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PHIN tests at CTF. C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev CLIC meeting 13.01.2012, CERN. Outline. Introduction NEG activation in PHIN gun Results from PHIN run in September 2011 Comparison with results from previous PHIN run Outlook. PHIN Photoinjector and CTF3. - PowerPoint PPT Presentation
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PHIN tests at CTF
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev
CLIC meeting 13.01.2012, CERN
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 2
Outline
Introduction NEG activation in PHIN gun Results from PHIN run in September 2011 Comparison with results from previous
PHIN run Outlook
13.01.2011
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 3
PHIN Photoinjector and CTF3
13.01.2011
FCT: Fast current transformerVM: Vacuum mirror SM: Steering magnet BPM: Beam position monitorMSM: Multi-slit Mask OTR: Optical transition radiation screenMTV: Gated cameras SD: Segmented dump FC: Faraday cup
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 4
Laser System
13.01.2011
1.5 GHzSynched oscillator
Cw pre-
amplifier
10W 3-pass amplifier
2-pass amplifier
3.5kW 8.3kW 7.8kW14.8mJ in 1.2μs
2ω3.6kW
4.67mJ in 1.2μs 4ω
1.25kW1.5mJ in 1.2μsHighQ front end
Cooling
AMP1 and AMP2
Harmonics
Booster amplifier
Harmonics test stand
320mW
To future CALIFES
laser
To PHIN
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 5
PHIN and CLIC Parameters
13.01.2011
DRIVE beam
Electrons
PHIN CLICcharge/bunch (nC) 2.3 8.4
train length (ns) 1200 140371bunch spacing(ns) 0.666 1.992bunch length (ps) 10 10
bunch rep rate (GHz) 1.5 0.5number of bunches 1802 70467
machine rep rate (Hz) 5 50margin for the laser 1.5 2.9
charge stability <0.25% <0.1%Cathode lifetime (h) at QE > 3% >50 >150
One main issue is to achieve long lifetimes with high bunch charge and long trains!
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 6
Improvement of Vacuum
From the experience with DC guns it is known that long cathode lifetimes are possible in case of excellent vacuum conditions:
Aim: To improve the vacuum conditions in PHIN to achieve longer cathode lifetimes.
Possible solution: Using state-of-the-art NEG pumps and coatings.
13.01.2011
G. Suberlucq
p < 1e-10 mbar
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 7
Activation of NEG Chamber in PHIN
13.01.2011
Layout PHIN gun:
Photocathode
Electronbeam
Laserbeam
Plan to improve
vacuum in two
steps: Activation of
existing NEG coated chamber around the gun
Activation of existing NEG coating in beam line and installation of additional NEG pump.
20 cm
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 8
NEG Activation Cycle
13.01.2011
Bake-out cycle: Pressure evolution:
Effect of the NEG pumping
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 9
Results of NEG Activation
13.01.2011
Layout PHIN gun:
PPenning
PBA
Results: Before bake-out: PBA=1.8e-10 mbar
PPenning=5.2e-11 mbar
After bake-out: PBA=1.3e-10 mbar PPenning=3.3e-11 mbar
RGA spectrum:
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 10
PHIN Run September 2011
High bunch charge production. Study of the impact of the bunch charge and train
length on the vacuum level. Lifetime measurements with comparable conditions
as during the PHIN run in March 2011. Lifetime measurements with long bunch trains. Two Cs2Te cathodes were used:
#182 (already in use during PHIN run in March 2011) #185 (new cathode)
13.01.2011
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 11
High Charge Production
Charge vs. laser energy scan with 50 ns long trains Linear response up to 5 nC Record bunch charge of 9.2 nC above CLIC requirements! Close to the theoretical limit of Qmax=9.47 nC for a beam size of
1.8 mm s x 1.25 mm s
13.01.2011
Cathode #185 Cs2Te
9.2 nC!
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 12
Impact of Bunch Charge on Vacuum
Vacuum can be maintained up to nominal bunch charge of PHIN of 2.3nC.
Pressure increase above nominal bunch charge probably due to losses inside gun.
A 1 GHz gun specially designed for CLIC might be able to maintain the vacuum up to a higher bunch charge due to larger apertures.
13.01.2011
Vacuum vs. bunch charge
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 13
Impact of Train Length on Vacuum
13.01.2011
Vacuum correlated to beam losses in the beam line When beam is optimized for good transport, the vacuum can be
maintained with increasing train length
Vacuum vs. train-lengthCorresponding beam lossesBetween FCT and Faraday cup
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 14
Data Acquisition System for Lifetime Measurements
Matlab program for automated QE measurements: Energy of reflected laser beam
from viewport (laser probe with sampler)
Charge (FCT with sampler) Manual measurements:
Full laser beam energy in CTF2 (laser probe with flipping mirror and sampler)
Full laser beam energy in laser lab (energy meter)
Charge (FCT, Faraday cup with oscilloscope)
Automated measurement of the vacuum level
13.01.2011
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 15
Automated QE Measurement
13.01.2011
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 16
Automated QE Measurement
13.01.2011
Drift of some (which?) equipment with 24 h period.
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 17
Lifetime Studies of Cs2Te Cathodes
13.01.2011
Cathode lifetime vs. vacuum
Correlation between lifetime and vacuum.
In high e-9 mbar/ low e-8 mbar < 50h lifetime was measured.
When vacuum is kept at low e-9 mbar lifetime is within specification.
Cathode #182
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 18
Lifetime Studies of Cs2Te Cathodes
13.01.2011
New cathode, first hours with short trains (2.3 nC, 350 ns) Vacuum of ~1.6e-9 mbar. Long lifetime within specifications. Conditions (except vacuum) comparable with measurements during
PHIN run in February/March before the NEG activation
Cathode #185
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 19
Long Bunch Trains
13.01.2011
Measurements were performed towards the end of the PHIN run with non-optimal vacuum conditions (6e-9 mbar).
No overnight measurements possible due to 4th harmonics crystal degradation.
Cathode #185 Cathode #185
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 20
Comparison with Short Trains
13.01.2011
Cathode #185Cathode #185
Similar results for short trains at the end of the run with the same vacuum conditions (6e-9mbar).
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 21
Comparison with Results from PHIN Run February/March 2011
13.01.2011
Vacuum was better during PHIN run in September.
Much less breakdowns. The lifetime was significantly
better: e.g. for 2.3 nC and 350 ns30 h vs. 250 h
September 2011
Cathode #182
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 22
Summary and Outlook
NEG coating in PHIN gun successfully activated. Systematic lifetime studies vs. bunch charge, train length and vacuum
carried out at PHIN. Record bunch charge of 9.2 nC measured.
Lifetime studies of Cs3Sb cathodes with green light planned for the next PHIN run in March 2012.
Further improvement of vacuum in PHIN planned for the PHIN run thereafter (installation of NEG pump, activation of NEG coating in beam pipe).
Installation of new laser system for CALIFES photoinjector planned for winter shutdown.
13.01.2011
C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 23
Roadmap
13.01.2011
Item Status
Phase coding Demonstrated
High bunch charge production CTF parameters achievedCLIC parameters achieved
Cathode lifetime Ok for short pulses. Further R&D needed for long trains.
Charge stability Work has been started on feedback stabilization
Laser system for 140 µs pulse trains
2nd harmonics generation feasible,4th harmonics generation could be feasible when beam is split into several parts and several crystals are used.
Integrated charge Ok for Cs2Te, tests to generate high integrated charge with green cathodes are planned in the photoemission lab.
50 Hz operation Tests can be done after installation of CALIFES laser