Work Package 7: Electron
spectrometers - preparation, setup and operation
Figure
0: Comparison of conventional (left) and paracentric (right)
entry focusing viewed in a SIMION simulation. Offsetting the entry
as in the paracentric case (right) is seen to improve focusing
conditions degraded by the fringing fields at the entry and exit
of the HDA. The HDA used in the APAPES measurements is a paracentric
hemispherical deflector analyzer (HDA) with a 2-D position sensitive
detector (PSD) (From Benis & Zouros, Nucl. Instrum. &
Meth. Phys. Res. A440 (2000) 462).
Figure
1: Photo of setup showing HV rack and distribution of voltages.
Figure
2: Precision 5kV power supply N-97N. Default settings for
running under computer control: TN3=100V (U Hand), TN2=5kV (Ust1).
The final equation determining the HV output is then: HV = UHand
*VTN3/10 + (Ust1 + VTN1 + VH1)*VTN2/10 where Ust1 and UHand are
the 0-10V DAC inputs. VH2 is only use for protection and controls
the maximum allowed HV output.
Figure
3: (Top) Photo of broken HDA exit grids (grid1 and 2 had
holes, while grid 3 as seen is completely broken) and (Bottom)
Electron spectrum taken with this broken grid (F=4 Rπ=81.6 mm,
Egun=-950 eV, W=900 eV, Lens scheme=Omer). The small extra peak
always remained at the same spot on the PSD while the other changed
with energy as expected.
Description of work package
Work Package
7
Start:
Month 7
Finish:
Month 18
Cost:
Title:
WP7:
Electron
spectrometers - preparation, setup and operation
Description:
Research Teams:
RT1, RT2, RT3
7.1 Hemispherical
Deflector Analyzer (HDA) - preparation and tests of operation:
7.2 Two-stage 450
parallel plate Analyzer (PPA) - preparation and tests of operation:
Existing HDA [Ben99a, b,
Zou02a] and PPA [Zou97a] spectrometers brought from Kansas must be prepared for use, cleaned, resurfaced
with conducting graphite coating (Aquadag) and tested for electrical high
voltage break down to 5kV. Special positioning stands for both systems
allowing for sensitive alignment must be built. Both MCP plates, found to
develop dead spots or hot spots after heavy and channeltron detector,
deteriorate over time will be replaced as needed, the cost included under
consumables.
7.3 Final test of
spectrometers -high voltage control and DAQ: Finally, the entire spectroscopy apparatus
connected to the DAQ (WP6) will be tested first with an e-gun and later with
collisional electrons.Further
improvement of the optics of deceleration stage in either type of
spectrometer is also planned using the simulation software SIMION for maximum
transmission optimization and improved energy resolution.
Deliverables:
1
Report and part of BS, MS or PhD thesis, DAQ software programs
WP7: Table of Activities in progress
Completed
Activity
Target Date
Placed HDA in chamber and
roughly aligned it - tested vacuum
Dec 2013
Order electroformed mesh for
HDA
Dec 2013
Connect all HV cabling to
HDA and test connectivity
Jan 2014
Replace mesh in HDA and PSD
where needed
Jan 2014
Open up HDA and clean thoroughly
Feb 2014
Place HDA back in chamber
and align after gas cell has also been aligned
Mar 2014
Test signal cables to PSD
with existing MCPs - test voltages to MCP
Mar 2014
Connect PSD to preamps and
data acquisition (DAQ) system (Ivan Valastyan)
May 2014
Test HDA with first hot wire
electron measurements (problems with lens
performance encountered - no focusing!)
May 2014
Test HDA with first hot wire
electron measurements- focusing problem solved after cleaning
lens and using e-gun with less intense beam
Jul 2014
Tests of mu-metal shielding
(ordered DC Milligauss Meter Model MGM from AlphaLab Inc.)
Sep 2014
Reinstalled hot wire e-gun
without foil hole aperture (bare filament)
Jan 2015
Removal of PSD to instal piezo-electric
motor
May 2015
Test complete h-variation system
and measure lineshapes for various h (still waiting to replace
problematic piezomotor control - also had problems with PSD
cables getting disconnected). Measured line shapes with e- gun
for hmin, hmin+6mm and hmin+12mm. hmin=23.075mm
Jun 2015
SIMION tandem ppa under construction and testing by Eleonore
Defaux (in progress)
Jun/Jul 2015
SIMION tandem ppa under construction and testing by Eleonore
Defaux (in progress)
Jun/Jul 2015
HDA exit grids discovered broken - all three were replaced
on June 27 - see Fig. 3
Jun 27 2015
Final Report on operation
of DAQ ready - work package completed
Technique for covering large apertures in ion optics with
electroformed metal
mesh, Robert J. Noll, Lloyd L. Ochalla, and James C. Weisshaar,
Rev.
Sci. Instrum. 62 (1991) 246
WP7: Additional Work
Installation of piezo-electric motor to move 2-D position sensitive
detector (PSD) - varying the distance h for optimal energy resolution
(see Refs. [1], [2], [3] below)
Video showing the motor moving the rod on which the PSD is attached
[MTS
file (57.2 MB)]