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EMMA Extraction / Diagnostic line
Bruno Muratori
STFC, Daresbury Laboratory
01/09/08
• Septum is - 70 degrees• Dipole to close dispersion is
only 10 degrees• Requirements are:
– Small beam– Dispersion = 0 on exit of
dipole• Difference between the two
bends very large:– Introduce more
quadrupoles ?– Introduce different
dipoles ?– Extract at different
location ?
EPAC08: EMMA diagnostic line
Option 2:10 degree bend→ 2 × 5 degrees& more quads
Option 3: Different extraction→ -70 degree septum &43 degree dipole & 4 quads
Option 1: More quadrupoles
Possible solutions
Option1: More quadrupoles
• Impossible to have small beam together with a matched dispersion
• Number of quadrupoles appears to be insignificant in this
• Resulting quadrupole strengths huge ! (3 × injection)
• Difference in bend angles far too great
• Also does not work with genetic algorithm due to James Jones
• Can this be shown analytically ?
Option2: Splitting the dipole & extra quads
• Problem actually worsens– Dispersion not closed– Beta very large– Dispersion very big (m)– Quad strength very large
• Again number of quadrupoles appears to have no effect in this
• Therefore third option is the only option available
• Yet another change for the engineers to endure …
Option3: Changing extraction point
• Dispersion matched easily• Betas very low• Quadrupole specifications
same as injection line !• Line very flexible
New diagnostic line layout
• Additional length → could re-use six SRS quadrupoles !• Rest of line unchanged• Still have
– Tomography– Space for possible deflecting cavity– EO section
Diagnostic line (1)
tomography EO
spectrometer
Diagnostic line (2)
• Ease of matching & tunability of line should be reflected in control room … (I hope !)
• Extra room for all the diagnostics which may be required for any eventual upgrades
• Betas remain very low• Deflecting cavity may be
located in optimum position (if we have it)
• Quadrupole strengths remain low for entire line
Tomography (1)
• Beam quite small on screen– ≥ 230 µm– need good OTRs or YAGs (?)– need good cameras
• Due to space restrictions– only 3 screens– 60° phase advance / screen
Tomography (2)
• Example taken from FLASH (45° phase advance / screen)
courtesy Ch. Gerth
Measurements
• Energy– First dipole & spectrometer at end with OTRs
• Projected transverse emittance– Quadrupole scans & tomography 60° phase advance / screen– Equivalent set-up in injection line for comparisons
• Bunch length– EO monitor downstream of the tomography section– No profile information
• Possibility of introducing a transverse deflecting cavity (TDC) to measure additional bunch properties
σz
L
0x
x
deflecting voltage
deflector bunch
screen
z
TDC Resolution (1)
• In absence of quadrupoles resolution increases with distance (L) from TDC to screen
σz
x
deflecting voltage
deflector bunch
screen
z
TDC Resolution (2)
• In the presence of interspersed quadrupoles this is not so and we must take into account of the entire transfer matrix from TDC to screen – there can be as many quadrupoles as desired
01 11 12''01 21 22
xx R R
xx R R
• Transverse displacement on screen is
• Beam size on the screen
• Transfer Matrix to screen gives
βd – deflector, βs – screen
• Want R12 big → sinΔψ = 1, βs fixed → make βd large
Transverse deflecting cavity (1)
deflecting cavity tomography EO
spectrometer
Transverse deflecting cavity (2)
Transverse deflecting cavity (3)
deflecting cavity tomography EO
spectrometer
0.95
1.35
1.6
Δµx = 90°
Δµy = 65°
1.13
Transverse deflecting cavity (4)
• Reverse of formula gives requirement of cavity voltage
• Take Δµ = 65° and φ = 0• For streaked bunch to be comparable to un-streaked bunch
• βx,y = 9 m at the deflecting cavity therefore we need, assuming an emmitance degradation to 10 µm and a bunch length of 4 ps
eV0 ≥ 0.23 MV @ 1.3 GHz
• Equality gives a streaked beam which is √2 times un-streaked beam– only rough idea of requirements– not enough for ≥ 10 slices (what we would like) → ~ 1 MV ?– longer bunch lengths / better emittance → lower voltage
20 0| sin cos |
N
z d
eV pcm c
Measurements with TDC
• Slice emittance & transverse profiles given by
– knowledge of R12 from TDC to screen
– one dimension on screen gives slice emittance– other dimension gives bunch length
• Slice energy spread given by– streaked beam and spectrometer
12 sind sR 01 11 12''01 21 22
xx R R
xx R R
• R matrix from TDC to screen known• Only need width at screen → slice emittance• Bunch length given by knowledge of kick
Longitudinalslices ~250 μm
Slice emittance measurements @ FLASH
courtesy Ch. Gerth
Energy
Time
Head
Tail
Unstreaked bunch
Energy spread measurements
courtesy Ch. Gerth
• FLASH operation at 650 MeV
Energy spread measurements (FLASH)
courtesy Ch. Gerth
Conclusions / Discussion
• Nice solution at long last … (Thursday of last week )– Beam very small throughout line
• Lots of tests still to be done but looks very flexible & workable• Steerers / correctors still to be included• Matching much easier than used to be (plus it works ! )
– Indication that this should be better during operation as well• Good characterisation of the beam at injection & extraction even
without TDC• Have good location for TDC should it be used in the future
– Realistic voltage parameters– Extra beam properties not available with EO– Currently looking at requirements for TDC with RF engineers