XBOX-2 Status and Crab Cavity Testing Ben Woolley G. Burt, A. - - PowerPoint PPT Presentation

XBOX-2 Status and Crab Cavity Testing

Ben Woolley

• G. Burt, A. Dexter, G. Mcmonagle, I. Syratchev, R.

Wegner, W. Wuensch, et. al EuCARD2 WP12 Meeting, CEA Saclay, France April 2014

Overview

• XBOX-2 Progress:

– System Layout & Diagnostics – LLRF tests and results – Installation Progress

• Crab Cavity Testing

– Design – Tuning Results – Cavity Diagnostics

• CLIC Crab Cavity Phase Stability and Synchronisation

– Introduction – Phase Stability Experiment

2

System Layout and diagnostics

LLRF mixing crate D.U.T HPRF PXI Vector Signal Gen.

• Temp. Control

Dark Current PXI Crate

XBOX-2 LLRF

Developments include:

• FPGA demodulation; could

potentially give us a spare channel (4ch+1ref  5ch + internal ref)

• phase feedback control in order to

keep the pulse compressor’s output pulse flat during temperature

• fluctuations. (±1°C tested stable)

XBOX-2 LLRF: Phase Stability

• Phase stability performance has

been measured. Approximately 0.24 degrees of phase jitter between adjacent channels (averaged over 300ns).

• However approximately 2 degrees

with respect to 10MHz reference

• Phase noise spectra indicate that

the main source of this jitter is the 2.9GHz local oscillator compounded by the x4 multipliers.

• A PLL based LO is under

development which will be tested in the coming weeks. 2.9GHz LO 2.4GHz LO 12GHz out 400MHz IF

• Meas. Noise

floor Phase (FPGA) Phase(mix w/ref) Amp (mix w/ref) Ref Amp Ref Phase

Xbox-2 Layout + Progress

• Scandinova Modulator
• Klystron (50MW, 1.5us pulse) For

Crab cavity test: “old” SLAC XL5

• Pulse compressor (250ns, ratio ~3)
• Stainless steel load

Installation Progress

• Safety doors and switches for personal

protection installed

• Electrical protection around the solenoid
• LLRF and diagnostics moved to the
• perating temperature controlled rack.
• Cabling between racks ongoing
• TWT installation and connection
• Access doors and safety chain to the

bunker

• Set-up of ceiling and additional shielding
• Connection of the remaining waveguide

network in the bunker

• Safety files and RP authorization
• Conditioning of the RF network
• Installation of supports, spectrometer

and diagnostics

• Installation of the first structure to be

tested

Klystron Vacuum + Gun Arcs

5kV

• We have decided to move the old

XL5 to the XBOX-2 test stand because it was starting to have many gun arcs.

• It can still produce enough power

(>20MW) to test the crab cavity without pulse compression.

• Gun arcs were possibly caused by a

faulty connection to the gun ion pump (pictured above). This was discovered when moving the klystron from XBOX-1.

Klystron Pulsing

• Managed to increase voltage reference on IGBT switches to 1150 V
• Repitition rate 50 Hz
• Heater current 20 amps
• Pulse width reference on modulator 0.8uS
• “noise” problems on waveform (IGBT switch cable , pulse tx ?)
• Some issues with the modulator (Pulse tuning circuit and interlock system)
• Klystron gun still breakdowns from time to time

1.5µS 343kV 220 Amps µPerveance = 1.1E-6 Pulse 0.8µS; Vkly 343kV

Crab Cavity: Single-feed prototype

Single feed prototype for test:

• RF design done at Lancaster P. Ambattu

and G. Burt.

• Design coordinated by CERN
• Manufacturing of disks at VDL, The

Netherlands

• Tuning at CERN.
• High power test at CERN.

Tuning of the Crab Cavity

11 12.02.2014 Tuning of CLIC Crab Cavity

centring V guiding the wire for bead- pull measurements nitrogen supply input (chosen and marked) tuning pins (4 per cell) temperature sensor cooling block

• utput (marked)

Before tuning

12 12.02.2014 Tuning of CLIC Crab Cavity

11.8 11.9 12 12.1 12.2 12.3 12.4

• 60
• 50
• 40
• 30
• 20
• 10

f / GHz S / dB

• 34.8
• 26.3

11.9922 simulated by Graeme Burt S11 11.96 11.98 12 12.02 12.04

• 60
• 50
• 40
• 30
• 20
• 10

f / GHz S / dB

• 34.8
• 26.3

11.9922 simulated by Graeme Burt S11

input reflection bead-pull @ 11.9922 GHz

1 5 10 0.02 0.04 0.06 0.08 sqrt(abs(S11)) Bead-pulling at 11992.2 MHz, 1 5 10

• 122
• 120
• 118
• 116
• 114

 / cell (DEG)

phase advance between cells cell#

• 0.032
• 0.03
• 0.028
• 0.026
• 0.024
• 0.022
• 0.02
• 0.018
• 0.045
• 0.044
• 0.043
• 0.042
• 0.041
• 0.04
• 0.039
• 0.038
• 0.037

Real(S11) Imag(S11) combined S11 in complex plane 1 2 3 2 4 6 8 10 12

After tuning

13 12.02.2014 Tuning of CLIC Crab Cavity

input reflection bead-pull @ 11.9922 GHz

11.8 12 12.2 12.4 12.6 12.8

• 60
• 50
• 40
• 30
• 20
• 10

f / GHz S / dB

• 34.8
• 37.9

11.9922 simulated by Graeme Burt S11 11.96 11.98 12 12.02 12.04

• 60
• 50
• 40
• 30
• 20
• 10

f / GHz S / dB

• 34.8
• 37.9

11.9922 simulated by Graeme Burt S11

1 5 10 0.02 0.04 0.06 0.08 sqrt(abs(S11)) Bead-pulling at 11992.2 MHz, 1 5 10

• 120
• 119
• 118

 / cell (DEG)

phase advance between cells cell#

• 4
• 2

2 4 6 8 x 10

• 3
• 0.018
• 0.016
• 0.014
• 0.012
• 0.01

Real(S11) Imag(S11) combined S11 in complex plane 1 2 3 2 4 6 8 10 12

Crab Cavity Diagnostics

Crab Cavity RF Load

Incident Power Reflected Power Transmitted Power Ion gauge readout Ion gauge readout 60 dB directional coupler Upstream Faraday cup signal Downstream Faraday cup signal RF In From Pulse Compressor WR90 Waveguide Input coupler Output coupler Beam-pipe Beam-pipe

Dipole Magnet

Collimator Readout Screen Uppsala Dark Current Spectrometer

• Single feed structure requires a

different feed to the accelerating structures.

• We can take advantage of extra

diagnostics with the Uppsala dark current spectrometer.

CLIC Crab Cavity Synchronisation

Cavity to Cavity Phase synchronisation requirement

degrees 1 S 1 c f 720

4 rms c x

   

Target max. luminosity loss fraction S f (GHz) x (nm) c (rads) rms (deg) t (fs) Pulse Length (ms) 0.98 12.0 45 0.020 0.0188 4.4 0.156

So need RF path lengths identical to better than c t = 1.3 microns over 35 m

RF path length measurement

Cavity Cavity Coupler 0dB or -40dB reflection Cavity Phase shifter Phase shifter RF Phase Measurement System & control

Magic Tee

48 MW 11.994GHz Klystron 200 ns 50 Hz rep. 4 kW 11.8GHz Klystron 5 μs pulse 5 kHz rep. Cavity Coupler 0dB or -40dB reflection Lossy Waveguide (-3dB) Lossy Waveguide (-3dB) Main pulse reflection 600 W

• 30 dB

coupler Power Meter Power Meter

Power Meter

12 MW

• 30 dB

coupler Power Meter Measurement pulse return 500W

• 30 dB

coupler

Waveguide phase stability test

11.94 GHz 11.992 GHz

Magic Tee

gas valve

C

S 

C 2 m waveguide sections

Moveable Short

H bend H bend H bend H bend H bend H bend

gas valve gas valve

Power detector

gas valve +23 dBm

• 10 dBm

+23 dBm

• 10 dBm

C C 10 dB 10 dB

Variable Attenuator Diode Switch Diode Switch Power detector Power detector Power detector Moveable Short Variable Attenuator

C C 20 dB 20 dB

p s s s s p p p p s s s s p p p p s s s p s p s p s p s p s p s s p s p s p s p s p s p s p s p s p s p s p s p s p s p p p s p

p = plane s = groove seal 2 m waveguide sections

• 1. Establish limit of resolution of

phase measurements for different pulse lengths

• 2. Investigate different mixers
• 3. Investigate ability to calibrate

phase measurements

• 4. Implement a piezoelectric

controller on the moveable short to stabilize waveguide

• 5. Study temperature and vibration

perturbations on waveguide

• 6. Investigate whether stabilization

at one frequency can equalize waveguide lengths for other frequency

Aims:

Phase Stability Test: Control

• 1. PXI based system has been

purchased with 4ch high resolution 16-bit ADC.

• 2. Also included is a 2ch 16-bit DAC

to control piezoelectric actuators which will vary the path length using the movable shorts in order to stabilize the RF path length.

• 3. Currently performing market

survey for piezoelectric actuators.

Future Developments

• Continue with the

commissioning of XBOX-2.

• Test the Crab Cavity up to

nominal gradient.

• Push the gradient to investigate

effect of dipole field on BDR.

• Continue preparation for the

waveguide stability experiment

• Develop and refine phase

measurement electronics

• Write and test feedback

algorithms for phase stabilisation

19

Thank You

Extra Slides

Future LLRF Generation and Acquisition for X-band test stands

IF 2.4 GHz Oscillator

9.6 GHz BPF Amp Vector Modulator RFout LOin LOout 12GHz vector modulated signal to DUT

2.9 GHz Oscillator

X4 freq.

RF LO LO IF RF

12 GHz BPF 12 GHz BPF 12GHz CW reference signal 2.4GHz vector modulated signal 2.4GHz CW reference signal 11.6 GHz BPF X4 freq.

LO IF RF Input 1

400 MHz LPFs

LO IF RF Input 2 LO IF RF Input 3 LO IF RF_Referance

12GHz CW reference signal 3dB hybrid Amp

IF Amps

Oscillators should be phase locked

1.6 GSPS 12-bit ADCs Digital IQ demodulation

Future Developments: XBOX-2

LLRF Board Fully Tested PXI hardware purchased and Software partially completed Functional plan completed CPI-XL5 tube fully conditioned at SLAC

LLRF Hardware Layout

• Fast phase measurements during the pulse (20-30 ns).
• Full scale linear phase measurements to centre mixers and for calibration.
• High accuracy differential phase measurements of RF path length difference (5 μs, 5 kHz).
• DSP control of phase shifters.

Linear Phase Detector DSP ADC ADC

Magic Tee

To Cavity To Cavity

Wilkinson splitters

• 30 dB

coupler DBM DBM DBM 10.7GHz Oscillator

• 30 dB

coupler Mechanical phase shifter for initial setup + calibration Fast piezoelectric phase shifter

DAC 1 Amp + LPF LP F Amp Power Meter To DSP DAC 2 From DAC2 To Mech. Phase Shifter Calibration Stage

LLRF Hardware Layout

• Fast phase measurements during the pulse (20-30 ns).
• Full scale linear phase measurements to centre mixers and for calibration.
• High accuracy differential phase measurements of RF path length difference (5 μs, 5 kHz).
• DSP control of phase shifters.

PLL controller MCU 10.7 GHz VCO Digital phase detector DBMs Power Meters Wilkinson splitter Inputs

Future Developments: XBOX-3

• 4 turn-key 6 MW, 11.9942 GHz, 400Hz power stations

(klystron/modulator) have been ordered from industry.

• The first unit is scheduled to arrive at CERN in October
• 2014. The full delivery will be completed before July

2015.

Online automatic adjustment of the compressed pulse (arbitrary) shape.

Summary

• TD26CC structure is conditioned up to 103MV/m for required

CLIC pulse shape and BDR.

• Gun arcs in the klystron have slowed progress.
• Work and planning to greatly expand our testing capability is

well underway.

Thank you for your attention!

Pulse to pulse phase error: XL5

• 50 consecutive pulses were recorded and the

RMS phase error point for point calculated.

• Measurable error at start of sample but reaches

the measurement noise floor (ADC noise) after 200ns.

Measurement noise floor ~0.75°

Expected Klystron Stability

• From kinematic model of klystron, phase and

amplitude stability depend on gun voltage, V:

• For the Scandinova modulator with measured

voltage stability of 10-4 phase and amplitude stability should be 0.12° and 0.013%.

• Observed error at start of pulse could be from TWT
• r LLRF: Fast phase shifter, voltage tuned attenuator,

diode switch pre-amplification, etc. -> Further investigation needed.

Klystron Vacuum + Gun Arcs

Klystron Vacuum + Gun Arcs