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ESS - SANS Instrumentation

Pulsed. Reactor. ESS - SANS Instrumentation. pulsed source SANS, using a wide range of wavelengths, uses more of the available flux than a continuous source. For same time average flux, count rates can be ~ 5 to 10 times better AND a wider simultaneous Q range with

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ESS - SANS Instrumentation

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  1. Pulsed Reactor ESS - SANS Instrumentation • pulsed source SANS, using a wide range of wavelengths, uses more of the available flux than a continuous source. • For same time average flux, count rates can be ~ 5 to 10 times better • AND a wider simultaneous Q range with • improved Q resolution (over most of Q) • BUT for Long Pulse, need long beam lines to keep good λ resolution. • BUT not too long as λ band will eventually be less than a 10% velocity selector! 2msec long pulse, coupled H2 monitor spectra at 5m(dashed), 10, 15, 25 and 100m, using t0=1300msec, n/cm2/sec/Å/sterad/pulse

  2. L1 = 2 – 12 m, sample at 19m, L2 = 2- 12 m, Qmin~ 0.002 Å-1EITHER unsurpassed simultaneous Q using TWO 1m square detectors at different L2.OR increased count rate from two detectors at similar L2 SANS – recent progress SANS2d at 10Hz ISIS TS-2being built !

  3. SANS – recent progress • 2006 - Revise these calculations from 2004 (and earlier ones from R.Heenan & ESS working group). • More realistic instrument (e.g. gravity) • More practical (e.g. chopper locations) • Comparison with the way D22 is actually used. • Perhaps limit L2 to 20m ? (smaller Q by tightening collimation, or using other methods)

  4. ESS - SANS Instrumentation • Count rate ~ (Q resolution)-4, needs careful comparisons ! • At long L2 for smaller Q count rate falls off very rapidly – and can become unusable, despite improved Q resolution. - SANS users understand this trade-off. • 1m square detector on D22 at ILL is usually run “off axis” – wider simultaneous Q ranges are a scientific necessity. • ESS running at 1/2 of 16.6Hz may be very attractive for much science (if prompt pulse & backgrounds are controlled).

  5. Generic SANS Instrumentation • Trend to using larger detectors – which if are arrays of linear psd gas tubes can be more flexible in size. • Still a need for high count rate, 5mm x 5mm pixel, 2d detectors. • High m guides or benders do not generally help SANS as they simply increase divergence (and bring more neutrons closer to the sample, increasing background).

  6. Other SANS techniques ? Trial mirrors JNOP • Several ideas are being actively developed around the world. Pulsed sources can help or hinder … • Focussing neutrons at detector can (just) out perform pinhole collimation at smaller Q. e.g. mirrors or polarised neutrons and magnetic sextupole lenses. Qmin ~ 10-3Å-1 ( ~ 0.6 μ)“easy”, Qmin < 3x10-4Å-1 ( ~ 2 μ) is harder. • Time of flight double crystal USANS, Qmin ~ 4x10-6Å-1 ( ~ 150 μ) – needs hot moderator ! • Spin-Echo SANS, G(z), z ~ λ2B, ~ 1nm to ~ 150 μ ? Time of flight offSPEC/ SESANS prototype at TU DELFT All are exciting but depend crucially on development of high quality hardware, which is on-going. Hard at present to design “reference” instruments for ESS ?

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