Numerical Tools for LCLS-II Vacuum Systems

Transcription

1 Numerical Tools for LCLS-II Vacuum Systems G. Lanza, D. Gill, SLAC National Accelerator Laboratory AVS, November 2 nd 2017 Doc. N. SLAC-PUB Work described in this presentation is supported by the United States Department of Energy.

2 Outline What simulations programs were used to design the LCLS-II vacuum system? What strategy was adopted at SLAC to simulate the pressure of the entire linac? 1. LCLS-II upgrade: from design to vacuum schematics 2. Gas Density simulation programs used for the vacuum design of LCLS-II beamline Molflow+ Pressure5 VacCalc VacTran 3. Examples for each program 4. Conclusions G. Lanza, AVS,

3 New Injector and New Superconducting Linac LCLS-II project. Existing Bypass Line New Cryoplant LCLS-II New Transport Line Two New Undulators And X-Ray Transport Exploit Existing Experimental Stations LCLS-II DOE Review, Oct 12-14, 2016 Slide 3 3

4 LCLS-II: Production of Vacuum Schematics Injector & L0 Cryoplant & cryo distribution Bypass BSY LTU EBD FEE L1 L2 L3 Extension line Proposed FACET II Bypass line Sector 0 SRF Cryomodules Sector 10 Sector 20 Beam (L0, L1, L2, L3) Dogleg Spreader Sector 30 joined by warm beamline sections LCLS-I crossover µ wall SXU HXU Undulators Dumps End Stations Z (m) Use of simulation programs to design a vacuum system that - allocate all the physical components of the accelerator system - meet the vacuum level requirements G. Lanza, AVS, 2017 Generated by the Mechanical Engineers Verified by the Vacuum Engineers Used by the Control Engineers 4

5 LCLS-II: Components in the electron beam MATERIALS: - Stainless steel - Copper - Tungsten 5

6 LCLS-II: Components in the photon beam G. Lanza, AVS, 2017 Flat mirror Courtesy of C.Hardin and D.Cocco, SLAC MATERIALS: - Stainless steel - Copper - Silicon - Tungsten - Aluminum - Kapton wires - Moving parts - 6

7 LCLS-II: Gas Density Simulation Programs INPUT Single components analysis - Outgassing rate of every material - Details of the geometry and exposed surface OUTPUT - Effective conductance - Component total outgassing rate - Position and size of the pumps in the component - Minimum pressure achievable by the component G. Lanza, AVS,

8 LCLS-II: Gas Density Simulation Programs Molflow+ a Monte-Carlo Simulator package developed at CERN To calculate the effective conductance of components To calculate the effective pumping speed of pumps To evaluate the local pressure Fast exploration for different parameters (failure analysis) G. Lanza, AVS,

9 LCLS-II: Gas Density Simulation Programs Reduce the amount of gas cryo-pumped by the RF cavities Pirani gauge Cryogenic side RT side 2 Ion pumps 200 l/s VQM 2 NEG cartridge CAPACITORR HV 1600 Cold Cathode gauge Total length: L=1250mm Ø=34.8mm Engineering Note: LCLSII-1.1-EN-0658: A differential pumping system for LCLS-II beam pipe cold-warm transitions G. Lanza, AVS,

10 LCLS-II: Gas Density Simulation Programs Molflow+ study of the Differential Pumping System between the room temperature and cryogenic beam line Gas composition of unbaked UHV clean LCLS beamline Total outgassing (N2 equivalent) Water outgassing (H2O equivalent) Hydrogen outgassing (H2 equivalent) Torr l / s cm2 Pumping time Torr l / s cm2 Torr l / s cm2 2 months 2x x x10-11 G. 6 Lanza, months AVS, x x x

11 LCLS-II: Gas Density Simulation Programs 16 IP NEG RGA 2 19 P=1x10-11 Torr Gas composition of unbaked stainless steel system pumped with NEG and ion pump after one year G. Lanza, AVS,

12 LCLS-II: Gas Density Simulation Programs Complete Beamline analysis INPUT - Component total outgassing - Components effective conductance - Simplified geometry OUTPUT - Beamline pressure profile - Position of the gauges - Position of pumps in between components G. Lanza, AVS,

13 LCLS-II: gas density simulation programs Pressur5: Developed at CERN in 1992 Pressure distribution and critical beam current for different gas Simulates molecular trajectories in a series of consecutive tubes of uniform cross section Ref: T.Xu, J.M.Laurent,O.Groebner Monte Carlo Simulation of the Pressure end the Effective Pumping Speed in the LEP Collider, CERN note CERN-LEP-VA/

14 LCLS-II: gas density simulation programs Pressur5: Simple consecutive structures Few possible geometries but possibility of using the effective conductance User friendly No hidden parameters To add one segment, all the following segments need to change. 14

15 LCLS-II Existing Bypass Line 15

16 LCLS-II: gas density simulation programs Pressur5: G. Lanza, AVS,

17 LCLS-II: Gas Density Simulation Programs VACCALC To calculate the pressure profile it solves the differential equation using: - transfer matrix - finite difference method Near Experimental Hutch Ref: A Method for Calculating Pressure Profiles in Vacuum Pipes, M. K. Sullivan, SLAC,

18 LCLS-II: Gas Density Simulation Programs VACCALC - Calculate the effective pumping speed of every component Suggested in case of complex beamline with multiple components Requires a previous data organization and preparation of input strings No user interface Courtesy of Armin Busse, SLAC 18

19 LCLS-II: Gas Density Simulation Programs VACCALC: Program output: G. Lanza, AVS, 2017 Courtesy of Armin Busse, SLAC 19

20 LCLS-II: Gas Density Simulation Programs VACCALC: G. Lanza, AVS, 2017 Courtesy of Armin Busse, SLAC 20

21 LCLS-II: Gas Density Simulation Programs VacTran Vacuum calculation software that solves analytically the pumping system equation Calculates the pump down time of a vacuum system, with and without gas loads Calculates the rate of pressure rise for a vacuum vessel based on its gas load Models simple conductance elements It is possible to import and digitize the pumping speed curve vs. pressure of a pump It s not free G. Lanza, AVS,

22 Conclusion Mechanical and Vacuum engineers at SLAC used the following gas simulation programs to design the new LCLS-II electron and photon beamline Simulation Programs Strengths Limitations Example Molflow+ Use of real geometry Complete documentation Requires modification and upload of 3D drawings Differential pumping system Pressure5 Easy to use Suitable for accelerator circular beamlines Requires re-entry of all data as designs change. BSY beamline VacCalc Inputs from Excel data file. No user interface Photon beamline VacTran Pump down plots, including viscous, transition and molecular flow. No pressure distribution Cryomodule insulating vacuum 22

23 Conclusion Mechanical and Vacuum engineers at SLAC used the following gas simulation programs to design the new LCLS-II electron and photon beamline Simulation Program Molflow+ Pressure5 VacCalc VacTran Conductance Calculation X X Pressure profile X X X Use of real geometry X User Friendly X Need prior computation of conductance X Need prior computation of pumping speed X X X Ease to change a parameter X X X Internal use of pumping speed vs P curve X Molecular flow regime X X X X Viscous and transitional flow regime X Free X X X 23

24 END Thank you