1. LINAC 4 source & LEBT measurement results
L4 BI Review 18-Oct-2011
F. Roncarolo
U.Raich, B.Cheymol BE-BI
L.M. Hein BE-ABP
Many thanks to many other colleagues

2. Contents Source and LEBT test stand introduction Diagnostics park
Emittance meter bias rings optimization
SEM grid, BCT and emittance measurement examples
Beam parameters and LEBT line characterization to date
Transmission
RFQ matching
BI L4 review - 18 Oct 2011
F. Roncarolo

3. Introduction Diagnostics
Test stand installed since Operated with 35 keV H- and 45 keV Protons (tests still on-going)
BI L4 review - 18 Oct 2011
Diagnostics
Faraday’s Cup + SEM grid (H+V) after 1st solenoid
SEM grid (H) in spectrometer line
Beam Current Transformer between two solenoids
Emittance-Meter
slit&grid (H+V)
Faraday Cup integrated in SEM grid tank
Will remain in the Linac4 tunnel LEBT
F. Roncarolo
Used at different stages during the test stand and then Linac 4 tunnel commissioning

4. LEBT Final configuration
BCT
Faraday’s Cup
H+V SEM grid
BI L4 review - 18 Oct 2011
F. Roncarolo

5. LEBT Commissioning Stages
Source
Emittance meter
Faraday’s Cup
Faraday Cup + SEM Grid
Sol. 1
Sol. 2
Slit
SEM grid
Completed with 35 keV H- and 45 keV Protons 1
Faraday’s Cup
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Completed with 45 keV Protons 3
RFQ Input
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Stage 4 just completed
Now: will re-check stage 1 while re-arranging LEBT to host RFQ (Jan 2011)
Beam Current Transformer (BCT)

6. Faraday Cup and BCT Beam Current Transformer
Read-out with 2 channels
CH1: Fast relative charge evolution
CH2: Average charge with time and total charge in 400us pulse
Down to 10ns sampling period
BI L4 review - 18 Oct 2011
(more details in L.Søby’s talk)
500 us Beam Pulse
Calibration Pulse of known (variable) amplitude
Faraday’s Cup
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Retractable
Read-out via scope
ADC readout possible, sampling 250 kHz

7. Source Emittance-Meter
SEM grid read-out 250kHz
Stepping motors to allow coarse + fine position tuning
SEM Grid V
BI L4 review - 18 Oct 2011
SLITs
SEM Grid H
Single stainless steel
blade with 2 slits
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8. Slit & Grid Principle For each slit position
 profile monitor gives beamlet divergence
Scanning slit position
 transverse phase space reconstruction  emittance
@ Linac 4 emittance-meter:
Profile monitor = SEM grids driven by stepping motors
Profile measurement resolution can be enhanced by programming small SEM grid steps for each slit position
BI L4 review - 18 Oct 2011
F. Roncarolo

9. Emittance-Meter: bias rings
SEM grid wire signal
determined by SE electrons generated by H- (or p) traversing the wire
Secondary electrons are also
Slit
Faraday’s Cup
and can reach the wires, perturbing the measurement
BI L4 review - 18 Oct 2011
The system is equipped with 2 guard rings
The polarization of the two guard rings and of the Faraday’s cup with DC bias voltages minimizes the measurement perturbance
The bias configuration has been simulated with CST MWS and verified with measurements
Faraday’s cup plate
F. Roncarolo

10. Emittance-Meter: bias rings simulations
Configuration considered initially: VP1>0 , VP2<0 according to simulations didn’t work, net field distribution lets many electrons emerging from P1 and the cup to reach the SEM grid
+ 500 V
BI L4 review - 18 Oct 2011
Electrons trajectories as simulated by CST Microwave Studio
Faraday’s Cup P1 P2
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- 500 V
Configuration proposed after simulations:
VP1,VP2, VCUP > 0
minimizes perturbation due to FC and P1 electrons
biasing the FC forbids charge measurements at the same time as emittance measurements

11. Emittance-Meter: bias rings setup with beam
During Emittance Measurement -all biases > 0 clearly optimizes the wire signal
During Beam charge measurement at the Faraday’s Cup (H- 35 keV)
-Need VP2 < 0 to retain secondary electrons that would escape the CUP
BI L4 review - 18 Oct 2011
F. Roncarolo
All well in agreement with MWS simulations

12. Emittance-Meter Measurement Example (I)
Emittance-meter measurement after 1st solenoid X’
H3+ H0
H2+
Protons
BI L4 review - 18 Oct 2011 X
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45 keV Proton source: different charge states produced by the source are focused differently as they pass through the solenoid

13. Emittance-Meter Measurement Example (II)
Transverse distribution vs Source RF power
Profiles extracted from Emittance Measurements
(phase space projection on HOR axis)
BI L4 review - 18 Oct 2011
F. Roncarolo

14. Emittance-Meter off-line analysis
BI Expert Off-line Analysis GUI
Working:
Phase space and profile plots
Histogram of wire signal levels
Background subtraction based on thresholding
RMS emittance calculation
Under development
Precise emittance evaluation via Scubexx algorithms
BI L4 review - 18 Oct 2011
F. Roncarolo

15. Emittance measurements after 1st solenoid
Effect of threshold and comparison between H- and Protons
Threshold:
 cut all wire signals below xx % of maximum wire signal  background subtraction
BI L4 review - 18 Oct 2011
Source exit,
20 kW RF power
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Measurement result very much dependent on off line data treatment….

16. ‘Exotic’ profile measurements
Profile Measurement performed after the second solenoid by measuring the Emittance meter FC current while scanning the slit position
BI L4 review - 18 Oct 2011
F. Roncarolo
This particular measurement proved
Source reproducibility (red and blue measurements taken in different days)
beam-solenoid misalignment (beam centroid depends on Solenoid current)

17. Energy Spread Measurement
SEM grid monitor used for 45 keV proton beam, spectrometer line
ON-LINE (same low and high level software for LEBT and Spectro line SEM grids)
OFF-LINE
BI L4 review - 18 Oct 2011
SEM grid profile that allowed determining the beam energy spread to be ~ eV after 1st solenoid
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Beam Size Evolution along pulse

18. LEBT Transport Measurements
Phase space distributions as measured at the source exit (before LEBT) and at the LEBT exit
HOR
VER
BI L4 review - 18 Oct 2011
Grey: measured at the source exit
Colored: measured after LEBT and reconstructed at source exit with theoretical optics
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19. RFQ Matching
Phase space distributions as measured and simulated (matched) at the RFQ input
HOR
VER
Grey: nominal beam to match RFQ input
Colored: measured for RFQ input
BI L4 review - 18 Oct 2011
F. Roncarolo
Best RFQ matching is achieved with Solenoid 1 settings that don’t give best transmission along LEBT (see also next slide)

20. LEBT Transmission Measurements
In general :
Solenoid 1 used to optimize transmission
Solenoid 2 used to optimize RFQ input matching
Current [mA]
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Sol1 [A]
Sol2 at 300A
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Best LEBT Transmission
Best RFQ Matching

21. Summary / Outlook Source and LEBT test stand operated for two years
Commissioning stages with 45 keV proton source almost completed
Beam parameter and optics characterization depended heavily on diagnostics
Faraday’s cup and BCT to validate transmission
Emittance meter to validate matching to nominal optics
Spectrometer SEM grid to measure energy spread
Test stand served also for diagnostics commissioning in visage of 3 MeV test stand and Linac4 permanent systems
BCT mechanics, electronics and acquisition software
Emittance meter acquisition software and offline analysis
BI L4 review - 18 Oct 2011
F. Roncarolo

22. BI L4 review - 18 Oct 2011
SPARE
F. Roncarolo

23. LEBT transmission table
RF-Power Source
21kW
30kW
40kW
48kW
60kW
2.32V/1.32V-1.36V
2.48V/1.48V
2.6V/1.6V
2.68V/1.64V
2.78V/1.76V
Configuration
No Iris
11mm
05mm
Sol1-Sol2-Steerers 
15.1
0.8
0.2
23.2
0.9
27.5
1.1
29.1
1.2
29.9
17.5
26.6
30.4
1.3
31.1
1.4
32.1
0.3
17.6 1
30.3
17.9
27.9
1.6
29.5
1.9
30.6 28
1.5
29.6
30.5 18
1.7
17.1
25.5 2
0.4
26.7
2.3
25.1
2.6
2.7 17
25.6
0.5
25.2
26.5
24.5
24.6
10.8
3.8
13.6
4.4
13.8
5.5
12.8
5.8
12.6
10.2
12.7
5.4
11.7
11.5
5.6
9.3
0.7
11.4
4.5
11.6
5.3
10.7
5.2
10.5
8.4
4.8
10.4
6.9 10
7.8
2.1 8
BI L4 review - 18 Oct 2011
F. Roncarolo
Beam current in mA
Beam Current saturation at ~50kW
Beam core is stable populated (?), as in case of 700A Sol1 most of the beam is scraped and
only the core is leaved. The change of RF-Power does not mainly influence FC2 readings.