Damping intense wake-fields in the main Linacs and PETS structures of the CLIC Linear Collider Vasim Khan: 1 st year PhD Student Supervisor: Dr. Roger Jones

Personal I have completed my MSc. in Physics from University of Mumbai (Bombay), India in June I have completed my MSc. in Physics from University of Mumbai (Bombay), India in June I was working as a Research Scientist in Society for Applied Microwave Electronic Engineering and Research (SAMEER) In Mumbai between July 2005 to Sept I was working as a Research Scientist in Society for Applied Microwave Electronic Engineering and Research (SAMEER) In Mumbai between July 2005 to Sept SAMEER is R & D lab. of Ministry of Information & Communication Technology, Govt. of India, is developing Medical Linear Accelerator (Linac) for Cancer Therapy. SAMEER is R & D lab. of Ministry of Information & Communication Technology, Govt. of India, is developing Medical Linear Accelerator (Linac) for Cancer Therapy. The basic structure of accelerator is side coupled, s-band, standing wave type. It is operated at  /2 mode. Maximum energy of bremsstrauhlung is 6 MeV. The basic structure of accelerator is side coupled, s-band, standing wave type. It is operated at  /2 mode. Maximum energy of bremsstrauhlung is 6 MeV.

University of Manchester + Cockcroft Institute I am working working with Dr. Roger Jones on damping intense wake-field in main Linac structure of CLIC Linear collider (Using HFSS 8.5). I am working working with Dr. Roger Jones on damping intense wake-field in main Linac structure of CLIC Linear collider (Using HFSS 8.5). CLIC is planned to collide electron and positron at energies of about 3TeV. The operating frequency of the collider is GHz in 2  /3 mode. The wake-field associated with the accelerating structure can severely effect the operation of the collider. CLIC is planned to collide electron and positron at energies of about 3TeV. The operating frequency of the collider is GHz in 2  /3 mode. The wake-field associated with the accelerating structure can severely effect the operation of the collider. It has theoretical as well as experimental aspects. Theoretical aspect involves the modelling of the wake –field in the accelerating structure, beam dynamics of the beam-wake interaction, studying the effect of wake-field on the beam stability & possible damping, detuning scheme. The experimentation of damping, detuning or both simultaneously will be carried out at CLIC test accelerator. It has theoretical as well as experimental aspects. Theoretical aspect involves the modelling of the wake –field in the accelerating structure, beam dynamics of the beam-wake interaction, studying the effect of wake-field on the beam stability & possible damping, detuning scheme. The experimentation of damping, detuning or both simultaneously will be carried out at CLIC test accelerator.

CLIC Parameters Proposed Figures RF Phasae advance/Cell 2  /3 Avg. Iris radius/Wavelength IP, OP iris radii 3.33, 2.4 (mm) IP, OP iris thickness 1.83, 0.83 (mm) IP, OP Group Velocity 1.93, 1.0 (%Vg/c) No. of Cells, structure length 25, 221 (mm) Bunch Separation 7 RF Cycles

NLC Structure CLIC test Structure NLC Structure CLIC test Structure

Damping by Detuning Wake Field is approximately proportional to the forth power of iris radius. In the detuning scheme, iris radius is reduced from first cell (3.33mm) to the last cell(2.4mm) and consequently synchronous frequency is achieved by adjusting the cavity radius. Wake Field is approximately proportional to the forth power of iris radius. In the detuning scheme, iris radius is reduced from first cell (3.33mm) to the last cell(2.4mm) and consequently synchronous frequency is achieved by adjusting the cavity radius. The wake –field is forced to partially decohere by detuning individual cells of each accelerating structure. The wake –field is forced to partially decohere by detuning individual cells of each accelerating structure. Manifold running parallel to beam axis will remove HOM but will also reduce the Q of the cavity. Manifold running parallel to beam axis will remove HOM but will also reduce the Q of the cavity. In NLC the bunch spacing is 1.4/2.8 ns, but for CLIC bunch spacin gis 0.5/0.58 ns, about 3 times smaller. Hence detuning must demand a more rapid fall-off in wake-field. In NLC the bunch spacing is 1.4/2.8 ns, but for CLIC bunch spacin gis 0.5/0.58 ns, about 3 times smaller. Hence detuning must demand a more rapid fall-off in wake-field.

Cell Structure :HFSS Cell Cell

Simulation results for first, mid and last cell Cell no. a(mm)b(mm)a1(mm)a2(mm)=a2/a1Vg/C(%)

Loss Factor Cell parameters i.e. iris and cavity radius follow an error function variation (ErF) and the wake-field falls off in a Guassian fashion. The kick factor weighted density function (Kdn/dF) is Guassian in frequency. Cell parameters i.e. iris and cavity radius follow an error function variation (ErF) and the wake-field falls off in a Guassian fashion. The kick factor weighted density function (Kdn/dF) is Guassian in frequency. The wake-field for short time scale is approximately given by the Fourier transform of the initial distribution. For short time scales wakefield is approximately given by: The wake-field for short time scale is approximately given by the Fourier transform of the initial distribution. For short time scales wakefield is approximately given by: W(s) ~∑ 2K n exp[-s  n /(2Q n )] exp(is  n )…………..(1) W(s) ~∑ 2K n exp[-s  n /(2Q n )] exp(is  n )…………..(1) Summation is carried over total no. of cells; Summation is carried over total no. of cells; K n &  n are uncoupled loss factor and synchronous frequency respectively. K n &  n are uncoupled loss factor and synchronous frequency respectively. K n = lVl 2 /4U………….(2) K n = lVl 2 /4U………….(2) The acatual wake-field that each bunch in the beam sees is given by the imaginary part of the above equation (1). The acatual wake-field that each bunch in the beam sees is given by the imaginary part of the above equation (1).

Band Partitioning Considering the band partitioning of kick factors in 206 cell DDS1 X- band structure (Facc= GHz) implies that largest kick factors located in the first dipole band. Considering the band partitioning of kick factors in 206 cell DDS1 X- band structure (Facc= GHz) implies that largest kick factors located in the first dipole band. CLIC design of Facc= GHz will shift the dipole bands up in frequency. CLIC design of Facc= GHz will shift the dipole bands up in frequency. Partitioning of bands changes with phase advance. Choosing a phase advance close to pi results in diminution of the kick factor for 1 st band and the enhancement of the 2 nd & 3 rd band. Same effect occurs at pi/2. Partitioning of bands changes with phase advance. Choosing a phase advance close to pi results in diminution of the kick factor for 1 st band and the enhancement of the 2 nd & 3 rd band. Same effect occurs at pi/2. For 2pi/3 mode such effect is not observe. For 2pi/3 mode such effect is not observe.

Loss factor Vs offset distance for Dipole bands of Cell no.1, 13 & 25. Cell No.1(Red) Cell No.13(Blue)Cell No.25(Green) Cell No.1(Red) Cell No.13(Blue)Cell No.25(Green) F 1 = GHzF 1 = GHzF 1 = GHz F 1 = GHzF 1 = GHzF 1 = GHz F 2 = GHzF 2 = GHzF 2 = GHz F 2 = GHzF 2 = GHzF 2 = GHz First Dipole Second Dipole First Dipole Second Dipole

Kick factor Vs offset distance for Dipole bands of Cell no.1, 13 & 25. Cell No.1(Red) Cell No.13(Blue)Cell No.25(Green) Cell No.1(Red) Cell No.13(Blue)Cell No.25(Green) K 1 = V/pC/mm 2 K 1 = V/pC/mm 2 K 1 = V/pC/mm 2 K 1 = V/pC/mm 2 K 1 = V/pC/mm 2 K 1 = V/pC/mm 2 K 2 = V/pC/mm2 K 2 = V/pC/mm2 K 2 = V/pC/mm2 K 2 = V/pC/mm2 K 2 = V/pC/mm2 K 2 = V/pC/mm2 First Dipole Second Dipole First Dipole Second Dipole

Loss factor Vs offset distance for first Sextupole band of Cell no.1, 13 & 25. Cell No.1(Red) Cell No.13(Blue)Cell No.25(Green) Cell No.1(Red) Cell No.13(Blue)Cell No.25(Green) F= GHzF= GHzF= GHz F= GHzF= GHzF= GHz

Plans for January-April 2008 Analysis of the present results. Analysis of the present results. Modeling of next higher order Dipole bands(3 rd,4 th,……) and Sextuple bands. Modeling of next higher order Dipole bands(3 rd,4 th,……) and Sextuple bands. Learning other code “GDFidL”. Learning other code “GDFidL”. Repeating whole exercise in GDFIdL. Repeating whole exercise in GDFIdL. Comparing results of HFSS 8.5 & GDFIdL. Comparing results of HFSS 8.5 & GDFIdL. ………….. Thank you. ………….. Thank you.