lbnl 88'' cyclotron operations

LBNL 88'' cyclotron operations

Status of the 88-Inch Cyclotron High-Voltage upgrade project

December 14, 2009

Ken Yoshiki Franzen

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Introduction The LBNL 88” cyclotron supports world-class research by

– the local low-energy nuclear scientific community

– LANL, LLNL, Sandia

– National Space Security community (BASE facility)

– Outside companies

Recently received funding for two upgrade projects:– RF– HV

Common goal: Increase reliability and efficiency!

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HV upgrade background• Space-charge effects limit

transport efficiency from ion sources into center of cyclotron

• For some groups (e.g. BGS) intensity is crucial, for others not really...

• Goal is to increase injection energy of key ion beams in the mid-range (20<A<136), in particular for 48Ca and 50Ti...

• … without impacting performance for other cases.

• Target injection voltage is 25 kV (if feasible up to 30 kV) which should provide user with an improvement >2.

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Injector System of the 88-Inch CyclotronElectrostatic mirror

Purpose is to deflect the beam 90°. Consists of 47° grid and electrode. Observe spots! Major culprit in achieving HV injection.

12 kV gnd

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Mirror inflector pros and cons

Pros Versatile Straightforward Easy to model

Cons Needs high voltage but current one does not go up to more than ~12 kV Grid degradation (sputtering) Decelerating beam

66Nuclear Instruments and Methods in Physics Research A 456 (2001) 177}189

z

ground

ground

Spiral inflector (Belmont and Pabot,1966)

-V

+V

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Spiral inflector pros and cons

Pros 100 % transmission. Lower voltage → Can do HV injection. No deceleration. Injected beam more centered.

Cons Narrow operational range. Difficult to model. More difficult to manufacture. Causes emittance growth due to fringe field effects.

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Spiral inflector main parameters

A=mv0

2

qE u

Rm=mv0qB

k'=tan θb

⇐ Height, or the radius of curvature of the electric field.

⇐ Magnetic radius which the ion orbit would have if there was no electric field. Notice that the center orbits transmitted through a spiral inflector is fixed.

⇐ Tilt, where θ is angle between Eu and total E vectors and 0≤b≤2.

Used to shift the orbit center.

⇐ Spiral inflector design parameter. Typical values is K=1.1.

K=A2Rm

k'

2

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• 88” center region space is very limited .

• A=25 mm, Rm=33 mm for Ar9+ (injection voltage 25 kV, extraction 200 MeV) → K=0.4

• Non-standard design, detailed modeling required.

Spiral inflector parameters (from notes by B. Laune)

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Modeling procedure (Step 1a) • Create FEM 3D model of a general spiral inflector based on an analytical

single particle model.

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Modeling procedure (Step 1b) Define potentials applied to all bodies and calculate electric fields in 3D.

Track beam through electric fields with a superimposed magnetic field.

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Modeling procedure (step 2a)

• Create FEM 3D model of a inserts compatible with spiral inflector geometry.

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Modeling procedure (step 2b)

• Track the beam leaving the spiral inflector through a electrostatic model of the updated cyclotron center region design with output of Step 1 as input parameters.

• Observe if particles make it to second gap.

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Modeling procedure (step 3) • Use a code from MSU (Z3CYCLONE) to track the beam from the center

region all the way out to extraction.

• Calculate the performance of each design in terms of transmission and energy.

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Tasks and Challenges

The current inflector shaft is only 2.125'' in diameter. How to fit everything in limited space?

• What about emittance growth?

• Add space-charge effect to the model.

System must be versatile enough to cover required operational range. Might need several inflectors/inserts sets. How long time to swap inflector/insert set-up? Reproducibility between swaps?

Important: Experimentally verify cyclotron modeling as early as possible in the design chain.

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Diagnostics

• Designed a wire probe which will be used to diagnose beam coming out of inflector.

– Ready to be tested and used to confirm model of current system.

– Could also be useful for present Operations.

• Also planning to design a scintillator probe giving additional beam diagnostics data.

r Spiral inflectoroutput beam

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Matching of beam lines to the upgraded cyclotron

Need to redesign buncher.

Need to redesign solenoid magnets of the injector line.

Redesign 72 degree bend magnet and assess bend capability of the existing beam lines.

Upgrade HV insulation of the ion sources.

What additional diagnostics do we need?

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Project Schedule

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Conclusion

• HV upgrade project is on track

• Many remaining issues to be resolved

• Initial Operation targeted for early 2012