L.E.N.A.

LENA: Fine Tuning a Low Energy Particle AcceleratorJohn Martin, Andrew Cooper, Keegan Kelly, Dr. Tom Clegg

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Transformer/Finger of DeathAcceleration Column SupportECR Gas Line BreakdownExtraction Cone Alignment BaseK-Mount Modifications2What is L.E.N.A.?Laboratory for Experimental Nuclear AstrophysicsHosts the 1 MV JN Van de Graaff and the 200kV ECR acceleratorPurpose: To measure the cross sections relevant to nuclear fusion in stars and supernovae

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Source: Mark R. LeachHow do we experimentally simulate supernovae and various phases of stellar evolution?Discussion of lab, accelerators, and purpose3

1234FusionBeam-Target Fusion4Overview of how LENA operates and where we wanted to improve the system4Motivation to Upgrade ECR Accelerator

Energy Range of DominantStellar NucleosynthesisRecent Studies at LENA:18O(p,)19F (Buckner et al. 2012)23Na( p, )24Mg (Cesaratto et al. 2013)17O(p,)18F (Buckner et al. 2015)

Low energy demands a large number of incident protons

Old beam produced 2-2.5 mA on target

High intensity proton beam = increased damage on the acceleration column

Large amount of radiation

5Discussion of the necessity of high intensity beams for low energy nucleosynthesis5

dSend in hydrogen gasSend in microwaves through Al3O2 and BNStrike the plasmaShape the plasmaAccelerate through electrodes

Old Electron Cyclotron Resonance (ECR) System

Parallel Plates6Discussion of the ECR Source physics 2/3 of diatomic molecules break into protons on a good day. Measured by analyzing magnetMagnet makes a magnetic bottle that shapes the plasma for optimal extraction6Perveance and Half Angular DivergencePerveance: Tendency for a charged particle beam to spread out Half Angular Divergence: The angle at which the beam leaves the apertureLarge dependence on distance, dUsing a system of equations you can solve for an optimal distance

Credit: CST Computer Simulation Technology AG. (Ziam et al. 2002)7Functions that determine perveance and half angular divergence and what paramaters need to be changed to optimize these quantities7New Beam Extraction System (Spherical System)

Plasma Chamber: 40 kVGround Electrode: 0 VSuppressor Electrode: -2 kVd?Pros: Stricter half-angular divergence Higher count rateBiased suppressor electrode Removable nose conesCons:Beam overheats the target Not optimized yetGround Electrode: 0 V8Discussion of the components to the three electrode system8Optimal DistanceSpherical SystemParallel SystemWhile this gets us close, it only models a two electrode system. L.E.N.A. hosts a three electrode system.Source: (Ziam et al. 2002)

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???LENADiscuss that the optimal distance is a rough estimate but we need the ability to adjust and test the optimal distance for a three electrode system9How to Optimize DistanceExtraction Cone locked in place and allowed to move front and back on a platformGear controlled externally allowing motion of 5 mm in either directionFine tune by testing on beam stops further down the beam path

10Installation and AlignmentBeam alignment is crucial for maximizing count rate Two degrees of freedom: azimuthal and left to rightBoth horizontal and vertical adjustments are coupled making adjustments difficultBack is locked in place from the yellow piece

1111Aperture Misalignment Front misalignedFirst electrode nose etched away by beamEmitted secondary electrons drawn into plasma chamberMolybdenum sputtered altering ECR and first electrode apertures

12The misalignment of the front as well as the back of the extraction cone12Propagating ProblemThe aluminum oxide and boron nitride barriers allowed microwaves in and kept the vacuum seal Emitted electrons from nose cone bombarded the platesBrittle properties combined with heat from the electrons caused the plates to shatter

13Will find a picture of the broken plates, discussion of secondary electron emission 13Alignment Base Modification

Additional two degrees of freedom: Rotary and Vertical AxisAllows for reversible adjustments (snap rings)Simpler ease of axisIndependent motion of front and back aperturesDrawings have been made and parts will hopefully be machined in the near future

14New degrees of freedom how they will be implemented14Acceleration Column SupportHeld together by compressionNo way to maintain the plates and ceramic casing Small leak detected on one of the O-Rings

15Discussion of the need for maintenance due to leaks

15Column SupportAluminum base plates and insulated plastic diagonal sheet20 polyethylene sliders inserted under all ceramics to keep aligned Allows translational motion along axis for maintenanceCurrently in machine queue

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Design implemented to solve this problem and the translational motion16AcknowledgementsDr. Tom Clegg, Primary Supervisor Andrew Cooper and Keegan Kelly, Graduate StudentsMark Emamian, Engineering AdvisorDr. Crowell, REU SupervisorRemaining L.E.N.A. professors and studentsT.U.N.L.Thank you!17ReferencesC. Iliadis, Nuclear Physics of Stars (Wiley-VCH Verlag, 2007).

Cooper, Andrew. Design of a New Acceleration System for High-Current Pulsed Proton Beams from an ECR Source APS Division of Nuclear Physics Conference. (2010)

H. Ziam, G.D. Alton, Review of Scientific Instruments 73, 595 (2002)

Iliadis, Christian. "Introduction to Nuclear Astrophysics." Proceedings of the 5th European Summer School on Experimental Nuclear Astrophysics. (2009)

J. M. Cesaratto, A. E. Champagne, T. B. Clegg, M. Q. Buckner, R. C. Runkle, and A. Stefan, Nucl. Instrum. Methods A 623, 888 (2010).

Lieberman, Michael A.; Lichtenberg, Allan J. (2005). Principles of plasma discharges and materials processing (2nd ed.). Hoboken, N.J.: Wiley-Interscience. 546. ISBN978-0471005773. OCLC59760348.

1818ECR Gas Line ArcingThe plasma chamber operates at 40kV higher than the 200kV tableThe gas line control sits at table voltage so as we pass gas through, the hydrogen ionizes and causes breakdown within the lineAfter testing we determined we are in a range where the mean-free-path is at an optimal distance for breakdown (Paschens Law)At high and low pressures and short and far distances higher voltages required for breakdown (pd dependence)

19ECR Gas Line Arcing due our Position in paschens curve19Pending SolutionsLarger diameter piping to reduce pressure and longer gas line Put the gas control valve in a 240kV box to eliminate potential differenceThis would require us to rewire all of labview and also put it in the boxPotentially use a raspberry pi as a substitute for labview and put it in 240kV box

Credit: Bit-Tech20Discussion of the large gas line, the rewiring of labview, and the potential use of a raspberry pi computer20Transformer/Finger of DeathMuch of the equipment on the table is operated by 220V AC wall voltageLarge transformer is required to safely get that voltage to 200kV of the tablePurchased a large transformer, filled it with dielectric fluid breakdown occurs through fluidAttempts: Change electrode styles to bullet connections Breakdown through oilReplace metal barrier with PVCBreakdown on table occurred

21Installation of the transformer and arising problems21Stellar Evolution and Nuclear Fusion

How do we experimentally simulate this?

Source: Mark R. Leach22Basic discussion of nuclear fusion and stellar evolution22