A. Aksoy Beam Dynamics Studies for the CLIC Drive Beam Accelerator A. AKSOY CONTENS ● Basic Lattice Sketches ● Accelerating structure ● Short and long range wakes ● Some results

A. Aksoy Introduction ● Work is based on finding best linac optics in order to transfer the beam to the delay loop (-combiner ring) in required tolerance. – The lattice has to prevent amplification of any jitter of the incoming beam. – It should also have a large energy acceptance and allow easy correction of the beam line. (strong focusing weaker focusing) – The final energy of the beam must be very stable since the energy acceptance of the Combiner Ring is limited. Energy spread should be less than about 1%. ● CLIC 2008 parameters and PLACET have been used for all calculations

A. Aksoy Basic Lattice Layout F. QuadDF. QuadAccel. Struc.Some add. Space for pickup ● Currently only FODO and triplet lattices was taken into account ● Both lattice cells have about 17 m length consist of 4 accelerating structure ● Accelerating structure has 3.75 m length (CLIC 2008 parameter list) ● There are 10 cm space between accelerators, distance between acc. and quads about 20 cm, quad lengths are 25 cm

A. Aksoy Accelerating Structure ● CLIC 2008 parameter list – 1 GHz SICA consist of 33 cell – Total length of accelerating structure 3.75 m – Gaps are equal for all cells although it differs for first and last cell a=54.4 mm b=118.5 mm L=99.96 mm g=80.76 mm

A. Aksoy Main effect; Wakes Due to fully loaded operation wakes are dominant ● The longitudinal kick experienced by the test particle per unit distance, divided by q 1, defines the longitudinal wake W L, ● and the transverse kick experienced by the test particle per unit distance, divided by q 1 x 1, defines the transverse wake W x. ● Distinguish between 2 regime; – Transient regime due to short range wakes – Resonant regime due to long range wakes v=c s x1x1 x2x2 q2q2 q1q1 The particles move near the axis are kicked by the field of first bunch thus; ● longitudinal kick is dominated by monopole fields (azimuthally indept.) ● and the transverse kick by dipole fields.

A. Aksoy Short Range Wakes in PLACET ● Short range wake expressions taken from ● Karl Bane, “Short-range Dipole Wakefields in Accelerating Structures for the NLC”, SLAC, for 206 cell Damped, Detuned Structure (DDS) ● This functions has the correct slope only for s=0 +, ● They are also similar for CTF3 3 GHz structure

A. Aksoy Short Range Wakes in PLACET ● Wakes for rms σ=2.5 mm bunch ● a) Gaussian bunch ● b) Longitudinal wake ● c) Transverse wake a)a) b)b) c)

A. Aksoy Long Range Wakes ● Dominant on emittance growth and causes BBU ● The model for CTF3 was taken into account for simulation – Q1=11 – Q2=400 – f=1GHz Long range wake at bunch position

A. Aksoy PLACET Results ● Initial beam parameters are same for both lattice type. Assumed that the beam injected drive linac at 50 MeV ● After matching beam the cell repeated till 2.3 GeV ● Total length of beamline about 1400 m consist of 326 accelerating structure ● Three times more quad for triplet than the FODO FODOTRIPLET

A. Aksoy Jitter Amplification for constant offset ● For tracking the jitter an offset was given to injected beam. ● long-range wakefields of first several bunches force the subsequent bunches to make growing oscillations. ● Subsequently offsets of accelerating structures or other beam line elements gives transverse deflecting kick to leading bunches. ● Sum of these effects bring a limit for jitter amplification. D. Schulte, PAC09 z c rrrr TRIPLET FODO

A. Aksoy Jitter Amplification for sinusoidal and random offsets z c ri z c FODO TRIPLET

A. Aksoy Emittance variation ● Emittance growth tracking through beamline for FODO and TRIPLET for different offsets ● Triplet lattice yields lower emittance growth for random and sine offsets.. FODOTRIPLET

A. Aksoy Conclusion and future plan ● This preliminary study shows that the performance of triplet lattice is better than FODO about multi bunch effects. ● Wake models should be revised and corrected (if necessary) ● Simulations will be renewed in details for different lattice types including doublet and different quad strengths. ● Acceptance parameters will also be simulated ● A magnetic bunch compressor will be studied as well at about 500 MeV energy