1. LARP Additions to the LHC Synchrotron-Light Monitors Alan Fisher SLAC National Accelerator Laboratory LARP CM18 Fermilab 2012 May 8

2. LARP Two Proposed Additions Beam-Halo Monitor Measures beam halo and shows the effect of a change in collimation Collaborators: SLAC: Jeff Corbett University of Maryland (College Park, MD): Ralph Fiorito, Anatoly Shkvarunets, Hao Zhang Fast Bunch-by-Bunch Beam-Size Monitor Measures RMS size of every bunch at 1 Hz Collaborators: SLAC: Jeff Corbett University of Victoria (Victoria, BC, Canada): Justin Albert 2012-05-082 Fisher—Synchrotron-Light Upgrades

3. LARP The Solar Corona and Beam Halo Lyot invented a coronagraph in the 1930s to image the corona Huge dynamic range: Sun is 10 6 times brighter than its corona Block light from solar disc with a circular mask B on image plane Diffraction from edge of first lens (A, limiting aperture) exceeds corona Circumferential stop D around of image of lens A formed by lens C Can we apply this to measuring the halo of a particle beam? Bernard Lyot, Monthly Notices of the Royal Astronomical Society, 99 (1939) 580 2012-05-083 Fisher—Synchrotron-Light Upgrades

4. LARP Beam-Halo Monitor Halo monitoring was part of the original specification for the synchrotron-light monitor. LARP’s involvement in both light monitors and collimation makes this a natural extension to the SLM project. But the coronagraph needs some changes: The Sun has a constant diameter and a sharp edge. The beam has a varying diameter and a profile that is roughly Gaussian An adjustable mask is needed 2012-05-084 Fisher—Synchrotron-Light Upgrades

5. LARP Point-Spread Function & Dynamic Range Image a point source onto an intermediate surface, and then re- imaged onto a camera First image the full beam: No masking on the intermediate surface Dynamic range limited by bright peak of image and by pixel resolution Typically 8 bits, a factor of 256 Mask on intermediate surface excludes light near peak Cover regions with brightness > 10% of peak Brighten the rest of the image by a factor of 10 Increase exposure time, reduce optical attenuation, or increase camera gain Widen mask to cover regions > 1% of peak; brighten the rest Repeat down to the 10 -5 contour This gives the point-spread function (PSF, response to a point source) over 7 orders of magnitude For halo: Measurement with beam, deconvolution with PSF 2012-05-08 Fisher—Synchrotron-Light Upgrades 5

6. LARP Fixed Mask with Zoom Optics 2012-05-08 Fisher—Synchrotron-Light Upgrades 6 Zoom lens Halo image Source Steering mirrors Masking mirror Image of source: Bright center passes through hole

7. LARP Zoom: Advantages & Disadvantages Advantages of zoom: Simple and cheap (if you can make the lens) Disadvantages of zoom: A very large zoom range is needed to measure over several orders of magnitude in intensity Zooming scales size of masked region, but shape of mask is fixed Several orders of magnitude down, the mask may need a different shape A zoom lens over the full SLM bandwidth (near IR to near UV) would have excessive dispersion Especially difficult when using only rad-hard materials Zoom with only reflective optics is even more difficult 2012-05-08 Fisher—Synchrotron-Light Upgrades 7

8. LARP Digital Micro-Mirror Device (DMD) 1024  768 grid of 13.68-µm square pixels Pixel tilts about the diagonal, toggling from −12° to +12° Mirror array mounted on a control board, which is tilted by 45° so that the reflections are horizontal. 2012-05-088 Fisher—Synchrotron-Light Upgrades

9. LARP DMD: Advantages & Disadvantages Advantages of DMD: Masking is very flexible due to individually addressable pixels Disadvantages of DMD: The pixels are somewhat large for the LHC RMS size: 14 pixels at 450 GeV, but only 3.4 pixels at 7 TeV Large distance from source to first focusing mirror demagnifies intermediate image by a factor of 7 Some improvement with a newer DMD for HDTV, with 10.8-µm pixels RMS beam size is 4.3 pixels at 7 TeV Beam is imaged onto tilted pixels of DMD plane: Virtual source plane for camera is not perpendicular to optical axis DMD has features of a mirror and a grating Fixed by tilting camera face for best focus across the image plane Known as Scheimpflug compensation 2012-05-089 Fisher—Synchrotron-Light Upgrades

10. LARP Camera Sensor Lens 3 Mirror Lens 1 DMD Lens 2 Lens 4 Image 2 Image 1 Mask Light from beam R. Fiorito, H. Zhang et al. (University of Maryland), Proc. BIW2010 High Dynamic-Range Imaging with a DMD No mask With mask 2012-05-0810 Fisher—Synchrotron-Light Upgrades

11. LARP DMD Optics on SPEAR3 at SLAC 2012-05-08 Fisher—Synchrotron-Light Upgrades 11 SPEAR3 e-beam Masked image Images of e-beam Camera Scheimpflug tilt

12. LARP SPEAR3 Masked at Intensity Thresholds 2012-05-08 Fisher—Synchrotron-Light Upgrades 12 ND 5ND 4ND 3 ND 2ND 1ND 0 Masked region 13 mm Stored 350-mA beam PIMAX intensified camera with 2-ms exposures No Mask DMD edge

13. LARP −3 log(I/I 0 ) 0 All 7 Decades First 3 Decades Last 4 Decades 25 mm Composite Images, Logarithmic Scales −7 log(I/I 0 ) −3−7 log(I/I 0 ) 0

14. LARP Adding a Halo Monitor to the LHC Optics During halo measurements: Insert DMD at intermediate image Return to main path with focus or path-length correction Rotate camera by Scheimpflug angle This layout is simplified for illustration. In actual implementation: Path might go upward from DMD and return to camera at Scheimpflug angle Or DMD might be used for all measurements, occasionally masking center Or use DMD to split core and halo light, and add a camera to image the halo 2012-05-08 Fisher—Synchrotron-Light Upgrades 14 Alignment laser Focus trombone F1 = 4 m PMT and 15% splitter for abort gap monitor Intermediate image Table Coordinates [mm] Slit Calibration light and target F2 =.75 m DMD Diffraction stop Cameras

15. LARP Testing with the LHC Optics Is dynamic range sufficient for beam halo? Diffraction should make a significant background Diffraction from imaging the peak Diffraction from edge of exclusion mask Scattering from edges of mirror facets A Lyot stop may be needed to reduce diffracted light Must measure the point-spread function with the LHC optics Trip to CERN in the next few months Use the test copy of the optics in the LHC tunnel (the BSRT) On a lab bench in Prévessin Decide how to rearrange optics Plan for installation during the long shutdown 2012-05-08 Fisher—Synchrotron-Light Upgrades 15

16. LARP Rotating Mask Bunch-by-bunch scans have limitations: 2 sec/bunch for good statistics: Scanning 2808 bunches takes 1.6 hours The expensive gated cameras may eventually be damaged by radiation Instead, an optical analog of a wire scanner that: Scans a thin slit across the synchrotron-light image of the proton beam Detects transmitted light with a photomultiplier Sorts the PMT pulses by bunch number and by slit position Gets profiles of every bunch at 1 Hz 3 slits at different angles on a rotating disk Horizontal, vertical and 45° profiles Beam size on major and minor axes, plus tilt of beam ellipse 2012-05-0816 Fisher—Synchrotron-Light Upgrades

17. LARP Movie: Mask Rotating across Beam x [mm] y [mm] 2012-05-0817 Fisher—Synchrotron-Light Upgrades

18. LARP Mask Wheel with Laser-Cut Slits Four sets of three laser-cut slits in a thin sheet of stainless steel, sandwiched between two thicker aluminum disks Rotation at 0.25 Hz for 1-Hz data 2012-05-0818 Fisher—Synchrotron-Light Upgrades

19. LARP Summer 2011: Mask Tested on SPEAR3 2012-05-08 Fisher—Synchrotron-Light Upgrades 19 Synchrotron light from SPEAR3 ring enters through hole PMT in metal box Mask wheel DC motor with gearhead and angle resolver Dark enclosure

20. LARP Summer 2011: Measured Bunch Profiles 2012-05-08 Fisher—Synchrotron-Light Upgrades 20

21. LARP Asymmetric Bunch Profiles: Irregular Slits Laser-cut slits, 15 µm by 20 mm All 12 slits cut in a single sheet of stainless steel Not all of equal quality: Photo shows 2 of the 12 slits used in the test 2012-05-08 Fisher—Synchrotron-Light Upgrades 21

22. LARP New Approach: Micro-EDM Slits Investigating micro-EDM rather than laser cutting EDM = Electric-Discharge Machining Cut individual slits rather than 12 on one sheet Select 12 that are highly uniform and parallel Pin them at correct angles on the wheel Photo shows sample slit, 125 µm by 2 mm, machined in stainless steel 2012-05-08 Fisher—Synchrotron-Light Upgrades 22

23. LARP Adapting to SPEAR3 Data acquisition for fast PMT pulses For LHC: DAB64x VME module with an IBMS daughter card Process data in real time For SPEAR3, we used a fast oscilloscope 2 Gsample/s with a 10-MSamp memory: 5-ms records One slit passes through the beam as the wheel rotates by ~10° 111 ms at the 0.25-Hz revolution rate intended for LHC Had to run wheel faster, at 6 Hz Recorded signal from one slit at a time, processed afterward Simultaneously acquired resolver signals (cosine and sine) Relates wheel angle slit and position to scope timebase SPEAR3 electron are an inexact substitute for LHC protons 2-ns bunch spacing (not 25 ns) and a 800-ns ring turn (not 89 µs) Far more synchrotron light: Attenuated light to avoid saturating PMT and draining capacitors that maintain PMT bias 2012-05-08 Fisher—Synchrotron-Light Upgrades 23

24. LARP Summary Two possible additions were tested on the SPEAR3 electron ring at SLAC Beam-halo monitor using a digital micro-mirror device Dynamic range of 10 7 for the SPEAR optical system The LHC optical design needs to be modified to add a DMD Measure the point-spread function and dynamic range on the test bench at CERN Rotating-mask bunch profiler Designed to measure the RMS size of each LHC bunch at 1 Hz Fast profiling demonstrated at SPEAR Needs to be tested further with more uniform slits Micro-EDM may be a substantial improvement over laser cutting 2012-05-0824 Fisher—Synchrotron-Light Upgrades