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Advanced vanced Beam m Instru trumentatio mentation n sup upporting porting AARD RD at t th the A0-Photoinj hotoinjector ector Manfred Wendt Fermilab 1 8/18/2008 A0-Photoinjector Review Agenda enda Motivation Proposed

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SLIDE 1

Advanced vanced Beam m Instru trumentatio mentation n sup upporting porting AARD RD at t th the A0-Photoinj hotoinjector ector

Manfred Wendt Fermilab

8/18/2008 1 A0-Photoinjector Review

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SLIDE 2

Agenda enda

  • Motivation
  • Overview on
  • long. beam diagnostics
  • OTR Introduction
  • Ongoing Activities

– Streak Camera – Martin-Puplett Interferometer – OTR Interferometer – EOM-based Time-of-Arrival

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  • Proposed New Activities

– Long. diagnostics using CTR – Long. bunch profile using EOS – HOM signal processing – Beam tests of a cold ILC cavity BPM prototype – Waveguide pickups

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SLIDE 3

Mot

  • tivation

ivation

  • Need a set of reliable basic beam instruments

(upgrades required, see also Ray’s talk):

– Intensity, position (orbit), transverse beam size (emittance)

  • AARD demands advanced beam diagnostics, in

particular in the longitudinal domain to study and

  • bserve the bunch dynamics in AARD experiments:

– Bunch length – Longitudinal bunch profile – Bunch time-of-arrival (wrt. RF phase, or relative between two locations)

  • No best “I can do everything” instrument available

to fully characterize longitudinal bunch parameters

– Calibration, measurement range (fs, ps) and time (single/multi shot), (non) invasive, resolution, reproducibility, etc.

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SLIDE 4

Lo Long ngitudinal itudinal Bea eam m Dia iagnostics nostics

Device Applicable bunch lengths Comments Streak camera

Ongoing activity, Bunch profile

1 – >100 ps

  • Well understood, expensive commercial device
  • Single bunch, single pass capability (intensity limited)
  • Dispersion effects dominate at short bunch length

measurements

  • Can provide arrival times and jitter

Martin-Puplett Interferometer

Ongoing, length

< few ps

  • Slow response, scanning using many macropulses
  • Susceptible to upstream CSR and wakefields
  • Missing phase information makes details of the bunch profile

difficult to obtain

CTR angular distribution

Proposed, length

< few ps

  • Parametric measurement of the bunch profile, bunch shape

must be assumed

  • Scanning over many macropulses
  • Susceptible to upstream CSR and wakefields

Electro-optical sampling

Proposed, profile

100 fs – 2 ps

  • Single shot capability, fairly expensive, needs a (high power)

laser synchronized to the beam

  • Must understand behavior of electro-optical crystal in the

frequency regime corresponding to the expected bunch length

  • Susceptible to upstream CSR and wakefields

Waveguide pickups

Proposed, length

200 fs – 2 ps

  • Inexpensive and simple, but calibration very difficult.
  • Does not give shape information, just rough bunch length

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SLIDE 5

(O (Opti ptical) cal) Tra ransition nsition Rad adiati iation

  • n
  • Transition radiation

– Charged particles passes through a media boundary – Monitoring of trans. beam profile (-> emittance), bunch length and energy

beam

2 2 2 2 2 2 2

) ( 1 ) , (            

c h e I d d U d

beam

courtesy A. Lumpkin

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SLIDE 6

Str treak eak Cam amer era a Pri rinc nciple iple

Based on VG by B.Yang for ANL/S35 review Phase-locked Delay Box C6878

81.25 MHz rf IN GPIB 81.25 MHz Sync Slit (set to 40 µm) Sine Wave from Synchroscan M5676

Sweep Signal

  • Ref. In
  • Dual-sweep streak camera Hamamatsu C5680 (1.5 ps FWHM res.)
  • Addition of M5676 synchroscan plugin module and the C6878

phase-locked delay box enabled new series of experiments at A0.

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SLIDE 7

Str trea eak k Cam amer era a Sum umma mary ry

  • Streak camera

– Views UV-visible light from a (intercepting or non-intercepting) conversion mechanism, e.g. OTR, OSR to observe the bunch. – Provides a 2-D bunch profile, allowing sliced measurements:

  • Vertical axis -> time axis
  • Horizontal axis: preserved (spatial, energy, spectral)
  • Features

– Synchroscan unit (81.25 MHz, phase-locked to master oscillator)

  • ~1 ps RMS jitter
  • Synchronous summing of micropulses (statistics, intensity)

– Delay unit provides long term stability – Dual-sweep allows simultaneous observation of micropulses

  • Resolution

– 1.5 ps FWHM (monochromatic), larger for broadband light

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SLIDE 8

Str treak eak Cam amer era a Res esults ults

  • Bunch length elongation with micropulse charge and

slice beam-size effects (50%) at 4 nC observed.

Lumpkin,Ruan: BIW08

t X

Charge (nC)

1 2 3 4 5 6 7 8

Bunch Length (ps)

10 15 20 25 30 35

10-15-07 R2 FWHM (ps) Rodion Diss. FWHM (ps) ASTRA 30.5 FWHM (ps)

20 ps ~10 mm

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SLIDE 9

Ste teak ak Cam amer era a Res esults ults (c (con

  • nt.

t.)

  • Bunch

compression and transit time changes for different momenta in double doglegs were measured. The line is a fit showing that R56 is 0.18 m

Lumpkin,Ruan: BIW08

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SLIDE 10

Str treak eak Cam amer era a Res esults ults (c (con

  • nt.

t.)

  • Emittance exchange results in bunch compression.

← 5-cell off ← 5-cell on

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SLIDE 11

Mar artin tin-Puplett Puplett Int nterfe erferometer rometer

  • Martin-Puplett interferometer

– Needs many beam pulses to resolve the temporal convolution – Difficult to calibrate the detectors

View from Top

Transition Radiation

Electron Bunch

 

 

   

) ˆ ( 3 2

) ( 1 ) ( ) ( ) 1 ( ) ( ) (

n x i

e x x d Q F F N N N I I

    

Coherent Incoherent

View from Top again

Motorized stage Polarizing Splitter Polarizing Splitter Input Polarizer Mirrors Mirrors Pyro Detector 1 Pyro Detector 2 Off-axis Paraboloidal Focusing Mirror

 

       ) ( cos ) ( ) ( 2 sin 2 2 cos 2 cos ) (

2 2 2 2 2 1 2 1 2 1

          I d I d S E I E I I I I I S

courtesy

  • R. Thurman-Keup

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SLIDE 12

MP MP Int nter erferometer ferometer Res esults ults

  • 25
  • 20
  • 15
  • 10
  • 5

5 10 15 20 25

  • 0.5

0.5 1 Interferogram  (ps) S() 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.2 0.4 0.6 0.8 Frequency (THz) Intensity (Arbitrary Units) Spectrum Adjusted Raw

  • 6
  • 4
  • 2

2 4 6 8 0.05 0.1 Bunch t (ps) Intensity (Arbitrary Units)

Emittance Exchange Cavity On

  • Measurement experiment 2008:

– Using improved pyroelectric detector (DESY) with suppressed interference – Measured spectrum does not show interferences

  • Bunch length measurement results

(deflecting mode cavity on/off), and comparison:

– Autocorrelation with ratio = 0.69 – Reconstructed bunch ratio = 0.43 – Streak camera ratio = 0.66

  • MP issues

– Detector response (low freq.) and calibration – Diffraction effects at lower wavelength

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SLIDE 13

MP MP Int nter erferometer ferometer: : Nex ext t Ste teps

  • Plans

– Calibration of the pyroelectric detector frequency response – Experiments with

  • ther detector types
  • Golay cell
  • Schottky detector

– Reproduction and improvements of the MP interferometer hardware (borrowed from DESY).

Martin-Puplett Interferometer (borrowed from DESY)

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SLIDE 14

OTR R Int nterfer erferometer

  • meter (O

(OTRI) RI)

OTRI apparatus at the A0 Photoinjector.

e-

Transparent film

L1

Al Coated film

L2 L3

MCP CCD Filter MCP screen MCP photocathod Interfering OTR Optical window Mirror with hole

OTRI normal incidence setup & optical readout. OTRI principle of operation.

e-

Mirror with hole Transparent film Mirror-like film Interfering OTR

~2

  • OTRI features:

– Beam divergence measurement – Beam energy (better accuracy) – Single shot measurement (no scanning)

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0.5 1.0 D: beam=5.0 mrad E: beam=7.0 mrad

E=16 MeV 2.5 m Mylar

E=0.1 MeV meas=0.9 mrad

D=0.6 mm

Intensity, r.u.

B: beam=1.8 mrad C: beam=3.3 mrad

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SLIDE 15

OTRI RI Res esults ults

  • Results

– Measurements taken with 2.5 µm Mylar and 6 µm Mica double foils – Mylar foils show very good agreement with simulation! – Beam divergence measurement accuracy ~ 15 %

The interference pattern

  • btained

at 450 incidence setup with Mylar (left) and Mica (right)

  • based

interferometers at the beam energy of 16 MeV. Measured (solid lines) and computed (dots) fringes for the Mylar (left) and Mica (right) - based interferometers at normal incidence, 16 MeV beam with the energy spread of 0.6% and the readout resolution of ≈0.9 mrad.

  • Next steps

– Experiment with thinner foils – Beam divergence measurements at higher beam energies – Measurements in the EEX line?!

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SLIDE 16

Tim ime-of

  • f-Arrival

Arrival / B / Bea eam m Pha hase

  • To quantize long. beam dynamics a sub-ps resolution bunch-by-bunch

time-of-arrival measurement is required!

  • An electro-optical modulator (EOM) fed by femto-second fiber laser pulses

utilizes the sampling of a high slew-rate pickup signal.

  • The bunch time-of-arrival is referenced to the RF master oscillator.

81 MHz

courtesy F. Loehl, DESY

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SLIDE 17

TOF F Pre reli liminary minary Res esults ults

Sigma = 51 mV

  • > 2.9 ps

Voltage-to-Time Calibration

  • Initial results:

– EOM setup established – First measurements taken – Resolution limited by

  • Noise & jitter sources

(EMI, 81.25 MHz master)

  • Pickup response
  • Long cable runs (> 50 ft)
  • Fiber laser PLL lock

– Resolution: ~3 ps (RMS)

  • Next Steps

– Identify and improve jitter source, improve system resolution (100-200 fs) – Improved beam pickup – New location with shorter cable runs (in the cave?!)

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SLIDE 18

Lo Long ng. . Dia iagnostics nostics us usin ing g CTR

Diameter D

Proposal from R. Fiorito and A Shkvarunets, University of Maryland

Coherent TR distribution for 16 MeV electrons at A0 for two bunch lengths

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  • Large target D >>  and far field

L >> 2

– Angular distribution does not depend on frequency – Measurement using OTR (visible)

  • Small target D <  and/or near

field L < 2

– Angular distribution depends on frequency – Measurement using coherent TR (CTR) (far-infrared)

  • Transition region D ~ 

– Angular distribution sensitive to bunch length – Tune D as function of  and  to be in this transition region – Map angular CTR distribution

  • f measure the bunch length
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SLIDE 19

Y [mm]

  • 60
  • 40
  • 20

20 40 60

Detector Signal [V]

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 experiment theory

PBU 0 Pulse=0.69ps RMS=5%

Res esults ults fro rom m PSI-SLS SLS (1 (100 00 MeV eV)

Double Gaussian bunch fit, RMS=1.26%,

  • 3.2ps time 3.2ps

0.57ps, Am=1; 2.84ps, Am=0.2, Shift=1.53ps Reference: paper WEPC21, DIPAC 07

Single Gaussian bunch fit 0.69ps, RMS=5% Energy distribution of CTR

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SLIDE 20

Ele lectro ctro-Optical Optical Sam ampling ling (E (EOS)

  • All 3 single shot scheme are

realized

  • Temporal decoding resolve

bunch length <100 fs using Ti:sapphire laser and GaP crystal at DESY

  • At DESY, deflecting mode

cavity proved the effectiveness

  • f EO techniques
  • Most current EO experiments

are done on high energy electron beams

  • Most current EO efforts are

focused on electron bunch length less than 200 fs.

Three common single shot EO detection techniques to measure sub-ps bunch length

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SLIDE 21

Com

  • mpar

parison ison of

  • f EOS Tec

echniques hniques

Spectral Decoding Temporal Decoding Spatial Decoding Pros

  • Simple laser system
  • Single shot measurement
  • High repetition rate
  • Large time window
  • High resolution (110 fs)
  • Single shot measurement
  • Simple laser system
  • Single shot measrement
  • High resolution (160 fs)
  • High repetition rate

Cons

  • Limited resolution (200 fs)
  • Distorted signals for e-

bunches < 200 fs

  • Complex laser system

(mJ laser pulse energy)

  • Low repetition rate
  • Complex imaging optics
  • Good for clocking, but

tough to get the e- bunch information

  • For the current A0 research requirements and laser

availability we will focus on the spectral and spatial decoding techniques.

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SLIDE 22

Pro roposed posed EOS Act ctiv ivitie ities s

1. Measure longitudinal bunch information of low energy electron beams

c R  2

EO resolution

  • What will happen when  is low?
  • Can we deconvolute the signal?

Here R is the distance between crystal and electron bunch center Current energy in A0 and upgraded A0 is a very good fit for this study

2. Investigate the use other laser wavelengths, via fiber lasers, for EO sampling at these bunch length.

Ti:Sa Laser Fiber laser Cost High Low Transport Free space Complicated Fiber Easier EO study Successfully Done

?

Recent simulations show that a fiber laser based EOS is feasible!

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SLIDE 23

HOM Sig ignals als for r Beam m Monit itoring

  • ring

1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 10

7

10

8

10

9

Raw Spectrum TE111 dipole band TM011 Monopole band TM110 dipole band

  • HOM as BPM

– TE111-6 narrow band read-

  • ut

– Beam-based calibration data, to orthogonalize the polarization planes of the excited eigenmodes per SVD algorithm.

  • HOM as phase monitor

– Comparison of the leaking 1.3 GHz fundamental (TM010) to the first monopole HOM (TM011) – Broadband Scope analysis – <0.10 @ 1.3 GHz resolution (equiv. ~200 fs RMS)

HOM Spectrum

Frequency (GHz)

Resolution ~ 5µm

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SLIDE 24

HOM Dev evelopment elopment & Ana nalysis lysis Pla lans ns

  • Develop read-out hard- and firmware for HOM Analysis

– Narrowband System:

  • Low-noise, high-IP3 downmix hardware based on SLAC/KEK/DESY

ILC collaboration experience

  • Try to to incorporate flexibility, tunable to downmix different dipole

and possibly monopole bands

  • Low cost per channel custom VME digitizers, capable of

processing the HOM signals using the onboard FPGA

– Broadband system: High-speed oscilloscope

  • HOM Analysis

– The above instrumentation can be used to provide beam position, trajectory, and phase measurements to optimize performance. – Because the HOM spectrum is a function of the cavity shape, the observed modes provide a powerful cavity diagnostic for study and simulation.

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SLIDE 25

Oth ther er Act ctiv ivities ities

  • Cold L-Band cavity BPM

– ILC collaboration activity – Beam test of a prototype – Verify tuning, signal

  • rthogonality and levels,

resolution, reproducibility

  • Waveguide Pickups

– Horn antenna, waveguide & diode detector assembly – Available frequency range: 90-900 GHz – Simple setup for relative bunch length estimation (SLAC ESA, CERN CLIC)

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SLIDE 26

Sum umma mary ry

  • Advanced beam instruments play a mission critical role

to characterize the beam parameters when performing current and future A0-Photoinjector AARD experiments.

  • A comprehensive, challenging A0 instrumentation plan is

proposed, it has some focus in the longitudinal domain:

– Utilizing advanced optical, electro-optical and microwave state-of-the-art technologies. – Continuing ongoing developments, i.e. streak camera, MP interferometer, OTRI, and time-of-arrival diagnostics. – Start of new activities, i.e. CTR, EOS, HOM, cavity BPM, and waveguide pickup instrumentation.

  • Local and international collaborations are established,

and are crucial for the success of the program!

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