Bob Zwaska IHEP - LBNF Beamline Meeting: Hadron Monitor 27 June 2016 NuMI Hadron Monitor

2 Robert Zwaska | IHEP - LBNF Beamline Meeting Outline Beam Monitoring in NuMI –Typical scans Hadron Monitor Design –Composition –Studies –Long-term issues Question of tolerances –Control of Systematic errors

3 Robert Zwaska | IHEP - LBNF Beamline Meeting Vertical Position (inches) Muon Alcove 1 Muon Alcove 2Muon Alcove 3    p   Target in - Horns on Target out -Horns off Vertical Position (inches) Hadron Monitor

NuMI Target Alignment Proton beam scanned horizontally across target and protection baffle Also used to locate horns Hadron Monitor and the Muon Monitors used to find the edges Measured small (~1.2 mm) offset of target relative to primary beam instrumentation. Pulse Height in Chamber (arb.) target baffle target baffle Graphite protection baffle Graphite target Water cooling line 21.4 mm 15.0 mm 11.0 mm 6.4 mm Horizontal Fin Target Horn Baffle p 

Hadron Monitor Distributions Intensity and width give information about material traversed –Scattering and Absorption Centroid gives direction of the beam Fluxes are very high –10 10 / cm 2 –Detector response is a question

6 Robert Zwaska | IHEP - LBNF Beamline Meeting System Design lots of ion chambers Hadron Monitor –7x7 grid  1x1 m 2 1 mm gap chambers –Radiation Hard design ~ 10 Grad exposure –Mass minimized for residual activation 57 Rem/hr Muon Monitors –9 tubes of 9 chambers each  2.2x2.2 m 2 3 mm gap chambers –Tube design allows repair High Voltage ( V) applied over He gas –Signal acquired with charge-integrating amplifiers

7 Robert Zwaska | IHEP - LBNF Beamline Meeting Ionization Chambers Parallel-plate geometry –Simple, uniform signal volume Ionization medium: Helium gas at atmospheric pressure –Low charge/cm 10.2  10.2 cm 2 Al 2 O 3 ceramic wafers Ag-plated Pt electrodes Holes in corners for mounting Adopt design with electrical & mechanical contacts in corner holes Chamber gap depends on station Sense wafer, chamber side

8 Robert Zwaska | IHEP - LBNF Beamline Meeting Simple Ion Chamber Models “Ionization Mode” is where: –Enough field applied to collect all ionized charge w/o loss –Not so much field that the gas amplifies the charge Higher rate of ionization leads to higher rate of recombination –Higher Voltage necessary to reach plateau To 1st order, charge densities increase in direction of motion, and are inversely proportional to their drift velocities –Get 1% loss at ~ 5 x / cm 2 Need to consider space-charge screening –Field drops according to: At intensity, field drops to zero over part of the chamber –Sets in ~ – / cm 2 Distance Across Chamber Charge Density Ions Electrons Chamber Gain 1 Chamber Voltage Plateau Proportional Higher Intensity

Booster Beam Test Two chambers tested (1mm & 2mm gas gap) 2 PCB segmented ion chambers for beam profile. Toroid for beam intensity Fermilab Booster Accelerator 8 GeV proton beam 5   protons/spill 5 cm 2 beam spot size 2001 Ion Chamber Beam Size Monitors Beam Direction Beam Dump

10 Robert Zwaska | IHEP - LBNF Beamline Meeting Chamber Response Simulation  Reproduce behavior seen in beam test  (1+1)-Dim. finite element model incorporating:  Charge Transport  Space Charge Build-Up & Dead Zone  Gas Amplification  Recombination Dead Zone 3x Applied Voltage! 1 mm separation 200 V applied 1.56  s spill Protons Protons

11 Robert Zwaska | IHEP - LBNF Beamline Meeting Plot the Charge/Proton 100 V 150 V 200 V 250 V Maxima Monotonically decreasing  Simulations show qualitative agreement to the interplay seen in the data  Loss of charge due to space-charge screening  Increase of charge due to beam-induced space charge build-up  Data allows to determine poorly-understood parameters (Townsend coeff, ions/p) Data  Simulation

12 Robert Zwaska | IHEP - LBNF Beamline Meeting Plateau Curves  Curves converge in a region of voltage near a gain of 1  Qualitative agreement between data and simulation Data Simulation

13 Robert Zwaska | IHEP - LBNF Beamline Meeting Predictions for the NuMI Beam 8 µs spill used – all other conditions the same Suggests loss of plateau in HadMon at / cm 2 –Muon Monitor does not lose until above 10x maximum flux Effects not included: –Electronegative impurities – not a problem in beam test –HV “sag” - dumping a large amount into RC circuits HV side solved, signal might be floating

14 Robert Zwaska | IHEP - LBNF Beamline Meeting Beam Plateaus Hadron Monitor Muon Monitor 1 ME LE Many plateaus curves at various intensities Standard beam configuration:  s spill –19 x protons  1.5 x 10 9 / cm 2 Hadron Monitor starts to show plateau depletion – V region still flat Muon Monitors show no significant depletion

15 Robert Zwaska | IHEP - LBNF Beamline Meeting Radiation Damage Tests Delivered 12GRad PEEK Al 2 O 3 ceramic Ceramic putty Ceramic circuit UT Nuclear Engineering Teaching Lab Reactor

16 Robert Zwaska | IHEP - LBNF Beamline Meeting Hadron Monitor has a Lifetime Degradation of the Hadron Monitor observed almost from the start –Certain number of damaged pixels at start More pixels drop out over time –Gradual increase in leakage voltage on HV side Uncertain HV on chamber, power supplies are strained –Gains become variable Helium gas poisoning not much of an issue for Hadron Monitor May be losing signal at high-charge Lifetime is 2-4 years in recent operations –Presently running HADM-03, have HADM-04 ready in storage HADM-01 & 02 are spent – may autopsy in near future –Present vendor has lost construction capability, design would need to be reconstructed

17 Robert Zwaska | IHEP - LBNF Beamline Meeting Other Design Options Sealed, individual detectors –Likely unsuitable due to changes in the gas composition – would need study –Could simplify pressure and integration issues –Still has problem with cabling Other detection options –Visible – needs rad-hard optics –Purely gaseous React components to produce a detectable by product –E.g aN 2 + bO 2 -> NO X Measure outside radiation area –RF Resonators

18 Robert Zwaska | IHEP - LBNF Beamline Meeting Nominal Tolerances Initially derived from NuMI –First pass at LBNF tolerances has been performed, but need to be repeated with optimized beam Detailed specifications on the Hadron Monitor and other detectors must come from simulated alignment operations

19 Robert Zwaska | IHEP - LBNF Beamline Meeting Hadron Monitor Sensitivity Has broad sensitivity to tolerances as it sits in remnant primary and secondary beams Most relevant parameters: –Intensity –Position –Width Most useful only in conjunction with other instrumentation and the features of beam devices

20 Robert Zwaska | IHEP - LBNF Beamline Meeting Summary NuMI Hadron Monitor has been vital for operations –Primary function is beam-based alignment of targets & horns –Secondary function is a diagnostic tool and long-term running NuMI Hadron Monitor has been susceptible to failure –Radiation and robustness primary factors LBNF/DUNE situation will be a factor of worse –Questions of temperature, robustness, and signal response

Bob Zwaska IHEP - LBNF Beamline Meeting: Hadron Monitor 27 June 2016 NuMI Hadron Monitor