Structure and rf processingprogress in Xbox 1

Jan Kovermann

Gallery

Bunker

Layout of the CERN x-band test stand (X-box 1)

Clockwise from top-left:• Modulator• Pulse compressor• DUT + connections• Accelerating structure

Burning questions addressed in this presentation

- Overall system status ?

- Weak points of the system?

- How is the structure doing?

- Ready for a ‘real’ test?

Overall system status

RUNNING

Overall system status

Taking data(looks like we have a test stand!)

Weak points of the system

- LLRF jitter (to be resolved by replacing a pin diode driver, will also need to check TWT stability)

- DAQ and operations software (small) issues

- Overall calibration and dynamic range adjustments of the fast IQ DAQ system (needs support from LLRF group)

- Make the pulse compressor work reliably

What is wrong with the pulse compressor?

- Very instable thermal equilibrium and high Q-factor together with unequal cavities makes it difficult to operate:

Thermal transient (rf ramping time) after each breakdown detunes the compressor Normal pulse before breakdown:

What is wrong with the pulse compressor?

Pulse after breakdown:Next breakdown follows quickly due to increased peak power at the beginning of the pulsed

caused by the temperature detuning of the pulse compressor

What is wrong with the pulse compressor?

32.4

32.6

32.8

33

33.2

33.4

33.6

33.8

34

34.2

34.4

Tem

pera

ture

[deg

C]

Result:The structure sees increasing peak power at the beginning of the pulse the BDR is

drastically increased The pulse compressor gets less average power due to frequent BDs The pulse compressor detunes even more Reflected power interlocks trigger and switches

the system off

What is wrong with the pulse compressor?

Vacuum history of BD cluster

Power/DC history of BD cluster

What is wrong with the pulse compressor?

Possible solutions:

- Carrier frequency tuning to flatten the pulse (implemented, but BDs seem to be far more likely to reoccur when at different frequency)

- Active mechanical tuning of piston tuners (dangerous, small movements create high reflection, algorithm still unclear, behavior far from expected)

- Active gain control resp. peak power limiting software (seems to be a reasonable approach, works when done manually)

AGC software will be implemented in the next weeks

- Last solution: Change the pulse compressor (new one ready for installation beginning of 2013)

T24 structure status

Now conditioning at 170ns flat top, 50Hz, max. gradient ~83MV/m at pulse compressor compatible BDR

Since 6th of November: 19Mps (~100 50Hz*hrs), 500BDs, 1PC BD

80MV/m, 2.5E-6

75MV/m, 2.8E-7

T24 structure status

Same plot in real time, reliability and stability needs improvement…Most important: Power stabilizing feedback and PC stability

T24 structure status

First points for the statistics

70 72 74 76 78 80 82 84

1.0E-07

1.0E-06

1.0E-05

f(x) = 2.35882915483332E-50 x^23.0112808327731

CERN T24 170ns

Series1

Power (Series1)

Gradient [MV/m]

BDR

per s

truc

ture

[1/s

]

Structure total ~250hThis plot: 44h @ 50Hz

+ 2.

4Mp

3.6Mp

+1.95Mp

T24 structure status

First points for the statistics (in another plot…)

70

T24 structure statusBut it is not that bad:

51ns 91ns 132ns

51ns 91ns 132ns

Note: Most of ACC-BD were not taken. Those are included in FC-UP events shown in green dots.

132ns

51ns

91ns

TD24R05 initial processing (KEK)

Ready for a ‘real’ test?

YES! But only after the implementation of several feedback

systems and LLRF improvements. Pulse compressor will limit

conditioning speed to less than 10E-5/p BDR…

New pulse compressor then?

Preliminary data analysis

A preliminary analysis of MKX data done by Wilfrid, thanks a lot for this!

Time jitter on fast RF pulses

High data rate signals (1 ns/sample) are affected by a strong jitter (few 100s of ns)

But not the slow data rate signals (4 ns/sample)

Examples of RF signals with BD

• Rather good signals: RF input stable, edges well defined, Input-Transmitted delay = 66 ns• BD burst visible on the FCUs• But different shapes between slow and fast digitizer

Other examples

• Early BD, sometime even before the compressed pulse, generate a large perturbation on the Input RF pulse (klystron, compressor ?)

• FCUs signals last very long (500 ns) and arrive late (ions ?)

Histogram of Ref-Out edges delta time

• Time difference between Reflected rising edge and Transmitted falling edge shows that BDs mainly occur in the first half part of the structure.

• Both “fast” and “slow” signals give consistent results (statistically)

Same analysis on data from 13 November

• 40 BDs events during 22 minutes

Comparison MKX / TBTS signals

MKX signals TBTS signals

• Up to now TBTS produces higher power (MKS still in conditioning)• Time shape are quite different• Both stands show a feedback effect of reflected power to the incident one

Some phase results

• Phases shown during 10 ns after the signal peak for all 40 BDs• Rather stable in Input, more or less in Transmission, drift in Reflection

Preliminary data analysis

Data quality seems to be ok, but recalibration is needed. We also need

to find the source of the rf power jitter and compensate the slow power

drift.