BL 11-2 Status and Scheduling Information 

Third Run 2001

         BL 11-2 user commissioning is in full swing.  March and April activities have centered around debugging and characterizing major electromechanical and optical systems of the beam line (motors, mirrors, and the 11-2 LN-cooled monochromator).  We are now preparing for the upcoming run, of which 5 1/2 weeks are scheduled for user beam.  Further commissioning work and new system testing will be interspersed between user beam periods.  Notably, this work will include feasibility tests using metal microcapillary microfocusing optics (2 to 10 mm range) and system tests on the BL 11-2 grazing-incidence XAS spectrometer.

       Several instrumental capabilities are still in the process of being brought on-line. We anticipate that the BL 11-2 monochromator will be limited to Si(220) phi=90 crystals throughout the run.  BL 11-2 is equipped with a collimating mirror located upstream of the monochromator (M0) and a focusing mirror (M1) located between the mono and the hutch.  At present, the beam line is performing best in either fully focused (both mirrors in) or fully unfocused (both mirrors out) modes of operation.  The third mode, unfocused collimated light (M0 in/ M1 out), is not recommended at present due to vertical beam motion.  We will attempt to fix this problem during the run.

FOCUSED MODE: Vertical beam motion in focused mode is ~20 mm over a 60 min. period (for an optimized focus).  Implementation of the M1 pitch feedback system (installation in early April) should reduce this motion to ca 7 mm.  Focused mode is not recommended for XANES measurements above 14 keV due to the presence of oscillatory energy calibration cycling (e.g., cyclic energy shifting of 0.5 eV with a period of about 60 min occurs at the U LIII edge).  The amplitude of energy shifting falls to ca 0.17 eV at 12 keV, and to 0.05 eV at 6 keV.  These effects are caused by 2.8 mrad pitch angle variations of M0, which is induced by 0.25 deg Celsius temperature variations in the low conductivity cooling water (LCW).  Recent attempts to solve this problem by decoupling the LCW supply line motion from the mirror mover have only modestly abated M0 motion.  As a result, we are considering implementation of an LCW input temperature stabilizing system for M0. 

UNFOCUSED MODE: Vertical beam motion in unfocussed mode is typically 20 mm over several-hour periods (attributable to SPEAR beam motion).  Monochromator energy resolution is at least as stable as at other SSRL XAS beam lines.  

Beam line 11-2 Characteristics at 2 T Wiggler Field

6 to 18 keV
  Focussed Unfocussed
Flux (photon•sec-1) 0.5 to 1.0 x1013 2.0 to 4.0 x1011* 
Energy Resolution (FWHM)  0.65 – 1.77 eV  0.7 – 7.3 eV** 
Beam size:  6   keV

                    19 keV 
0.4 x 2 mm 

0.25 x 1 mm 
6.6 x 40 mm 

(full vert/horz)†
*1x10mm aperture.  **2 mm vertical slit in hutch.  †For reference, beam lines 4-3 and 4-1 give 5.0 to 2.0 x1010 photon•sec-1 (1x10mm spot, Si(220) crystals) over this energy range.
 

Glitch Curves

 Si(220) F=90

  4.5 to 7.4 KeV

  6.9 to 8.5 KeV

  7 to 9.5 KeV

  9 to 10.48 KeV

  10.45 to 11 KeV

  11 to 15 KeV

  15 to 19 KeV

  19 to23 KeV

  23 to 27 KeV
 

 

 

 

BL 11-2 front hutch table with 30-element energy dispersive Ge detector array.

 

 

 

LBL actinide chemistry group, June 2000.

 

 

 

LANL radionuclide sample enclosure, Feb. 2001.
UPDATED April, 20, 2000