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SNS BLM System Overview Detectors, Measurements, Simulations

SNS BLM System Overview Detectors, Measurements, Simulations. Alexander Zhukov Saeed Assadi SNS/ORNL. SNS Accelerator Complex. Accumulator Ring: Compress 1 msec long pulse to 700 nsec. Front-End: Produce a 1-msec long, chopped, H- beam. Extraction. Injection. RF. Liquid Hg Target.

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SNS BLM System Overview Detectors, Measurements, Simulations

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  1. SNS BLM System Overview Detectors, Measurements, Simulations Alexander Zhukov Saeed Assadi SNS/ORNL

  2. SNS Accelerator Complex Accumulator Ring: Compress 1 msec long pulse to 700 nsec Front-End: Produce a 1-msec long, chopped, H- beam Extraction Injection RF Liquid Hg Target 1 GeV LINAC 1000 MeV 2.5 MeV 87 MeV 186 MeV 387 MeV RTBT Ion Source HEBT DTL RFQ SRF,b=0.61 SRF,b=0.81 CCL

  3. BLMs at SNS • Major MPS device • Fast MPS – abort the current beam pulse within 10 μS (hardware – analog integrator), not applicable to RTBT • Slow MPS – keep average loss reasonable • Diagnostic device - machine tuning • Activation “planning” • Activation decaying • Activation buildup? • Halo measurement with the help of WS Detectors used • Ion chambers ~300+ • Neutron detectors ~30+ • Low level neutron detector 8 • PMTs ~10+

  4. Ion Chambers • Argon filled, 113 cc volume, 2 kV bias. • Response 70 nC/Rad • Slow ~1 μS (charge collection)

  5. Neutron Detector • 35 mm poly moderator • Li (n,alpha) • Scintillator • PMT • 104 – 108n/cm2/s • 0.03eV - 3MeV

  6. Low Level Neutron Detector • 85 mm poly moderator • B (n,alpha) • Counter • 102 – 104n/cm2/s • 0.03eV-10 MeV

  7. PMT • Scintillator • PMT • Response 50 pC/MeV • Fast ~10 nS

  8. IC 1 mS ND Proton Energy, MeV Neutron Detector vs. Ion Chamber • Commons • Analog output • Same electronics, low level software, MPS interface • Differences • Waveform shape (neutron moderation in NDs) • Distance range: IC – local, ND remote • HV controlled dynamic range for NDs • Neutron signal originates from beam loss only, in contrast there are several x-ray sources

  9. Challenges: Low energy part of linac • low energy beam (<20MeV) • IC not sensitive enough • ND sensitive, but hard to calibrate (no sufficient experimental data for reliable simulation) • Still the biggest issue • PMTs are supposed to help Warm linac PMTs

  10. 1 mS Beam loss X-ray Challenges: WF subtraction • Cavity X-rays give significant input to loss signal • The software subtracts the RF only waveform (the beam rep rate is 59.9 Hz to allow one reference signal per 10 seconds) • Fast MPS is compromised

  11. Noise BLM BLM HV OFF HV ON PMT PMT Loss Challenges: RTBT noise RTBT noise/EM interference with the beam or image current • Problem is present • with beam only • Gets worse with • beam charge • increase

  12. Challenges: RTBT noise (continued) • Low Level NDs • Counter output (solves noise issue) • Registration of time distribution effectively increases dynamic range • Capable of registering losses from 1 mini-pulse • Need time to collect statistics 10 s ~ 600 pulses 1 mini -pulse saturation 150 mini -pulses 10 mS

  13. Loss / WS conversion constant WS and halo studies • Attempt to improve WS performance in halo part • Special scintillating fiber • Ordinary IC • Scan of loss signal vs WS position gives good measurement around the beam center, but halo shape isn’t really detectable • Optimized fiber is being designed

  14. shutdown begins Activation decaying • NDs in SCL • HV ramped up • Using gamma sensitivity

  15. Currently running production system Electronics and Low Level Software • Standard IC & ND amplifier • High channel density • Obsolete parts (big problem!) • 3 gains jumper settable • VME ADC • 24 bits for dynamic range (~10 bits digitizing noise) • High channel density • 100 kS sampling rate • VxWorks based EPICS running WF subtraction at 60 Hz • PMT custom made amplifier/HV boards + cRIO + LabVIEW RT • Low Level ND LabVIEW on Windows

  16. Electronics and Low Level Software Future • FPGA based WF subtraction • Test with cRIO based PMTs currently installed • Increase of sampling rate is desirable • Choosing FPGA platform • VxWorks vs. PXI vs. cRIO ? • Smart devices for higher beam availability • Every detector has its own hot pluggable data acquisition board • Complete replacement of 1 channel should not affect other channels (no beam downtime) • Full remote configuration: all setup data come from one source (Oracle)

  17. High Level Software Lossviewer2 (XAL application) BLM statistics web site

  18. Beam PARMILA • RF, dark current • ??? • Low Energy Protons MCNPX • MARS, SHIELD, G4 • High Energy • Hadrons (primary protons, cascade hadrons) MCNPX, SHIELD, G4, MARS • Low Energy Neutrons MCNPX, G4 Proton Energy, MeV • Electromagnetic Showers MARS, • EGS4, G4 • Low Energy electromagnetic interactions • EGS4, G4 Simulations (MC transport codes) Ultimate goal Recreate the loss location and absolute valueusing BLM measurements

  19. Thank you!

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