Presentation on theme: "Superconducting Ion Source Development in Berkeley"— Presentation transcript:
1 Superconducting Ion Source Development in Berkeley Daniela Leitner, S. Caspi, P. Ferracin, C.M. Lyneis, S. Prestemon, G.L. Sabbi, D.S. Todd, F. TrillaudMotivation for developing superconducting ECR ion sourcesKey parameters for the performance of an ECRVENUS Source ProjectSome results and status of the VENUS ECR ion sourceFuture ECR ion source – Path to 56 GHz ECRISHIAT 2009, Venice, Italy
2 ECR ion sources have made remarkable improvements over the last few decades, but the demand for increased intensities of highly charged heavy ions continues to growSupermafios (Geller, 1974)15 eµA of O6+VENUS (2007)2850 eµA of O6+Factor200increaseVENUS, FRIBMSU, USASC-ECRIS,RIKEN, JapanSPIRAL 2, GANIL, France270 eµA U33+ and 270 eµA U34+525 eµA U35+1mA Ar12+
3 High Intensity Uranium Production The demonstrated VENUS source performance shows that these ion beam intensity requirements are possibleVENUS 28GHz or GHzO6+2860 eμAO7+850 eμAO8+ 400 eμAAr12+860 eμAAr17+36 eμAXe35+28 eμAXe42+.5 eμAU34+200 eμAU47+5 eμAHigh Intensity Uranium Production6kW 28 GHz770 W 18 GHzRequired temperature of 2100 C in a 4 T B field
4 Minimum-B field Confinement Higher magnetic fields and higher frequencies are the key to higher performanceMinimum-B field ConfinementSolenoid CoilsSextupolee- heatingµwavegasionsne ωrf2qopt log ω3Resonant electron heatingwe = = wrfe•BmAdd picture of AECRECR (1983)0.4 T, 0.6 kW, 6.4 GHzAECR-U (1996)1.7 T, 2.6 kW, GHzVENUS (2001)4.0 T, 14 kW, GHz
5 ne $ Normal conducting Super conducting Higher magnetic fields and higher frequencies are the key to higher performanceVENUS 56 GHz predictedNormal conductingVENUS 28 GHzAECR 14 GHzAnalyzed beam current [eµA]ECR 6 GHzSuper conductingne $Argon Charge StatesAdd picture of AECRECR (1983)0.4 T, 0.6 kW, 6.4 GHzAECR-U (1996)1.7 T, 2.6 kW, GHzVENUS (2001)4.0 T, 14 kW, GHz
6 ChallengesSuperconducting MagnetCryogenic TechnologyX-rays from the PlasmaIon Beam Transport
8 Superconducting Magnet Structure 56 GHz: two options Sextupole-in-SolenoidGeometry (VENUS)Solenoid-in-SextupoleGeometry (SECRAL)Minimizes the peak fields in the sextupole coilsStrong influence (forces) of the solenoid field on the sextupole endsMinimizes the influence of the solenoid on the sextupole fieldSignificantly higher field required for the sextupole magnet surface due to the larger radius of the coilsStrong forces on the solenoid coils
9 Superconducting Magnet 56 GHz: Magnetic Analyses Critical line and magnet load lines: NbSn3NbSn3Current Density through the superconductorMagnetic Field on the conductor
10 Superconducting Magnet Structure: Magnetic Analyses Goal: Achieve 4.2T on the plasma chamber wall radially and 8 T and 4 T on axisSolenoid-in-SextupoleCurrent Density through the superconductorMagnetic field and current density requirements exceed the capability of NbSn3Magnetic Field on the conductorThis geometry can be ruled out as candidate for a 56 GHz ECR ion source
11 Superconducting Magnet Structure: Magnetic Analyses Goal: Achieve 4.2T on the plasma chamber wall radially and 8 T and 4 T on axisSextupole-in-SolenoidCurrent Density through the superconductor2.5 Kelvin temperature margin for the SextupoleOperates at 86% of current limitsMagnetic Field on the conductorThis geometry is challenging but feasible with current NbSn3 technology
12 Sextupole-in-Solenoid: Clamping Structure Maximum peak field on the coil (15.1 T, 862 A/mm2 )There are two limits to the maximum achievable field with this designMaximum force on the end point (up to 175 MPa)To control these forcesIn the end region each layer is subdivided in two blocks of conductors separated by end-spacers.The number of turns per block and the relative axial position of the end spacers were optimized to reduce the peak field in the end region.The coils are lengthen to reduce the peak fieldShell type support structure
13 Sextupole-in-Solenoid: Sextupole Magnet 4-layer coils using cables (675 conductors/coil)The same cable design is currently used by the LARP program to develop high field quadrupoles for future LHC luminosity upgrades (peak fields 15 T)A practice coil winding for the LARP quadrupole (HQ)Cable propertiesStrand Dia0.8 mmFill factor~ 33%No strands35Cable~ 15.2x1.5 mmThe cable design requires high 8.2kA current leads, the 56 GHz cryostat will most likely require He filling during operation.
14 Sextupole-in-Solenoid: Clamping Structure A shell-based structure using bladders and keys provides a mechanism for controlled room temperature pre-stress.Pre-stress is then amplified by the contraction of an aluminum shell during cool-down.The method was developed at Superconducting magnet group at LBNL and successfully applied to high field magnets.2D cross section structure analyses has been conducted on the two critical regionsStress values are close to the maximum acceptable valuesNeeds full 3D analyses
15 Quench protection Energy stored in the VENUS magnet is 800kJ Passive Quench ProtectionBurned LeadHTC leadsEnergy stored in the VENUS magnet is 800kJVENUS coils do not require active quench protectionLeads need protection for adequate coolingEnergy stored in the 56 GHz Magnet 5.5MJActive Quench protection with heaters at the coils (75% coverage, results in peak temperatures in the coil of 280K)Lead protection (Lesson from the VENUS quench failure)LNLHeSol 1Sol 3Sol 2Sextupole CoilSol 1Sol 3Sol 2Spliced sextupole lead wire
16 Other ChallengesSuperconducting MagnetCryogenic TechnologyX-rays from the PlasmaIon Beam Transport
17 Cold Mass with Coils Enclosed A major challenge for high field SC ECR ion sources is the heat load from bremsstrahlung absorbed in the cryostatTechnical Solution VENUS Aluminum Plasma Chamber with 2mm Ta x-ray shieldCold Mass with Coils EnclosedPlasmaHV Insulator2mm TantalumX-ray ShieldCold Mass with Coils EnclosedWater Cooling Groovesat the plasma Flutes
18 (10s of ) watts of cooling power must be reserved for the cryostat. A major challenge for high field SC ECR ion sources is the heat load from bremsstrahlung absorbed in the cryostatwithoutshieldHV Insulator2mm TantalumX-ray ShieldwithshieldWater Cooling Groovesat the plasma Flutesmm Ta shielding effectively attenuates the low energy bremsstrahlung, but becomes transparent for x-rays above 400keVThe high energy tail of the x-ray spectrum increases substantially at the higher microwave frequency(10s of ) watts of cooling power must be reserved for the cryostat.
19 Beam transport is a challenge for high field SC ECR ion sources Beam emittance grows with magnetic field at extraction (therefore with heating frequency)
20 Beam transport is a challenge for high field SC ECR ion sources Todd et al., Rev. Sci. Inst A316
21 Simulation of oxygen beam extraction and transport ExperimentO7+O7+ExperimentTodd et al., Rev. Sci. Inst A31610 cm
22 SummaryThe requirements of the next generation heavy ion accelerator continue to drive ECR ion source developmentHigher magnetic fields and higher frequencies are the key to higher performance200eµA of U33+ and U34+ have been produced, high temperature oven development is key for long term production56 GHz ECR ion source magnet structures are feasible with current NbSn3 technologyDevelopment should start now to be ready for operation in 5-10 yearsUnderstanding of the plasma physics and the beam transport is important for the design of the next generation superconducting ECR ion sources
23 Key parameters for an ECR ion source performance Solenoids and Sextupole forma minimum-B field confinement structurePlasma is resonantly heated with microwaveswe = = wrfe•Be- heatingµ-wavemeMagnetic flux linef=28 GHz, B= 1TrLamor=0.01…1 mmIONSPlasmagasKey parametersIon confinement times i~msPlasma densities ne/cm3Electron temperature TeeV to MeVCharge exchange/ neutral gas density exAdd picture of AECR
26 The high energy tail of the x-ray spectrum increases substantially at the higher microwave frequency withoutshieldwithshieldThe scaling of the electron energy temperature with frequency has important consequences for 4th generation superconducting ECR ion source with frequencies of 37GHz, 56GHz. Several (10s of ) watts of cooling power must be reserved for the cryostat.