Technical aspects of the ATLAS efficiency & intensity upgrade

Technical aspects of the ATLASefficiency & intensity upgrade

Peter N. Ostroumov

ATLAS Users Workshop, August 8-9, 2009

2P.N. Ostroumov ATLAS Efficiency & intensity upgrade August 8-9, 2009

Content

Limitations of the current ATLAS configuration– Efficiency of CARIBU beams

– High-intensity ion beams (~0.1 mA)

ATLAS, >10x intensity upgrade– Phase I & II

Phase I: ARRA funding– New CW RFQ

– New G=0.075 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, G=0.075

– RFQ: hardware development and test

– SC cavity EM optimization and mechanical design

– Initial studies of EBIS charge breeder for CARIBU


The goal

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 pA), 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 pA

PHASE I, ARRA, $9.86M project

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 pA Increase existing ATLAS capabilities for low-intensity ion beams with

improved acceleration efficiency (beam energies from 10.2 to 26 MeV/u)

PHASE II, additional $35M


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 (>10 pA)

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,….


CARIBU

Tandem New cryomodule

Current ATLAS Layout


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


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 pAMedium intensity ion beams ~1.0 pA (current ATLAS performance)High intensity ion beams ~10 pA


CARIBU

Gas cell + Mass Separator

EBIS

MHB RFQ MEBT 2 new cryomodules Energy upgrade cryomodule

ATLAS High-Intensity Upgrade, PHASE II (Total $45M)

1) 14 QWR, G=0.075, f=72.75 MHz2) EBIS charge breeder3) Upgraded ECR4) Gas cell and Mass Separator

2 Booster and 2 ATLAS cryomodules

Available space for future experiments


Phase I: Beam energies as function of Q/A

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

2 PII Cryo. 12 cavities (existing) 1 New Cryo. 6 QWR @ 72.75 MHz for β ~ 0.075 (new) 3 Booster Cryo. 16 cavities (existing) 2 ATLAS Cryo. 12 cavities (existing) 1 Upgrade Cryo. 7 QWR @ 109.125 MHz for β ~ 0.15 (existing)


Phase I: Example Beams

Z A Q High 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



2 PII 1 New 3 Booster 2 ATLAS 1 Upgrade

Phase I: Q/A = 1/7 - Cavity Voltage Profile

P.N. Ostroumov ATLAS Efficiency & intensity upgrade August 8-9, 2009

Phase II

2 PII Cryo. 12 cavities (existing)

2 New Cryo. 14 QWR @ 72.75 MHz for β ~ 0.075 (new)

2 Booster Cryo. 12 cavities (existing)

2 ATLAS Cryo. 12 cavities (existing)

1 Upgrade Cryo. 7 QWR @ 109.125 MHz for β ~ 0.15 (existing)

Q/A High 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



Phase II: Example Beams

Z A Q High 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



ATLAS Efficiency and Intensity Upgrade schedule (PHASE II)Development,

Activity installation (Year) Comments

1 New Charge Breeder based on Electron Beam Ion Source 2010-2013

2 R&D, resonator development, RFQ construction 2009- 2012 Phase I, funded

2 Infrastructure improvements 2010-2013Cryogenic distribution 2010-2011 Phase I, partiallyImprovements of the SRF Facility 2010 fundedBuilding modifications 2013Decommissioning of the Tandem 2013

3 Front end systems: LEBT, MHB 2010-2011

4 ATLAS improvements for higher intensity beams 2009-2013ECR 2011Focusing system, RF system, Diagnostics and Controls 2011-2013Administration, Safety 2009-2013

5 New cryomodule fully populated with 2010- 2012resonators, couplers, tuners, βG=0.075

6 One more cryomodule fully populated with 2011- 2013resonators, couplers, tuners, βG=0.075

7 New experimental equipment 2013New CARIBU Source Transfer Facility 2013In-flight Beam Separator 2013

Phase I, funded


CARIBU

MHB RFQ MEBT New cryomodule Energy upgrade cryomodule

ATLAS High-Intensity Upgrade: PHASE I (ARRA)

1) Modify PII-1, install RFQ2) G=0.075, f=72.75 MHz – one cryomodule3) LHe system upgrade


PHASE I – ARRA

Build new RFQ to boost beam energy to ~250 keV/u for q/A=1/7– 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 (G=0.06 cavities)

Upgrade LHe distribution system: higher efficiency and reliability


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

ATLAS: 10 meters between the MHB and the RF LinacAfter the MHB Low current (<1 pA) 0.5 mA

MHB - RF Linac

distance is 3.5 m


1/7≤q/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, R0=7.5 mm

High-temperature furnace brazing ~100 kW RF power 2 circuits of temperature-stabilized

water-cooling systems

RFQ


60.625 MHz RFQ will be very similar to the FRIB prototype

Pre-brazed assembly Prototype RFQ

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/A1/7

Fabrication technology:High-T furnace brazing, OFE copper


80.65% captured to the central bunch


ARRA: new cryomodule with QWR @ 72.75 MHz, βG=0.075

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

25 cm109.8 cm

3 cm

14 cm


Couplers

Existing ATLAS couplers (≤ 1 kW)

Proposed high-power (~10 kW) capacitive coupler


Tuners

AEU pneumatic slow tuner:

excellent performance

Replace VCX with piezoelectric tuner– Can handle higher accelerating gradients

Piezoelectric fast tuner,tested on spoke cavities

0

2

4

6

8

10

12

14

16

EA

CC (

MV

/m)

R331 R332 R333 R334 R335 R336 R337

Without VCXOperational


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


Frequency verification: Simulations vs Experiment


RFQ

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


Current activities on new ARRA: Booster replacement project

Develop and prototype QWR, f=72.75 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


ATLAS Energy Upgrade Cryomodule


ATLAS Energy Upgrade Cavities are ready to drop into the box cryostat


New coupler

(cm)

Double window: cold and warm


Prototyping

Fast piezoelectric tuner Capacitive coupler Use the existing half-wave resonator

and new test cryostat


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


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

B EBIS LEBTFrom CARIBU

Mass-Separator

To ATLAS

Post- Accelerator1+ (2+)Q+

Q/A1/7A=80-160

B: RFQ Buncher

EBIS: Electron Beam

Ion Source

LEBT: Low Energy Beam

Transport

EBIS charge breeder design is based on BNL Test-EBIS: Double e-gun approach: 2A/5 kV and 0.2A/2 kVElectron 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


EBIS R&D 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


Summary of upgraded ATLAS ion beams and future activities (no stripping is assumed)

PHASE I PHASE II

Energies of high intensity beams (~10 pA)

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 pA)

8.1 – 21.4 MeV/u 10.2 - 26 MeV/u

Transmission efficiency of CARIBU beams

80% 80%

Major upgrades 1) New CW RFQ

2) A new cryomodule of beta=0.075 QWR

3) Improve LHe distribution system

1) Upgraded ECR for stable beams, higher intensities

2) EBIS charge breeder

3) One more cryomodule of beta=0.075 QWR

4) Relocated SRF, upgrade of ATLAS sub-systems

5) New experimental equipment


Conclusion

The Physics Division has developed detailed plan for future ATLAS upgrade – PHASE I – two ARRA projects

– ARRA-funded ATLAS upgrade is based on R&D 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.

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Technical aspects of the ATLAS efficiency & intensity upgrade

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