Introduction to the Electron Beam Diagnostic Session

1
Introduction to the Electron Beam Diagnostic
Session
TESLA Test Facility

• Dirk Nölle
• DESY, MPY
• 9-2579
• Dirk.Noelle_at_desy.de

TTF II Review Meeting, Salzau, January 2003
2
Overview of the Session

• D. Nölle Introduction
• M. Wendt Status of Beam Position, Charge and
  Phase Monitors
• K. Honkavaara, A. Chanci OTR Systems
• M. Koerfer Optical Fibre Dosimetrie
• M. Jablonka Toroid Protection System

3
Challenges of the Diagnostics

• LINACs are Open Loop Systems
• Beam Parameters change and have to be measured in
  different Parts of the Machine
• Measurements need Single Bunch Resolution over
  the whole Bunch Train.
• Pulse to Pulse and Bunch to Bunch Fluctuations
  have to be detected.
• High Duty Cycle Single Pass Machines can destroy
  Themselves
• Radiation Damage, Heat Load
• Need a very sensitive fast acting Protection
  System.
• Threshold and Reaction Time is determined by the
  most sensitive
• Component (? 3 ?s).
• Ultra short compressed Electron Bunches
• How to measure bunch lengths in the 100 fs
  Regime?
• Strong Dependency of Electron Beam and SASE
  Performance
• Characteristics (Intensity, Spectrum, Pulse
  Length)
• FEL Intensity shows statistical fluctuations
• Operator needs FEL Parameters and their
  Statistics.

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LINAC - Storage Rings

• LINAC
• Pulsed System with large Fluctuations
• Triggered Electronics have to take Pulses with
  the rep. Rate of the Bunches.
• (9 MHz for TTF II)

• Storage Rings
• Closed loop Equilibrium System
• Watch beam Parameters under stable Conditions.
• Systems can be much slower and can average over
  long Times.
• Precise Measurements in the Frequency Domain.

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... further Complication

• What do Monitors see
• Mean value of charge per bunch
• Mean value of position per bunch
• Projected emittance
• ...
• What is contributing to the FEL process?

Lasing Fraction
Longitudinal Charge Distribution measured at TTF
I
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Areas of Special Interest for Diagnostics
bunch compressors

• Remark TTF has everything, a big Machine also
  has, but everything concentrates in a limited
  Area !

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Butter and Bread Diagnostics

• Charge

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T1

• Need to Measure
• Charge
• Charge Distribution of the Bunches in the Beam
  Pulse
• Transmission along the Machine

• Fast Toroid System
• Single Bunch Resolution
• Time Constant lt 110 ns
• Bunch Rep. Rate 9 MHz
• Range 0.1 to 5 nC
• Accuracy ? 10-3

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Butter and Bread Diagnostics

• Charge
• Beam Position

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• Warm Parts of TTF II
• Striplines, Pickups
• Use a modular electronics system for all BPMs
• Single Shot, Single Bunch Readout
• External Trigger
• Variation of the Beam Position over the Macro
  Pulse
• Striplines installed and aligned inside the Quads
  (Res. lt 30 µm, 34 mm Pipe)
• Button Arrays (8 Pickups/Monitor) for the BC
  (manage large variation of Beam Position)
• Pickups in the Diagnostic Blocks between
  Undulator Sections and 2 inside each Undulator
  (Res. ?10 µm)
• In the Accelerating Modules
• Cold Cavity BPMs
• Cold Reentrant Cavity in ACC1 (by CEA)

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Butter and Bread Diagnostics

• Charge
• Beam Position
• Transverse Electron Distribution

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Screens

• Screens (OTR, YAG Screens)
• Beam Size (typical O(100µm)),
• Measure Emittance, Energy Distribution
• Resolution ? 20 µm
• Interceptive
• Low Damage Threshold (3 10 bunches)
• (Presentation by A. Chianci, this Session)
• Extraction of Coherent FIR Radiation
• Measurement of Compression and Bunchlength

OTR Station for TTF II
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Wire-Scanner

• Wire Scanners
• Machine Modified CERN Scanners with a V Fork
  and 45 Assembly with Respect to the Beam
• x and y measurement with one device
• combined with an OTR in the same housing
• Undulator New developed Type with an
  unidirectional Drive Unit (Presented by M.
  Sachwitz Undulator Session)

OTR/Wirescanner Chamber
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Butter and Bread Diagnostics

• Charge
• Beam Position
• Transverse Electron Distribution
• Dark Current

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Dark Current

• Dark Current is emitted in RF Structures
• Fills every RF-bucket
• Produces losses along the machine
• Contributes to Cryo-Load
• Main Contribution emitted by the Gun
• Increases with the age of the cathode
• Cathode has to be changed if DC exceeds a given
  threshold
• Measure DC by Sum Signal of a
  Reentrant Cavity BPM
• Resolution O(500 nA)
• Redesign for a 34 mm Beam Pipe will be started
  ASAP

Dark Current at TTF I Sum Signals of Reentrant
Cavity BPMs sampled between the Laser driven
Bunches
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Butter and Bread Diagnostics

• Charge
• Beam Position
• Transverse Electron Distribution
• Dark Current
• Phase

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Phase

• Ring Electrode installed in a Thick Flange
• Broadband, Position independent Signal
• One installed after the Gun, each magnetic
  Chicane (BCs and Collimator)

• Due to magnetic Bunch Compression Energy
  Fluctuations turn into Phase Fluctuations
• Beam Signal mixed with the (1.3 GHz) Master
  provides a Signal proportional to the Beam Phase
• Time Of Flight Measurement Resolution ? 0.5 or
  1 ps (tested with TTF I Stripline as a Pickup)

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Butter and Bread Diagnostics

• Charge
• Beam Position
• Transverse Electron Distribution
• Dark Current
• Phase

• More detailed Information provided
• by M. Wendt
• and K.Honkavaara/A. Chianci later this session

this is not sufficient for a SASE Machine!
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Bunchlength and CompressionScale Resolve
Structures of 100 fs and less

• Qualitative Optimization of the Compression
• Phase Tuning to maximize the coherent FIR
  Emission from the Beam.
• Emission ? n2 for ?s ? ?
• Use of simple Pyro-Detectors in the FIR

• Quantitative Measurement of Bunch Length
• Use coherent FIR Radiation and Autocorrelation
  Methods.
• Transverse Mode Cavity (integrated Streak Camera)
• Electro-Optical-Sampling
• ? presented in the ACC7 Session from yesterday

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Protection Systems

• SASE LINAC
• Big Welding Machine
• Big X-Ray Tube
• Therefore
• Need very fast Interlocks to avoid Mechanical
  Damage.
• Need continuous Monitoring to minimize Radiation
  Damage.
• Transmission and Loss based Systems
• Thresholds given by most sensitive Component
  (Undulator)
• Fast and Slow Systems
• Reaction Time by Worst Case Events (and Signal
  Travel)

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Slow Loss Monitoring Systems

• TLDs
• TLD crystals located at sensitive regions
  (undulator section)
• Document the Irradiation Profile over long Times
• Data on a weekly Basis
• Optical Fibers used as Dosimeters
• Small Opt Fiber Coils installed close to the
  Undulator Gap
• Transmission Decrease of the Fiber due to
  Radiation Damage
• Allows
• Avoid Operation Modes with medium high losses
• Correlation of Dose Measurement with operation
  Modes
• Reaction Time ? 1h
• Talk by M. Körfer, this session

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Fast Beam Inhibt System
Reaction Time for Fast Channels ? O(?s)

• Modular System made of fast Beam Interlock
  Concentrators (BIC)
• BIC Modules can be cascaded, Input Mask and Event
  Status controlled by PLC
• Interlock Inputs Different Systems using Same
  Interface and Communication Protocol Protection
  Systems, RF, Fast Acting Valves, ....

Talk by M. Staack in the Timing and Controls
Session
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Transmission Based Protection System for TTF II
Pairs of Current Monitors fast acting Interlock
Electronics

• Inhibit Pairs for TTF II
• T1 T9 Whole Machine (FEL Mode)
• T1 T11 Whole Machine (Bypass Mode)
• T2 T6 2nd System for both Modes
• T6 T10 Make sure the beam is send to the beam
  dump

• Used for Beam Inhibit
• Charge Measurement only

Detailed Information Presented in this Session by
M. Jablonka, CEA
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Loss Monitor Systems

• ? 50 Fast Loss Monitors (Photomultipliers) at
  critical Machine Parts
• Used as fast input Channels for the Fast Beam
  Inhibit system

PM Operation Panel of TTF I
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SASE Diagnostics

• Tolerances on Machine Settings are very tight!
• Light Production has to be controlled and
  optimized by the Operator
• Strong Interaction with Photon Diagnostics (Talk
  by R. Treusch)
• Operator needs to keep optimum Performance
• SASE Signal Statistics
• Radiation Spectrum (Pulse Length)
• (few modes only ? high peak power, Operation
  Experience of TTF I)

MCP has been calibrated for different voltage
settings dynamic range 107
Thin lines Single Shot Spectrum Bold Average
over many Shots
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Consequences of Budget Shortage

• Priorities
• Complete Vacuum System for the Maschine
• Start with Commissioning of the Injector
• Get new stuff going with minimized effort
  (e.g.Toroids)
• Reuse TTF I Components (e.g. BPM Electronics,
  Cameras)
• Complete Infrastructure required
• Technical Interlock System (BIS/BIS)
• Do everything that gets more expensive afterwards
  (Tunnel Holes)
• Keep Developments running
• Try to allocate Budget to continue running
  delepoments and prototyping (e.g. BPM
  Electronics, OTR Stations, loss Monitors)
• Still need moderate Budget for these aims