Period (and angle) Analysis

Period (and angle) Analysis

Go to HETG at XRCF

Results and Discussion

(Updated 9/17/97 dd)

The results to date suggest adopting the following calibration values:

GratingAverage PerioderrorXRCF Rowland Spacingerror
LEG9912.16+/- 0.998788.04+/- 0.5
MEG4001.41+/- 0.108782.8+/- 0.5
HEG2000.81+/- 0.058782.8+/- 0.5
GratingXRCF mean AngleerrorOpening Angleerror
LETG+0.010+/- 0.05N/AN/A
HETG-0.225+/- 0.059.934+/- 0.008

The periods (in A) are the sub-assembly values because XRCF measurements (and spacing) are not accurate (double checked) enough to require a change. The mean dispersion angles are for XRCF and are a good starting point for flight; the HETG opening angle should be the same for XRCF and flight.

The HEG/MEG period difference seen between sub-assembly (HeCd,HeNe) and XRCF-AL-K (assuming a spacing of 8788.04)(of about a part in 500) is assumed to be due to a mis-placing of the HETG at XRCF. Thus, for now the HETG position at XRCF is set to be 8782.8 mm to have reasonable agreement between XRCF and sub-assembly periods. The cause for the (alleged) displacement has not been determined.

The period errors are all taken as the sub-assembly values, again because (with an HETG displacement assumption) XRCF measurements are in agreement and do not provide any smaller error bounds.

The XRCF Rowland Spacing, 8788.04 +/- 0.5 mm is based on data supplied by Scott Texter (TRW) in a diagram dated 8/15/97. The HETG and LETG were each measured to be within 0.05 mm of this mean spacing value. (HETG = 345.984 inches, LETG = 345.986 inches). This value differs by 5.24 mm from the value implied by design documentation (see Location of HETG at XRCF).

Flight Grating Spacing

Scott Texter reports that EK measures the as-installed HETG to be 0.009 inches closer to the HRMA than designed, so expected flight spacing is 8633.69+0.009*25.4 = 8633.92 mm. The error on this is probably 0.2 mm or less (HRMA-grating spacing). However the HRMA-focus spacing may still have error of order 0.5 mm. Likewise, the as-installed LETG distance is 8633.69 - 0.0043*25.4 = 8633.58 mm.

Analysis chain


Plots of XRCF Period Determination Results

Assumptions: Rowland distance = 8788.04 mm, hc = 12.3985, Al-K is at 1.4867 keV. TOGA rowland distance = 5366.55 mm.