# Presentation: 606846

## 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?

## Neutron fluences are ~ 10 that of charged particles at Hadron Monitor & Alcove 0 locations
Hadron Monitor insensitive to horn focusing
Muon Monitor distributions flat

- Robert Zwaska
- NBI 2003

- Neutron fluences are ~ 10 that of charged particles at Hadron Monitor & Alcove 0 locations
- Hadron Monitor insensitive to horn focusing
- Muon Monitor distributions flat

- Particle Fluences

## Function of the Hadron Monitor

- As target monitor

- (1st fin broken)

- Monte Carlo

- As alignment tool:

- Data!

## Function of the Muon Monitors

**LE Beam**

- Alcove 1

- Alcove 2

- Monte Carlo!

- Monte Carlo!

## Requirements for Monitors

- 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)

|  | Muon Monitors
(Low Energy Beam) |  |  | Muon Monitors
(High Energy Beam) |  |  | 
Hadron monitor
 |
| --- | --- | --- | --- | --- | --- | --- | --- |
| Element | Alcove 1 | Alcove 2 | Alcove 3 | Alcove 1  | Alcove 2 | Alcove 3 |  |
| Distance from target (m) | 739 | 751 | 769 | 739 | 751 | 769 | 725 |
| Charged Particle Flux (107/cm2/spill) | 1.1 | 0.23 | 0.09 | 3 | 1.7 | 0.22 | 2500 |
| Radiation Level (106 rad/yr.) | 6.6 | 0.7 | 0.15 | 18 | 10 | 0.7 | 2000 |
| Parent Particle Threshold (Gev) | 4 | 10 | 18 | 4 | 10 | 18 | <1 |
|  Beam Flux(r=0)/
Flux(r=1m) | 1.3 | 1.1 | 1.1 | 2.1 | 1.5 | 1.5 | -- |
|  Beam Shift for Horn 1 Offset (cm) | 2.5  1.5 | 0.6   1.5 | 1.3   1.5 | 23   1.5 | 12.8   1.5 | 3.3   1.5 | -- |

## 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

- 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)

## Detector Construction Details

## Ceramic Parallel Plate Ion Chambers

- Muon Monitor Arrays
- 3 stations at 740,750,770m
- 9x9 IC array
- Max flux 4107 /cm2/spill
- 3mm plate separation
- Bias voltage 100V-500V

*Kapton Cables*

*Chambers*

*Tray*

*Annoyingly complex signal connection post*

*Am**241** calib. source*

*Signal connections*

*Aluminum*
*Wire Gasket*

*HV*
*connections*

*HV*
*feedthrough*

## Muon Monitor Calibration

- 31 Tubes calibrated
- Require 1% precision calibration
- Tubes flushed with N2 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

- Hadron Monitor
- Max flux ~109/cm2/spill
- Rad levels ~2 x 109 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)

- Beam
- Absorber

- Support
- Rail

- Gas Lines

- Kapton cable

- Shield door

- External cables

## Early R&D Efforts

## Radiation Testing

- Exposed to 12GRad over 3 months.
- Corresponds to 6 NuMI yr @ hadmon.

- Before

- After

- After

- After

- Ceramic

- Kapton Wire

- Peek

- (UT-Austin 1 MW fission Reactor)

## 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109 - 51012 protons/spill
- 5 cm2 beam spot size

- 10 November 2001

## 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

## Expect our chambers to see background neutrons
Mon Alcove 1 with ~2108 n/cm2/spill
HadMon  ~21010 n/cm2/spill
These neutrons are few 10’s MeV  can benchmark a toy  MC of neutron scattering using a PuBe radioactive source (En ~ 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

- Expect our chambers to see background neutrons
- Mon Alcove 1 with ~2108 *n*/cm2/spill
- HadMon  ~21010 *n*/cm2/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**

**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/cm2/2E13 POT

## Bench Tests

- Robert Zwaska
- NBI 2003

- 3 chambers, Am241 source (*E*** =5.3 MeV)
- Setup useful to study
- Chamber plateau
- Electrostatic screening
- Cross talk
- Charge recombination

## 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

## Observations on Chamber Performance

- Observations on Chamber Performance

## Correct for Pressure Variations

## Pressure Corrections (cont’d)

- Pressure Corrections (*cont’d*)

## Gas Quality Annoyances

- Need laura’s plot showing gas issues..

*Bad quality*
*Gas added*

*Increase*
*flow*

*Decrease*
*flow*

*Increase*
*flow again*

*New gas*
*bottles*

## Hadron Mon. Linearity

- Final
- Operating
- Point

- Initial
- Operating
- Point

- 1.64 nC/1012ppp

- 1.46 nC/1012ppp

## Muon Chamber Linearity

- Linearity with particle fluence pretty good
- Nonlinearity of 3% per 400pC seen – space charge??

- LE Beam Data

- slope16 pC/1012ppp

## Monitor     Gas System Instrumentation

- 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

## Gas System Installation

- Gas Delivery Line

- Wiring Gas Rack

- High Pressure Manifold

- Distribution & DAQ Racks

## Observations In Beam

- Horn Current (kA)

- Alcove 2

- Alcove 1

- Horn Current Stability

- NuMI-only
- Mixed mode

- Stripline Temperature (C)

- Muon

## 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*

- Apertures

- Attenuation through water

- No water

- No Water

- Partially Full

- Target full

**Vertical Beam Position @ Target (mm)**

**Horizontal Beam Position @ Target (mm)**

## 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)**

## Target Recovery

*Water Pumped from Target Can*

- Multiple scattering through H2O

- 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**

## 1st 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/1012ppp

**Hor. Beam Position @ Target (mm)**

**Hor. Beam Position @ Target (mm)**

## 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

- No Water

**Hor. Beam Position @ Target (mm)**

**Hor. Beam Position @ Target (mm)**

## Beam-Based Alignment of Target using Mon and HadMon

- Beam-Based Alignment of Target using Mon and HadMon

- Graphite protection ‘baffle’

- Graphite target

- Water cooling line

- 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

## Horizontal Target Scan (HE Position)

- Target appears to be -1.5mm with respect to primary beam centerline.

## 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

## 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).