Latest ILC DR wiggler simulations M. Pivi, T. Raubenheimer, L. Wang (SLAC) July, 2005.
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Latest ILC DR wiggler simulations M. Pivi, T. Raubenheimer, L. Wang (SLAC) July, 2005
2 ILC 17 km TESLA DR wiggler sections (TESLA) Wiggler: Peak field 1.68 T Period 0.40 m Chamber semi-axis 16x9mm ~rectangular with antechambers on both sides (TESLA) Wiggler: Peak field 1.68 T Period 0.40 m Chamber semi-axis 16x9mm ~rectangular with antechambers on both sides Different models for the wiggler field: a) dipole b) c) Vacuum chamber design with ante-chambers, Reduced number of photons Cylindrical expansion model, Wolski-Venturini Cartesian model, Halbach
3 Figure 1: Horizontal, vertical, and longitudinal magnetic field as a function of longitudinal position for Cartesian (red dot symbols) and cylindrical models (blue dot symbols) at x=2 mm and y = 1 mm from the wiggler axis. ILC 17 km TESLA DR wiggler sections
4 Recent simulations Benchmarking of ECLOUD and POSINST in ILC TESLA DR wiggler Simulated electron cloud density with POSINST vary SEY params (Ex. deltamax=1.3, Emax=190eV). Photoelectrons rate is 0.007 electrons per meter per positron. Wiggler field “Cartesian” model. Rectangular chamber with semi-axis axb=16x9mm and two antechambers 10mm full size on both sides.
5 Recent simulations Benchmarking of ECLOUD and POSINST in ILC TESLA DR wiggler Simulated electron cloud density with POSINST (SEY params deltamax=1.3, Emax=190eV). Photoelectrons rate are 0.007 and 0.0007 photo-electrons per meter per positron. Wiggler field “Cartesian” model. Rectangular chamber with semi-axis axb=16x9mm and two antechambers 10mm full size on both sides. max =1.3
6 Methodology 1)Pertinent parameters for three different rings (17 km, 6 km and 3 km circumference) [: “For some studies (e.g. electron-cloud build-up) it probably is not necessary to study every lattice in detail, but pick one in each circumference.”] 2)Electron cloud build up is simulated for the different regions (arcs, wigglers, straights) considering different secondary emission yields. 3)For the wigglers simulations the field can be modeled at various levels of sophistication, and the importance of refined models has to be explored; 4)Single-bunch wake fields and the thresholds of the fast single-bunch TMCI-like instability are estimated; 5)Multi-bunch wake fields and growth rates are inferred from e-cloud build up simulations; 6)Electron induced tune shifts will be calculated and compared; 7)Predictions of electron build up from different simulation codes are compared; 8)Implemented in the simulations will be countermeasures which may be proposed as the ILC DR design evolves. DR task 6: Specify SEY limits from the electron cloud - working plan -
7 Specify SEY limits from the electron cloud - working plan for task 6 - Expressions of interest and available tools Build-up simulation codes are PEI (KEK), POSINST (LBNL/SLAC), ECLOUD (CERN), and CLOUDLAND (BNL/SLAC). Instability simulation codes are PEHTS (KEK) and HEADTAIL (CERN) for single-bunch instabilities, and PEI-M for multi- bunch instabilities (KEK). Multi-bunch wake fields can be extracted from POSINST and ECLOUD. There also exists a single-bunch instability code written by Y. Cai at SLAC. DESY, INFN, and CERN are collaborating in the EUROTeV WP3 ECLOUD subtask, the goals of which overlap with the ILC WG3 ‘electron-cloud’ task. Rainer Wanzenberg (DESY) has started a compilation of ring and beam parameters. Further contributions are highly welcome! Comparisons with existing machines A benchmarking program is ongoing at the CERN SPS and at DAFNE, in addition to PSR, PEP-II and KEKB, and can support the predictions.
8 ILC DRs electron cloud build-up simulation benchmarking between CERN, SLAC, KEK codes. Need to Prioritize DRs from list for simulations Use common SEY model/s. Sensitivity studies. Electron cloud collective instability simulations. By October 2005 task force 6 Co-ordinators deliver the information that will be necessary for making a DR configuration selection. Future Directions
9 Previous simulations: Following previous set of build-up simulations using POSINST, with previous ILC DR parameters Note: - SEY thresholds (with this particular SEY model) - Dependence of cloud density with vacuum chamber size (need to choose standard DR vacuum chamber sizes for simulations comparison purposes)
10 Arc bend simulations. Equilibrium electron density as a function of the chamber size. Assuming a fixed SEY peak max =1.4 Beam pipe semiaxes Hor, Vert = 22, 18 mm Previous simulations: Generation in the DR arcs Previous simulations: Generation in the DR arcs Fixed SEY max =1.4 and varied vertical chamber size Beam pipe semiaxes Hor = 22, Vert = 18 to 30 mm Simulations electron-cloud using POSINST: 17km long DR arc bend with antechamber. SEY threshold occurs at peak SEY~1.2-1.3. SEY model parameterization assumes a variable E max [LHC Proj.Rep-632]
11 Previous simulations: SEY thresholds for the DR 6 km and 3 km The SEY thresholds for the development of an electron cloud in the dipole regions are max = 1.1÷1.2 for the 6 km DR and max = 1.0÷1.1 (!) for the 3 km DR option. Electron density in units of e m 3 as a function of time for an arc bend in the 6 km DR option (Left) and the 3 km DR option (Right), assuming a chamber radius 22mm and including an antechamber design (full height h=10mm).
12 - Arcs and wiggler sections: aiming at SEY 1.2 - not an issue in long straight sections, provided a good coating (TiN, TZrV NEG) with SEY < 1.9. Large chamber size. E cloud Color coding Sections 17 km dogbone DRE - cloudSEY threshold arcs dipoleexpected1.3 wigglers sectionsexpected1.3 Long straight sectionspreventable1.9 e-cloud expectations in the positron DR Average neutralization levels and single-bunch (SB) instability electron cloud density thresholds for various damping ring options in units of [10 12 m -3 ]. The average density thresholds are for a ring modeled as a dipole region. Circumference 17 km6 km3 km Neutralization e [10 12 m -3 ] 0.86.015 Simulated e in arcs max = 1.4 0.48.017 SB: e threshold [10 12 m -3 ] 0.21.03.0 Sim. e / SB threshold 2.08.05.7