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FCC-e + e - injector complex

FCC-e + e - injector complex. Ozgur Etisken CERN & Ankara University. Thanks to:

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FCC-e + e - injector complex

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  1. FCC-e+e- injector complex Ozgur Etisken CERN & Ankara University Thanks to: M. Aiba (PSI), F. Antoniou(CERN), A. Apyan (Yerevan Phys. Ins.), A. Barnyakov (BINP), M. Benedikt (CERN), T. Bondarenko (BINP), I. Chaikovska (LAL), T. Charles (Un. Melbourne & CERN), R. Chehab (LAL), A.K. Ciftci (IUE), K. Furukawa (KEK), B. Harer (CERN), B. Holzer (CERN), T. Kamitani (KEK), I. Koop (BINP), A. Levichev (BINP), N. Lida (KEK), P. Martyshkin (BINP), F. Miyahara (KEK), D. Nikiforov (BINP), S. Ogur(CERN), K. Oide (KEK), E. V. Ozcan (Bogazici U.), Y. Papaphilippou (CERN), S. Polozov (MEPhI), L. Rinolfi (CERN), J. Seeman (SLAC), T. Tydecks (CERN), F. Zimmermann (CERN) O. Etisken - FCC Workshop @Antalya 2019

  2. Outline • Injector baseline • Linac • up to 6 GeV • Positron production • Damping ring @ 1.54 GeV • Bunch compressor • Pre-booster ring up to 20 GeV • SPS (baseline) • Alternative design • Main booster ring • Conclusion e+/e- O. Etisken - FCC Workshop @Antalya 2019

  3. Injection filling scheme The main booster: 400 MHz BR, 20 ns bunch spacing, around 50-16640 bunches (of 130000 bucket) 0.32-2 s ramping time From 1 to 16 times injection into the main booster from SPS. …………….... ……………… ………… 20 ns 60 ns ………… ………… ………… From 50 to 520 times injection into the SPS from linac …………. 400 MHz SPS, 0.2 ramping time, 20 ns bunch spacing, around 50-1040 bunch (filled 50-1040 of 9200 buckets) 50-100 ms 60 ns 60 ns ……………… 2.8 GHz Linac, accelerating 1 or 2 bunhes 100-200 Hz repetition rate 60 ns bunch spacing (should be >50ns due to avoid beam break due to longed-ranged wake) Y. Papaphilippouet al. O. Etisken - FCC Workshop @Antalya 2019

  4. Bootstrapping Bunch charge does not change from the linac through BR. It is accumulated in the collider ring. The interleaved first fill of the collider is shown below (left) and top-up injection can be arranged to keep the charge imbalance to less than (right). The recently developed bunch schedules meet the requirements for all FCC-e+e- operating modes. A gradual decrease of the charge will be taken into account, such that the top-up is maintained within . S. Oguretal. O. Etisken - FCC Workshop @Antalya 2019

  5. Electron gun • The custom built RF gun has a normalized transverse emittance of <10 , and can provide up to 6.5 nC of charge at around 10 MeV. • The RF gun is based on a parallel coupled accelerating structure and has permanent magnets in the irises to reduce the beam size and limit emittance dilution. • It is planned to use material based on IrCe alloy as the photocathode because this provides acceptable lifetime with high charge extraction at high repetition rate. • The injector complex is designed to accelerate 3.4 nC electron or positron in a bunch, the charge extracted from the electron source are intentionally designed to be higher in order to have safety margins. • Apart from RF gun for the low e- beam, a thermionic gun will also be utilized in order to supply 10 nC of bunch charge for positron beam. A.M. Barnyakov, D.A. Nikiforov, A.E. Levichev (BINP) O. Etisken - FCC Workshop @Antalya 2019

  6. Linac (up to 6 GeV) The normal conducting linac will be fed by two electron sources, one will be the RF gun for the low emittance e- beam, and the second is the thermionic gun to provide higher charge needed for creating enough positrons from a hybrid target. The linac consists of S-Band structures accelerating the beam up to 6 GeV. Linac up to 1.54 GeV Linac up to 6 GeV (1.54-6 GeV) S. Oguretal. O. Etisken - FCC Workshop @Antalya 2019

  7. Damping Ring Two bunches per RF pulse in the linac, the bunch to bunch spacing was chosen as 60 ns. Two bunches per RF pulse in the linac will become a train in the DR. 5 trains with a 100 ns spacing and a bunch-to-bunch spacing 60 ns in the linac (Circumference should be around 240 m 800ns) • 2 straight section, • 6.64 m long wigglers, • 7 % energy acceptance, • 8 mm Dynamic aperture S. Ogur et al. O. Etisken - FCC Workshop @Antalya 2019

  8. Positron production e- 200 MeV Flux concentrator • Same linacused for positron production @ 4.46 GeV with bunch intensity of 4.2 x 1010particles.Positron beam emittances are reduced in DR @ 1.54 GeV. • After target, the capture section is composed of an AMD followed by the capture linac embedded in a DC solenoid magnetic field used to accelerate the beam until about 200 MeV. • Presented studies show that the comparable positron yield (1 Ne+/Ne-). • Detailed study is going on. And schemes with the bypass under consideration as well. I. Chaikovska, P. Martyshkinet al. O. Etisken - FCC Workshop @Antalya 2019

  9. Bunch Compressor FCC-e+e- injector requires two 1800 turnaround loops to transport the positron beam from the damping ring to the lower energy section of the linac. In addition, bunch compression is required to reduce the RMS bunch length from 5mm to 0.5 mm, prior to injection into the linac. Following the second loop, before the beam is injected back into the linac, is the location of the bunch compressor. (TBA to keep the beam size grow min.) Beam parameters at the damping ring exit CSR cancellation techniques were applied to minimize the emittance growth across the compressor to 6.8%. T. K. Charles et al. O. Etisken - FCC Workshop @Antalya 2019

  10. Pre-Booster Ring Two options are being considered for pre-booster synchrotron: using the existing SPS(baseline) or a new ring. The PBR basically needs to accept the beam from the linac (longitudinally and transversely) and increase the energy up to 20 GeV with the required beam parameters by main booster ring (BR). The injected parameters from linac and the required beam characteristics, defined by the BR and the linac, are summarized in tables below. O. Etisken - FCC Workshop @Antalya 2019

  11. Parameter Scaling for PBR • Scaling of dipole magnetic field of the main BR as a function of the filling factor and energy (left). • Scaling of extraction energy of the PBR as a function of the filling factor and circumference under a limit of 50 MeV energy loss per turn (right). • Scaling of horizontal emittance, energy loss per turn, horizontal damping time, energy spread as a function of the filling factor (FF) and circumference (C) for the PBR. • Considering the energy loss per turn to be around 50 MeV and average filling factor of 0.7-0.8, corresponding circumference is around 2.5-3 km. O. Etisken - FCC Workshop @Antalya 2019

  12. Main Cell and Phase advance 0.15m 0.15m 5.31 m 5.31 m kq1 0.1 m kq2 kq1 0.3 m 0.1 m 0.3 m 0.5 m 0.1 m 0.5 m 0.1 m 0.3 m 13.22 m • The phase advance of FODO are selected differently in the arc and in the straight sections as serving for different purposes. • The emittance of the ring is mainly determined by the cell in the arcs. The phase advance is needed to be chosen around 1350to ensure the minimum emittance. • In addition, the phase advance of a FODO in the straight sectionis chosen around 900 which provides the minimum beta function and efficient performance for the injection and extraction elements. • Lastly, the phase advance of the straight section is tuned for the working point optimization. Min. εx around 0.38 Min. β around 0.25 O. Etisken - FCC Workshop @Antalya 2019

  13. Damping wiggler magnets • The PBR needs to dump the beam to the equilibrium state, in less than half of a second, otherwise it will lengthen the PBR injection flat bottom and thus the whole injector cycle. • In this respect, damping wiggler (DW) magnets are proposed for achieving the desired damping time. • The damping time of the PBR is reduced to 0.1 s from 0.26 s with a wiggler peak field of 1.3 T and a total wiggler length of 16.2 m. O. Etisken - FCC Workshop @Antalya 2019

  14. Phase advance in the arc h/v emittance is mainly determined by arcs in the ring. Thus, FODO phase advance in the arc is scanned to observe the behavior of some important parameters like emittance, chromaticity, tune shift with amplitude, momentum compaction factor etc. • Minimum emittance can be obtained with the horizontal phase advance ̴ 0.383. • Emittance is getting higher slightly while the vertical phase is getting higher. • With the experience from CLIC damping ring considering the reaction of the lattice with alignment errors, 0.11is chosen for the vertical phase. O. Etisken - FCC Workshop @Antalya 2019

  15. Optics designs and layout The design of the PBR composes of 4 arcs and 4 straight sections. • Straight sections: • 5 cells, • Allocated for • Wiggler magnets, • RF elements, • Injection and extraction elements. Zero-dispersion section 5 FODO cell with close to 90 degree phase advance Dispersion suppressor and beta matching area Wigglers 1FODO with wiggler magnet is used to reduce the damping time at the injection energy in each straight section. Same wiggler structure with CLIC DR: x 8 wiggler = 16.2 m Arc: 35 FODO cells Phase advance is 137.8 degree Blue: dipole magnet Red: quadrupole magnet Green: sextupolemagnet O. Etisken - FCC Workshop @Antalya 2019

  16. Working point • Tune working point on a resonance diagram up to 5th order are shown on the plot above. • Systematic (red), non-systematic (blue), normal (solid) and skew (dashed) resonances are pointed. • The horizontal and vertical phase advances in the straight sections of the PBR are selected to be (µx, µy) = (0.383/0.11),(µx, µy) = (0.248/0.249) in the arcs and in the straight sections, respectively. • Thus, the working point of the PBR is (Qx,Qy) = (71.78/25.24). O. Etisken - FCC Workshop @Antalya 2019

  17. Frequency map analysis • DAsimulations were carried out with MADX-PTC. Particles with different initial conditions were tracked for 10000 turns. The calculation is performed including sextupoles and fringe fields for 0/1.5/-1.5 without magnet errors. • The plots below show the initial positions of the particles with the color coded diffusion coefficient () which is a measure of the frequency change in time. Large negative values of D indicate better stability whereas close to zero values shows chaotic motion. = -1.5% = 0 = 1.5% - As a result, the DA is calculated around 8 mm in horizontal plane for the determined working point as satisfying the requirement of the DA for the PBR. O. Etisken - FCC Workshop @Antalya 2019

  18. RF Voltage and Energy Acceptance The value of the maximum momentum deviation, for which a particle may have and still undergo stable synchrotron oscillation, is called the momentum acceptance of the accelerator. • Considering the maximum energy spread of the beam extracted from the linac, the energy acceptance is aimed to be 1.5% for the PBR design at injection energy. • The figure on the left shows the dependence of the energy acceptanceand the energy loss per turn with the RF voltage and the energyof the PBR. • Therefore, the minimum RF voltage is calculated as 3.6 MV to assure 1.5% energy acceptanceat injection and it increases up to 67MV at extraction energy. O. Etisken - FCC Workshop @Antalya 2019

  19. SPS as FCC e+e- pre-booster Using the SPS as a pre-booster for the FCC e+e- imposes some extra constraints, as minimum modifications can be applied to the existing machine. The SPS lattice is designed with FODO cells and the dispersion suppression is achieved by keeping the total arc phase advance a multiple of 2π. • The ring consist of 6 arcs and 6 straight sections, • 6 identicalperiods;eachsuper periodis composed of 18 FODOcells, • Eachsuper-period is around1.15km, • Τhecircumference is around6.9 km, • 744 dipoleswith6.26 m length. • Main limitations for SPS as FCC e+e- PBR: the damping time at injection and the emittance at extraction. Thus, the proposals are: • to move horizontal phase advance to 3π/4 (Q40)(SPS usuallytuned to π/2 phase advance for fixed target beams with integer tune of 26 (Q26) and since 2012 to 3π/8 (Q20) for LHC beams and considering even Q22), • to insert wiggler magnets. O. Etisken - FCC Workshop @Antalya 2019

  20. Robinson wiggler for SPS The Robinson wiggler (RW) is composed by a series of combined function magnets and theoretically changes the damping partition () by modifying the 4th synchrotron radiation integral (). • Due to the high energy loss per turn, the use of a Robinson wiggler in combination to the damping wigglers are being investigated. • The plot shows an analytical parametrization of the horizontal emittanceand energy spread with the damping partition. • Even though it is possible to achieve the required horizontal emittance with a combination of damping and Robinson wiggler magnets, the energy spread and energy loss per turn become still high at 20 GeV extraction energy of the SPS. • In this respect, different extraction energy options have been considered and the impact on the extracted beam parameters, based on MAD-X. O. Etisken - FCC Workshop @Antalya 2019

  21. SPS with different energies Different extraction energy options are investigated and summarized parameter can be seen below. It becomes clear that the 16 GeV option provides a reasonable energy spread, energy loss per turn and emittance at the same time. O. Etisken - FCC Workshop @Antalya 2019

  22. Phase advance in SPS • The Phase advance scanning of a FODO for SPS has been performed to find the optimum point in terms of emittance, chromaticity (h/v), momentum compaction factor, tune shift with amplitude. • Limited area can provide the required emittance and thus determines the horizontal integer of tune of the ring. limited area for achieving the required emittance O. Etisken - FCC Workshop @Antalya 2019

  23. Working point and DA = -1.5% = 1.5% = 0 • The horizontal and vertical phase of a FODO are selected to be (µx, µy) = (0.3747/0.24). The working point of the SPS is (Qx,Qy) = (40.38/26.71). • DA simulations were carried out with MADX-PTC. Particles with different initial conditions were tracked for 4400 turns. • The calculation is performed including sextupoles and fringe fields for on-momentum particles without magnet errors. O. Etisken - FCC Workshop @Antalya 2019

  24. RF Voltage and Energy Acceptance Considering the maximum energy spread of the beam extracted from the linac, the energy acceptance is aimed to be 1.5% for the PBR design at injection energy. • Figure on the left shows the dependence of the energy acceptanceand energy loss per turn with the RF voltage, energy spreadand the energy of the SPS. • Therefore, the minimum RF voltage is calculated as 25 MV to assure 1.5% energy acceptance at injection and it increases up to 45 MV at the extraction energy. O. Etisken - FCC Workshop @Antalya 2019

  25. Collective effect estimates for SPS and alternative ring • Collective effects is a phenomena which includes the evolution of a particle in a beam by the external EM fields and the extra EM fields created by the presence of other particles. Collective effects includes all the effects of these interactions with beam itself, beam-beam and beam environment. • The effects can cause tune changes, emittance growths and even beam loses. • Thus, investigating the collective effects and the instabilities is important for the PBR options. • Here, estimates have been made for the following effects: • Space charge, • Longitudinal – wave instability, • Transverse mode coupling instability (TMCI), • Coupled bunch instabilities, • Ion effects, • e-cloud, • Coherent synchrotron radiation (CSR), • Intra-beam scattering (IBS). O. Etisken - FCC Workshop @Antalya 2019

  26. Space charge • Corresponds to a continuous gradient error along the ring, • Causes tune shift, • Large tune shift may cause an emittance growth. The incoherent (direct) space charge tune spread is given by: = Bunch population = electron radius = Circumference = Beam length = h/v emittance (geo.) = Dispersion = Momentum spread • The tune shift in the vertical plane is calculated for the injected parameters and equilibrium state at injection energy. • The space charge incoherent tune shift for both the SPS and the alternative design is not very large. • The tune shift in horizontal plane should be smaller due to the emittance. • The coherent tune shift by the space charge (indirect, image charges) should be much smaller since it is inversely proportional to the square of the chamber radius rather than beam size. • The space charge is not expected to be a limitations for the FCC e+e- PBR. O. Etisken - FCC Workshop @Antalya 2019

  27. Longitudinal -wave instability The resistive wall impedance of the vacuum chamber may cause a source of longitudinal microwave instability and transverse mode coupling instability (TMCI). A broad band impedance (short lived wake) is expected to cause microwave instability above a threshold. The threshold for the longitudinal microwave instability can be evaluated: The Boussard criterion for long. microwave instability; = *D. Brandt et al., “Beam Dynamics Effects in the CERN SPS Used as a Lepton Accelerator”, in Proc. 13th Particle Accelerator Conf. (PAC’89), Chicago, IL, USA, Mar. 1989, pp. 1205–1208. • The threshold of longitudinal microwave instability (Boussard criterion) is higher than longitudinal impedance for SPS and alternative PBR. O. Etisken - FCC Workshop @Antalya 2019

  28. Transverse Mode Coupling Instability The resistive wall impedance of the vacuum chamber may cause a source of longitudinal microwave instability and transverse mode coupling instability (TMCI). In the transverse plane, head-tail interaction through a wake field can drive the bunch unstable. The threshold of strong head tail instability (also known as TMCI) can be estimated by: The transverse impedance is linked to the longitudinal one; = = b= beam pipe radius (40 mm for SPS, 30 mm for alt. PBR), (e=1.602*10-19) =/c : bunch length in ps • The transverse impedance exceeds the threshold for the SPS at the equilibrium state, • The transverse impedance is well lower than the threshold for the alternative ring. O. Etisken - FCC Workshop @Antalya 2019

  29. Ion effects The residual gas in the vacuum can be ionized and create positive ions by the electron beam in the accelerator. These ionsmay be trappedfor the ions which exceed a critical mass. The field from the trapped ions effects the electron beam and cause tune shift and emittance growth. Ions effects stronger at the tail of train since ion density becomes stronger with every bunch. The critical mass for trapping of a singly charged ion is: Tune shift introduced by the ion cloud at the end of the train: Rising time of the fast ion instability: @ eq. @ inj. • Trapping condition must be fulfilled in both x and y, so Ay is calculated since it is smaller, • Rise time is around 86 for alternative ring (with 10-10mbarr) and around 70 (with 10-11mbarr) for SPS, • Small tune shifts and long enough rise times that can be compensated with a feedback system, provided that ultra-low vacuum pressure can be achieved. O. Etisken - FCC Workshop @Antalya 2019

  30. E-cloud ‘Ionization of the residual gas’, ‘emission of electrons from photoelectric due to SR’ and ‘electron desorption from the vacuum chamber’ may generate e-cloud inside the vacuum pipe of the accelerator. And the e-cloud may affect the beam by causing instability. The e-cloudbuild up stops at a density roughly equal to the neutralization density, where the attractive force from the beam is on average balanced by the space-charge field of the electron cloud. Tune shift induced by e-cloud: Threshold density for the instabilities is: Neutralization density is: ; Angular oscillation frequency of the electrons interacting with the beam: • For both options, the neutralization density exceeds the threshold. However, the tune shifts for both options are not big. O. Etisken - FCC Workshop @Antalya 2019

  31. Coupled bunch instabilities The growth time of the coupled bunch instabilities by the transverse resistive wall has been estimated: Growth rate : • The growth times are long enough for damping with feedback system for both options. O. Etisken - FCC Workshop @Antalya 2019

  32. Coherent synchrotron radiation Emission of coherent synchrotron radiation by electron-positron beams may effect other beams as causing microwave instabilities. And this may cause an emittance growth. Theoretically, an intensity threshold can be calculated for estimation. Stupakov – Heifets Conditions for CSR: is momentum compaction factor, is energy spread, is electron radius. For alternative ring the condition-2 is satisfied but condition-1 is not. For SPS, both conditions are not satisfied. Thus, the CSR instability seems “not possible” for both rings. So, the Stupakov-Heifets parameter becomes: SPS Alt. 6 6 the microbunching instability can develop if the bunch length is large enough: 0.28*10-3 0.98*10-3 0.9*10-3 0.3*10-2 421 1100 277 741 C.1 4 3 307 250 4.1 1.3 Another necessary condition for the instability: 3.78 568 9233 18525 5000 1.02 C.2 *G. Stupakov and S. Heifets,”Beam instability and microbunching due to coherent synchrotron radiation” PHYSICAL REVIEW SPECIAL TOPICS - ACCELERATORS AND BEAMS, VOLUME 5, 054402 (2002). O. Etisken - FCC Workshop @Antalya 2019

  33. Intra-beam scattering Intra-beam scattering (IBS) is a small angle multiple Coulomb scattering effect between charged particles within accelerator beams, leading changes to beam parameters, especially on beam emittance. The plots show the first results of the emittance evaluation in time including Intra-beam scattering (IBS) effect for SPS and alternative ring. O. Etisken - FCC Workshop @Antalya 2019

  34. Main Booster The last stage of the FCC-ee injector chain is a 98 km full energy injector housed in the same tunnel as the collider. The magnetic lattice is of FODO structure. Two optics are used: first, a 900/900 optics for the operation at 120 GeV and 182.5 GeV, second, a 600/600 optics for 45.5 and 80 GeV. Layout the FCC hadron collider, which defines the geometry of the FCC main tunnel B. Harer, T. Tydecks et al. O. Etisken - FCC Workshop @Antalya 2019

  35. Conclusion • The baseline scheme for the FCC-e+e- injector complex is introduced • The design of injector complex provides the requirements for the collider ring • The RF-gun is ready for prototyping (?) • Linac design up to 6 GeV is completed • Linac up to 20 GeV is also under consideration • Optimization studies on-going for positron production • Pre-booster optimization and alternatives are going on • 16 GeV alternative ring is also under consideration • Main booster design is completed • Collective effects in the rings is continuing O. Etisken - FCC Workshop @Antalya 2019

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