Laserwire at the ATF extraction line

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Laser-wire at the ATF extraction line

• Laser Based Beam Diagnostic
• (Laser-wire UK collaboration)
• Chafik Driouichi
• Royal Holloway University of London
• 19th April 2005

http//www.pp.rhul.ac.uk/lbbd/meetings/meeting10/
index.html
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Outline

• Whats already there and shouldnt worry about.
• Issues to worry about when designing the Optics
  Transport.
• Relay optics, is it needed?
• Laser beam diameter its implication on the
  optics (2 or 3).
• Laser power too high. Do we need all that power?
• - Coatings
• - Safety devices
• Lens tolerances system alignment
• Scanning range
• Optics table (what should be there?)
• Define responsibilities
• Plan for next trip
• Summary discussion

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Whats already there?

• Laser
• P 1 GW, tpulse 200 - 300 ps, rep.rate 6.25
  Hz, Ø6 mm.
• Part of the beam transport (from laser hut to the
  tunnel)
• Control signal system is partly there easy to
  integrate in our DAQ
• Wire scanner (should be repaired by now!)

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Issues to worry about (1)
Relay Optics
Risk ? Relay optics might spark the air due to
the laser power.
Laser hut
missing
Ext. Line
Divergence is small ? No need for a relay !!!
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Issues to worry about (2)
Beam diameter implication on the optics
Focusing lens incl. 3 elements
Beam diameter 6 mm
f 60 mm ? 532 nm ?f 1 ?m
To achieve ?f 1 ?m, one needs ?L 10 mm
Can a 2 optics accommodate the beam ? Certainly
not! ? 3 optics _at_45
incidence
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Issues to worry about (3)
Laser Damage Threshold (LDT)
E 300 - 400 mJoules Pulse length 200 - 300
ps Beam diameter 2.R 6 mm
Power density
1.4 Joules/cm2
CVI Coating ? 5 Joules/cm2 _at_ 532 nm for a pulse
duration of 8 ns.
LDT (8 ns) 1.4 Joules/cm2 .
? 9 Joules/cm2
? CVI coating is not enough !
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Issues to worry about (4)
CVI Technical Optics claims coating with LDT 20
Joules/cm2
Best candidate so far !
However
Dust or grease ? highly absorbing areas Laser
cavity instability ? random hot spots
- Environment conditions critical, but can be
taken care of (enclosed system). - Laser best
performance needs to be identified and controlled
(laser parameters needs to be measured at the
beginning of each run)
Shintake ? We dont need to use the full power of
the laser.
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Optics (Breadboard in tunnel)
The breadboard should contain

• High power Beam Shutters one in the laser hut,
  the second just at the entrance of the optics
  breadboard (interlocked).
• Coarse alignment system (global alignment of the
  setup) done when putting the system together for
  first time by using apertures, red light, PSDs.
• Waist monitor measure the waist at the entrance
  of the focusing system (will be done by dumping
  most of the beam and sending the remaining
  fraction to a CCD camera).
• An adjustable Beam Expander 2 lenses, one fixed,
  the other one is on a translation stage in order
  to fully collimate the beam
• Fine alignment system 2 steering mirrors
  combined with 2 PSDs.
• Scanner PI S330 ? ? 2 mrad, f1KHz, high
  repeatability
• Attenuators, beam dumps, ND filters,.
• Powermeter Molectron or Ophir.
• A fast photodiode for time measurement.

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Alignment
A coarse alignment will be done at first when
installing the system by using a red light,
apertures, PSDs along the beam path.
PSD2

• Fine alignment will be done using
• - 2 steering mirrors MS1 MS2
• ? will have a 2 axis rotations
• - 2 PSDs
• ? will be finely aligned with respect to
  the focusing lens) in order to bring the beam
  within the tolerance of the focusing lens
  (off-axis lt1 mm tilt lt5 mrad).

? tilt
PSD1
A setup is being developed at RHUL.
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Screenshot from ZEMAX of the alignment setup
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Scanning range

• If we suppose that
• s e-beam size
• N number of sigma scans
• ? N x s /f

Example f 60 mm N 5
? (?m) 1 6 ? (mrad) 0.08 0.5
Scanner PI S330 ? 2.5 mrad, f1KHz, good
repeatability.
Other options (A.O E.O) are being investigated.
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ZEMAX screenshot of the beam path
e-beam
x
200
z
Scanning platform
700
300
500
Beam Telescope
MS2
400
100
MS1
800
400
100
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ZEMAX Simulation
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Responsibilities
KEK
Laser hut access Support for the Breadboard,
enclosure for the system (pipes, box
) Wire-scanner
RHUL/OXFORD/UCL (all what will be on the
breadboard)
Breadboard (1.5m x 1m or 2m x 1m) Optics
mirrors, focusing lens, Scanner, diagnostics
tools (beam profilers), photodiode, PSDs, beam
dumps, beam shutters, energy meter, .
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Plan for next KEK trip
Laser Optics Transport

• Get familiar running the laser, and measure its
  beam properties
• (triggering, jitter, energy, )
• Agree with ATF on safety issues related to Optics
  Transport.

e-beam optics

• Validate the e-beam optics (profile measurement
  with wire scanner)
• Get familiar with the ATF control system
  (dispersion corrections,
• Wire-scanner, BPMs,)
• APD v.s. PMT
• Get some collision even with the e-Compton setup.

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Summary
Optics Transport

• No Relay optics
• Safety devices Beam shutters will be placed in
  both HUT
• entrance of Breadboard (Spiricon)
• Coating still a confusion, but will be sorted
  out in a couple of days
• Reduce the laser power to several 10s MW.
• Optics will be 2 before Beam Expander, and 3
  mirrors post-BE.
• System alignment is being developed at RHUL
• Scanning PI S330 (other technologies are being
  investigated)
• Zemax simulation ? meetings our goals.

Companies/Providers identification has already
started
KEK Trip
Critical to meet all goals mentioned earlier.