Design Optimization of MEIC Ion Linac & Pre-Booster B. Mustapha, Z. Conway, B. Erdelyi and P. Ostroumov ANL & NIU MEIC Collaboration Meeting JLab, October 5-7, 2015

Content  Purpose: More Compact Design of the Ion Injector  Cost Reduction  The Original Linac Design  A New More Compact Linac Design & Potential Cost Savings  Key Components / Parameters of the New Linac Design –Normal Conducting RFQ and IH Structures –High Performance Superconducting QWRs and HWRs –Optimized Stripping Energy and Voltage Profile –RF Power & Tuning –Lower Injection Energy to the Pre-booster/Booster  A New More Compact Pre-Booster Design  Summary & Future Work B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7,

Original Linac Design (2012): Layout & Main Features B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7,  Warm front-end up to ~ 5 MeV/u for all ions  SC QWR section up to 13 MeV/u for Pb ions  A stripper for heavy ions for more effective acceleration: Pb 28+  67+  SC high-energy section (QWR + HWR) up to 280 MeV for protons and 100 MeV/u for Pb ions  Total linac length of ~ 130 m with a total pulsed power of 560 kW

New Linac Design (2015): Layout & Main Features B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7,  The same warm front-end up to ~ 5 MeV/u for all ions  A single high-performance QWR module up to 8.2 MeV/u for Pb ions  A stripper for heavy ions for more effective acceleration: Pb 30+  61+  High-energy SC section (QWR + HWR) up to 130 MeV for protons and 42 MeV/u for Pb ions  Total linac length of ~ 55 m with a total pulsed power of 260 kW

Comparison of Linac Designs and Potential Cost Savings B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7,  The new design is ~ 1/3 the construction cost VS Item / ParameterOriginalNewComments Frequency (MHz) Stripper at (MeV/u)138.2Depends on W out Protons (MeV)280130Lower output W Pb (MeV/u)10042Lower output W SC modules165~ 1/3 Cost Total Length13055~ 1/2 Tunnel cost Total Power (kW)560260~ 1/2 Operation cost

Key Components / Parameters of the New Linac Design  A Normal Conducting Front-End: RFQ and IH Structures  High-Performance Superconducting QWRs and HWRs  Optimized Stripping & Voltage for Heavy-ions  Pulsed RF Power & Tuning  Lower Injection Energy to the Pre-booster/Booster B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7,

Normal Conducting Front-End: RFQ + IH Structure B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7, A 100 MHz 4-rod pulsed RFQ also exist at BNL ATLAS 60 MHz 4-vane RFQ BNL EBIS Injector 100 MHz IH Structure

High-Performance QWRs developed at ANL for ATLAS B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7,  A single QWR is capable of delivering 4 MV E peak ~ 60 MV/m and B peak ~ 90 mT ATLAS 72MHz QWR Conditioning

High-Performance HWRs developed at ANL for FNAL B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7, FNAL/PXIE MHz HWR  A single HWR is capable of delivering 3 MV E peak ~ 60 MV/m and B peak ~ 70 mT

Preliminary QWR and HWR Designs for MEIC Linac B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7, ParameterQWRHWRUnits β OPT Frequency100200MHz Length (β ) 45 cm E PEAK /E ACC B PEAK /E ACC mT/(MV/m) R/Q  G4284  E PEAK MV/m B PEAK mT E ACC 10.5 MV/m Phase2030deg No. of cavities2114 MEIC QWR Design MEIC HWR Design

Optimized Stripping Energy and Cavity Voltage Profile B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7,  Stripping energy optimized for lowest total voltage requirement  SC Cavity Voltage profile optimized for lead ions  SC Cavity re-phasing produces much higher energy for protons Total Linac Voltage vs. Stripping Energy (Optimized for Pb ions) SC Cavity Voltage Profile (Optimized for Pb ions)

RF Power & Tuning  Pulsed Operations: ~ 10% duty cycle  Lower dynamic load  Pulsed solid state RF amplifiers are less costly than for CW  Additional RF power may be needed to extend the frequency tuning band width  Lorentz detuning can be controlled by initial frequency offset between stand-alone and driven modes  Due to pulsed operation, different mechanical modes are exited leading to greater micro-phonics than in CW mode  Piezo tuner can be used for HWR to control micro-phonics, QWR will need more studies due to pendulum oscillation mode B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7,

Lower Injection Energy to the Pre-booster/Booster  Lower output energy of the linac, 130 MeV protons & 42 MeV/u for Pb  More important space charge (SC) effects in the following pre- booster/booster  SC effects are mitigated by the appropriate design and beam formation scheme of the pre-booster/booster  The original 280 MeV injection energy was conservative in terms of space charge  possible to lower the injection energy B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7,

Original Pre-booster Design (2012) B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7,  Figure-8 design to preserve beam polarization  Below transition energy: 3 GeV for protons, 670 MeV/u for Pb ions  234 m circumference with adequate space for insertions: e-cooling, RF system, injection, extraction, correction and collimation From Linac

Design Iterations for a more Compact Pre-booster B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7, Design criteria: Half the circumference Not cross γ transition ParameterSquareHexagonalOctagonal Circumference, m120 Arc length, m Straight section length, m Maximum β x Maximum β y Maximum dispersion β x at injection Normalized dispersion at injection: D/√ β x Tune in X Tune in Y Gamma transition Gamma at extraction (3 GeV)4.22 Momentum compaction factor Number of quadrupoles Quadrupole length, m0.4 Quadrupole half aperture, cm555 Maximum quadrupole field, T1.5 Number of dipoles24 Dipole bend radius, m888 Dipole angle, deg15 Dipole full gap, cm555 Maximum dipole field1.6  

New More Compact Pre-booster Design (2015) B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7,  A 120 m long Octagonal Design  Same injection and extraction features as the original design  Four dispersion-free sections  Will require Siberian snakes for polarization  Injects to large booster with storage ring

Comparison of Pre-Booster Designs and Cost Savings B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7,  The new design is ~ 1/2 the construction cost VS Item / ParameterOriginalNewComments N. of 15 o Dipoles3624- N. of Quads9540- Total N. of Magnets131641/2 Cost Total Length /2 Tunnel cost

Design Parameters and Optics of the New Pre-booster B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7, ParameterOctagonal Circumference, m120 Arc length, m6.7 Straight section length, m8.3 Maximum β x 15.3 Maximum β y 21.0 Maximum dispersion4.2 β x at injection6.0 Normalized dispersion at injection: D/√ β x 1.71 Tune in X3.01 Tune in Y1.18 Gamma transition4.7 Gamma at extraction (3 GeV)4.22 Momentum compaction factor0.045 Number of quadrupoles40 Quadrupole length, m0.4 Quadrupole half aperture, cm5 Maximum quadrupole field, T1.5 Number of dipoles24 Dipole bend radius, m8 Dipole angle, deg15 Dipole full gap, cm5 Maximum dipole field1.6  Keeping pre-booster 3 GeV  Low field for Siberian snakes

Space Charge & Tune Shift In New Pre-booster Design B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7, ParameterProtons 208 Pb Charge at source130 Energy at Stripper (MeV/u)338.2 Charge after stripper161 Energy at Linac exit (MeV/u)13042 Number of ions in pre-booster SC tune shift  SC tune shifts in new pre-booster design are below 0.25 for the same number of ions as the original design  More detailed studies of SC are needed to better control emittance growth  Beam simulations using MAD and COSY  Due to lower ion energy and high charge state, dynamic vacuum instability may be an issue (ex. GSI studied this effect)

Summary & Future Work  A New more compact lower energy Linac design –Less number of cavities, much shorter tunnel –~ 1/3 construction cost of the original design  A new more compact Pre-booster design – Less number of magnets, half the circumference –~ 1/2 construction cost of the original design  The 3 GeV octagonal pre-booster will / could use –Low field Siberian snakes to control ion polarization –Electron storage ring as ion large booster? (Derbenev & Ostroumov)  Future work –Space charge studies in pre-booster –Injection and beam formation schemes –… B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7,