Light Source Diagnostics Hywel Owen ASTEC Daresbury Laboratory - - PowerPoint PPT Presentation

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Light Source Diagnostics Hywel Owen ASTEC Daresbury Laboratory - - PowerPoint PPT Presentation

Nov 21, 2022 186 likes •420 views

Light Source Diagnostics Hywel Owen ASTEC Daresbury Laboratory This Talk Not a review of light source diagnostics Good summaries at EPAC/PAC/DIPAC, etc. J.Safranek (ICALHEPS99) J.Clarke (EPAC94) R.Hettel Instead: a

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Light Source Diagnostics

Hywel Owen ASTEC Daresbury Laboratory

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This Talk

Not a review of light source diagnostics Good summaries at EPAC/PAC/DIPAC, etc.

J.Safranek (ICALHEPS’99) J.Clarke (EPAC’94) R.Hettel

Instead: a collection of various thoughts on diagnostics

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SLIDE 3
  • Dipole source - 5mrad
  • Plane SiC Mirror
  • 400-800nm

SiC Mirror (120°) TVM Primary Mirror Box (Station 13.1) Valve Mask From Dipole 13 Station 13.2 Optics Benches Shielding

Optical Diagnostic Layout (SRS)

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SLIDE 4

Main Mirror (Optical)

Visible/uv wavelengths Resolution limit ~100 um 2nd-generation spot sizes ~100-1000 um 3rd-generation spot size ~10-100 um Cope with heat loads by thermocouple and moving mirror Very good for basic diagnostics and commissioning SRS diagnostic beamline mirror

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SLIDE 5

Simple Installed SR Monitor

  • Simple, cheap
  • No excuse for not having one!

CLS Booster

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SLIDE 6

Pinhole Camera (APS)

CdWO4 Scintillator imaged onto CCD

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SLIDE 7

EBPM Resolution

  • um resolution or better

possible from EBPMs

  • Depends upon current and

required bandwidth

  • Can have thermal effects (e.g.

~50 um at ALS)

  • However, this is not the whole

story…

Swiss Light Source digital BPM

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SLIDE 8

BPM Mounts

  • 2nd-generation sources have

BPMs fixed only to vessel (or none at all!)

  • Get large movements….

CLS EBPM fixed directly to girder

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SLIDE 9

BPM Movement

NSLS BPM Motion Also seen at other sources SRS, ALS… Caused by heating, pressure from

  • ther components etc.

ESRF Feedback

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BPM Mounting Methods

BPM Quad Experiment

  • The ground moves too:
  • ALS vertical >100um
  • DIAMOND >100um expected

seasonal (water content in 14m chalk/clay)

  • SLS ~1mm seasonal change in

C

  • Magnet mount design can give

lateral creep:

  • ESRF (damping mounts)
  • SRS >1mm! (frame mount +

ageing floor)

  • Survey errors (20-50 um typical on

girder)

  • Can add linear encoders
  • SLS resolution ~0.5 um
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SLIDE 11

Photon BPMs also have problems

  • Tungsten Vane Monitors
  • see edge of beam
  • can’t avoid dipole radiation
  • sensitive to beam size
  • changes with undulator gap
  • Can ‘map’ response with

motion

  • Developing energy-resolved

TVM using hemispheric analysers

Light seen by ESRF TVM

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SLIDE 12

Girder Alignment (SLS)

  • 5-point support with roller

cams:

  • >1mm in 5 deg. of freedom
  • Software can automate

movements

  • Will also be used in DIAMOND
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SLIDE 13

Girder ‘Response’ Matrices (SLS)

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SLIDE 14

Orbit Correction Using Girders

Only theory so far…

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Hydrostatic Levelling Systems

ESRF (Electronic) MAX-II (Optical) ~um resolution Optical triangulation sensor Windshield Problems with contamination mould etc. in water

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Building and Accelerometer Mounts

Jointed floor to stop wind on building shell affecting storage ring (CLS) (300 mm slab on thick glacial till) Accelerometer Mounts to measure transmission of vibration across joint Not tried yet…

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OTR Screens

Screen – Al on Mylar

  • Linear
  • Fast response (sometimes too fast!)
  • Narrow viewing angle can be a problem –

roughen surface?

  • Can combine with fluorescent screens

Installed monitor (CLS Transfer Line)

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SLIDE 18

Photon Counting to Measure Bunch Filling Pattern

PMT Base 583 Disc. 584 Disc. Delay Orbit Clock Unit 457 TAC TRUMP 8k MCA MCB Server Application LabVIEW Remote PC Local PC Positive Output Negative Output Timing Output Timing Output Start Stop Input Input Peltier Cooler RF Master Osc. (499.7 MHz) 3.123 MHz EISA Bus 449-2 Ratemeter Ethernet LabVIEW Photons RS232 AB302 Filter Wheel

Single NIM Crate +Detector Optics

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How Photon Counting Works

Takes around 60s to build good statistics No good for single shot or in damping ring!

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Cleaning Bunches by Resonant Excitation

1 10 100 1000 10000 100000 1000000 500 1000 1500 2000 2500 3000 3500 4000 4500 Channel No. Counts Before After 1 10 100 1000 10000 100000 1000000 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 Channel No. Counts Before After

Removal of Neighbouring Bunches (+2ns, -2ns and -4ns) Removal of +106ns and

  • 106ns contamination

+106ns

  • 106ns

Main Bunch Artefacts Main Bunch

  • 2ns
  • 4ns

+2ns

Set frequency to vertical tune of parasitic bunches (~10 kHz above main bunch) (SRS, ~20 mA main bunch current at 2GeV)

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SLIDE 21

Streak Camera

2 ps resolution (500 fs at ESRF) Signal to noise (contrast ratio) around 1:103

  • cf. streaking electron beam

down to 20fs About 200,000 dollars/euros…

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SLIDE 22

Typical Results (APS Multibunch)

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SLIDE 23

Decoherence After Kick (APS)