tesla test facility ttf ii review meeting, salzau, january 2003 introduction to the electron beam...

TESLA Test Facility

TTF II Review Meeting, Salzau, January 2003

Introduction to the Electron Beam Diagnostic Session

Dirk Nölle DESY, MPY

[email protected]

TESLA Test Facility

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

TESLA Test Facility

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.

TESLA Test Facility

... 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?

Longitudinal Charge Distribution measured at TTF I

Lasing Fraction

TESLA Test Facility

Areas of Special Interest for Diagnostics

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

bunch compressors

dump

Las

er superconducting cavities

rf-gun FELbeam

undulatorcollimator

TESLA Test Facility

„Butter and Bread Diagnostics“

• Charge

TESLA Test Facility

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

• Need to Measure – Charge – Charge Distribution of the

Bunches in the Beam Pulse– Transmission along the

Machine

T1 T8T2, T3 T4,T5 T6, T7 T9

T10

TESLA Test Facility


• Charge

• Beam Position

TESLA Test Facility

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. < 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)

Electron Beam

TESLA Test Facility


• Charge

• Beam Position

• Transverse Electron Distribution

TESLA Test Facility

• 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

Screens

TESLA Test Facility

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)

e-

OTR

WS

OTR/Wirescanner Chamber

TESLA Test Facility


• Charge

• Beam Position


• Dark Current

TESLA Test Facility

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

TESLA Test Facility


• Charge

• Beam Position


• Dark Current

• Phase

TESLA Test Facility

Phase

• 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)

Ring Electrode installed in a „Thick Flange“– Broadband, Position

independent Signal– One installed after the Gun,

each magnetic Chicane (BCs and Collimator)

TESLA Test Facility


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

… this is not sufficient for a SASE Machine!

More detailed Information provided

•by M. Wendt •and K.Honkavaara/A. Chianci later this session

TESLA Test Facility

Bunchlength and Compression:Scale: 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

TESLA Test Facility

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)

TESLA Test Facility

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 1hTalk by M. Körfer, this session

TESLA Test Facility

SubBeam InterlockConcentrator n

MainBeam InterlockConcentrator

SubBeam InterlockConcentrator II

SubBeam InterlockConcentrator

III

............................

............................

Machine InhibitInput

(Laser)

InhibitDetectionChannel








SubBeam InterlockConcentrator I

SubBeam InterlockConcentrator n


Beam Inihibit System(BIS)- Software System on a PLC- Control of Operation Modes- Control of distibuted local Interlocks

ProgramInterlockMasks

and ReadStatus

of the BICs

Stop MachineOperation or

SwitchOperation

Mode in Caseof Event

Fast Beam Inhibt System

• 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, ....

Reaction Time for Fast Channels: O(s)

Talk by M. Staack in the „Timing and Controls“ Session

TESLA Test Facility

Transmission Based Protection System for TTF II

•Used for Beam Inhibit•Charge Measurement only

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

Pairs of Current Monitors + fast acting Interlock Electronics

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

Las

er

T1 T8T2,T3 T4,T5 T6, T7 T9

T10

TESLA Test Facility

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

TESLA Test Facility

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 detector

MCP detector

Gold wire250 µm

SiC mirror

SASE radiation

U

MCP has been calibrated fordifferent voltage settings dynamic range: 107 Thin lines: Single Shot Spectrum

Bold: Average over many Shots

TESLA Test Facility

TESLA Test Facility

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

tesla test facility ttf ii review meeting, salzau, january 2003 introduction to the electron beam...

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