NuMI Secondary Beam MonitorsS. Kopp

University of Texas at Austin

I. Detector DescriptionII. Chamber PerformanceIII. In-beam ObservationsIV. My rant: is it a flux monitoring or measuring tool?

November 10, 2003 Robert ZwaskaNBI 2003

2

109 P

artic

les

/ cm

2 / s

pill

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 1Alcove 2Alcove 3107

106

Muo

ns /

cm2 /

spi

llRadius (cm)

Particle Fluences

Function of the Hadron Monitor

• As target monitor

(1st fin broken)

Monte Carlo

• As alignment tool:Data!

LE BeamLE BeamAlcove 1 Alcove 2

Function of the Muon Monitors

HE BeamHE Beam Alcove 1 Alcove 2

Monte Carlo!

Monte Carlo!

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

monitorElement 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

Tar

get

Hor

n 1

Baf

fle

BP

M x

BP

M y

Pro

file

BP

M x

BP

M y

Pro

file

334.

233

4.4

334.

9

346.

634

6.9

347.

4

356.

1

357.

0

357.

7

359.

8

Hor

n 2

366.

4

369.

4

Had

ron

Mon

itor

1077

Tor

oid

Cro

ssha

ir

Cro

ssha

ir

Cro

ssha

ir

Muo

nM

onit

or

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 Arrays3 stations at 740,750,770m 9x9 IC arrayMax flux 4107 /cm2/spill3mm plate separationBias voltage 100V-500V

Kapton Cables

Chambers

Tray

Annoyingly complex signal connection post

Am241 calib. source

Signal connections

AluminumWire Gasket

HVconnections

HVfeedthrough

12

Muon Monitor CalibrationMuon 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)

BeamAbsorber

SupportRail

Gas Lines

Kapton cable

Shield doorExternal cables

Early R&D Efforts

19

Radiation TestingRadiation 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 beam5109 - 51012 protons/spill5 cm2 beam spot size

10 November 2001

21

High Intensity Beam TestHigh 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

• Expect our chambers to see background neutronsMon Alcove 1 with ~2108 n/cm2/spillHadMon ~21010 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

Compton e (PuBe ’s)

Recoil Nuclei (from Neutrons)

PuBe Source

Mon Backgrounds from NeutronsPuBe 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)

Neu

tron

s/cm

2 /2E

13 P

OT

November 10, 2003 Robert ZwaskaNBI 2003

23

Bench Tests• 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

Correct for

Pressure Variations

Pressure Corrections (cont’d)

Gas Quality Annoyances

• Need laura’s plot showing gas issues..Bad qualityGas added

Increaseflow

Decreaseflow

Increaseflow 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 DataLE Beam Data

slope16 pC/1012ppp

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)

Pre

ssur

e (T

orr)

HadMonAlc 1Alc 2Alc 3

Ter

mpe

ratu

re (

°F)

• Monitor Temperature and Pressure to <1% to control detector signals

32

Gas System Installation

Gas Delivery Line

Wiring Gas Rack

High Pressure Manifold

Distribution & DAQ Racks

Observations In Beam

Hor

n C

urre

nt (

kA)

Alc

ove

2A

lcov

e 1 Horn Current Stability

NuMI-onlyMixed mode

Str

iplin

e T

empe

ratu

re (C

)M

uon

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 waterNo Water

Partially Full

Target full

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

Further Evidence of Multiple Scattering

0/120

6.13)725( Xt

GeV

mradmHad

• Expect spot size at HadMon dominated by multiple scattering in target hall material:

• If more material is present, we add radiation lengths:t/X0 (t/X0) + (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 RecoveryWater 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.

Had

ron

Mon

itor

RM

S (m

m)

4/20/05

Had

mon

Sig

nal m

V/1

012pp

p

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)

40

Beam-Based Alignment of Target using Mon and HadMon

Graphite protection ‘baffle’

Graphite target

Water cooling line

target

hornbaffle

• 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

Horizontal Target Scan (HE Position)

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

baffle baffletargettarget selected

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).