1. HBD Transmission Monitor: Update on Assembly & Testing HBD Working Group Meeting 8/29/06 B. Azmoun Brookhaven National Lab

2. 8/29/06B. Azmoun, BNL General Layout Mirror Stepping Motor Gas cells Sample Chamber Slits (Recip. Disp. = 40A/mm  Band- pass = 40A) Collimation Box Light focusing Optic D2 Lamp McPherson 234/302 VUV Spectrometer Monochrometer

3. 8/29/06B. Azmoun, BNL Exterior Gas Cell Stabilizers (adjustable) Gas In/Out ports Lamp Monitor (PMT: CsI PC) Turbo Pump/Full Range Vac Gauge (P = 4x10 -5 mbar) Gas Cell PMT (CsI PC) Electronics 2 Picoammeters (ref, Sample) Switch Lamp Power Supply 2 Stepping Motor Controllers (Monochrometer, Moveable Mirror) Laptop PC (Labview Control panel) RS232 – USB Controller PMT Aperture

4. 8/29/06B. Azmoun, BNL Interior Uncorrected Diffraction Grating : beam position doesn’t change w/ wavelength Cylindrical Mirrors: light collection & collimation Reference Beam Splitter: two mirrors spaced 5mm apart clip the top and bot. edge of the beam and focus each onto Ref. PMT. Moveable Mirror: As mirror is translated, the beam is successively sent through each gas cell The Central portion of the beam (sweet spot) continues through the gas cells ALIGNMENT (Grating @ zero-order) Monochromater Light collimating Optics Reference Mirror Moveable Mirror Gas Cell Stabilizer Beam Size @ PMT aperture (19mm diam.)

5. 8/29/06B. Azmoun, BNL Labview Control Panel  Select wavelength range  Select wavelength step size  Scan which gas cells  Select number of data points for each current measurement  Set path for file (tab delimited text, includes wavelength, mean current, sigma)

6. 8/29/06B. Azmoun, BNL PMT Current Output Reference and Sample Spectra have different shape?…possibly due to difference in reflectivity of mirrors and/or additional MgF2 window Just discovered late last night: lamp grossly misaligned in its mount (removed for polish)…once aligned, we’ll get a much bigger signal!

7. 8/29/06B. Azmoun, BNL Beam Ray Tracing (very similar to what is observed) Output of Collimation Optics @ Moveable Mirror @ Exit Flange @ PMT After aperture D2 Lamp Monochrom. Light Coll. Optics

8. 8/29/06B. Azmoun, BNL Beam Astigmatism  The divergence in the beam leads to a beam spot that is slightly larger than the PMT aperture and/or the cell diam. (this is including the halo…the sweet spot is well contained, however it is preferable to eliminate all stray/peripheral rays and produce a well defined beam spot on the PC)  Due to the inherent astigmatism of the beam, any attempt to reduce the size of the beam results in significant attenuation (i.e. in attempting to eliminate peripheral rays only (@ the PMT), it is more likely to eliminate a significant number of central rays)  Weak solution: Vertical Slits placed right after the ref. mirror and Horizontal slits placed at the exit port to the cell provide some collimation, but there is still significant attenuation.  Better Solution: Place long collimator tube (with opaque surface) inside gas cell and eliminate all rays that hit the surface. By definition, all unwanted rays are eliminated, while all of the central rays make it through the aperture, and produce a well defined spot.  Were we too cautious???

9. 8/29/06B. Azmoun, BNL Work to be Done  PMT Protective “Fence” After all, the PMT seal on the gas cell is contiguous with the interior of the HBD.  Must Perform real transmission measurement to test this seal, and perform a full dry run Finishing up plumbing for (in lab) gas system (Gas in/out + Analysis)  Labview program debugging almost complete  Finally will install in Hutch (in ~2 weeks) …Assuming all goes well