessandro D’Elia (Dec 2008, Univ. of Manchester PDRA based at CERN)  Vasim Khan (PhD student, Sept 2007)  Nick Shipman (PhD student Sept 2010, largely focused on breakdown studies)  Part of EuCARD ( European Coordination for Accelerator Research and Development) FP7 NCLinac Task 9.2  Major Collaborators: W. Wuensch, A. Grudiev, I. Syrachev, R. Zennaro, G. Riddone (CERN) 2. FP420 –RF Staff Wake Function Suppression for CLIC -Staff V. Khan, CI/Univ. of Manchester Ph.D. student Finishing 2011!? A. D’Elia, CI/Univ. of Manchester PDRA based at CERN (former CERN Fellow). N. Shipman, NEW! CERN/CI/Univ. of Manchester Ph.D. student

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Overview Three Main Parts: 1.Initial designs (three of them).  CLIC_DDS_C. 2.Further surface field optimisations  CLIC_DDS_E(R). 3.Finalisation of current design. Based on moderate damping on strong detuning. Single-structure based on the eight-fold interleaved for HP testing  CLIC_DDS_A 4. Concluding remarks and future plans.

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Introduction –Present CLIC baseline vs. alternate DDS design  The present CLIC structure relies on linear tapering of cell parameters and heavy damping with a Q of ~10.  Wake suppression is effected through waveguides and dielectric damping materials in relatively close proximity to accelerating cells.  Choke mode suppression provides an alternative, but as shown for SW (V. Dolgashev et al), it will negatively impact R sh -planned TW structures are worth investigating though (see WG talk by J. Shi)  A viable alternative is presented by our CLIC_DDS design - parallels the DDS developed for the GLC/NLC, and entails: 1. Detuning the dipole bands by forcing the cell parameters to have a precise spread in the frequencies –presently Gaussian Kdn/df- and interleaving the frequencies of adjacent structures. 2. Moderate damping Q ~

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec EPAC, 26 June 2008W. Wuensch, CERN HOM damping waveguides Magnetic field concentration – pulsed surface heating High electric field and power flow region - breakdown Short range wakefields Cooling Vacuum pumping Alignment Beam and RF GHz, 2π/3 with a mm period Current CLIC Baseline Accelerating Structure

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec ) RF breakdown constraint 2) Pulsed surface temperature heating 3) Cost factor Beam dynamics constraints 1) For a given structure, no. of particles per bunch N is decided by the /λ and Δa/ 2) Maximum allowed wake on the first trailing bunch Wake experienced by successive bunches must also be below this criterion Ref: A. Grudiev and W. Wuensch, Design of an x-band accelerating structure for the CLIC main linacs, LINAC08 CLIC Design Constraints

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Initial CLIC_DDS Designs Three designs 1.Initial investigation of required bandwidth to damp all bunches (~3GHz) –succeeds to suppress wakes, fails breakdown criteria! 2.New design, closely tied to CLIC_G (similar iris  a), necessitates a bandwidth of ~ 1 GHz. Geometry modified to hit bunch zero crossings in the wakefield -succeeds from breakdown perspective, tight tolerances necessary to suppress wakes! 3.Relaxed parameters, modify bunch spacing from 6 to 8 rf cycles and modify bunch population. Wake well-suppressed and satisfies surface field constraints. CLIC_DDS_C (  f ~ 3.6 , 13.75%) –SUCCESS (on suppressing wakes and meeting breakdown criteria) Three designs 1.Initial investigation of required bandwidth to damp all bunches (~3GHz) –succeeds to suppress wakes, fails breakdown criteria! 2.New design, closely tied to CLIC_G (similar iris  a), necessitates a bandwidth of ~ 1 GHz. Geometry modified to hit bunch zero crossings in the wakefield -succeeds from breakdown perspective, tight tolerances necessary to suppress wakes! Three designs 1.Initial investigation of required bandwidth to damp all bunches (~3GHz) –succeeds to suppress wakes, fails breakdown criteria!

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec StructureCLIC _G Frequency (GHz)12 Avg. Iris radius/wavelength /λ 0.11 Input / Output iris radii (mm) 3.15, 2.35 Input / Output iris thickness (mm) 1.67, 1.0 Group velocity (% c)1.66, 0.83 No. of cells per cavity24 Bunch separation (rf cycles) 6 No. of bunches in a train 312 Lowest dipole ∆f ~ 1GHz Q~ Initial CLIC_DDS Design –  f determination CLIC_DDS Uncoupled Design Bandwidth Variation  Variation CLIC_G 

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Uncoupled parameters Iris radius = 4.0 mm Iris thickness = 4.0 mm, ellipticity = 1 Q = 4771 R’/Q = 11,640 Ω/m vg/c = 2.13 %c Iris radius = 2.13 mm Iris thickness = 0.7 mm, ellipticity = 2 Q = 6355 R’/Q = 20,090 Ω/m vg/c = 0.9 %c Cell 1 Cell 24 (f/ = %) 2.3 Relaxed parameters tied to surface field constraints Cct Model Including Manifold- Coupling  Employed spectral function and cct model, including Manifold- Coupling, to calculate overall wakefunction.

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec b Rc a a+a1 R 59 Structure Geometry Cell parameters a1 t/2 a L Iris radius Cavity radius Sparse Sampled HPT (High Power Test) Fully Interleaved 8-structures a min, a max = 4.0, 2.13 b min, b max = 10.5, 9.53 Structure Geometry: Cell Parameters

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Avoided crossing Uncoupled 2 nd mode Uncoupled 1 st mode Uncoupled manifold mode Coupled 3 rd mode Light line Relaxed parameters –full cct model Avoided crossing Uncoupled 2 nd mode Uncoupled 1 st mode Uncoupled manifold mode Coupled 3 rd mode Light line  Dispersion curves for select cells are displayed (red used in fits, black reflects accuracy of model)  Provided the fits to the lower dipole are accurate, the wake function will be well- represented  Spacing of avoided crossing (inset) provides an indication of the degree of coupling (damping Q) End Cell Mid-Cell Avoided crossing Uncoupled 1 st mode Uncoupled manifold mode Coupled 3 rd mode Light line Uncoupled 2 nd mode First Cell

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec cells 8-fold interleaving 24 cells No interleaving 192 cells 8-fold interleaving Manifold Coupling slot Dipole mode Manifold mode ∆fmin = 65 MHz ∆tmax =15.38 ns ∆s = 4.61 m ∆fmin = 8.12 MHz ∆tmax =123 ns ∆s = m ∆f=3.6 σ =2.3 GHz ∆f/fc=13.75% Summary of CLIC_DDS_C Meets design Criterion?

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec CLIC_DDS_E  Enhanced H-field on various cavity contours results in unacceptable  T (~65° K).  Can the fields be redistributed such that a ~20% rise in the slot region is within acceptable bounds?  Modify cavity wall  Explore various ellipticities (R. Zennaro, A. D’Elia, V. Khan)

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Circular Square Elliptical Convex Concave CLIC_DDS_E Elliptical Design b a

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Circular Square ε=-8.28 ε=-4.14 ε=-2.07 Convex ellipticity Concave ellipticity Single undamped cell Iris radius=4.0 mm CLIC_DDS_E Elliptical Design –E Fields

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec CircularRectangularElliptical (Convex) Elliptical (Concave)  of cavity 1∞ f acc (GHz) Eacc(V/m) H sur max /Eacc (mA/V) E sur max /E acc Iris radius = 4.0 mm Iris thickness = 4.0 mm CLIC_DDS_E Elliptical Design, Single Undamped Cell Dependence of Fields on  Chosen design

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Optimisation of cavity shape for min Circular (  =1) Rectangular (  =∞) ε=4.14 ε=2.07 ε=1.38 ε =0.82 ε=0.41 Undamped cell Optimised parameters for DDS2 Circular cell ε=0.82 ε=1.38 Manifold-damped single cell CLIC_DDS_E Single-Cell Surface Field Dependence on ε  Iris radius ~4mm. For both geometries  Averaging surface H over contour  =1.38 See WG talk by Vasim Khan

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Efficiency ∆f dipole ∆T P in  Optimisation of parameters based on manifold damped structures.  Vary half-iris thickness.  3-cell simulations, with intermediate parameters obtained via interpolation.  Choose parameters with minimal surface E-field, pulse temperature rise, and adequate efficiency. Chosen optimisation (CLIC_DDS_E) CLIC_DDS_E, Optimisation of:, ∆f and Efficiency

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec RcRc h r1r1 2*r 2 r2r2 h1h1 r 1 +h+2r 2 r1r1 a1 a2a2 g=L - t L a t= 2a 2 Radius = 0.5 mm Variable parameters (mm) Cell #1Cell#24 a b a a1a22a2 Rc r Constant parameters (mm) All cells L r10.85 h4.5 h11.25 cavity and manifold joint 1.0 Rounding of cavity edge CLIC_DDS_E: Detailed Geometry

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec ParameterDDS1_CDDS2_EModified to achieve ShapeCircularEllipticalMin. H-field (mm) Min. E-field R c 1to 24 (mm) Critical coupling DDS1_C DDS2_E 3. Impact on Parameters: CLIC_DDS_C to CLIC_DDS_E DDS1_C DDS2_E

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec CLIC_DDS_E -Fundamental Mode Parameters DDS_E DDS1_C DDS_E DDS1_C DDS_E DDS1_C DDS_E Vg R/Q Q EsEs HsHs  Group velocity is reduced due increased iris thickness  R/Q reduced slightly  Surface field and  T reduced significantly by using elliptical cells

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec DDS_C DDS_E 3. Wake Function for CLIC_DDS_E -Dipole Circuit Parameters DDS_C DDS_E DDS1_C ∆f=3.5 σ =2.2 GHz ∆f/f c =13.75% a 1 =4mm a 24 =2.3mm   Cct   Avoided Crossing   Avoided crossing  x is significantly reduced due to the smaller penetration of the manifold.  Some re- optimisation could improve this

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec DDS1_C DDS2_E 3. Consequences on Wake Function Spectral Function Wake Function

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Rounding necessitates reducing this length (moves up) Rounding  To facilitate machining of indicated sections, roundings are introduced (A. Grudiev, A. D’Elia).  In order to accommodate this, R c needs to be increased  DDS2_ER.  Coupling of dipole modes is reduced and wake-suppression is degraded. How much? DDS2_E DDS2_ER RcRc 4. CLIC_DDS_E: Modified Design Based on Engineering Considerations  

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Light line Avoided crossing Uncoupled 2 nd Dipole Mode Cell # 1 Cell # CLIC_DDS_ER Dispersion Curves Uncoupled Dipole mode Uncoupled manifold mode Cell # 1 Cell # 24 Light Line  

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec CLIC_DDS_E :Rc= mm (optimised penetration)  CLIC_DDS_ER : Rc=6.8 mm const (a single one of these structures constitutes CLIC_DDS_A, being built for HP testing)  Wakefield suppression is degraded but still within acceptable limits. 4. CLIC_DDS_E vs CLIC_DDS_ER Wakefield Spectral FunctionWakefunction

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec  Info. on the ability of the 8-fold interleaved structure to sustain high e.m. fields and sufficient  T can be assessed with a single structure.  Single structure fabricated in 2010/1 st quarter 2011, CLIC_DDS_A, to fit into the schedule of breakdown tests at CERN. 4. CLIC_DDS_A: Structure Suitable for High Power Testing  Design is based on CLIC_DDS_ER  To facilitate a rapid design, the HOM couplers have been dispensed with in this prototype.  Mode launcher design utilised  SRF design complete!  Mechanical drawings, full engineering design completed!  Qualification end cells fabricated. Recently received (Oct !)!

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Cell # 1 Cell # CLIC_DDS_A: Structure Suitable for High Power Testing  Non-interleaved 24 cell structure –first structure of 8-fold interleaved structure chosen.  High power (~71MW I/P) and high gradient testing  To simplify mechanical fabrication, uniform manifold penetration chosen Illustration of extrema of a 24 cell structure

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec CLIC_DDS_A Fundamental Mode Parameters

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Max. Values Esur=220 MV/m ∆T = 51 K Pin= 70.8 Eacc_UL=131 MV/m Sc=6.75 W/μm 2 RF-beam-eff=23.5% ∆T 35*Sc Esur Eacc Pin Dashed curves : Unloaded condition Solid curves: Beam loaded condition CLIC_G Values Esur=240 MV/m ∆T = 51 deg. Pin= 63.8 Eacc_UL=128 MV/m Sc=5.4 W/μm 2 RF-beam-eff=27.7% 4. CLIC_DDS_A Parameters

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec cells No interleaving 24 cells No interleaving Undamped Damped Q avg ~ CLIC_DDS_A Wake  Wake of a non-interleaved 24 cell structure –first structure of 8-fold interleaved structure chosen.  Motivated by high gradient testing  Wake is measurable and provides a useful comparison to simulations (but will not, of course, meet beam dynamics criteria)  FACET tests of wake at SLAC?

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Matching CLIC_DDS_A  Firstly, match-out either end of structure with regular cells:  Structure for test will utilise a mode launcher  Initially, simulate a structure with one regular cell and two matching cells at either end and we study the minima in S 11 as a function of the geometrical parameters of the matching cells (a, L –adopt L variation, rather than b, from space considerations)  Add additional (2, then 3) identical standard cells (const. imp) and follow the same procedure and modify parameters of matching cells to minimise S 11  The matching condition (on a, L) is that which coincident with all 3 simulations.  Secondly, once complete, match-out the full, tapered structure based on this match. I/P

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Beam Port11 Port 2 E-field 4. CLIC_DDS_A  Match-out the full, tapered structure  E-field and S 11 shown ~198.6mm Matching cell Surface E-Field Axial E-Field 5.0 See WG talk by Alessandro WG D’Elia 7.5 E s (V/m x10 4 ) E z (V/m x10 4 ) z (mm) z (mm) 0 225

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec V 26 in = 1 W2678 G 26 in = 1 W13481 P in CLIC_DDS_A S Params S12 S22 S GHz G Hz Q -50dB 0dB  /2  (GHz)

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Water pipes for cooling Vacuum flange Power input Power output Tuning holes Cutaway-view Bea m V.Soldatov, CERN 4. Mechanical Eng. Design of DDS_A

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Cell Qualification of CLIC_DDS_A  VDL (NL) have machined and measured several cells –end cells. New!(recvd by CERN Oct 2010)  Global profiles made with optical Zygo machine are illustrated for disk 24  Design, tolerance bounds and achieved profile shown  ETA of all cells –December 2010  Bonding of complete structure by 1 st quarter of G. Riddone, CERN Quarter cell contours Cell edge contours x (mm) 0.5 mm 1.5mm Measured Specified

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec Cell Qualification of CLIC_DDS_A  Local profile made with an optical Zygo machine  Local profiles indicate < 50nm variation in surface roughness  Cell 24 displayed G. Riddone, CERN -40 nm +40 nm

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec I/P at  /2  =15.9GHz 4. Work in Progress/R&D Opportunities  CLIC_DDS_A is equipped with mode launchers  CLIC_DDS_B includes full HOM ports  Initial studies on matching the HOM coupler for CLIC_DDS_B in progress (dipole band ~ 15.9 GHz – 18 GHz) Sic  Moving to a high phase advance (HPA) structure allows other parameters to be optimised  5  /6 phase advance structure design in progress (for initial design see Linac2010)  In the HPA design further features being explored  Additional manifold (8)  Influence of SiC rods on overall Q Enhanced Coupling Standard DDS Manifold Additional Manifold

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec  CLIC_DDS_A : RF (including mode launcher matching cells) and mechanical design has been completed.  Qualifications cells fabricated (VDL)–all cells by last quarter 2010  Structure will be subsequently bonded in the first quarter of 2011, -- ready for high power testing in 2011 at the CLIC test stand.  CLIC_DDS_B: Includes HOM couplers and interleaving. HOM coupler design in progress. 4. Final Remarks  Transfer cell fabrication to Morikawa in collaboration with KEK  Cell ETA April qualification cells, followed by full 24 cells  RF measurements (S21) at KEK  Bonded full structure ETA June 2011 (fits in with CLIC test stand programme available Sept 2011)  New CLIC_DDS R&D in progress:  HPA: High phase advance design is being studied. It Allows optimisation of the remaining parameters –minimise surface fields, wakefields at stipulated v g  Further optimisation is being explored by implementing additional manifolds and with the potential for the insertion of SiC rods to reduce the Q further

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec  I am pleased to acknowledge a strong and fruitful collaboration between many colleagues and in particular, from those at CERN, University of Manchester, Cockcroft Inst., SLAC and KEK.  Several at CERN within the CLIC programme, have made critical contributions: W. Wuensch, A. Grudiev, I. Syrachev, R. Zennaro, G. Riddone (CERN), T. Higo Y. Higashi (KEK). Acknowledgements 1.R. M. Jones, et. al, PRST-AB, 9, , V. F. Khan and R.M. Jones, EPAC08, V. F. Khan and R.M. Jones, LINAC08, V. F. Khan and R.M. Jones, Proceedings of XB08, R. M. Jones, PRST-AB, 12, , R. M. Jones, et. al, NJP, 11, , V. F. Khan and R.M. Jones, PAC09, V. F. Khan, et. al, IPAC10, V. F. Khan, et. al, LINAC10, CLIC DDS Related Pubs.

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec CLIC_DDS_A Mechanical Eng. Design

XB-10, ICFA Mini-Workshop, R.M. Jones, Cockcroft Inst., 30 th Nov-3 rd Dec RF parametersUnitDDS_ADDS_HPA42DDS_HPA32 Phase advance / cellDeg Iris thicknessmm4/ /2.8 Bunch population Q (In / Out)-5020 / /7045 R’ (In / Out)MΩ/m51 / /102.4 vg/c (In / Out)%2.07 / / 0.45 Eacc max (L./UnL.)MV/m105 / / 14390/ 138 P in MW ∆T max sur oKoK51 48 E max sur MV/m S c max W/μm RF-beam efficiency% Comparison 2π/3 vs 5 π/6