DESY / 07.03.2005Hans Weise TTF / VUV-FEL Status and Some Words of Fast Kickers Hans Weise / DESY DESY meeting with KEK ILC Delegation (March 7th 2005)

DESY / 07.03.2005Hans Weise

TTF / VUV-FEL Status

and

Some Words of Fast KickersHans Weise / DESY

DESY meeting with KEK ILC Delegation (March 7th 2005)


RF gun

FEL experimental

area

bypass

4 MeV 150 MeV 450 MeV 1000 MeV

undulatorscollimator

bunch compressorLaser

bunch compressor

accelerator modules

TESLA Test Facility Linac – Phase IIFEL User Facility in the nm Wavelength Range

(VUV) and R&D for the ILC


TTF / VUV-FEL Status as of January 13th, 2005

The VUV-FEL Set-up:

• installation completed until end of 2004

• includes RF gunfive accelerator modulestwo bunch compressorselectron beam collimationelectron and photon beam diagnosticsundulator section

• still missing are

• the 3.9 GHz rf system at the end of the first accelerator module (needed for short wavelength FEL operation, scheduled for 2006)

• some electron beam diagnostics, esp. beam position monitors

• sixth accelerator module to increase the electron beam energy to 1 GeV

• the photon beam transport to the user‘s experimental hall

• the user‘s photon beam lines (to be commissioned until 5/2005)


Electron beam commissioning done with single bunches per bunch train

Measured beam emittance (90%) at 120 MeV (BC2 section) is 1.3 pi mm mrad in both planes without compression at 0.5 nC; compression slightly decreases beam quality (as expected) but the beam quality seems to be good enough for lasing at 30 nm; shorter wavelengths need 3.9 GHz system in order to keep the emittance small.

Chosen beam energy is 450 MeV, thus corresponding to 30 nm

First spontaneous spectrum was taken in 12/2004

At present beam based alignment is used to find the correct electron beam orbit inside the undulator, i.e. first lasing should happen soon.

VUV-FEL Status as of January 13th, 2005


VUV-FEL Status as of January 14th, 2005 • We now have six weeks of SASE operation

• Photon pulse energy increased to typ. 5 µJ (a factor 2 below saturation)

• Photon beam parameters measured with excellent agreement to theoretical predictions

• Stable FEL operation over typ. 15 minutes; then slight tuning necessary

• 90% emittance of compressed bunches approx. 1.6 mm mrad in both planes

• some control loops established in order to stabilize SASE

• still some trouble with the beam orbit inside the undulator

First lasing established on January 14th!!!

average bunch charge 0.6 nC first accel.module ACC1 approx 6 deg off-crest electron beam energy at BC2 set for 125 MeV accel.modules ACC2/3 on-crest (within 1-2 degrees) accel.

BC3 (bunch compressor) on with currents set for 380 MeV beam energy in undulator 450 MeV undulator optic: FOFO and all undulator correctors off, quadrupole movers have not been activated.

FEL gain: 1E5 (saturation would correspond to 1E7) Photon pulse energy ~1 micro-Joule Photons per pulse 5E11

photons/sec*mm2*mrad2*0.1BW

At present some shut-down activities

• connect undulator beamline with user‘s photon beam lines

• modify interlock system

Restart on March 21st.


RF gun

FEL experimental

area

bypass

4 MeV 150 MeV 450 MeV 1000 MeV

undulatorscollimator

bunch compressorLaser

bunch compressor

accelerator modules

accelerator modules undulator section

VUV-FEL Setup / Overall Layout


The goals for the XFEL:

charge 1nC

x,y 1.4 µm

z ~ 20 µm (80 fs)

E, uncorr < 2.5 MeV

At TTF and PITZ (DESY) we are already close to these parameters.

TTF / VUV-FEL as Prototype for the XFEL Injector

σz = 2.0 mm 112 µm 22 µm RF Gun s.c. Acc.3rd harm.Structure

s.c. Booster Linac Bunch Compressor Main Linac

100 MeV 500 MeV


The TTF2 Tunnel installation basically follows the old TESLA design…

With all its advantages and disadvantages.

TTF2 / VUV-FEL Tunnel Layout


TTF2 Installation / Warm Beam Line Sections


Accelerator is housed in a 5.2 m diameter tunnel ~ 15 - 30 m underground.

Klystrons in tunnel are connected to modulators in an external hall by 10kV pulse cables.

Preferred installation concept is suspension from tunnel ceiling

RF pulse cable

accelerator module

klystron

XFEL Linac Tunnel Layout


De-rated 10MW MBK

Bouncer-type

modulator

var. Q_ext with

adjustable coupler

and/or waveguide tuner

12m TTF-like acc. modules

eight 9-cell Nb cavities at 2K,

Q0=1010

5 MW RF

source

Acc 1 Acc 2 Acc 3 Acc 4

RF Unit of the XFEL (32 cavities)


Mechanical tuner (frequency adj.)

DA

C

DA

C

ADC

ADC

LowLevel

RF System

vector sum

vector demodulator

pickup signal

MBK Klystron

vector modulator

cavity #1 cavity #8

coaxial coupler

circulator

stub tuner (phase & Qext)

accelerator module 1 of 2

RF Operation of s.c. Cavities

TTF RF Unit1 klystron for 2 accelerating

modules8 nine-cell cavities each


Cavity quench detection algorithms and exeption handling procedures analyze the probe signals...

1st quench: Cavity 2 Eacc=19 MV/m

2nd quench: Cavity 6 Eacc=21 MV/m

3rd quench: Cavity 1 Eacc=24 MV/m

Stable Module #1* operation with slowly but steadily increased gradient

RF Operation of Accelerator ModulesAbove its Performance Limit (e.g. Module 1*)


RF Operation of Accelerator ModulesAbove its Performance Limit (e.g. Module 1*)

The maximum operating gradient of s.c. cavities

• is set by cavity quench, field emission, or Q-degradation – not by structure breakdown

• is not a hard limit. A too high gradient results in increased cryogenic load, radiation, and dark current

• does not trip off cavities in ns but in typ. 100 µs if cavities are operated at the threshold

An exception handler as part of the LLRF can avoid quenches.

• Action can be taken prior to the next pulse.

• Consequences for the machine safety are very positive, i.e. correctly injected bunches will not be lost in the linac.

In a high gradient long pulse run in spring 2002, an accelerator module was operated with stable beam (5 mA, 800 µs) close to its gradient limit.

The acc. module was operated with a typ. module on-time of 90% at increasing gradients: 39 days at 19.5 MV/m, 800 µs, 5 Hz 4 days at 20.0 MV/m, 800 µs, 1 Hz 1 Hz operation due to beam oper. 6 days at 21.5 MV/m, 800 µs, 1 Hz laser + gun were limited


TTF Cavities above 25 MV/m Gradient

0

5

10

15

20

25

30

35

40

0 500 1000 1500 2000 2500

t [ms]

Ea

cc[M

V/m

]

10 out of 16 cavities in modules ACC4 / ACC5 can be operated flat top at approx. 29 MV/m

Cav.5 @ ACC1 was electropolished and reaches 35 MV/m flat top after module installation


Dark Current MeasurementThe on-axis dark current was measured for modules ACC4 / ACC5.

Only one cavity in module ACC5 produced a mentionable dark current.

• captured dark current could be measured at the exit of ACC5

• there was no d.c. from this cavity at the entrance of ACC4

• the d.c. decreased as a function of time

after module commissioning (August 2003) 100 nA at 16 MV/m increasing by a

factor 10 for each 4.4 MV/m gradient stepi.e. approx. 10 µA at 25 MV/m

May 4th 100 nA at 20 MV/m increasing by a factor 10 for each 3.7 MV/m gradient step, i.e. 1.2 µA at 25 MV/m

September 22ndafter a few weeks on-time at 20 – 25 MV/m250 nA at 25 MV/m

• detuning of cavity no. 6 left over an integrated dark current of the order of 20 to 25 nA at 25 MV/m average gradient

Reminder:

The TESLA limit is defined by additional cryogenic losses:

The captured d.c. has to stay below 50 nA per cavity. (see TESLA Report 2003-10).

Dark Current vs. RF phase with respect to neighbouring cavities is just as expected

(max min) over pi/2


1st beam (bypass)

• re-commissioning of gun + injector

• setup cavity phases ACC2-5 beam energy

• setup bunch compression

• setup beam linear optics, optimize orbit

• commissioning of diagnostics

• re-commissioning of gun + injector• setup cavity phases ACC2-5 beam energy• setup bunch compression• setup beam linear optics, optimize orbit• commissioning of diagnostics

done

done

done

on-going

on-going

First measurement before adjustment

after adjustment

TTF2 / VUV-FEL Beam Commissioning


FEL 30 nm 1 bunch

• setup collimation

• emittance measurements and optics matching

• beam-based alignment in undulator section

• commiss. of photon diag. with spon. emission

Beam

wirescanner

quadrupole

beam

Ion pump

stretched wire position

control system

granite baseplate

A. Fateev et al., Dubna

MCP Diagn.



Saturation & 6-100 nm

• commissioning of FEL diagnostics

• study of FEL beam, compression schemes, etc.

• establish reproducible settings, etc.

FEL hall PETRA tunnel

beam dump

gas absorber photon diagnosticsphoton

diagnostics

LINAC tunnel



Long time operation of all 5 acc. Modules.

VUV-FEL Commissioning.

First lasing achieved.

Stable operation / saturation spring 2005.

Start user operation in spring 2005

TTF2 / VUV-FEL Outlook

Accelerator Module ACC6 with electro-polished cavities should first be tested in a separate test stand. Schedule: a.s.a.p., but not before end of 2005.

1.0E+09

1.0E+10

1.0E+11

0 10 20 30 40

AC70 AC72

AC73 AC78

AC76

Electro-polished Cavities Measured in Vertical Test

Accelerating Gradient (MV/m)

Un

load

ed Q

ual

ity

Fac

tor

109

101

0

101

1

0 10 20 30 40


VUV-FEL Program for 2005

The 2005 operation time is divided in different blocks. Under the assumption of no unexpected shut downs, all requests can be full-filled.

Some reserve is within the individual operation periods.


The actually used pulser ready for the connection to a fast kicker or the ATF kicker

A Fast Pulser for a Fast ATF Kicker

Frank Obier & (Hans Weise)


Test kicker (stripline in vacuum); matching not optimized

1.5 m cable RG213 between pulser and kicker

• reflection at both stripline ends (right plot)

• and some ringing as a consequence of the reflection (left plot)

Stripline used for pulser tests



Schalter HTS 80-12UF ton=10ns

10 ns switch 6.5 kV 70 A

All pictures show the same signal but have different scaling in order to look at ripple and ringing.

The 10 ns Switch



Schalter HTS 80-12UF ton=10ns

40ns

6,8‰

3,7 %

Same pulse, different scaling (zoom)

Picture shows ringing at almost acceptable amplitude.

Ringing at the end of the pulse.



Schalter HTS 80-12UF ton=10nsAnd now a ceramic kicker…


Documents

DESY / 07.03.2005Hans Weise TTF / VUV-FEL Status and Some Words of Fast Kickers Hans Weise / DESY DESY meeting with KEK ILC Delegation (March 7th 2005)