BOOSTER LASER PROFILE MONITORCommissioning and Data Collection

David JohnsonAccelerator Physics Center

Proton Source Department MeetingJune, 23, 2011

OUTLINE

Concept Linac Installation Profile Examples Hardware Issues Optimization Conclusions

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CONTRIBUTORS

David Johnson (APC/HINS) group leader Jim Zagel (AD/I) electronics and integration support Carl Lundberg (AD/I) electronics and mechanical support Dave Slimmer (AD/I) software support responsible for LabView Jim Galloway (AD/I) electronics and mechanical support Ray Tomlin (AD/PS) laser support guru Vic Scarpine (AD/I) responsible for HINS LPM design and installation Manfred Wendt (AD/I) provided button BPM's, and Inst. Dept. support Kevin Duel (AD/MS) mechanical engineer for chamber construction and

installation Hogan Nguyen (PPD/SiDet) provided scintillator and PMT for electron detector Vladimir Kashkin (TD) designed electron separation magnet Peter Prieto (AD/I) Timing board design Glenn Johnson (AD/I) timing board layout Wayne Schmitt (AD/Safety) help with radiation measurements Mark Lebrun (AD/MS co-op) radiation shielding design Booster Department (particularly Todd and Kent)

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CONCEPT

Utilize photons from Nd:YAG laser ( l = 1064 nm) to photodetatch the outer electron from the H- ions creating neutral H0 atoms and free electrons.

Photodetachment cross section (for Nd:YAG) is ~3.8E-17 cm2 Fraction neutralized where F is photon flux

and t is the crossing time For a 50 mJ 10 ns laser pulse with an average laser size of 200 um,

we neutralize about 92 % of the H- passing through the laser. The liberated electrons are swept into electron detector by weak

magnetic field. With a laser beam diameter << H- beam, we can scan the laser

across the H- beam and collect the electrons at each position of the scan thus giving us a density profile of the H- beam.

For typical source currents of ~ 35mA -> 200 MHz bunch intensities of ~1E9 with a bunch separation of ~5 ns. For a laser pulse duration of ~10 ns we impact only a single bunch each linac cycle.

Fneut ef 1

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LINAC INSTALLATION

launch box

optics box

laser transport

vacuum chamber

chute

Q8

Mirror boxes

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FERMILAB 400 MEV CONFIGURATION

viewports (laser beam dump not shown) electron detector port

button BPM

optics box

H- beam

electron magnet

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LINAC INSTALLATION

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CROSS SECTION OF THE LPM

Scan limits determined by size of laser dump viewport

+/- 33mm/264mm-> 125mr +/- 7.16o optical (+/3.58o mechanical)

Beam center -> +/-20 mm scan limits

Mask at input viewport limits laser excursion to prevent launching laser up or downstream in vacuum chamber

Cambridge Technology scanner +/- 1 degree/volt -> input voltage of

3.58V Repeatability 8 microradians

Optics Box

3” beam pipe

Electron magnetpole tips

1 3/4 ” beam pipe

Not to scale

Viewport:AR coated2.69”dia

Anodized MASK

Max angle +/- 6o

Anodized laserdump w/PD

Mirror box

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INTERIOR OF THE OPTICS BOX

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LASER LAUNCH BOX

YM1LM1LM2

LM1LM2

CM1A1

A2

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ELECTRON TRAJECTORIES

6/22/2011 2:15 PM 10

110mm4.331”

265 mm10.433”

114.3mm4.5”

150 mm5.906”

6” flanges

4 5/8” flanges

2 ¾” flanges

3x4” tube

3”round beam tube

1.5” round beam tube

Magnet pole

Magnet coil

114.3mm4.5”

600 mm23.31”

Optics box

Beam tube

Electron collector tube

Need to transitionFrom 3x4” tubeto 3” round with bellows at each end

Peak dipole field ~ 175 Gauss

Integrated dipole field ~ +/- 70 G-mfrom each half of the magnet ,Net integrated dipole ~ 0.61 G-m.Results in a displacement of ~0.4 mmand angle of ~19 ur.

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ELECTRON DETECTION

Electron energy 218 keV Optical detection

Scintillator (polystyerene doped with N-Methyl-chloride) 3” diameter 1” thick with 100A aluminized coating on vacuum side and walls

Electron detection nearly 100%

25 ns dopant decay time Scintillator made at FNAL

Photomultiplier Tube (Hamamatsu 580 12-stage)

Currently using an 8 bit 1 Gs/sADC scope card in LPM computer to monitor PMT voltage into 50 ohms.

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IMPACT OF LPM MAGNET ON BOOSTER BEAM

See motion on downstream BPM’s. Peak distortion is seen at VPQ15 of something less than 2 mm and ~0.7 mm at VPFOIL. (This is well within the long term drift/tuning of injection positions)

NO impact on losses of injection efficiency is seen.

Orbit distortion at injection can be compensated (if desired by -0.5 amp on VTQ8)

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PMT RESPONSE

PMT high voltage on/magnet off Turn on magnet (with PMT on)

Move laser timing inside the beam pulse

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FRONT PAGE IMAGE /CONTROL

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SCAN SPECIFICATIONS /TIMING MODULE

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LASER ENERGY AND TIMING

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COMPARISON OF MW AND LPM

Multiwire Data taken March 23, 2011$1D 11 turns @ 4E12

LPM profile taken on June 8, 2011On $14 cycle (single bunch)

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PMT RESPONSE VS PMT HIGH VOLTAGE

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PROFILE EXAMPLE

Scan range -18 to 18 mm

PMT HV 700 V

Small peak area ~ 2.3% ofMain bunch

Bunch intensity ~1E9

72 data points across scan10 beam samples/data point

Is this real beam or reflection?

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INVESTIGATE BUMP AT 17 MM

Increase PMT voltage to 1 kV

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HARDWARE ISSUES

Laser power supply damaged by radiation Moved power supply up stairs

Scanning galvanometers issues Optical position feedback loop maxed out

voltage Suspect darkened led – working with vendor Order new galvanometers

Axis select galvanometer issues Not meant to operate in vertical orientation Looking for suitable alternative

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OPTIMIZATION

Currently we are using laser at full energy to get a 10 ns laser pulse. This limits the PMT high voltage due to the limited dynamic range of the ADC. We need to further optimize the laser

energy/timing, PMT high voltage, and better understand the PMT signal and ADC.

Data analysis is just starting…

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CONCLUSIONS

The BLPM can parasitically and nondestructively measure transverse profiles of beam in the 400 MeV line.

Single (up to a few) bunch measurements possible at any selectable position within the bunch train.

The system is very sensitive and can be used to measure and characterize halo.

Data analysis and optimization just starting. Lessons learned to be applied to future systems

for HINS and Project X

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