LHC Emittance and Profile Measurements Workshop

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					Emittance and Profile Measurements: LEDA, LANSCE, and other Mesa
                              Facilities



           LHC Emittance and Profile-Measurement Workshop
                        J. Douglas Gilpatrick
                  Los Alamos National Laboratory
                          LANSCE Division
                           July 3 & 4, 2000
                                Introduction

•   Profile measurements used on LEDA and proposed Halo Experiment
•   Profile measurements under development for APT/ATW
•   Emittance Measurements used at LANSCE, LEDA and other mesa facilities
•   Measurements of LANSCE
•   Summary of the LEDA Experiences




July 3 &4, 2000           LANSCE Beam Diagnostics Team                      2
    LEDA Slow Wire Scanner Verified Beam Width for Beamstop Protection
           and Performed ―Quad Scans‖ Emittance Measurement.
                                                                                               1.4
•   Wire scanner: based on LANSCE design
                                                                                                                      Vert ical
     –   Fiber bias: optimize secondary electron coefficient                                                          Horizontal
     –   Only one sense wire in beam at a time                                                   1




                                                                           Normalized Charge
     –   2 bias wires on either side of sense wire
     –   Senses emitted secondary electrons depleted from fiber
                                                                                               0.6
     –   Two fibers used: 100-mm SiC/C
     –   Processing electronics: replacement charge is integrated with a
         lossy integrator.
                                                                                               0.2
•   Peak and cw current densities: 16- to     0.1-mA/mm2
•   Nominal peak beam current: 100 mA
                                                                                               -0.2
•   Normal operation pulse lengths: 0.02- to 0.5-ms                                                   -60 -40 -20 0    20 40 60
                                                                                                           Pos ition (mm)
     – RF blanking: powering RFQ after injector pulse has stabilized
•   Typical dynamic range: 200:1




    July 3 &4, 2000               LANSCE Beam Diagnostics Team                                                           3
    Wire Scanner Fiber Clamping Technique Improves the Reliability of the
             Electrical Connection and Mechanical Fiber Support

•     Mechanically support the wire and keep it under
      tension during motion and thermal loading.
       – Two techniques used at LANSCE and LEDA
             • SiC/C fiber: drawn-Cu tube crimped clamp (see picture)
             • C fiber: plated, no spring, soldered pad
•     Why develop new design?
       –   Older design difficult to attach.
       –   Time consuming process to assemble connections.
       –   Requires the exact length of wire.                           Old Fiber Connection
       –   We need to be able to hold a smaller diameter fiber.
•     New collet based clamp advantages (halo
      experiment)
       –   Easier/quicker to attach wire.
       –   Allows use of a smaller-diameter wire.
       –   Doesn’t require the exact length of wire.
       –   Spring is not in the signal circuit

                                                                        New Fiber Connection
July 3 &4, 2000                   LANSCE Beam Diagnostics Team                                 4
          LEDA Wire-Scanner-Fiber Secondary and Thermionic Emission

•     Measured secondary emission coefficient: 3.3%
                                                                                           40
•     Thermionic emission limitation (see graph)                                                                          9 mA S. E. Emission
                                                                                                                          T.E. 2nd order Fit




                                                                      Electron Cu rren t
       – Distorts profile core distribution shape                                          30                             S. E.
                                                                                                                          T. E.
•     Two SiC fiber robustness tests performed




                                                                            (mA)
                                                                                           20

       – Positioned fiber in beam core, varied pulse length
                                                                                           10
             •   Acquired optical spectrometer data, 450- to 750-nm
                                                                                                    Seco ndary Emission        Thermion ic Emissio n
       – Initial conclusion: fibers more robust than expected                               0
                                                                                                0          0.5             1           1.5             2
                                                                                                       Time during Beam Mac ropulse (ms)
             •   1st
                  test: fiber severed at 25 ms
                  – Some indication outer jacket dislodged at 4 ms
             • 2nd test: fiber severed at 2 ms
       – Optical data and thermionic-electron-data correlated
             • Optical data and simulation w/o thermionic emission
               bracket fiber temperature of 1575K to 2050K
•     Considered ionizing radiation detection methods:
      6.7-MeV protons on SiC or C barely produces
      sufficient g radiation over background



    July 3 &4, 2000                  LANSCE Beam Diagnostics Team                                                                            5
    Halo Measurement Experiment will have Integrated Wire Scanner and
    Halo Scraper Profile Measurement Capable of Detecting 5 rms Widths

•    Installing a 52 FODO magnet lattice between existing
     LEDA RFQ and HEBT.                                                           C/Cu Scrapers

      – First beam possibly by early September
•    9, X- & Y-axis wire scanner/halo scraper assemblies     C Fiber
     installed
                                                                 Stationary
•    Purpose: to detect two different mismatch modes             Beam Tube
                                                                Diameter: 28 mm
      – Quadrupole and ―breathing‖ mode
      – Goal: answer how halo is produced
•    Wire scanner fiber: 33-mm C fiber, detect secondaries
•    Scraper: Graphite brazed on Cu
      – Range out protons in 1.5-mm thick graphite
•    Additional measurement: detect 4.4-MeV gammas
     resulting from 6.7-MeV protons on graphite scraper
•    Simulated distributions show wire scanner can detect to
     4 rms widths
•    Simulated halo scraper measurement acquires beam
     distribution data to 5 rms widths
July 3 &4, 2000               LANSCE Beam Diagnostics Team                                6
            LEDA Beam Induced Fluorescence (BIF): Introduction

•   Technique demonstrated on FMIT, ATS, GTA, and now LEDA
•   APT/LEDA Motivation: needed a method to verify beam tune during cw and
    high duty factor beam operation
     – No other technique available that could fit in the limited space
•   Photon flux density and S:N dependent on beam current density, beam
    velocity, and background gas partial pressure
•   Relative radiance measurements were done in the early 80’s at LANL in
    preparation for FMIT
     – 91 mW/sr-cm2
           • 100 mA/cm2, 80 keV, 2 X 10-5 Torr of N2
     – Similar experiences on ATS and GTA
     – Remeasured the radiance data on LEDA, presently analyzing the data




July 3 &4, 2000                LANSCE Beam Diagnostics Team                  7
                                LEDA BIF Beamline Apparatus

•     Camera: Kodak DCS 420m w/ DEP image intensifier
       – Digital camera in Nikon body (1524 X 1012 CCD chip)
             • Digital camera inexpensive
                – If CCD damaged by radiation, easily replaced
       – Intensifier installed on camera by InterScience, Inc.
             • Variable Gain from 1 to 4000, 40 ns gating
       – Overall illuminance: 0.6 mlux
•     Lens system: Computar f/1.8
       – 16 mm to 160 mm remote-control zoom lens
       – Century Precision Optics relay lens, mates camera to lens
•     N2 gas injection system
       – Maxtek piezoelectric valve
             • Throughput range: 0-6 torr-liters per sec
       – Backpressure control system
             • Maintains auxillary N2 gas supply pressure for piezoelectric valve
                – Balzers RVC-200 feedback controller
                – Balzers EVR-116 flow control valve
                – Balzers PKR-250 gauge

    July 3 &4, 2000                   LANSCE Beam Diagnostics Team                  8
    N2 BIF Spectral Lines have Short Lifetimes With Respect to the N2
                        Molecule Transit Times.

•   Using a cooled detector, acquired spectral data of N2
    background-gas interaction with protons.
     – N2 partial pressure: 5 X 10-6 Torr
•   Beam conditions:
     – 100-mA peak
     – 60% to cw duty factor conditions
•   Spectrometer: Jarrell-Ash 0.25-m
     – Gratings: 150, 600, and 1800 grooves/mm
•   Primary lines: 391- and 427-nm
     – Much less intense line at 480 nm
•   Debate: molecular or atomic lines?
•   In either case: process is single transition from higher
    energy state to ground state.
     – If atomic process, lifetimes of 0.1- and 0.2-ms
•   Another gas, Kr?
     – H2 or O2 not options - have longer metastable states

July 3 &4, 2000               LANSCE Beam Diagnostics Team              9
     Compared the BIF and Wire-Scanner (WS) Profile Measurement
              Techniques with Reasonably Good Results.

•   Background gas fluorescence and wire scanner profile
    measurements installed at the same beamline location
     – Allowed for direct comparison
     – Beam conditions: 100 mA, 1 to 10 ms, 6 Hz
     – Acquired fluorescence data over 6 or 7 beam pulses
•   Varied quad just upstream of profile measurements
     – Low signal to background: error bars 2- to 3-mm
•   Varied an upstream steering magnet
     – B IF reported beam movement: 5.6 mm
     – WS reported beam movement: 6.5 mm
•   BIF and WS steering and width data agree within 10%
                    Q4       BIF      BIF      ws       ws
                  current    Fits   Moment    Fits   Moment
                    (A)     (mm)     (mm)    (mm)     (mm)
                   146       8.6      8.6     6.97     6.54
                   157       9.4      9.5     8.02     7.52
                   170       10.5     10.6    9.17     8.61
                   177       11.5     11.5    9.85     9.35
                   183       12.1      12    10.42     9.9
                   189       12.8     12.4   10.77    10.22
                   196        14      13.3   11.28    10.65
                   209       14.8     13.7   12.29    11.71

July 3 &4, 2000                       LANSCE Beam Diagnostics Team   10
                    Development of APT Profile Measurements

•   Residual Gas Ionization
     – Proton beam ionizes the residual gas resulting in free electrons
     – Free electrons accelerated into detector with parallel E and B fields
          • Two operation modes
             – Low B field, single electron orbit to detector
                 » 125 kV per m,0.023 T
             – High B field, small Larmor radius
                 » 10 to 100 kV per m, 0.08 T
     – Detector is a moving scintillator, coupled out of vacuum by quartz fiber optics
          • Gd2SiO5 (GSO) or Lu2SiO5 (LSO): approximately 2 mm X 2 mm X 0.5 mm
             – Highly radiation resistant, 109 rads
             – Light output: GSO 25% of NaI, LSO 76% of NaI
     – In situ resolution calibration: 124-nm light on 0.1-mm Au-coated Ni wire
          • Suppression grid 1 cm above high-voltage electrode
     – Resolution goal: 50 mm, 100 mm likely adequate
     – Performing bench tests and, hopefully, tests in Line-D
•   Flying Wire
     – We are investigating wire speeds and fiber robustness

July 3 &4, 2000                   LANSCE Beam Diagnostics Team                           11
         LANSCE Facility Profile Measurements (Source, M. Plum)

•   Wire Scanners
     –   Fibers: 0.125-mm W, 0.1-mm SiC, 0.033-mm Ni, 0.033-mm C
     –   Typically, two wires in X pattern - causes crosstalk
     –   Springs at one end of wire or fiber.
     –   Detect depleted charge from wire due to secondary emission
     –   Typically have bias field about wire to optimize secondary emission signal
            • Use variety of bias field arrangements (nearby wires, rings, actual sense wire,etc.)
•   Harps
     – 4‖ (10 cm) w/ 0.033-mm C fibers
            • 100 to 300 mA-hours lifetimes, current densities, vacuum
     – 13‖ (31 cm) w/ 0.1-mm SiC fibers,
            • 1000 to 5000 mA-hours lifetimes, current densities, vacuum
•   Multiple wire scanners used in emittance measurement, similar in concept to
    above quad scan




July 3 &4, 2000                    LANSCE Beam Diagnostics Team                                      12
      Correlated Emittance Measurements used on the LANSCE Mesa

•   Slit & Collector (GTA, LANSCE, ATS)
     – Slits
           • Water-cooled graphite/Cu (low energy)
               – Slit widths: 0.1- to 0.4- mm
           • BeCu (> 100 MeV)
               – Slit Witdhs: 0.63- mm
           • Collectors: Cu foil/Mica or Cu foil/Kapton sandwich
               – Spacing: 0.1- to 0.25- mm
     – Drift distance and collector spacing defines angular resolution
•   Laser Induced Neutralization Diagnostic Approach (LINDA)
     –    Used in H- beamlines, GTA, ATS, etc.
           • 2 to 6 MeV beams
     – Laser optical beam dissociates one of the electrons from the H- particle
           • H0 allowed to drift to a sandwich secondary emission collector for angular divergence
                – Bend away residual H- to ―waste‖ beam dump.
           • During GTA and ATS, had problem maintaining sufficiently small optical beam through
             transverse dimension of beam pipe to resolve particle beam phase space
           • Solution: optically illuminated all of beam for short time period during macropulse
                – Traditional slit defined the width portion of phase space
July 3 &4, 2000                  LANSCE Beam Diagnostics Team                                    13
               ―Quad Scan‖ rms Emittance Measurement used on LEDA

•     Quad Scans (LEDA, LANSCE)
       – Limited to rms type measurements, i.e., not correlated
       – Technique
             • Upstream quad (Q1 or Q2) is adjusted
             • Beam waist is transported from upstream to downstream
               side of profile measurement
             • 5 to 10 profiles acquired with several near the waist (3
               required)
             • Perform least squares fit of rms width data to transport
               model
             • Models                                                                     WS Profile
                 – No space charge effects, simple quadratic equation                         BIF Profile
                    sufficient (not adequate for LEDA)                    Q1   Q2   Q3   Q4
                 – Various beam particle and envelope codes have been
                    used for space charge effects
                      » TRACE-3D, IMPACT, LINAC, etc.
       – Early results show that this method can put an upper
         boundary on the measured emittance
             • TRACE-3D does not model space charge correctly
             • Working on a full 3-D nonlinear space charge model

    July 3 &4, 2000                  LANSCE Beam Diagnostics Team                                     14
    For the LEDA Halo Experiment, Exploring an Altered Version of a Slit-
              and-Collector Emittance Measurement Technique
                                                                                     x’
•     Challenge: LEDA 6.7-MeV 100-mA proton beam                              Slit            Foil scatters
                                                                                               this portion
      too high power density for even a graphite/Cu slit                                     of phase space.

       – Range for 6.7 MeV protons in C: 0.3 mm
                                                                                                     x
•     Solution: Substitute a 6-mm W foil with a 0.3 rms
      width slit in place of the traditional thick slit
       – Those protons passing through the foil will have a              BEAM PHASE SPACE AT FOIL

         low, wide background distribution resulting from
         Moliere scattering.
•     Downstream of foil slit, perform standard wire
      scanner profile measurement for angular
      distribution on those protons passing through the
      foil slit
•     Issues we are investigating
       – Foil survivability: peak foil temperatures of 3000 K
       – Scattering angle needs to be sufficiently large to not
                                                                  0.25 mm slit, 37-mrad rms scattering angle,
         destructively interfere with the downstream angular
                                                                        1.6-mm X 3.5-mrad rms beam,
         distribution measurement.                                          1-m Slit to WS distance


July 3 &4, 2000                 LANSCE Beam Diagnostics Team                                    15
                         Summary of Experiences on LEDA

•   Slow wire scanners were used over a larger beam current density range due to
     – LEDA’s ability to greatly reduce the duty factor
     – SiC fiber was more robust than initially expected
           • Expect similar results with 33-mm C fiber
•   Correlation between wire scanner and BIF results is reasonably good and
    within experimental error
•   BIF is only technique viable at the 100-mA low energy cw beam conditions
    and can be fit into beamline.
     – Intensified digital camera choice shows promise for least expensive solution
•   Quad-Scan-emittance-measurement technique must include nonlinear space
    charge in the modeling of the beam transport to properly predict the rms
    emittance.




July 3 &4, 2000                  LANSCE Beam Diagnostics Team                         16
                            Beam Diagnostics Team

              Dean Barr                               David Madsen
             Don Bruhn                               Derwin Martinez
              Tom Cote                                     Jim O’Hara
              Lisa Day                                 Pat Paterson
          Doug Gilpatrick                              Martin Pieck
          Mike Gruchalla                                   John Power
              Pam Gurd                                     Ray Roybal
             Andy Jason                                    Phil Roybal
             Tom Jones                                     Bill Sellyey
        Jim Kamperschroer                              Brad Shurter
            Kay Kasemir                                Matt Stettler
            John Ledford                             Robert Valdiviez
          Walter Lysenko                              Rozelle Wright
July 3 &4, 2000             LANSCE Beam Diagnostics Team                  17
                                             References, BIF

•   C. Y. Fan, ―Emission Spectra Excited by Electronic and Ionic Impact‖, Phys. Rev. 103, pp. 1740-1745 (1956).
•   R. W. Nicholls, E. M. Reeves, and D. A. Bromley, ―Excitations of N 2 and O2 by 0.5 and 1 MeV Protons‖, Proc. Phys.
    Soc. (London) 74, pp. 87-91 (1959).
•   R. H. Hughes, J. L. Philpot, and C. Y. Fan, ―Spectra Induced by 200-keV Proton Impact on Nitrogen‖, Phys. Rev.
    123, pp. 2084-2086 (1961).
•   J. L. Philpot and R. H. Hughes, ―Spectroscopic Study of Controlled Proton Impact on Molecular Nitrogen‖, Phys.
    Rev. 133, pp. A107-A110 (1964).
•   R. W. B. Pearse and A. G. Gaydon, The Identification of Molecular Spectra, Chapman and Hall, NY.
•   J. S. Fraser, ―Developments in Non-Destructive Beam Diagnostics‖, IEEE Trans. on Nucl. Sci. NS-28, pp. 2137-2141
    (1981).
•   D. D. Chamberlin, G. N. Minerbo, L. E. Theel, and J. D. Gilpatrick, ―Noninterceptive Transverse Beam Diagnostics‖,
    IIIE Trans. on Nucl. Sci. NS-28, pp. 2347-2349 (1981).
•   D. D. Chamberlin, ―Noninterceptive Beam Diagnostics‖, AIP Conference Proceedings 139—High-Current, High-
    Brightness, and High-Duty Factor Ion Injectors, La Jolla Institute 1985, edited by George Gillespie, Yu-Yun Kuo,
    Denis Keefe, and Thomas P. Wangler, pp. 37-44 (1986).
•   D. P. Sandoval, R. C. Garcia, J. D. Gilpatrick, K.F. Johnson, M. A. Shinas, R. Wright, V. Yuan, and M. E. Zander,
    ―Video Profile Monitor Diagnostic System for GTA‖, 1992 Linear Accelerator Conference, edited by C. R.
    Hoffmann, pp. 247-249 (1992).
•   R. Wright, M. Zander, S. Brown, D. Sandoval, D. Gilpatrick, and H. Gibson, ―Image Processing and Computer
    Controls for Video Profile Diagnostic System in the Ground Test Accelerator (GTA)‖, 1992 Linear Accelerator
    Conference, edited by C. R. Hoffmann, pp. 674-676 (1992).
•   D. P. Sandoval, R. C. Garcia, J. D. Gilpatrick, M. A. Shinas, R. Wright, V. Yuan, and M. E. Zander, ―Fluorescence-
    Based Video Profile Beam Diagnostic: Theory and Experience‖, in Beam Instrumentation Workshop, AIP Conference
    Proceedings 319, edited by Robert E. Schafer, pp. 273-282 (1994).



July 3 &4, 2000                        LANSCE Beam Diagnostics Team                                                18

				
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