1. NuMI Secondary Beam Monitors S. Kopp University of Texas at Austin I. Detector Description II. Chamber Performance III. In-beam Observations IV. My rant: is it a flux monitoring or measuring tool?

2. November 10, 2003Robert Zwaska NBI 2003 2 10 9 Particles / cm 2 / spill 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Neutron fluences are ~ 10  that of charged particles at Hadron Monitor & Alcove 0 locations Hadron Monitor insensitive to horn focusing Muon Monitor distributions flat Alcove 1 Alcove 2 Alcove 3 10 7 10 6 Muons / cm 2 / spill Radius (cm) Particle Fluences

3. Function of the Hadron Monitor As target monitor (1 st fin broken) Monte Carlo As alignment tool: Data!

4. LE Beam Alcove 1 Alcove 2 Function of the Muon Monitors HE Beam Alcove 1 Alcove 2 Monte Carlo!

5. Concerns High Rad Levels Response to high particle fluences Inaccessibility –Chambers inaccessible during beam operations –Hadron monitor activated to 58 R/hr after 1yr, impossible to repair (requires remote handling procedure to replace) Requirements for Monitors Muon Monitors (Low Energy Beam) Muon Monitors (High Energy Beam)Hadron monitor ElementAlcove 1Alcove 2Alcove 3Alcove 1Alcove 2Alcove 3 Distance from target (m)739751769739751769725 Charged Particle Flux (10 7 /cm 2 /spill) 1.10.230.0931.70.222500 Radiation Level (10 6 rad/yr.)6.60.70.1518100.7  2000 Parent Particle Threshold (Gev) 4101841018<1  Beam Flux(r=0)/ Flux(r=1m) 1.31.1 2.11.5 --  Beam Shift for Horn 1 Offset (cm) 2.5  1.50.6  1.51.3  1.523  1.5 12.8  1.5 3.3  1.5 --

6. Detecting Phases of the Moon? Initial efforts by the monitoring group focused too much on secondary beam monitors as a ‘single system’ which could diagnose every possible problem in NuMI beam Better plan developed to many, smaller systems Target Horn 1 Baffle BPM x BPM y Profile BPM x BPM y Profile 334.2 334.4 334.9 346.6 346.9 347.4 356.1 357.0 357.7 359.8 Horn 2 366.4 369.4 Hadron Monitor 1077 Toroid Crosshair Muon Monitor BPM (position) SEM (spot size, position, halo) Toroid (intensity) Baffle Thermocouple (halo) Target Budal (alignment) Horn BDot (B field) Horn Stripline (current) Hadron Monitor (alignment, target integrity) Muon Monitor (flux)

7. Detector Construction Details

8. Ceramic Parallel Plate Ion Chambers

9. Muon Monitor Arrays  3 stations at 740,750,770m  9x9 IC array  Max flux 4  10 7  /cm 2 /spill  3mm plate separation  Bias voltage 100V-500V

10. Kapton Cables Chambers Tray Annoyingly complex signal connection post Am 241 calib. source

11. Signal connections Aluminum Wire Gasket HV connections HV feedthrough

12. 12 Muon Monitor Calibration 31 Tubes calibrated Require 1% precision calibration Tubes flushed with N 2 gas Each chamber irradiated with 1 Ci  - source. Plateau currents for irradiated and non-irradiated configurations Pressure & Temp monitored Plateau curve for one irradiated ion chamber Plateau current of single chamber for repeated source placements Plateau currents for all 288 ion chambers

13. Hadron Monitor Max flux ~10 9 /cm 2 /spill Rad levels ~2 x 10 9 Rad/yr 7x7 array of Ion Chambers -1 mm gap Residual activation 58R/hr -Construction 54lbs Al, 4lbs stainless Components Rad Tested up to 12GRad (6 NuMI years)

17. Beam Absorber Support Rail Gas Lines Kapton cable Shield door External cables

18. Early R&D Efforts

19. 19 Radiation Testing Exposed to 12GRad over 3 months. Corresponds to 6 NuMI yr @ hadmon. Before After Ceramic Kapton Wire Peek (UT-Austin 1 MW fission Reactor)

20. 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  10 9 - 5  10 12 protons/spill 5 cm 2 beam spot size 10 November 2001

21. 21 High Intensity Beam Test Key point: ion drift out of gas chamber can be slow compared to beam pulse -  results in space charge At highest intensity, chamber non-linear due to recombination in gas Voltage plateau lost at high intensity

22. 22 Expect our chambers to see background neutrons  Mon Alcove 1 with ~2  10 8 n/cm 2 /spill HadMon ~2  10 10 n/cm 2 /spill These neutrons are few 10’s MeV  can benchmark a toy MC of neutron scattering using a PuBe radioactive source (E n ~ 1-10 MeV) During normal NuMI beam operations: –Hadmon will see 0.3% background from neutrons –MuMon#1 will see 0.7% background from neutrons Compton e  (PuBe  ’s) Recoil Nuclei (from Neutrons) PuBe Source  Mon Backgrounds from Neutrons PuBe Source Ryan Keisler During the December 3-4 test we hit the absorber directly with the proton beam Expect signals from  Dump muons  neutrons GEANT MC of NuMI beam Debbie Harris Neutrons Energy (GeV) Neutrons/cm 2 /2E13 POT

23. November 10, 2003Robert Zwaska NBI 2003 23 Bench Tests 3 chambers, Am 241 source (E  =5.3 MeV) Setup useful to study –Chamber plateau –Electrostatic screening –Cross talk –Charge recombination

24. Thoughts on Early R&D Too diffuse in questions asked -- Lacked decent MC Too much focus on system that would survive Armagedden Insufficient focus on systems issues –gas monitoring –calibrations –radiation field all around detectors, cables, etc –software systems Required improved connection to rest of beam line –design for beam dump –layout of alcoves –infrastructure for chambers Early FNAL-university difficulties

25. Observations on Chamber Performance

26. Correct for Pressure Variations

27. Pressure Corrections (cont’d)

28. Gas Quality Annoyances Need laura’s plot showing gas issues.. Bad quality Gas added Increase flow Decrease flow Increase flow again New gas bottles

29. Hadron Mon. Linearity Final Operating Point Initial Operating Point 1.64 nC/10 12 ppp 1.46 nC/10 12 ppp

30. Muon Chamber Linearity Linearity with particle fluence pretty good Nonlinearity of 3% per 400pC seen – space charge?? LE Beam Data slope  16 pC/10 12 ppp

31. 31  Monitor Gas System Instrumentation Needed even more redundant instruments available in case of failure Since have added parallel instrumentation on gas quality (ion chambers outside in tunnel) Pressure (Torr) HadMon Alc 1 Alc 2 Alc 3 Termperature (°F) Monitor Temperature and Pressure to <1% to control detector signals

32. 32 Gas System Installation Gas Delivery Line Wiring Gas Rack High Pressure Manifold Distribution & DAQ Racks

33. Observations In Beam

34. Horn Current (kA) Alcove 2 Alcove 1 Horn Current Stability NuMI-only Mixed mode Stripline Temperature (  C) Muon

35. Target Leak Hadron Monitor signal on target dropped by 40%  we infer the equivalent of 41cm of water in the beam path “Notch” indicates water level Beam’s Eye View Graphite protection ‘baffle’ Graphite target Water cooling line Apertures Attenuation through water No water No Water Partially Full Target full Vertical Beam Position @ Target (mm)Horizontal Beam Position @ Target (mm)

36. Further Evidence of Multiple Scattering Expect spot size at HadMon dominated by multiple scattering in target hall material: If more material is present, we add radiation lengths: t/X 0  (t/X 0 ) + (t’/X’ 0 ) Can use this distribution to derive extra radiation lengths. Can see evidence of water, even horiz fin (pre-accident curves). Decrease in  at gaps is helpful cross check, but difficult to use quantitatively since the beam is being clipped on the left and right, and is saturating the HadMon on the right. Horizontal Position @ Target (mm)

37. Target Recovery Water Pumped from Target Can Multiple scattering through H 2 O Target back-pressured and pumped Progress tracked by hadron monitor Water below level of the leak unable to be pumped, necessitated target removal and repair Partially Full No Water Water level indicated by beam instrumentation after efforts to drain target in place, confirmed with boroscope Cooling line Vertical Beam Position @ Target

38. 1 st Attempt to Reinstall (Dried out) Target Notice the interesting feature – additional material in the beam? Data at beam right starts to look a lot like pre-accident. Flange was made incorrectly. Hadron Monitor RMS (mm) 4/20/05 Hadmon Signal mV/10 12 ppp Hor. Beam Position @ Target (mm)

39. Successful Reinstallation of Target On 4/25, 4/27, and 4/28 scans were taken after fixing the problem of the spool piece interfering with the beam on the left side. Shown below are the 4/28 data compared to the pre-leak data. The scans actually look better because the spot size was larger in March. No Water Hor. Beam Position @ Target (mm)

40. 40 Beam-Based Alignment of Target using  Mon and HadMon Graphite protection ‘baffle’ Graphite target Water cooling line target horn baffle As beam scans horizontally or vertically, can strike –Target –Horn-protection baffle –Gap in between horn and target Distance between struck-object and Horn 1 determines energy

41. 41 Horizontal Target Scan (HE Position) Target appears to be -1.5mm with respect to primary beam centerline.

42. baffle target selected

43. Closing Thoughts We’d lacked a serious MC for the muon monitors, only solving this now after 1.5 years! Monitor hardware performs well (2GRads!), and I’m thankful I don’t have any photos of it after irradiation in the beam (must look worse than Jim’s horn?!) Hadron monitor has very useful online role, not so useful offline (rates difficult to predict) – acts as an alarm and diagnostic tool. Muon monitors have tendency to be ignored online because we lack crisp interpretation for the data – some utility shown offline, however. Fluxes are difficult to measure, but essential for cross section experiments. Key issues –muon monitors’ sensitivity/overlap with the flux –backgrounds from  -rays, neutrons –Shielding geometry

44. References S. Kopp et al, “The Secondary Beam Monitoring System for the NuMI Facility at FNAL,” accepted in Nucl. Instr. Meth. R. Zwaska et al, “Beam-based Alignment of the Target Station Components of the NuMI Facility at FNAL,” accepted in Nucl. Instr. Meth. D. Indurthy et al, “Study of Neutron-Induced Ionization for Helium and Argon Chamber Gases,” Nucl. Instr. Meth. A528, 731 (2003) R. Zwaska et al, “Beam Tests of Ionization Chambers for the NuMI Beam at Fermilab,” IEEE Trans. Nucl. Sci. 50, 1129 (2003). D. Naples et al, “Ionization Chambers for Monitoring in High-intensity Charged Particle Beams,” Nucl. Instr. Meth. A496, 293 (2003). S. Kopp, “Accelerator Neutrino Beams,” submitted to Physics Reports, (available in SPIRES).