FP7 NC WP 9 Task 9.2, Meeting #3, R.M. Jones, CERN, 7 Dec 20091

Roger M. JonesContribution from

Cockcroft Institute andThe University of Manchester

FP7 NC WP 9 Task 9.2, R.M. Jones, CERN, 7 Dec 2009

Roger M. Jones (Univ. of Manchester faculty)Alessandro D’Elia (Dec 2008, Univ. of Manchester PDRA based at CERN)Vasim Khan (Ph.D. student, Sept 2007)Part of EuCard ( European Coordination for Accelerator Research and Development) FP7 NCLinac Task 9.2

Collaborators: W. Wuensch, A. Grudiev, R. Zennaro (CERN)

2. FP420 –RF StaffWake Function Suppression for CLIC -Staff

V. Khan, CI/Univ. of Manchester Ph.D. student (pictured at EPAC 08)

A. D’Elia, CI/Univ. of Manchester PDRA based at CERN (former CERN Fellow).

FP7 NC WP 9 Task 9.2, R.M. Jones, CERN, 7 Dec 2009

Structure CLIC_G

Frequency (GHz) 12

Avg. Iris radius/wavelength

<a>/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 cavity 24

Bunch separation (rf cycles)

6

No. of bunches in a train

312

Lowest dipole∆f ~ 1GHzQ~ 10

Baseline CLIC_G Design => DDS1

CLIC_DDS Uncoupled Design

Re erf n 4i t / 2 2where : (t, f )

erf n / 2 2

22 tt

Truncated Gaussian :

W 2Ke (t, f )

Bandwidth Variation Variation

CLIC_G

FP7 NC WP 9 Task 9.2, R.M. Jones, CERN, 27 Dec 2009

Single Structure Wake

∆fmin = 65 MHz∆tmax =15.38 ns∆s = 4.61 m

∆fmin = 32.5 MHz∆tmax =30.76 ns∆s = 9.22 m

∆fmin = 16.25 MHz∆tmax = 61.52 ns∆s = 18.46 m

∆fmin = 8.12 MHz∆tmax =123 ns∆s = 36.92 m

Two-fold interleaving

Four-fold interleaving

Fails design criterion!

Meets design criterion!

Eight-fold interleaving

DDS1: Relaxed parameters (RP)–Wakefunction

<a>/λ=0.12 , ∆f = 3.6σ= 2.3 GHz, ∆f/favg= 13.75% %

FP7 NC WP 9 Task 9.2, R.M. Jones, CERN, 27 Dec 2009

Parameters CLIC_G (Optimised) [1,2]

CLIC_DDS1(Sparse sampled, Single structure)

CLIC_DDS1(8-fold

interleaved)

Bunch space (rf cycles/ns) 6/0.5 8/0.67 8/0.67Limit on wake (V/pC/mm/m) 7.1 5.6 5.3*Number of bunches 312 312 312Bunch population (109) 3.72 4.7 5.0*Pulse length (ns) 240.8 273 272.2*Fill time (ns) 62.9 42 40.8*Pin (MW) 63.8 72 75.8*Esur max. (MV/m) 245 232 236Pulse temperature rise (K) 53 47.3 51RF-beam-eff. 27.7 26.6 26.7*

Figure of merit (a.u.) 9.1 8.41 8.29*

[1] A. Grudiev, CLIC-ACE, JAN 08[2] H. Braun, CLIC Note 764, 2008* Mean value of 8 structures

DDS1: RF Summary

FP7 NC WP 9 Task 9.2, Meeting #3, R.M. Jones, CERN, 7 Dec 20096

• A first prototype of a single non-interleaved structure will be fabricated.

• Initial DDS, will be fabricated with a view to ensure it sustains High gradients.

• Mechanical realization will be done at CERN –Alessandro D’Elia will ensure this is completed (full engineering design).

• Aim at High Gradient tests by the end of 2010.

6

DDS Prototype CERN Tests

FP7 NC WP 9 Task 9.2, R.M. Jones, CERN, 7 Dec 2009

•As a result of the Oct 2009 collaborative 2-week CERN visit by Vasim further optimisation of the DDS is envisaged.•Vasim, Riccardo and Alessandro have settled on a revised geometry•Potential to reduce surface pulse temperature heating •Initial design indicate T ~ 20% less than DDS1

Elliptical geometry

DDS2 Wakefield and High Gradient Optimisation

FP7 NC WP 9 Task 9.2, R.M. Jones, CERN, 7 Dec 2009

~40 K

Single structure

Single structure

8-fold interleaved8-fold interleaved

Tolerable limit ~ 247 MV/m

DDS2 Preliminary SimulationsTolerable limit ~ 56 K

FP7 NC WP 9 Task 9.2, Meeting #3, R.M. Jones, CERN, 7 Dec 20099

• October 2009, Vasim visited CERN for 2 weeks in order to collaborate with Alessandro and Riccardo

• The original structure has been reviewed and a significant change in cell geometry has been proposed

• The new geometry exhibits promising surface fields: Hsur/Eacc ~ 4.45mA/V (limit 5.1-5.2mA/V) in cell 1

Esur/Eacc ~1.66 (limit 1.8) in cell 24 (consistent HFSS + MWS/CST simulations)

• Initial simulations indicate wakefield is well-damped (f ~ 2.16 GHz ~ 3.48 )

• Calculations made on the overall efficiency of DDS2 are comparable to CLIC_G

• Further simulations are needed to refine this design –in progress!

DDS2 Prototype CERN Tests

FP7 NC WP 9 Task 9.2, Meeting #3, R.M. Jones, CERN, 7 Dec 200910

Acknowledgements• We (UMAN) are pleased to acknowledge a fruitful

collaboration with R. Zennaro, A. Grudiev, G. Riddone and W. Wuensch!

Recent Publications• **V. Khan and R.M. Jones, Investigation of an alternate means of wakefield suppression in the main linacs of CLIC,

Proceedings of Particle Accelerator Conference (PAC 09), Vancouver, BC, Canada, 4-8 May 2009.

• **R. M. Jones, Wake field Suppression in High gradient linacs for lepton linear colliders, Phys. Rev. ST Accel. Beams 12, 104801, 2009, 14pp.

• R. M. Jones, V. A. Dolgashev, and J. W. Wang, Dispersion and energy compensation in high-gradient linacs for lepton colliders, Phys. Rev. ST Accel. Beams 12, 051001 2009, 11pp.

• R.M. Jones, C.E. Adolphsen, R.H. Miller, J.W. Wang , T. Higo, Influence of fabrication errors on wake function suppression in NC X-band accelerating structures for linear colliders, New J. Phys.11:033013,2009, 13pp.

• ** Published during period of FP7.

FP7 NC WP 9 Task 9.2, Meeting #3, R.M. Jones, CERN, 7 Dec 200911

• DDS1, as reported in detail at the SLAC workshop, has been abandoned in order to focus on a new geometry, DDS2, which offers superior surface fields (max TDDS2 ~ 40K, cf TDDS1 ~ 51K )

• First draft of the main geometrical parameters for first and last cell will be available this month –not expected to change radically during further optimisation in Jan/Feb 2010.

• Prior to Christmas break technicians will be provided with preliminary parameters for mechanical feasibility design.

• Optimization of the new cell geometry is expected to be finalised by, at the latest, Jan/Feb 2010.

• Vasim will visit CERN for 3 weeks in Feb (2 weeks to finalise design and,1 week to verify HFSS simulations)

• Structure will be high power tested towards end of 2010

Summary of CLIC DDS