Electron beam experiments at FAST in 2017 A. Halavanau, J. Hyun, P. - - PowerPoint PPT Presentation
Electron beam experiments at FAST in 2017 A. Halavanau, J. Hyun, P. Piot, C. Thangaraj and T. Sen April 10, 2017 A. Halavanau, J. Hyun, P. Piot, C. Thangaraj and T. Sen Electron beam experiments at FAST in 2017 April 10, 2017 1 / 47 Outline
April 10, 2017
Electron beam experiments at FAST in 2017 April 10, 2017 1 / 47
1 Introduction and updates
Experiments at FAST in 2016
2 Canonical Angular Momentum (CAM) dominated beams
Theoretical background Beam moments gymnastics Round-to-flat transformation
3 Experimental plan for Run 2017
Flat beam generation THz radiation generation
4 Additional materials
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IOTA/FAST facility - high-brightness 300 MeV electron beams
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Future experiments
1.3 GHz SRF accelerating cavity transport studies:
arXiv:1701.08187; accepted in Phys. Rev. Accel. & Beams (2017)
Channeling radiation experiment:
(2016) UV laser shaping experiments:
//FERMILAB-TM-2634-APC
Simulations and potential experiments:
IPAC15, p. 1853 (2015) and MORE...
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12, T03002 (2017).
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Electron beam emittance was meassured via simple geometrical (ǫ = σ1
z
2 − σ2 1) and quadrupole scan technique
20 40 60 80 100 20 40 60 80 100 20 40 60 80 100 120 140 20 40 60 80 100 120 140X120 X111 Reference: Data by A. Romanov, P. Piot; Proc. of NAPAC16: TUPOA19; Green, A. MS Thesis, NIU (2016)
Charge, Q ǫnx, µm ǫny, µm <1 pC 0.25 ± 0.1 0.3 ± 0.1 50 pC 1.6 ± 0.2 3.4 ± 0.1
analysis in progress; will be reported separately
used to confirm/update
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1 Conventional application - electron cooling (Derbenev, Ya.,
UM-HE-98-04-A); proposed for JLEIC and other facilities
2 Emittance partitioning via flat beams (interest of ILC group) 3 Supressing microbunching instabilities in IOTA (collaboration
with R. Li, JLab)
4 Several possible radiation experiments (dielectric structures,
microundulators, channeling, etc.) can be done at FAST CAM beams production at FAST is an important first step
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Motivation: flat-beam generation, compression, and application to the generation of tunable THz narrowband radiation. Goals:
1 Produce canonical angular momentum dominated (CAM)
beams (pionereed at Fermilab A0)
2 Set up and optimize on the fly the round-to-flat beam
transformer (RTFB)
3 Generate extreme eigen-emittances ratio (> 300) (NEW) 4 Demonstrate compression of flat beam and investigate
emittance dilution during the process (NEW)
5 Demonstrate the use of flat beam to generate THz radiation
using the mask method (NEW)
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Relativistic Hamiltonian of the particle (m, q, P): H = c(m2c2 + (P − qA)2)1/2 + qφ − mc2, where φ, A - scalar (vector) potential. Note, that: −∂H ∂θ = dPθ dt = 0, therefore θ is a cyclic variable and Pθ is a constant of motion. Pθ = γmr 2 ˙ θ + qrAθ = const Conservation of canonical angular momentum or Busch’s theorem
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Total canonical angular momentum
L = γmr 2 ˙ θ + 1 2eBz(z)r 2 (1) The norm of | L| can be computed as L = | r × p| = xpy − ypx. Redefine as < L >= eB0zσ2
0:
L ≡< L > /2γmc = const where B0z is the field at the cathode, σ0 is the RMS spot at the cathode and σ is the RMS beam size. The particle total mechanical momentum p = pr^ r + pθ^ θ + pz^ z has non-zero ^ θ-component resulting in CAM-dominated beam.
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a) Emittance-dominated beam (ǫu) b) CAM-dominated beam (magnetization L ≡< L > /2γmc) c) Space charge dominated beam (space charge parameter K) σ′′ + k2
l σ − K
4σ − ǫ2
u
σ3 − L2 σ3 = 0,
kl = eBz(z)/2γmc is Larmor wavenumber, K = 2I/I0γ3 is the perveance, I and I0 are the beam and Alfven current respectively
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Define 4D-emittance as ǫ4D = ǫ2
u =
Σi =
σ2 κσ2 κ2σ2 + σ′2 −κσ2 −κσ2 σ2 κσ2 κ2σ2 + σ′2
,
where ǫu = σσ′ (doesn’t depend on κ) and κ = L/σ2. Total 4D-emittance is conserved det(JΣ − iǫ±I) = 0, where I and J are respectively unit and symplectic unit matrix.
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Eigenemittances: ǫ± =
u + L2 ± L → ǫ+ ≈ 2L; ǫ− ≈ ǫ2 u
2L Emittance ratio or “flatness”: ǫ+ ǫ− = 4L2 ǫ2
u
= 1 p2
z
e2B2
0z
σ2 σ′2 Example calculation: σ+ =
βx,yǫ+ → ǫu=2 µm → ǫ+ = 40µm,
ǫ− = 0.1µm → βx,y = 8m, σ+ = 1.8mm and σ− = 0.09mm Burov, A., Phys. Rev. E 66, 016503 (2002) Kim, KJ., PRSTAB, 6, 104002 (2003).
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Round-To-Flat Beam transformer Let the transformer be described by R′
RTFB = Q3D3Q2D2Q1, where
Di =
di 1
±qi 1
matrix respectively. Consider three quadrupoles skewed at 45 deg. as RRTFB = M−45R′
RTFBM45, where Mφ is rotation matrix
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Let the RTFB transfomer transport be described by R =
B C D
Σi =
ΣXY ΣYX ΣYY
ΣXY = 0 leads to: AΣXX ˜ C + AΣXY ˜ D + B ˜ ΣXY ˜ C + BΣYY ˜ D = 0 (2) Round beam → ΣXX = ΣYY = Σ0 and ΣC = −˜ ΣXY
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4 × 4 matrix RRTFB can be also represented in 2 × 2 block form as: RRTFB =
B C D
a − b a − b a + b
R′
RTFB =
b
B + BΣ0˜ A + AΣC ˜ A + B ˜ ΣC ˜ B = 0. Guess solution A+ = A + B and A− = A − B such that A− = A+S, where S some symplectic matrix (can be defined by ΣXX, Y. Sun PhD thesis, FNAL (2005))
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FAST quadrupoles: K = (10.135 × 40 Iq)/(1.8205 × p [MeV /c]), Leff = 17cm q1 = ±
d2dTs12 , q2 = (d2 + d3)(q1 − s21) − s11 d3(d2q1s11 − 1) , q3 = d2(q2 − q1q2s12) − s22 d2(d3q2s22 + q1s12 − 1) + d3(s12(q1 + q2) − 1) Least-squares method can be used for correcting (q1, q2, q3) for chromaticities and other second order effects
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Matrix S can be defined as correlation: Y = SX → S = ΣYXΣ−1
XX
where X, Y are 2×1 phase space vectors. Alternatively, it can be defined as: S = ± 1 |ΣXX|JΣ−1
XX = ∓1
ǫ
κ2σ2 + σ′2
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Case : S =
0.781
q1, m−1 q2, m−1 q3, m−1 Linear model 1.84
0.23 Elegant simplex (1000 p.) 1.88
0.20
properties of the distribution
analytical SRF cavity model)
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Fermilab A0 CAM removal demonstration:
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1 Optimize round beam emittance via multislit tool 2 Start with low B0z value and demonstrate RTFB
transformation
3 Switch to high B0z configuration and optimize RTFB adapter 4 Produce highly asymmetric beams at 2.2 nC (interest of
JLEIC group)
5 Study flat beam compression in the chicane by using multislits
at X107 and X118 locations
6 Proceed to THz radiation generation using multislit in bunch
compressor
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will be a byproduct (many applications)
required for electron cooling
cathode Bmax ~ 0.3T
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Parameter Value Units Initial emittance (norm.) <2 µm Beam energy 50 MeV Slice energy spread <5 keV Charge 200 pC Bunch length 5 ps Beta-function (CC2 exit) 8 m Dipole bending radius 0.958 m Dipole length 0.301 m Dipole angle 18 degrees R56
m Beam-based alignment: Romanov, A., arXiv:1703.09757 [physics.acc-ph]
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MAM → CAM → L → Σ → RTFB → ǫ+/ǫ−
Assumption:
Canonical Angular Momentum (CAM) is fully trasferred to Mechanical Angular Momentum (MAM)
Two methods of measuring CAM:
1 Using multi-slits, observe relative shear of the beamlets 2 Using microlens arrays, produce multi-beam and observe
rotation
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Fermilab A0 2004 Run (PRSTAB 7, 123501 (2004)):
Multislit beamlets Angular sheering < L >= 2pz σ1σ2 sin θ
D
, where pz is momentum, D is the drift length Conservation of L
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Goal: Measure CAM without inserting any diagnostic hardware in the beamline except YAG viewers Method:
1 Create electron beam that looks like array of thin dots 2 “Magnetize” the beam with solenoids at the cathode 3 Infer mechanical momentum by measuring the rotation on the
screen
θ
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AWA 2016/17 Run (submitted to PRAB):
Bucking-Focusing solenoids
YAG screens beam axis
Matching solenoid
Linac 1 RF gun
YAG2 YAG3 YAG1
1.01 2.79 5.51
Multi-beam projected on the cathode, two YAG screens used to determine relative rotation → calculate L.
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Layout for laser homogenizer
−10 10 −10 10 Y (mm) YAG1 −10 10 −10 10 YAG2 −10 10 −10 10 Y (mm) −10 10 −10 10 −10 10 −10 10 Y (mm) −10 10 −10 10 −10 10 X (mm) −10 10 Y (mm) −10 10 X (mm) −10 10Joint collaboration with Northern Illinois University
MLA plate
Resulting distribution can be flat-top
Optical transport requires custom imaging solution
Homogenized beam More intensity! Regular beam clipped with iris
Multi-beam
References: FERMILAB-TM-2634-APC (arXiv:1609.01661), FERMILAB-CONF-16-460-APC (Proc. of NAPAC’16)
Both beams were produced at 18/50 MeV Advantages of the MLA: 1) Flat-top homogenized laser spot 2) Reduction of beam emittance by factor of 3! 3) Multi-beam pattern generation 4) Available off-shelf!
−10 −5 5 10 x (mm) −10 −5 5 10 y (mm) −10 −5 5 10 x (mm) −10 −5 5 10 −10 −5 5 10 x (mm) −10 −5 5 10 10 20 30 40 10 20 30 40 ky (mm−1) 10 20 30 40 10 20 30 40 10 20 30 40 10 20 30 40 10 20 30 40 kx (mm−1) 10−3 10−2 10−1 100 < I(kx) > 10 20 30 40 kx (mm−1) 10−2 10−1 100 10 20 30 40 kx (mm−1) 10−2 10−1 100Electron beam experiments at FAST in 2017 April 10, 2017 30 / 47
Multi-beam shearing
−10 10 −10 10 y (mm)
YAG1
−10 10 −10 10
YAG2
−10 10 −10 10 y (mm) −10 10 −10 10 −10 10 −10 10 y (mm) −10 10 −10 10 −10 10 x (mm) −10 10 y (mm) −10 10 x (mm) −10 10
via microlens array laser shaping technique (submitted to PRAB)
cathode and observed at two locations
beamlet spacing is calculated
D
n
2a1
2 (m sin θ), n
is number of beamlets, a1 beamlet pitch, m = a2/a1 is the magnification, θ is skew angle.
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−400 −200 200 400 Bucking solenoid current (A) 20 40 60 80 100 120 θ (deg.) YAG1 YAG2
Skew angle θ
0.0 0.5 1.0 1.5 2.0 2.5 3.0 (mm)−1 0.00 0.05 0.10 0.15 0.20 0.25 Bunching factor −10 −5 5 10 x (mm) −10 −5 5 10 y (mm) kx ky
Resulting value of B0z compared with Impact-T simulations
−400 −200 200 400 Bucking solenoid current (A) 200 400 600 800 1000 1200 1400 1600 B0z (Gauss) ImpactT Experimental
(30 fC), error bars are big (can be reduced)
beamlet formation
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settings for RTFB can be computed
installation is completed)
FERMILAB-CONF-16-460-APC)
straightforward
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1 20 nm horizontal emittance (below thermal) at FAST 2 Analytical model for RTFB with online optimization via
Elegant
3 Start-to-end full bunch simulations on NIU GAEA cluster
(work in progress)
4 Parameter space study via Impact-T on NIU NICADD
cluster (work in progress)
5 Possible neural network RTFB optimizer (with A. Edelen)
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Schematics of the experiment Bunch compressor
chicane
energy modulation
modulation
at X121 location
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Bunching factor: b(ω) = 1
N | n exp(−iωtn)|. N - total number of
particles, n - particle index number. Radiation spectrum:
dωdΩ
= [N + N(N − 1)b(ω)2]
dωdΩ
, where
dωdΩ
fluence associated to the considered electromagnetic process (Transition Radiation). Further analytical consideration in progress
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To Streak Camera X121 TR Path D3 SR Path Optical Switching and Interferometer Box D4 SR Path Not Quite Visible Ceramic Gap Ceramic Gap Signal vs. RF Phase Interferometer Autocorrelation Traces Streak Camera Bunch Length vs. RF Phase
Horn Antenna with Waveguide
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Transmission rate through mask: 33%
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Energy chirp can be used as a parameter knob
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1 CAM beam generation is a byproduct with many outcomes 2 FAST flat beam configuration can be used for numerous
radiation generation experiments
3 THz radiation generation using multislits in the chicane will
be attempted during Run2017
4 Analytical considerations for RTFB transfomer and flat beam
compression are in progress
5 Various tools and instruments developed and will be reused
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Acknowledgements:
(POSTECH) for their significant contribution to the MLA research
FAST and useful comments
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Accelerating cavity properties were studied during Run2016
Conclusions:
procedure (experimentally confirmed for CG-method)
Outcomes:
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−30 −20 −10 10 20 30 0.0 0.2 0.4 0.6 0.8 1.0 R11, R33 −30 −20 −10 10 20 30 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 R12, R34 (m) −30 −20 −10 10 20 30 φ (deg) −0.4 −0.2 0.0 0.2 0.4 R21, R43 (m−1) −30 −20 −10 10 20 30 φ (deg) 0.2 0.4 0.6 0.8 1.0 R22, R44 −30 −20 −10 10 20 30 −0.2 −0.1 0.0 0.1 0.2 R13, R31 −30 −20 −10 10 20 30 −0.2 −0.1 0.0 0.1 0.2 R14, R32 −30 −20 −10 10 20 30 φ (deg) −0.2 −0.1 0.0 0.1 0.2 R23, R41 −30 −20 −10 10 20 30 φ (deg) −0.2 −0.1 0.0 0.1 0.2 R24, R42 −30 −20 −10 10 20 30 φ (deg) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 |R|4×4 28 30 32 34 36 38 40 42 γi 0.0 0.1 0.2 0.3 0.4 0.5 |R|4×4
(left) transfer matrix R elements; (right) determinant R4×4 as a funciton of phase (φ) and injected γi (See FERMILAB-PUB-17-020-APC for details)
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(left) Braking radiation spectrum of Al; (right) Diamond (C − 110) response to electron beam
1 First attempt at FAST 2 Detector alignment procedure has to be improved (will be) 3 Acquisition algorithm has to be improved (will be)
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