Infrared Extraction Update

Infrared Extraction Update

L. Carr, D. Arena, A. Blednyk, S. Coburn, V. Ravindranath and NSLS-II Team

NSLS-II EFAC Review 10-11 May 2007

BROOKHAVEN SCIENCE ASSOCIATES

Infrared Outline

• NSLS-II Infrared beamlines and requirements: quick refresher

• Infrared Extraction:– revised extraction geometry*– large gap dipoles (excellent long-wavelength performance).– 1st mirror heat load*

• Performance Figures

• Beamline locations (brief)*

• Environment (noise: vibration, EMI, etc.)– stability taskforce & workshop requirements

• Top-off issues*

• Bunch structure(s) for timing * addresses specific EFAC concerns and recommendations


Science and IR Source Requirements

• Biological , Chemical, Environmental, Materials, Space …– 4000 cm-1 (=2.5 m) to < 400 cm-1 (=25 m)

• mid and far-IR microprobe• mid-IR chemical imaging (raster scanning area imaging)

– Imaging needs an extended source to optimally illuminate.

• Materials (especially under extreme conditions)– Mostly “single point” spectroscopy

• high pressures and temperatures• laser pump-probe• cryospectroscopy• high magnetic fields, spin resonance

– 4000 cm-1 down to ~ 2 cm-1 (=5 mm)

mid-IRstandard port

far-IRlarge port


Mid-IR Extraction: Standard Dipole

• Chamber with 24mm high interior• Plane 1st mirror, with slot• 14 mrad V (avg.) by 50 mrad H

– small reduction in V compared to internal toroidal mirror extraction

• Collects dipole and 0° edge radiation• Other details to be determined:

– required slot length to allow x-rays to pass– beam impedance– mechanical mirror mounting – mirror cooling (back or end surface)

care to avoid sources of vibration

Standard NSLS-II Dipole

“conventional” extraction

S. Coburn


FIR and mm-wave Extraction: Large Gap Dipole Chamber

S. Coburn

• Chamber with 78mm high interior• Plane 1st mirror, with slot• 42 mrad V (avg) by 50 mrad H

– small reduction in V compared to internal toroidal mirror extraction, but less risk from waveguide cutoff effects (shorter distance)

• Collects dipole and 0° edge radiation• Other details to be determined:

– required slot length to allow x-rays to pass– beam impedance– mechanical mirror mounting – mirror cooling (back or end surface)

care to avoid sources of vibration

Large Gap Dipole

View into exit port

Special chamberconstruction

S. Coburn

ee

Have adopted largest of proposed dipole designs


Mid-IR Brightness

NSLS II

VUV/IR


Far-IR Brightness

cutoff effect due to chamber shieldingc ~ (h3/)1/2


Initial FEA Analysis of Surface Deformation

• New extraction: Beam no longer at grazing incidence onto 1st collection/extraction mirror.

• Calculation with internal H2O cooling, no slot:– Relative longitudinal error = 3 m– Relative transverse error = 8 m

V. Ravindranath

Conclusion: Conclusion: will need slotwill need slot

500ma, 3.6 GeV


Locations for IR Extraction

Standard dipole Mid-IR ports:

• can be placed in proximity to related science activities (not constrained by accelerator symmetry requirements).

Large gap dipole Far-IR ports:

• Large gap dipoles limited to 3 symmetric locations around ring. Both dipoles in a DBA cell, but typically only 2nd dipole available for IR extraction (due to ID upstream of 1st dipole).

• Plan to locate 1 large-gap dipole cell-pair downstream of RF straight section (no ID, can use both dipoles for IR).

Result: maximum of 4 far-IR extractions. (prefer downstream of RF, not injection)

Beamline floor plans: TBD

“exaggerated” NSLS-II with 3 long straights, showing a symmetric arrangement of large-gap dipole pairs.

candidate location for large gap dipole cell


IR Requirements for Stability Taskforce & Report

Stability of electron beam through dipoles:

• Specification request: – Position: 1 m V, 3 m H– Angle: 3 rad V, 6 rad H

• Corresponds to 7% of beam size (compare to 10% overall NSLS-II specification).

• Requirement defined to deliver:– minimum 300:1 S/N in worst-case-scenario– would be ~ 30X better than existing NSLS VUV/IR– frequency range up to 20 kHz.

• Can benefit from even better stability (additional 30X will put noise near background for essentially all measurements).


NSLS II Infrared Capacity

• In most cases, 2nd dipole of DBA cell is potential IR extraction location.– Slot in 1st mirror should allow for a downstream soft x-ray (BM) beamline. – 3-pole wiggler & IR edge extraction probably incompatible (both a 0° and angular pattern approaching

1/).

• Mid-IR: plan to develop beamlines 5 beamlines on 3 separate extractions:– H = 50 mrad & V ~ 14 mrad (avg.)– Special chambers required, but otherwise standard dipole (flexibility).

• Single extraction port can serve 2 or 3 microprobe endstations.• Or entire 50 mrad horizontal can serve a single FPA imaging spectrometer

– 3 ports 1 split into 3 microprobes, 2 for FPAs = 5 beamlines. Can add more ports for growth.– Plan to locate in proximity to other Biological / Imaging beamlines (e.g. XRF, XANES).

• Far-IR / THz / mm-waves: plan to develop 3 beamlines on 3 separate extractions (max = 4):– H = 50 mrad & V ~ 42 mrad (avg.)– Special chambers and special large-gap dipole magnets– Single endstation per extraction.– Locations constrained by 3-fold ring symmetry and RF straight


Top Off Issues

• NSLS-II injection approximately once per minute:– expect some beam motion for ~ 1 second

• IR spectrometer data collection “styles”:1. long scan time, averaging many short (< 1 second) scans2. raster scan imaging (~ 1 minute per point, but ~ 1000 points)3. ultra-high resolution spectroscopy (> 5 minutes for single scan).

• Software:– macros and VB scripts to monitor “beam available” signal, pause collections.

(R. Smith: testing a script to see how 1 and 2 can be managed).– more work necessary for 3.


RF Buckets, Bunches and Timing

• Infrared has been one of the key users of the storage ring bunch structure for time-resolved studies (methods dependent on bunches themselves).

– no benefit from crab cavities, indirectly from laser slicing (CSR)

– not limited to IR … all techniques where beam is not resolvable and fast detection not sufficient.

• Issues:– Bunch lengths (BL for NSLS II will be 10s of picoseconds)

– Pulse Rep. Frequencies (PRFs) & synchronization to mode-locked lasers• 499.7 MHz RF, ring circumference = 792m, harmonic number = 1320 x x x x x

• Mode-locked Ti:sapphire prefers 76 to 82 MHz, 75 to 100 MHz for Nd:YLF, more options with fiber lasers– note: 500MHz/6 PRF= 83.3 MHz

– Jitter (bunches relative to RF, to each other) below 10% of bunch RMS, especially for frequencies > 1 kHz.

• sets NSLS-II RF phase system stability requirements – stringent, but possible.

– Harmonic cavity effects, de-tuned operations, low- lattices: Still to be investigated.


Symmetric Fills and PRFs for NSLS-II h=1320Factors Bunch Fill Mode PRF (MHz) Ti:Sapphire PRF (MHz) Nd:YAG/YLF PRF (MHz)

1 1320 499.682 660 249.843 440 166.56

2 2 330 124.92 5 264 99.936 100

2 3 220 83.28 83.3 2 2 2 165 62.46 2 5 132 49.968 5011 120 45.42545

2 2 3 110 41.64 41.6 3 5 88 33.312 33.3

2 2 5 66 24.984 252 11 60 22.71273

2 2 2 3 55 20.82 20.8 2 3 5 44 16.656 16.7 16.73 11 40 15.14182

2 2 2 5 33 12.492 12.52 2 11 30 11.35636 5 11 24 9.08509 9.09

2 2 3 5 22 8.328 8.33 8.332 3 11 20 7.57091 7.57

2 2 2 11 15 5.67818 2 5 11 12 4.54255 4.54

2 2 2 3 5 11 4.164 4.16 4.162 2 3 11 10 3.78545 3.79 3 5 11 8 3.02836 3.03

2 2 5 11 6 2.27127 2.272 3 5 11 4 1.51418 1.51 1.51

2 2 2 3 11 5 1.89273 1.89 2 2 2 5 11 3 1.13564 1.142 2 3 5 11 2 0.75709 0.757 0.757

2 2 2 3 5 11 1 0.37855 0.379 0.379


Summary

• Updated Infrared extraction– more conventional side-extraction, 1st plane mirror, with slot to allow x-rays through.– very large gap dipoles, unsurpassed far-IR performance for incoherent SR.– generally higher mid-IR brightness than existing NSLS VUV/IR, expect high stability too.

• Capacity:– Plan to develop 3 extractions each (mid-IR & far-IR) during early phases of NSLS II operations.

• corresponds to 8 beamline endstations, compare to existing 6 on NSLS VUV/IR– Potential for growth (especially mid-IR).

• Stability:– Requirements to achieve S/N at least 30X better than NSLS VUV/IR.– More is better!

• Pulse Repetition Frequencies (PRFs):– h=1320, booster at 1/5th for efficient filling of NSLS-II ring in top-off.

• Needing more attention: detailed impact of top-off injection on various IR measurement methods.

Documents

Infrared Extraction Update