Design Optimization of MEIC Ion Linac & Pre-Booster

B. Mustapha, Z. Conway, B. Erdelyi and P. OstroumovANL & NIU

MEIC Collaboration MeetingJLab, 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, 2015

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Original Linac Design (2012): Layout & Main Features

B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7, 2015

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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: Pb28+ 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, 2015

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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: Pb30+ 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, 2015

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The new design is ~ 1/3 the construction cost

VS

Item / Parameter Original New Comments

Frequency (MHz) 115 100 -

Stripper at (MeV/u) 13 8.2 Depends on W out

Protons (MeV) 280 130 Lower output W

Pb (MeV/u) 100 42 Lower output W

SC modules 16 5 ~ 1/3 Cost

Total Length 130 55 ~ 1/2 Tunnel cost

Total Power (kW) 560 260 ~ 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, 2015

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Normal Conducting Front-End: RFQ + IH Structure

B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7, 2015

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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, 2015

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A single QWR is capable of delivering 4 MV voltage

@ Epeak ~ 60 MV/m and Bpeak ~ 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, 2015

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FNAL/PXIE - 162 MHz HWR

A single HWR is capable of delivering 3 MV voltage

@ Epeak ~ 60 MV/m and Bpeak ~ 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, 2015

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Parameter QWR HWR UnitsβOPT 0.15 0.30

Frequency 100 200 MHzLength (β) 45 45 cm

EPEAK/EACC 5.5 4.9 BPEAK/EACC 8.2 6.9 mT/(MV/m)

R/Q 475 256 G 42 84

EPEAK 57.8 51.5 MV/m BPEAK 86.1 72.5 mTEACC 10.5 10.5 MV/m

Phase 20 30 degNo. of cavities 21 14

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, 2015

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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, 2015

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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, 2015

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Original Pre-booster Design (2012)

B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7, 2015

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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, 2015

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Design criteria: Half the circumference

Not cross γ transition

Parameter Square Hexagonal OctagonalCircumference, m 120 120 120

Arc length, m 13.6 9 6.7Straight section length, m 16.4 11 8.3

Maximum βx 18 15.6 15.3Maximum βy 30 21.5 21.0

Maximum dispersion 11.6 6.6 4.2βx at injection 14.9 5.9 6.0

Normalized dispersion at injection: D/√ βx 3.01 2.72 1.71Tune in X 2.09 2.34 3.01Tune in Y 0.90 1.22 1.18

Gamma transition 2.46 3.57 4.7Gamma at extraction (3 GeV) 4.22 4.22 4.22

Momentum compaction factor 0.164 0.078 0.045Number of quadrupoles 20 30 40Quadrupole length, m 0.4 0.4 0.4

Quadrupole half aperture, cm 5 5 5Maximum quadrupole field, T 1.5 1.5 1.5

Number of dipoles 24 24 24Dipole bend radius, m 8 8 8

Dipole angle, deg 15 15 15Dipole full gap, cm 5 5 5

Maximum dipole field 1.6 1.6 1.6

New More Compact Pre-booster Design (2015)

B. Mustapha Design Optimization of Ion Linac & Pre-booster MEIC Collaboration Meeting, Jlab, October 5-7, 2015

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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, 2015

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The new design is ~ 1/2 the construction cost

VS

Item / Parameter Original New Comments

N. of 15o Dipoles 36 24 -

N. of Quads 95 40 -

Total N. of Magnets 131 64 1/2 Cost

Total Length 234 120 1/2 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, 2015

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Parameter OctagonalCircumference, m 120

Arc length, m 6.7Straight section length, m 8.3

Maximum βx 15.3Maximum βy 21.0

Maximum dispersion 4.2βx at injection 6.0

Normalized dispersion at injection: D/√ βx

1.71

Tune in X 3.01Tune in Y 1.18

Gamma transition 4.7Gamma at extraction (3 GeV) 4.22

Momentum compaction factor 0.045Number of quadrupoles 40Quadrupole length, m 0.4

Quadrupole half aperture, cm 5Maximum quadrupole field, T 1.5

Number of dipoles 24Dipole bend radius, m 8

Dipole angle, deg 15Dipole full gap, cm 5

Maximum dipole field 1.6 Keeping pre-booster energy @ 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, 2015

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Parameter Protons 208PbCharge at source 1 30

Energy at Stripper (MeV/u) 33 8.2Charge after stripper 1 61

Energy at Linac exit (MeV/u) 130 42Number of ions in pre-booster 2.52 1012 4.5 1010

SC tune shift 0.19 0.22

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, 2015

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