Title: Introduction to the Electron Beam Diagnostic Session
1Introduction 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
2Overview 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
3Challenges 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.
4LINAC - 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.
5... 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
6Areas of Special Interest for Diagnostics
bunch compressors
- Remark TTF has everything, a big Machine also
has, but everything concentrates in a limited
Area !
7Butter and Bread Diagnostics
8T1
- 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
9Butter and Bread Diagnostics
10- 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)
11Butter and Bread Diagnostics
- Charge
- Beam Position
- Transverse Electron Distribution
12Screens
- 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
13Wire-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
14Butter and Bread Diagnostics
- Charge
- Beam Position
- Transverse Electron Distribution
- Dark Current
15Dark 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
16Butter and Bread Diagnostics
- Charge
- Beam Position
- Transverse Electron Distribution
- Dark Current
- Phase
17Phase
- 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)
18Butter 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!
19Bunchlength 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
20Protection 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)
21Slow 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
22Fast 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
23Transmission 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
24Loss 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
25SASE 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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27Consequences 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