facet collimator systems for longitudinal bunch shaping
DESCRIPTION
FACET Collimator Systems for Longitudinal Bunch Shaping. Joel England FACET Users Meeting Tues Oct 9, 2012. Collimation for Bunch Shaping. Initial beam. "notch" mask. "jaw" mask. Muggli, P., et al. PRL 101 , 054801 (2008). - PowerPoint PPT PresentationTRANSCRIPT
FACET Collimator Systems for Longitudinal Bunch Shaping
Joel England
FACET Users Meeting Tues Oct 9, 2012
Collimation for Bunch Shaping
Muggli, P., et al. PRL 101, 054801 (2008).
Initial beam "notch" mask "jaw" mask
Collimators have recently been installed in Sector 20 to provide adjustable masks of two types:
"notch" collimator: movable tantalum blade for two-beam (drive/witness) operation- could potentially be modified for other mask designs if desired
"jaw" collimator": pair of transverse scrapers for ramped bunch (high tr. ratio) operation- can also be used to remove high or low-energy "tails"
Collimator Locations
June 11-15, 20123
W-chicane lattice (cartoon)
collimators
for 2-bunch generation
E-collimation, ramped bunches
Collimator Location
chicane lattice (cartoon)
collimators
collimator location
Collimator Location
collimators
R56 = -10mm (2-bunch config) R56 = 0mm (ramped bunch config)
recently installedMarch 3, 2012
3 FACET ConfigurationsCollimator End of W-Chicane
"A""B"
location "A"
location "B"
R56 = 4mm R56 = 10mm R56 = 0 mm
full compression overcompressed undercompressedW-chicanecompression factor
high-current single bunch
drive/witnessconfiguration
ramped bunch
notch
jaws
Notch Collimator
recently installedMarch 3, 2012
beam axis
notch collimatorinsertable blade
schematic of notch collimator
notch collimator
jaw collimator
FACET: 2-bunch case
8
8
x ∝ ΔE/E ∝ tDisperse the beam in energy
Adjust final compression
...selectively collimate
x [mm]
dp
/p [
%]
dp
/p [
%]
z [mm]
Exploit Position-Time Correlation on eExploit Position-Time Correlation on e-- bunch to create bunch to create separate drive and witness bunchseparate drive and witness bunch
Exploit Position-Time Correlation on eExploit Position-Time Correlation on e-- bunch to create bunch to create separate drive and witness bunchseparate drive and witness bunch
Modeled using similar analytic framework (CSR) as LCLS as well as tracking/shower codes
Modeled using similar analytic framework (CSR) as LCLS as well as tracking/shower codes
130 µm
courtesy M. H
ogan
Measurement of 2-Bunch Scenario
Slide courtesy of M. Litos
Jaw Collimator
e-beam axis
y
x
y
xadjustable momentum slit
separately moveable titanium blocks
Note: beam dimensions are exaggerated forillustrative purposes
z
x
Ramped Bunch at FACET
Due to upstream compression, need R56 = 0 in chicaneCollimators can remove low-E tail.
Ramped bunch has L = 200 µm ; Ipeak = 4 kA ; nb/n0 = 17kpL/2 = 10 for plasma n0 = 3x1017 cm-3
Λ =0.5 for Ip = 4 kAnb / n0 =17 nb / n0 =33
n0 =3×1017cm−3 n0 =0.75 ×1017cm−3
R =kpL / 2 =10 R =kpL / 2 =5n0 → n0 / 4
E+ =18.7 GV/mE+ =37.5 GV/m E+ =E0 Λ
However, to avoid hosing instability, require R ≤ 5
W chicane
Ramped Bunch: PWFA
1. Particle phase space generated with ELEGANT simulation of beamline.2. Focusing of beam at plasma transition (plasma lensing) modeled in Mathematica.3. Beam parameters used in QUICKPIC to model propagation in 1.2e17 cm-3 plasma.4. Resultant transformer ratio from longitudinal E-field is R ~ 6.
R = E+/E- = 6
orange: beam, blue: plasma
beam direction
W. An
PIC simulation courtesy W. An
Ramped Bunch: DWA
• ACE3P (Cho Ng)• Axial beam current with 200µm ramped bunch• 1.2 nC beam charge
Transformer R ~ 1.5 (vs. 1.2 for back of envelope calc)
E+ = 540 MV/m(vs. 780 MV/m for back of envelope)
vb
ID: 200 µm; OD: 330 µm;glass tube (smallest of E-201 tubes currently in use)
DWA Gradient
14
Dispersion relation for TM/TE modes at speed-of-light: A.M. Cook, PhD Dissertation, 2009.
solutions where curve crosses x-axis
for fiber diameter a = 30µm, b = 300µmTM01 excitation occurs for k-1 = 16 µm
For expected FACET ramped bunch length of L =160 µm
This gives TR ~ k L / 2 = 5
Note: FACET IP spot size ~ 20 µm
Summary
• 1. Collimators have been installed at FACET for generation of 2-bunch and ramped bunches.
• 2. High-transformer ratio PWFA studies require a pre-ionized plasma.
• 3. Possibility of doing nearer-term DWA studies using existing structures from E-201 program.
• 4. Optimal excitation of the fundamental DWA mode requires smaller tubes (limited by e-beam bunch size) or longer ramps.
• 5. Difficult to further reduce R56, but may get longer bunches by re-phasing.
• 6. Initial studies indicate possibility of interesting wake amplitudes and transformer ratios.
Thank You!
SLACMark HoganMike LitosJoel FredericoSpencer GessnerErik AdliSelina LiDieter WalzChristine ClarkeC-K. Ng
UCLAGerard AndonianWarren MoriChan JoshiWeiming An
Tsinghua Univ.Wei Lu
Max Planck InstitutePatric Muggli
Application for DWA
17
E− =4Nbremc
2
a8πε −1
εσ z + a⎛
⎝⎜⎞
⎠⎟
R =E+
E−
=kL / 2
E+ =RE−
[Cook, et al., PAC 2009]
Transformer Ratio
18
For a triangular bunch of length L, the wake function is given by
Transformer ratio is obtained by extremizing the top and bottom lines and dividing:
This solution is valid for all kL (in linear 1D). For kL > 1, it can be approximated by R ~ k L / 2
DWA Structures for E-201
19
1502002606209251130
k-1 (µm) k L/2
0.60.50.40.160.110.08
Tube diameters appear large for high-TR with the current nominalramped bunch parameters.
cutoff wavenumbers for speed-of-lightsolution to TM dispersion relation
Assume nominal L = 200 µm
Tube geometries for E-201 Experiment at FACET, courtesy of G. Andonian
Gradient Estimate
20
For smallest diameter tube (fused silica).Variation in L corresponds to linac phase variation for R56 = 0Assumes 3nC initial bunch + collimation loss of ~ 50%
Retarding field (inside bunch) Accelerating field (behind bunch)
TR ~ 3 for longer bunches