Booster Laser Profile Monitor

1. David Johnson Accelerator Physics Center Commissioning and Data Collection Proton Source Department Meeting June, 23, 2011 Booster Laser Profile Monitor

2. Concept Linac Installation Profile Examples Hardware Issues Optimization Conclusions Outline

3. 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) contributors

4. 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. concept

5. Q8 vacuum chamber optics box chute Mirror boxes laser transport launch box Linac installation

6. viewports (laser beam dump not shown) electron detector port button BPM H- beam electron magnet optics box Fermilab 400 mev configuration

7. Linac installation

8. Viewport: AR coated 2.69”dia 3” beam pipe Max angle +/- 6o Anodized MASK Mirror box Anodized laser dump w/PD Electron magnet pole tips 1 3/4 ” beam pipe Optics Box Not to scale • 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 Cross section of the Lpm

9. Interior of the optics box

10. Laser launch box LM2 LM1 YM1 CM1 A1 LM2 LM1 A2

11. Electron Trajectories Peak dipole field ~ 175 Gauss Integrated dipole field ~ +/- 70 G-m from each half of the magnet , Net integrated dipole ~ 0.61 G-m. Results in a displacement of ~0.4 mm and angle of ~19 ur.

12. 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. Electron detection

13. 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) Impact of lpm magnet on booster beam

14. PMT response PMT high voltage on/magnet off Turn on magnet (with PMT on) Move laser timing inside the beam pulse

15. Front page image /control

16. Scan specifications /timing module

17. Laser energy and timing

18. Comparison of MW and lpm LPM profile taken on June 8, 2011 On $14 cycle (single bunch) Multiwire Data taken March 23, 2011 $1D 11 turns @ 4E12

19. PMT response vs pmt high voltage

20. Profile example Scan range -18 to 18 mm PMT HV 700 V 72 data points across scan 10 beam samples/data point Is this real beam or reflection? Bunch intensity ~1E9 Small peak area ~ 2.3% of Main bunch

21. Investigate bump at 17 mm Increase PMT voltage to 1 kV

22. 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 Hardware Issues

23. 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… Optimization

24. 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 conclusions