[4.2.2.1.3] 350 keV FEL Gun Studies
Author/caretaker: D. Kehne
Date: 12/23/96
Rev: 1.0
GOALS
MUST
Achieve "nominal" beam parameters for FEL operation
- 350 keV
- 135 pC
- 8 p mm-mrad (norm. rms)
- 50-70 degrees
- 20-40 keV-degrees
Achieve stable operation at 350 kV
Develop a procedure to reproduce beam conditions using only
diagnostics that will be in the FEL injector
SHOULD
Operation at >350 kV
Perform parameter studies to understand gun physics
- Rap 0.5, 1.0, and 2.0 mm
- Charge/bunch from ~0.1 - 250 pC
Emittance measurements vs solenoid settings
If done properly, the last item satisfy all other goals except operation at
voltages > 350 kV.
Comparison of ITS and FEL Injector Diagnostics
Diagnostic In ITS? In 10 MeV ITS?
Laser Spot profile at cathode yes yes
Solenoid centering yes yes
Beam Current yes ?
Light Box Harp ? ?
ax, bx, ex at 350 keV yes no
DE vs f yes no
Bunch length at 350keV yes no
ef yea, maybe no
Spot before unit no yes
10 MeV diagnostics no yes
Need harp scans at light box during 350 keV runs to develop a reference
for later 10 MeV studies.
Does/Will gap monitor work?
Must have sufficient data base of runs at 350 keV to be somewhat
confident of 10 MeV ITS beam.
Outline of Experimental Plan
I. Calibration/Testing of equipment (1 week)
A. Hardware checkout
B. Cavity gradient vs kick calibration
C. Beam with cavity tests
D. Determine setting lens 2 that produces minimum spot size at the
slit
E. Determine setting lens 2 that produces minimum spot size at
straight ahead harp
F. Determine minimum DE for low charge bunches
II. Beam Experiments at 250 keV - Cavity effects (2-3 days)
A. Several preselected points matching previous 250 keV data
B. Look for significant discrepancies (making emittance worse)
III. Parameter Studies (24 hours per aperture setting)
A. Rap = 0.5, 1.0, and 2.0 mm
B. Q from 0.3 pC to 400 pC
C. Data
1. Size at Light Box
2. Transverse emittance and Energy Spread at slit
3. Bunch Length at Aperture
4. Energy Tilt/Longitudinal Emittance
5. Beam current
IV. Lifetime studies
A. Average will be high when aperture is in
B. The cathode will be in a hostile environment
Work Remaining to be Done
Automation of the longitudinal data taking (2 weeks)
Data analysis (2 weeks)
Finalizing parameter sets (1 week)
- Beam conditions
- Lens settings
- Error analysis/noise levels of each set
- Poisson comparison of new solenoid
Finish beam line installation
Install cathode stalk (~1st week of January)
Bake/activation ~3 weeks
Estimated time for first beam: Feb. 1
Summary of Parameters - PARMELA
Ipeak = 0.01 Amps, sr = Rmax
st [psec] Rmax[mm] Q [pC] 4sf[deg] 4sE[keV] 4ef[keV-deg] exrmsN[p mm-mrad] 4efslice[keV-
deg]
15 0.5 0.38 33 0.35 1.5 0.14 0.3
25 0.5 0.63 54 0.31 2.5 0.15 0.3
15 1.0 0.38 33 0.48 2.5 0.3 0.4
25 1.0 0.63 54 0.46 4.2 0.3 0.4
15 2.0 0.38 33 0.8 4.7 0.6 0.8
25 2.0 0.63 54 0.81 7.9 0.6 0.8
Ipeak = 0.27 Amps, sr = Rmax
st[psec] Rmax[mm] Q[pC] 4sf[deg] 4sE[keV] 4ef[keV-deg] exrmsN[p mm-mrad] 4efslice[keV-deg]
15 0.5 10 37.3 3.2 7.0 0.6 0.8
25 0.5 16.7 58 2.7 12 0.7 0.3
15 1.0 10 36 3.33 8.2 0.7 0.3
25 1.0 16.7 57 2.84 13 0.8 0.5
15 2.0 10 35 3.0 8.0 0.9 0.8
25 2.0 16.7 56 2.6 13.4 1.0 0.7
Ipeak = 1.0 Amps, sr = Rmax
st[psec] Rmax[mm] Q[pC] 4sf[deg] 4sE[keV] 4ef[keV-deg] exrmsN[p mm-mrad] 4efslice[keV-deg]
15 0.5 38 45 6.3 10.4 1.8 0.5
25 0.5 63 65 6.1 20 2.4 0.5
15 1.0 38 42 7.3 14 1.7 0.5
25 1.0 63 63 6.9 25.5 2.0 0.5
15 2.0 38 40 7.5 16 2.1 0.9
25 2.0 63 61 7.4 30.4 2.4 1.0
Ipeak = 2.7 Amps, sr = Rmax
st[psec] Rmax[mm] Q[pC] 4sf[deg] 4sE[keV] 4ef[keV-deg] exrmsN[p mm-mrad] 4efslice[keV-deg]
15 0.5 100 55 9.5 16 11 0.9
25 0.5 167
15 1.0 100 52 11.5 18 4.0 0.5
25 1.0 167 72 12 35 5.4 0.8
15 2.0 100 47 13 23 4.0 1.0
25 2.0 167 69 13.3 45 4.8 1.0
Ipeak = 6.7 Amps, sr = Rmax
st[psec] Rmax[mm] Q[pC] 4sf[deg] 4sE[keV] 4ef[keV-deg] exrmsN[p mm-mrad] 4efslice[keV-deg]
15 0.5 250 SCR - - - -
25 0.5 416 SCR - - - -
15 1.0 250 65 17 36 20 1.3
25 1.0 416 72 12 35 5.4
15 2.0 250 60 20 33 8.5 1.3
25 2.0 416 81 21 59 11 1.4
Q = 135 pC, sr = Rmax
st[psec] Rmax[mm] Q[pC] 4sf[deg] 4sE[keV] 4ef[keV-deg] exrmsN[p mm-mrad] 4efslice[keV-deg]
15 0.5 135 SCR - - - -
25 0.5 135 71 8.8 26 11 0.5
15 1.0 135 55 13 19 6 0.6
25 1.0 135 69 10 30 4 0.6
15 2.0 135 51 15 26 5 0.7
25 2.0 135 66 11 37 4 1.0
Error Estimates
Available power from kicker: 450 W
Bunch length:
Nominal beam size at straight-ahead harp: 4sx 1 mm
Bunch lengths to be measured range from 33 to 80
At 200 W, deflection at harp is 5.4/mm.
- For 60 4s bunch length, 4sx 11 mm. (10-to -1)
- ~5 degree resolution
At 400 W, deflection at harp is 3.8/mm.
- For 33 4s bunch length, 4sx 8.7 mm. (8.8-to-1)
- ~4 resolution
Longitudinal Emittance
Nominal beam size at straight-ahead harp: 4sx 0.5 mm
At 400 W, deflection at slit is 9/mm.
E-f tilt error
Finite beam size at slit causes 4 of bunch to contribute to energy
spread of sampled beamlet.
This is a problem when there is significant energy tilt.
Nominal 4s energy spreads to measured range from 0.3 keV to
1 keV
To make energy error due to tilt small, want energy tilt error
<0.1 keV
This occurs when when energy tilt slope ts is
ts[keV/degree]*4 < 0.1 => ts<0.025 keV/degree
Nominal tilts range from 0.1 keV/degree to 0.25 keV/degree
Can be deconvoluted
Error due to misalignment
0.05 keV -- assuming 0.3 error in tilts of slit and harp
Error due to stray field gradients
0.05 keV
0
Error due to Energy spread induced by cavity
0.2 keV -- assuming < 1 mm diameter spot size at cavity
Finite Slit Size Error
0.1 keV
_________________________________________________
Additional questions:
1. What is sensitivity to HVPS droop?
2. What is actual laser pulse length?
3. What is sensitivity of longitudinal emittance to solenoid?