Status and R&D program of the CLIC Power Extraction and Transfer - - PowerPoint PPT Presentation

Status and R&D program of the CLIC Power Extraction and Transfer Structure (PETS)

Igor Syratchev for the CLIC team

A fundamental element of the CLIC concept is two-beam acceleration, where RF power is extracted from a high-current and low-energy b d l h l b h h

Drive beam

beam in order to accelerate the low-current main beam to high energy.

Main beam

PETS

Accelerating structures RF power

Drive beam current & energy Extraction efficiency PETS design development chart Drive beam current & energy RF power constrains On/OF capability RF power production needs RF power constrains PETS design RF components Beam transport and stability RF components Module layout and fabrication technology fabrication technology High power High power tests

PETS design

G

C a Q R

2

/

−

=

For the fixed phase advance and iris

m a L L m B a

extr Av

) ) ( (

2 / 1

− × =

/

2 2 2 b

Q R F L I P ω =

G gr

C a V

advance and iris thickness:

n P C C B L n L L

struc G I T struc Av

4 = − × =

1. For the chosen layout (LUNIT ) and the number of PETS per unit, the aperture is uniquely defined. 2. In general the bigger aperture (longer PETS) favors the beam dynamics. 3 The longitudinal slots are mandatory to

4

g b

V F L I P ω =

) ( ) ( a L L n L L

extr T struc

− − × =

3. The longitudinal slots are mandatory to provide transverse HOM damping As a result of multiple compromises, the PETS aperture a/λ = 0.46 (m = 2) was chosen.

I b

C F I =

2 2

ω m n P P

struc ×

=

) (a L m L

extr PETS PETS 135 MW Quad Drive beam

100 A 2.4 GeV 0.24 GeV (0.87 km) Deceleration: ~6MV/m

Accelerating structure x4 135 MW 240 ns Main beam

1.2 A 9 GeV 1500 GeV (21 km) Acceleration: 100 MV/m

P – RF power I – Drive beam current L – Active length of the PETS Fb – single bunch form factor (≈ 1)

PETS cross-section

The PETS are large aperture, high-group velocity and overmoded g g p y periodic structures. In its final configuration, PETS comprises eight octants separated by 2.2 mm eight octants separated by 2.2 mm wide damping slots.

E (135 MW) 56 MV/

The PETS bars

Special matching cell E max (135 MW)=56 MV/m Electric field RF power density H max (135 MW)=0.08 MA/m

One of the eight PETS bar

PETS RF power extractor

Baseline design Damped modification (in progress)

11.424 GHz couplers

20

eters, dB

reflection

Electric field

12 GHz couplers measured face-to-face (blue) and as simulated with HFSS (red)

60 40

S pareme

isolation

30 20 10

rameters, dB

11.5 11.7 11.9 12.1 12.3 12.5

Ferquency, GHz

Magnetic field

11.7 11.8 11.9 12 12.1 12.2 50 40 30

S par Frequency, GHz

In the high group velocity structures, the frequency of the transverse mode is rather close to the operating one (13.0 GHz in our case). The only way to damp it is

HOM damping in PETS

to use its symmetry properties – damping with the slots.

1 .10 4

No slot

GDFIDL Transverse modes spectra HFSS

10 100 1 .10 3

V/A/m/mm (log) With slot No slot

GDFIDL

E-field (color maps) and pointing vectors (arrows):

15 30 45 60 0.1 1 10

Re (Zt) V

12

Frequency, GHz

β β β ω

β ω

⎭ ⎬ ⎫ ⎩ ⎨ ⎧ − − × ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × =

− − ⊥ ⊥

1 ) 1 ( 1 sin 2 ) (

) 1 ( 2

L z e c z K q z W

c Q z

In the presence of the longitudinal slots, the transverse mode field pattern is dramatically distorted. The new, TEM-like nature of the mode significantly

β β − > =

⊥

1 , ) ( L z z W

increases the group velocity, in our case from 0.47c to almost 0.73c. However there is practically no damping in this configuration. To do that we must to introduce the radial impedance gradient in the slot that we must to introduce the radial impedance gradient in the slot - to create the radial component of the pointing vector.

HOM damping in PETS

With the proper choice of the load

Moderate damping (tgδ=0.1) Strong damping (tgδ=0.32)

PETS transverse impedances With the proper choice of the load configuration with respect to the material properties makes it possible to couple the slot mode to a number

• f heavily loaded modes in dielectric
• f heavily loaded modes in dielectric.

This gives a tool to construct the broad wakefields impedance.

Fixed eps=24

eps eps

The material for the load optimization was chosen in 2006! C tl t t f i d t th i ith 1 Th l d t b d t d i ti l Currently, we can not get from industry the ceramic with reproducible properties, however certain suggestions towards absorbing ceramic for the PETS can be done:

tgδ

1. The load geometry can be adopted in every particular case. In general, lowering eps., the load volume will be increased. Making it higher does not really help! It can be recommended to target the eps range between 15 and 25, ith f t ds hi h l s with preference towards higher values. 2. The tgδ of at least 0.3 (and higher) would be the choice. 3. The wide frequency band 9-18 GHz must be addressed.

PETS testing chart RF power sources External RF power source Drive beam

RF high power g p source RF power

• ut

RF power in RF power

• ut

Drive beam

CTF3 (CERN + Collaborations) ASTA (SLAC) CTF3 (CERN + Collaborations) Two beam test stand (CERN + Collaborations)

Objective: to understand the limiting factors for the PETS ultimate performance.

• Access to the very high power levels (300 MW)

and nominal CLIC pulse length.

• High repetition rate – 60 Hz.

Objective: to demonstrate the reliable production of the nominal CLIC RF power level throughout the deceleration of the drive beam.

Test beam line (CERN + Collaborations) Test beam line (CERN + Collaborations)

Objective: to demonstrate the stable, without losses, beam transportation in a presence of the strong (.50%) deceleration.

PETS high power tests at CERN (TBTS)

• Different scenarios of the drive

beam generation in the CTF3

• In order to demonstrate the nominal CLIC power level

DBA CR DL

TBTS

CTF3 CTF2

#1

and pulse length, it was decided to implement a different PETS configuration – PETS with external re-circulation.

V i bl S litt To the Load Round trip efficiency: 75% Round trip delay: 22 ns

<30A

TBTS

CLEX CTF2

#2

Variable Splitter (coupling: 0→1) Variable phase shifter PETS output PETS input

<30A

#3

Drive beam PETS input

14 A

#3

4 A 150 Tc Tp

Expected PETS power production with re-circulation. The calculation followed the measured performance of all the components

• To compensate for the lack of current, the

active TBTS PETS length was significantly increased: from the original 0.215 m to 1 m.

100 150

MW

Pn 0.9 ⋅ Pn p

5.0 A 6.0 A

CLIC nominal

Operation mode #1 #2 #3 CLIC Current, A <30 14 4 101 Pulse length, ns 140 <240 <1200 240 50

Power,

3.5 A 4.0 A 240 ns

Bunch Frequency, GHz 12 12 3 12 PETS power (12 GHz), MW <280 61 5 135 200 400 600 800

Time, ns

CLIC nominal

PETS high power tests at CERN (TBTS)

20 10 0.5

B B

F 40 30 1.5 1

S11 S11 S11, dB S12, dB

11.7 11.8 11.9 12 12.1 12.2 50 2

S12 S12 Frequency, GHz

PETS high power tests at CERN (TBTS)

Number of the standard and new RF waveguide Number of the standard and new RF waveguide components were designed and fabricated to operate the TBTS at a high RF power.

Variable high power RF power splitter 3dB H-plane splitter Variable high power RF power splitter 3dB hybrid Variable high power RF phase shifter Dry stainless steel high power RF load Variable high power RF phase shifter Variable high power RF phase shifter Directional coupler Parts of the dry stainless steel high power RF load

PETS high power tests at CERN (TBTS)

PETS processing history in 2008 Typical waveforms with recirculation PETS processing history in 2008 Typical waveforms with recirculation

model current measurements

15.11.08 14.12.08

PETS high power tests at CERN (TBTS)

… and we can explain how it works!

PETS installed in the ASTA bunker

• 11. 424 GHz PETS measurements after final assembly

Assembly of the eight PETS bars.

10 0.5 0.18 − 11.422 20 1

S11, dB S12, dB

26.5 − 11.25 11.35 11.45 11.55 11.65 11.75 40 30 2 1.5

S11 S12 S11 S12

11.424 GHz PETS ready PETS installed into the ASTA test area at SLAC

Frequency, GHz

PETS processing at ASTA in 2008 … and in 2009

132 ns

Evidences of breakdown

Typical pulse shape

“…At the moment the PETS are running at ~100 MW peak with 133 ns pulse width. The progress is very slow. The reason for the

Traces of breakdown

p g y w. f extremely slow slope is that when a breakdown occurs it is very violent! In some cases it trips the ion pumps and we have to wait for a while to be able to start them

Traces of breakdown

f m

• again. This is not a reasonable way to run or

make progress. Hence the idea is to take the PETS out and to examine it. If we see the reason for this

264 ns

behavior we learned something, if not, we do something, either clean, etch or back them and try again.” Message from Sami Tantawi (11.02.09)

100 Hours

g ( )

In 100 hours, the PETS was processed up to ~ 95 MW x 132 ns (cf. 135 MW and 240 ns in CLIC). For most of the time the processing was limited by heavy out gazing inside the system including PETS.

Where we are?

• 1. At least 100 MW x 132 ns has been reached in

klystron experiments. y p

• 2. The beam driven PETS with power recirculation

has been successfully operated up to 30 MW. I 2009 Next: In 2009…

• 1. The PETS RF high power performance will be

demonstrated (yet we do know the hard limit) demonstrated (yet we do know the hard limit).

• 2. First two beam acceleration in the TBTS.
• 3. The ON/OF prototype RF high power testing.

p yp g p g

PETS ON/OFF Du in m hin p ti n th l tin st u tu nd/ PETS During machine operation the accelerating structure and/or PETS will suffer from the number of RF breakdowns. Currently we have a little information about the actual behavior of Currently we have a little information about the actual behavior of the structures at a very low (by design: <3x10-7 /pulse/meter) breakdown trip rate and so it might be necessary to switch the single structure/PETS OFF and re-process it structure/PETS OFF and re process it. In order to maintain the operation efficiency we want to do the switching OFF very fast – between the pulses (20 msec). switching OFF very fast between the pulses (20 msec).

ON OFF

Active reflector #1. External Load

The ON/OF concepts with

Drive beam RF load

The ON/OF concepts with external active element.

Method# 1 2 3

High power splitter

Minimal # Structure to be switched OFF 1 2 2 The PETS breakdown switching OFF no yes* yes

*

Phase advance 1800 #2. External Recirculation

switching OFF Extra hardware:

• Active reflector (new)**
• Splitter (new)**

C l ⊗ ⊗ ⊗ ⊗ ⊗ ⊗

• Coupler
• Load
• ⊗

⊗

• PETS (OFF) operation:
• Travelling wave

⊗ ⊗

• #3. Internal Recirculation
• Partially standing wave
• ⊗

PETS power production:

• Nominal

Reduced ⊗

• ⊗
• ⊗

Phase advance 1800

• Reduced
• ⊗

⊗

* To be studied/demonstrated!

The PETS response for the single bunch excitation GDFIDL RF bunch

Example: The PETS signal in

HFSS Spectra of the reflector (red) and the PETS coupler (blue) The single bunch response of the system with arbitrary reflection can be now reconstructed:

( )

∑ ∫

∞ −

=

N t j n SB

d e P C R B t A

2

) ( ) ( ) ( ) ( 2 1 ) ( ω ω ω ω ω

ω Example: The PETS signal in the OFF state (180 degrees)

( )

∑ ∫

= ∞ − n 0

2π

Round trip number Bunch Reflector Coupler PETS

~ Ph s

dv nc nd r fl cti n

The multi-bunch response is simply the sum of the single bunch’s ones:

∑

M

~ Phase advance and reflection

∑

=

− − =

m bs SB MB

m t t A t A

1

)) 1 ( ( ) (

Bunch number Bunch spacing

With proposed external controls we can guarantee the strong (< -20 dB) suppression of the RF power the strong ( 20 dB) suppression of the RF power delivery to the accelerating structure.

RF pulse envelopes at the PETS output

Discussion 1 I f th b kd i PETS th

0.5 1

S power

ON Rectangular pulse

1. In a case of the breakdown in PETS the situation is not so obvious. However the RF pulse time structure and 25% saturated power allow to expect the PETS safe b h i Th m st di s d d

2 .10 8 4 .10 8 6 .10 8 8 .10 8 1 .10 7 1 2 .10 7 1 4 .10 7 1 6 .10 7 1 8 .10 7 0.5

PETS

OFF 0.25

• behavior. The more studies are needed.

2. The first analyzes of the PETS behavior during the after breakdown consequent pulse with a quarter power can soon be t st d t SLAC

2 .10 4 .10 6 .10 8 .10 1 .10 1.2 .10 1.4 .10 1.6 .10 1.8 .10

time, sec

tested at SLAC. 3. The relevant RF high power tests will be done in 2009 using TBTS PETS at a time when the external ON/OFF device will be fabricated and tested fabricated and tested.

1

wer

Ramped pulse example. For the beam loading compensation.

0.5

PETS pow

0.25

2 .10 8 4 .10 8 6 .10 8 8 .10 8 1 .10 7 1.2 .10 7 1.4 .10 7 1.6 .10 7 1.8 .10 7

• time. sec

CLIC waveguide network

11.424 GHz choke mode flange prototype To allow the independent transverse alignment of the two linacs in CLIC, the special, contact-free choke mode flanges (CMF) are planned to be used CMF x y

10 F1

Dynamic range for the accepted performance (S11< -45 dB)

X shift: ± 0 25 mm

40 30 20

S11, dB

X – shift: ± 0.25 mm Y – shift: ± 0.5 mm Z – shift: ± 0.5 mm Twist: < 50

11 11.2 11.4 11.6 11.8 50

Frequency, GHz

Twist: < 5