1. Maria ELENA Angoletta for the RF team
RF & longitudinal diagnostics: status, new features, observations & plans
Maria ELENA Angoletta for the RF team
Extended ECC 7 March 2019

2. In ELENA RF workpackage
Outline
RF system
Status and typical operation
New features in 2018
Observations
Longitudinal diagnostics (processing*)
Status, usage & examples
Plans (≥ 2019)
Conclusions
[ * for the hardware: see Wolfgang’s talk after this one]
In ELENA RF workpackage
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

3. 1. RF system: status LLRF HLRF
Implements in frontend all required features.
Some features to be finalised / validated (ex: PAUSE, retrieval of Oasis signals during cycle).
Integration (RF cycle editor) to be completed by ELENA/OP.
LLRF + longitudinal diagnostics racks in ELENA hall, protected by transparent acrylic panels.
HLRF
New amplifier (PSB-style) installed in 2019 to minimise maintenance. No changes from the LLRF view (TBC slightly different transfer function?).
Reduced HLRF max voltage (500 Vp until Nov , 100 Vp after)
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

4. 1. RF system: operation for pbars
Injection/extraction synchro, phase+radial loops, multiple RF segments for ecooling.
Bunched-beam cooling, bunch rotation (settings, not specific features).
Single harmonic operation.
Extracted beam at h = 1, 2 and 4 (top to bottom).
Three RF segments & various harmonics tested.
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

5. 1. RF system: operation for H- ions
Source synchronised to LLRF (no injection synchro enabled in LLRF)
Beam phase + radial loops, extraction synchro
Single harmonic operation.
H- production cycle and extraction to GBAR.
H- MD study cycle
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

6. 2. RF system: new features in 2018
Frequency program: new (numerical) implementation
Frequency program: averaging
Btrain diagnostics
Extraction synchro loop
Wider cavity limits
Reduced maximum voltage in HLRF system (new LLRF-HLRF power chain)
Operation with RF segments
The team finally developed and commissioned more new features than we expected!
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

7. 2a. Frequency program: new implementation
Deployed higher resolution frequency program (before startup 2018) to remove frequency “quantisation” effect due to low magnetic value.
Exported to LEIR + PSB for uniformity approach (no quantisation there)
End of 2017 run
2018 startup
Limited numerical resolution. At low energy frequency program is quantized (~40 Hz)
Sub-HZ resolution over whole Btrain range
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

8. 2b. Frequency program: averaging
Improved-resolution frequency program follows Btrain oscillations → ELENA OP required frequency program “smoothing”.
User-selectable moving average (up to 20 ms) deployed (May 2018).
Validated in MDs but not used operationally (loops seemed enough).
NB: radial loop frequency contribution higher for long averaging!
Freq. program synoptic with moving average
Increased radial loop contribution when averaging. Radial loop frequency in [2700 Hz, Hz] for 12.5 ms averaging; in [1200 Hz, -400 Hz] for no averaging.
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

9. 2c. Btrain diagnostics
Set of diagnostics requested by Btrain experts to evaluate Btrain stability/calibration.
Feature available in frontend in July 2018, integrated in controls infrastructure in October 2018.
Value
Units
Source of value
Btrain from White Rabbit interface
10 nT
DSP B
Frequency contribution from Btrain Hz
Number of particles obtained from LPU signal
Radial position from orbit system mm
DSP C
Frequency contribution from radial loop
Number of particles obtained from TPU signal
Btrain diagnostics published by LLRF in 2018
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

10. 2d. Extraction synchro loop
Deployed in July 2018 (pbars and H-). Includes optimisation features (gain ramp etc) to provide smooth closure and operation.
Beam: several user-selectable beam harmonics possible.
Extraction reference: other harmonics implemented but depends on cabling. We will remain with h=1.
Beam h
Ref h
Comments 1
Operational case for H- operation
Antiprotons operation 2
Operational case for H- operation with 85 kV source before new cavity voltage limits 4
Harmonics used operationally
Example of extraction synchro process
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

11. 2e. Wider cavity limits
Deployed in July 2018 to allow with 85 kV H- source
Smooth voltage change between ranges for cavity loops stability.
Hardcoded. Will be changed to adapt to 100 Vp max HLRF configuration (→ next slide)
Frequency range
[kHz]
Max voltage
[Vp]
120 – 130
Raised linearly from 30 kHz to 65 kHz
130 – 140
Raised linearly from 65 kHz to 100 kHz
140 – 500
100 V
Raised linearly from 100 kHz to 500 kHz
500 V
Outside above ranges
0 V
Wider cavity limits deployed in July 2018
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

12. 2f. Reduced maximum cavity voltage
HLRF configuration + HLRF-LLRF power chain optimised (6/11/2018) to reduce noise injected into beam.
Max voltage in HLRF reduced from 500 Vp to 100 Vp,
Effect not (yet) fully appreciated: we’ll stay at 100 Vp max for now.
ELENA LLRF-HLRF power chain to reduce noise injected to the beam
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

13. 2g. Operation with RF segments
First version of RF segments (same h/phase settings for all segments) in July 2018 → MATLAB script to setup segments-related settings.
Final FESA classes for integration with the RF cycle editor on 2 Nov
FESA classes for different h/phase settings in each RF segment deployed on 9 Nov.
Antiproton cycle with three RF segments and the various harmonics tested.
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

14. 3. RF system: (some) observations
Effect of gap opening on beam
Non sinusoidal gap return for high cavity voltages
Many more observations shown in Davide’s presentation:
hot topic for ELENA’s performance!!
M. E. Angoletta “ELENA LLRF STATUS” ECC 19 July

15. 3a. Effect of gap opening/cavity loops on beam
Gap relay takes ~23 ms to open. Servoloops start as soon as gap opens.
Closed loop: visible effect on the beam depending on delay from gap opening to voltage ramping.
Feedforward control: no effect on the beam
Important: open moment!
→ not self-bunching but result of cavity loops servoing to 0 V induced voltage/noise.
Longitudinal structure visible via Tomoscope and Oasis signals for various opengap timing values.
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

16. 3b. Non-sinusoidal gap return for high voltages
Bunch rotation (August 2018) requires voltage step. Implemented with ~high cavity voltage (100 Vp)
Distortion observed in gap return
Only for high voltages (≥~100 Vp)
For closed loop as well as for feedforward control
Reason not fully understood: power chain, HLRF ampli, other?
Power chain + HLRF amplifier changed in November 2018
→ investigation to be restarted.
Closed loop control of cavity voltage.
Stored traces: 40 V voltage program;
coloured traces: 100 V voltage program.
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

17. Outline RF system Longitudinal diagnostics (processing) Plans (≥ 2019)
Status and typical operation
New features in 2018
Observations
Longitudinal diagnostics (processing)
Status, usage & examples
Plans (≥ 2019)
Conclusions
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March 2019

18. 4. Longitudinal diagnostics: status & usage
In summer 2018 longitudinal diagnostics deployed in LLRF boards.
Bunched beam intensity from one (LPU,TPU) and two (LPU) harmonics.
Intensity with two harmonic measured as for AD (downconverted data).
Bunch length (two harmonics, LPU only).
Same process as for AD, where data is calculated but not available to user.
Intensity + bunch length available as Oasis signals:
Easy correlation in Vscope window with other signals/phenomena
Debunched-beam measurements (intensity, Δp/p from Schottky signals analysis of downconverted LPU signals) not available.
FFT tests done with LLRF Oasis (downconverted) TPU data
USAGE
Intensity meas. extensively used to see efficiency improvements.
Bunch length not used operationally in 2018.
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

19. 4. Longitudinal diagnostics: examples
Antiproton cycle (production)
H- cycle (MD)
First RF segment (from injection into ELENA to first cooling plateau)
Acceleration and deceleration
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

20. 5. Longitudinal diagnostics: observations
Dependence of measurement on beam intensity
Calibration
Team priority for
development/validation/ commissioning
was given to LLRF in 2018 run!
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

21. 5a. Dependence on beam intensity
Intensity estimate: higher for long bunches, lower for short bunches (i.e. with higher peak density).
Dependence visible more on TPU-derived signals than LPU-ones.
Effect disappears for lower beam intensities
Non-linearities (ex: saturation) somewhere in signal DAQ path??
→ Must be understood!!
Voltage changes generate synchrotron oscillations.
Bunch length + height oscillations
Visible more on TPU than on LPU (1 h type) intensity signals
Same as before but radial steering added
Bunch length + height oscillations + radial position oscillations generated
Same oscillations visible on TPU intensity
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

22. 5b. Measurements calibration
Bunch-length calibration: not done.
Intensity calibration: empirical calibration wrt. extracted beam measured in AD extraction line. Optimistic calibration!
Possibly better calibration “from the bottom”, i.e. wrt. TRIC measurement (absolute calibration) in ELENA extraction line.
Other options under evaluation.
NB: intensity points in cycle (AD-style) might be useful (ex: to be put in elogbook).
Intensity measurements summary table for AD
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

23. Outline RF system Longitudinal diagnostics (processing) Plans (≥ 2019)
Status and typical operation
New features in 2018
Observations
Longitudinal diagnostics (processing)
Status, usage & examples
Plans (≥ 2019)
Conclusions
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March 2019

24. Plans: LLRF Re-check with beam various observations from 2018
Re-commission cavity loops with new HLRF ampli. Deploy new cavity limits for 100 Vp operation [aim: 2019*]
Re-commission/operate 2nd harmonic (shaping) loop [aim: 2019*]
Support development of RF cycle editor by ELENA/OP [aim: 2019*]
Validate/finalise additional features, ex:
Longer Oasis timebase (currently 2.5 s/div, longer than for other signals) and Oasis data retrieval during cycle [aim: 2019*]
PAUSE operation (low priority for ELENA?)
Remote control of LLRF programmable amplifiers. H/w + s/w. [aim: 2019, if possible]
* Assuming there is a ELENA ring run in 2019, timings, controls…
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

25. Plans: longitudinal diagnostics
Move data processing to dedicated board (third board in LLRF) [aim: 2019*]
Re-check with beam various observations from 2018
Implement remote control of LPU head ampli [low priority?]
If required and financed [~10 kCHF] deploy ObsBox in ELENA, receiving data from LPU and/or TPU [planned in post-LS2 AD to replace current Schottky/intensity measurement system. → next slide ]
* Assuming there is a ELENA ring run in 2019, timings, controls…
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

26. WP 26: Technical choices (cont’d)
Layout & functionalities for new AD LLRF + intensity/Schottky system
Bunched-beam intensity calculated in time by ObsBox [integration + baseline subtraction]
→ removed dependence on bunch shape.
ObsBox: 128 GB memory on board → can store > 1000s of MHz
Fiber optic data transfer LLRF to ObsBox (also timing events)
FFT FESA classes based on BI ones

27. Conclusions ELENA LLRF frontend implements all functional requests.
Integration to be completed, improvements will be deployed.
Experience useful for post-LS2 AD LLRF (common approach).
ELENA long. diagnostics implemented in LLRF boards.
Will be moved to dedicated board in LLRF crate.
ObsBox could be useful for ELENA (synergy with AD system)
Several points/question marks to be analysed in future runs.
Overall excellent progress & results.
What’s next? We must know requests & machine plans to reserve & plan manpower (busy LS2!)
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March

28. SPARE SLIDES (… because you never know…)
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March 2019

29. ELENA LLRF + long. diag. final layout
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March 2019

30. Bunched beam intensity from 2 LPU harmonics
𝑵 𝑷 =𝒄𝒂𝒍∙ 𝑰 𝟎 𝒇 𝑹𝑬𝑽
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March 2019

31. Loops contribution
Loops contribution for pbar cycle h = 1, 4, 4 (November 9th 2018)
M. E. Angoletta “RF and longitudinal diagnostics” ECC 7 March 2019