Technical aspects of the ATLAS efficiency

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Technical aspects of the ATLASefficiency
intensity upgrade

• Peter N. Ostroumov

ATLAS Users Workshop, August 8-9, 2009
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Content

• Limitations of the current ATLAS configuration
• Efficiency of CARIBU beams
• High-intensity ion beams (0.1 mA)
• ATLAS, gt10x intensity upgrade
• Phase I II
• Phase I ARRA funding
• New CW RFQ
• New ?G0.075 cryomodule
• Upgrade of LHe distribution system
• Current technical developments related to AIP and
  ARRA
• Linac design optimization
• Prototyping the cavity sub-systems
• Development of new QWR, ?G0.075
• RFQ hardware development and test
• SC cavity EM optimization and mechanical design
• Initial studies of EBIS charge breeder for CARIBU

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The goal
PHASE I, ARRA, 9.86M project

• Increase overall transmission of any ion beam
  including CARIBU radioactive beams to 80 as
  compared to the intensity of DC beam from the ion
  source or charge breeder
• Deliver 5 MeV/u medium-intensity (10 p?A),
  medium-mass ion beams for experiments related to
  the synthesis of superheavy elements
• Increase reliability and efficiency of the LHe
  distribution system
• Deliver full ATLAS energies at beam intensities
  of 1 p?A

PHASE II, additional 35M

• Increase efficiency of charge breeding by using
  EBIS
• For low intensity CARIBU beams (107 ions/sec)
  the efficiency can reach 15
• Produce and accelerate stable ions to 6-16 MeV/u
  (depending on Q/A) with intensity up to 10 p?A
• Increase existing ATLAS capabilities for
  low-intensity ion beams with improved
  acceleration efficiency (beam energies from 10.2
  to 26 MeV/u)

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Efficiency and Intensity Limitations of the
current ATLAS

• Previous generation ECR
• Low Energy Beam Transport
• Multi-Harmonic Buncher
• Low voltage, strong space charge effects
• As a result not efficient for high current beams
  (gt10 p?A)
• Low transverse acceptance of the first PII
  cryostat
• The aperture diameter of the first cavity is 15
  mm, the second cavity 19 mm
• The transverse acceptance is 0.6 ? mm-mrad,
  normalized
• Strong transverse-longitudinal coupling in the
  first cavities at high field emittance growth
• Longitudinal emittance growth
• Non-adiabatic motion in the phase space, low
  acceptance, emittance growth for high-intensity
  beams and beam losses
• Beam steering in the split-ring cavities,
  especially for light ions
• RF system was not designed to compensate beam
  loading
• Cryogenics, Radiation Shielding, Control system,
  Beam diagnostics,.

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Current ATLAS Layout
New cryomodule
Tandem
CARIBU
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Feasible solutions

• ECR Upgrade existing ECR
• EBIS Increase efficiency of CARIBU beams by
  factor of 2 and higher
• Low Energy Beam Transport Re-design, more
  frequent focusing, possibly electrostatic
• Multi-Harmonic Buncher
• Increase voltage (water cooling), move closer to
  the RF accelerator
• Low transverse acceptance of the first PII
  cryostat
• Replace with the normal conducting RFQ
  accelerator
• Longitudinal emittance growth due to high
  accelerating fields
• Adiabatic acceleration in the RFQ up to 250
  keV/u, no emittance growth
• Beam steering Replace two Booster cryostats with
  new cryostat with 6 or 7 ?/4 cavities
• RF system was not designed to compensate beam
  loading New couplers, new RF system
• Cryogenics, Shielding, Controls,
  Diagnostics,.Upgrade

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Beam time structure and intensities

• Maintain 12.125 MHz beam time structure 80 ns
  between bunches

In the following discussions Low intensity ion
beams (CARIBU) 0.1 p?A Medium intensity ion
beams 1.0 p?A (current ATLAS
performance) High intensity ion beams 10 p?A
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ATLAS High-Intensity Upgrade, PHASE II (Total
45M)

• 14 QWR, ?G0.075, f72.75 MHz
• EBIS charge breeder
• Upgraded ECR
• Gas cell and Mass Separator

Gas cell Mass Separator
Available space for future experiments
2 Booster and 2 ATLAS cryomodules
EBIS
CARIBU
MHB RFQ MEBT 2 new cryomodules Energy
upgrade cryomodule
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Phase I Beam energies as function of Q/A

• 2 PII Cryo. ? 12 cavities (existing)
• 1 New Cryo. ? 6 QWR _at_ 72.75 MHz for ß 0.075
  (new)
• 3 Booster Cryo. ? 16 cavities (existing)
• 2 ATLAS Cryo. ? 12 cavities (existing)
• 1 Upgrade Cryo. ? 7 QWR _at_ 109.125 MHz for ß
  0.15 (existing)

Q/A High Intensity Energy (MeV/u) Low Intensity Energy (MeV/u)
1/1 14.2 34.5
1/2 8.8 21.4
1/3 6.7 16.0
1/4 5.4 12.9
1/5 4.6 10.8
1/6 4.0 9.3
1/7 3.6 8.1
Note High intensity energy is before
the booster Low intensity energy is
the full energy
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Phase I Example Beams
Z A Q High Intensity Energy (MeV/u) Low Intensity Energy (MeV/u)
8 16 6 7.2 17.5
18 40 12 6.2 14.8
36 84 25 6.1 14.7
54 136 28 4.7 11.1
92 238 34 3.6 8.1
Note High intensity energy is before the
booster Low intensity energy is the
full energy
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Phase I Q/A 1/7 - Cavity Voltage Profile
2 PII 1 New 3 Booster
2 ATLAS 1 Upgrade
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Phase II
2 PII Cryo. ? 12 cavities (existing) 2 New Cryo.
? 14 QWR _at_ 72.75 MHz for ß 0.075 (new) 2
Booster Cryo. ? 12 cavities (existing) 2 ATLAS
Cryo. ? 12 cavities (existing) 1 Upgrade Cryo. ?
7 QWR _at_ 109.125 MHz for ß 0.15 (existing)
Q/A High Intensity Energy (MeV/u) Low Intensity Energy (MeV/u)
1/1 25.2 41.7
1/2 15.5 25.9
1/3 11.6 19.5
1/4 9.4 15.8
1/5 8.0 13.3
1/6 6.9 11.6
1/7 6.1 10.2
Note High intensity energy is before
the booster Low intensity energy is
the full energy
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Phase II Example Beams
Z A Q High Intensity Energy (MeV/u) Low Intensity Energy (MeV/u)
8 16 6 12.7 21.2
18 40 12 10.8 18.0
36 84 25 10.7 17.9
54 136 28 8.2 13.6
92 238 34 6.1 10.2
Note High intensity energy is before the
booster Low intensity energy is the
full energy
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ATLAS Efficiency and Intensity Upgrade schedule
(PHASE II)
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ATLAS High-Intensity Upgrade PHASE I (ARRA)

1. Modify PII-1, install RFQ
2. ?G0.075, f72.75 MHz one cryomodule
3. LHe system upgrade

CARIBU
MHB RFQ MEBT New cryomodule Energy
upgrade cryomodule
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PHASE I ARRA

• Build new RFQ to boost beam energy to 250 keV/u
  for q/A1/7
• 80 efficiency of bunching and acceleration,
  upgrade MHB
• Capable to accelerate 1 mA beams
• Build a new cryomodule with 6 SC cavities, ?G
  0.075
• Capable to accelerate 1 mA beams
• New high-power coupler
• Based on design of the Energy Upgrade Cryomodule
• Modify the first cryomodule of the PII
• Remove the first 2 cryomodules of the Booster
  (?G0.06 cavities)
• Upgrade LHe distribution system higher
  efficiency and reliability

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Multi-Harmonic Buncher, 58Ni15 , 35.7 keV/u

• ATLAS 10 meters between the MHB and the RF
  LinacAfter the MHB Low current (lt1
  pmA) 0.5 mA

MHB - RF Linac distance is 3.5 m
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RFQ

• 1/7q/A 1
• Injection energy 30 keV/u
• 60.625 MHz, 5th harmonic,
• 3.0-meter length
• 80 efficiency of beam capture
• for acceleration
• Voltage 90 kV, R07.5 mm
• High-temperature furnace brazing
• 100 kW RF power
• 2 circuits of temperature-stabilized
• water-cooling systems

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60.625 MHz RFQ will be very similar to the FRIB
prototype
Pre-brazed assembly Prototype RFQ
Fabrication technology High-T furnace brazing,
OFE copper

• Stable operation in wide dynamic range of RF
  power
• The highest voltage is 91 kV (limited by
  available RF power)
• Q-factor Simulation 9300, Measured 8860
• 3-meter long RFQ will provide 250 keV/u ion
  beams, Q/A??1/7

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80.65 captured to the central bunch
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ARRA new cryomodule with QWR _at_ 72.75 MHz,
ßG0.075

• Electromagnetic optimization is complete
• Reduced BPEAK/EACC
• Reduced EPEAK/EACC
• Expected performance
• VMAX 2.5 MV
• BPEAK 600 Gs
• EPEAK 45 MV/m
• About 50 better performance
• than the ATLAS Upgrade
• Cryomodule

14 cm
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Couplers

• Existing ATLAS couplers ( 1 kW)

• Proposed high-power (10 kW) capacitive coupler

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Tuners

• AEU pneumatic slow tuner
• excellent performance
• Replace VCX with piezoelectric tuner
• Can handle higher accelerating gradients

Piezoelectric fast tuner, tested on spoke cavities
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Current activities on new ARRA-RFQ project

• Project documentation
• WBS
• Schedule off-line commissioning in June 2012
• Implementation Plan
• Study of the transmission of high-intensity beams
  through the PII, beam steering, transverse
  acceptance.
• Design optimization of the accelerator
• LEBT, RFQ, matching to the PII cryostat
• RFQ prototype
• Modify RF coupler with additional cooling and
  test
• Build slug tuners, install and test
• EM simulations of the RFQ resonator
• Accurate frequency calculation
• Minimize length and RF power

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Frequency verification Simulations vs Experiment
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RFQ

• Test high-power coupler (120 kW) with an
  additional cooling
• Build and test slug tuners

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Current activities on new ARRA Booster
replacement project

• Develop and prototype QWR, f72.75 MHz cavity.
  The following features will be implemented
• Highly optimized EM design
• SC cavities with beam steering compensation
• New approach for electropolishing of QWRs
• Develop and test adjustable (1-1/2) capacitive
  coupler to handle 10 kW RF power.
• Develop piezoelectric tuner
• Apply the vast experience gained during the ATLAS
  Energy Upgrade cryomodule

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ATLAS Energy Upgrade Cryomodule
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ATLAS Energy Upgrade Cavities are ready to drop
into the box cryostat
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New coupler
Double window cold and warm
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Prototyping

• Fast piezoelectric tuner
• Capacitive coupler
• Use the existing half-wave resonator
• and new test cryostat

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60 MHz 20 kW CW amplifier is available both for
the test of the RFQ segments and can be retuned
to 72 MHz for conditioning of SC QWRs

• Was purchased for testing of the prototype RFQ

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Charge Breeder based on EBIS for CARIBU beams

• Low intensity of CARIBU beams allows us to
  efficiently apply EBIS for charge breeding.
  Compared to ECR
• Factor of 2-3 higher efficiency
• Significantly higher purity
• EBIS parameters are less demanding than the BNL
  EBIS
• Major challenges are
• precise alignment of electron and ion beam
  required
• achieve high acceptance and short breeding times

Q/A?1/7
A80-160
From CARIBU
To ATLAS
B
EBIS
LEBT
Q
Mass-Separator
1 (2)
Post- Accelerator
EBIS charge breeder design is based on BNL
Test-EBIS Double e-gun approach 2A/5 kV and
0.2A/2 kV Electron beam current density 300
A/cm2 (BNL 575 A/cm2) Breeding time 30 40
ms Efficiency 15, can be higher by factor of
2-3 when shell closure effect is applicable
B RFQ Buncher EBIS Electron Beam
Ion Source LEBT Low Energy Beam
Transport
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EBIS RD for the CARIBU beams

• In collaboration with BNL
• Build low-emittance 1 injector, beam diagnostics
  for breeding efficiency measurements for
  low-intensity beams
• Study shell closure effects at the BNL test-EBIS.
  For this purpose ANL will build low-current,
  high-perveance electron gun

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Summary of upgraded ATLAS ion beams and future
activities (no stripping is assumed)
PHASE I PHASE II
Energies of high intensity beams (10 p?A) 5.4 MeV/u (1/4 Q/A) to 9 MeV/u 6.1 MeV/u (1/7 Q/A) 16 MeV/u
Energies of low intensity beams (1 p?A) 8.1 21.4 MeV/u 10.2 - 26 MeV/u
Transmission efficiency of CARIBU beams 80 80
Major upgrades New CW RFQ A new cryomodule of beta0.075 QWR Improve LHe distribution system Upgraded ECR for stable beams, higher intensities EBIS charge breeder One more cryomodule of beta0.075 QWR Relocated SRF, upgrade of ATLAS sub-systems New experimental equipment
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Conclusion

• The Physics Division has developed detailed plan
  for future ATLAS upgrade
• PHASE I two ARRA projects
• ARRA-funded ATLAS upgrade is based on RD results
  performed for FRIB, ATLAS AIP
• We are in the stage of preliminary design for
  both ARRA projects
• Schedule
• Commissioning of the RFQ efficiency upgrade
  September 2012
• Commissioning of the Booster replacement
  cryomodule high-intensity medium mass beams
  December 2012.
• PHASE II is not funded yet, can be completed by
  the end of 2013 if the funds become available in
  FY10.