1. C.F. Feb

2. A-line PR18

3. A-line PR18

4. GDET: the FEE N2 fluorescence X-ray detector

7. 800 eV X-rays, torr
Upstream counter
Downstream counter

11. Issues:
If performance is poor because of photon statistics - - -
we removed the UV-pass optical filter on a downstream counter ---
light intensity increased by ~ X 20 !
removed it on the other downstream counter
Had to reduce gain by ~ X 30 because of PMT/base sag
Difficult to find an opportunity to check statistics while it’s in use
But: base line fluctuations can lead to 2% fluctuation of summed signal

12. Time jitter: I seem to see about 1 ns jitter
This is measured by the edges of the PMT signals relative to the time axis
Is it real (or a ghost of base line fluctuations)?
Source? The FADC (Aquiris) has an internal free-running clock.
How does it respond to the control system trigger?
X-ray jitter relative to control system trigger?
Effect: Could be ~3% for high energy short pulses,
< 0.5% for low energy long pulses

13. What next?
# Reduce time jitter effect by widening the pulse summation time interval
* Could be tested by recording and analyzing traces (as Alan points out).
* Ideally use a summation interval tailored pulse width, i.e. pressure
* Include the fast early pulse? Does it scale with beam intensity?
# Operate top and side PMTs at different operating points
* to get a built in handle on linearity of response
# Vary the PMT HV as well as the N2 pressure to stay above base line
fluctuations as far as possible. Needs an on-line prescription.
# Remove the UV-pass filters on the upstream counters

14. # More invasive changes
* Switch to a gated ADC rather than 1 GHz FADC
* Replace the multialkali 3/4 –inch PMT with a
high peak current, low gain, bialkali tube,
and a high current, tapered, high capacitance base
*** needs a redesign of the PMT section (don’t forget the mag. field).
Yet more invasive changes ---
# Use the nitrogen only as a source of ionizing scatter
# install a solid scintillator in place of the aluminum liner.
# optimize the PMT for the (faster) scintillator
# probably can do without the solenoid
# N2 jet ???
 an R&D project