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PHIN tests at CTF C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev CLIC meeting 13.01.2012, CERN

PHIN tests at CTF

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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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Page 1: PHIN tests at CTF

PHIN tests at CTF

C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev

CLIC meeting 13.01.2012, CERN

Page 2: PHIN tests at CTF

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

Page 3: PHIN tests at CTF

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

Page 4: PHIN tests at CTF

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

Page 5: PHIN tests at CTF

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!

Page 6: PHIN tests at CTF

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

Page 7: PHIN tests at CTF

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

Page 8: PHIN tests at CTF

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

Page 9: PHIN tests at CTF

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:

Page 10: PHIN tests at CTF

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

Page 11: PHIN tests at CTF

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!

Page 12: PHIN tests at CTF

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

Page 13: PHIN tests at CTF

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

Page 14: PHIN tests at CTF

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

Page 15: PHIN tests at CTF

C. Hessler, E. Chevallay, M. Csatari, S. Doebert, V. Fedosseev 15

Automated QE Measurement

13.01.2011

Page 16: PHIN tests at CTF

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.

Page 17: PHIN tests at CTF

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

Page 18: PHIN tests at CTF

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

Page 19: PHIN tests at CTF

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

Page 20: PHIN tests at CTF

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).

Page 21: PHIN tests at CTF

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

Page 22: PHIN tests at CTF

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

Page 23: PHIN tests at CTF

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