Electron energy stabilityElectron energy stability(observations after the HV regulation repairs)(observations after the HV regulation repairs)

Recycler MeetingApril 30, 2008

A. Shemyakin

2

IntroductionIntroduction

In 2008, HV stability – related issues were the main reason for a downtime Jan 19-20 – shutdown to repair HV regulation circuitry in the

terminal Apr 2-3 – shutdown to repair broken HV readbacks in the terminal Apr 10-12- shutdown to repair GVM (bearing replacement)

Right now there are no known with HV regulation problems However, we need to keep adjusting time to time the energy

manually to provide optimum cooling This report is based on data from high-dispersion BPMs I looked at several sets of data showing various aspects of

the energy stability Long run with the e-beam on axis on 12-Apr-08 15 and 24 April, when temperatures were changing April 29: snapshots of 720 Hz BPM signals

3

Energy reconstruction from dispersive BPMsEnergy reconstruction from dispersive BPMs

Beam position in return line Y-BPMs as a function of GVMVLT 12-Apr-08 MI was not ramping 0.1A

Y-BPMs in the return line can be used for the purpose of energy tracking Generally, the problem is

sensitivity of beam position to MI ramps

-6

-5

-4

-3

-2

-1

0

1

2

3

4.278 4.28 4.282 4.284 4.286 4.288

GVM, MV

BP

M,

mm

R:BYR01S R:BYR03S R:BYR04S R:BYR05S

Linear fit, mm/MVR:BYR01S R:BYR03S R:BYR04S R:BYR05S

325 -271 -644 -448

4

Long run on 12-Apr-2008Long run on 12-Apr-2008

E-beam was left running on axis for 13 hrs MI was off, no pbars Software HV regulation

loop was off as well R:GVMVLT and return

line dispersive BPMs were recorded from D44 Initial values were

subtracted BPM mm values were

converted to energy using coefficients from the previous slide

In plots below, R:BYR0# refers to a such value, in keV

GVM reading is much more stable than the energy calculated by BPMs

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

0 1 2 3 4 5 6 7

Time, hr

dE

(b

y R

01),

keV

-5

-4

-3

-2

-1

0

1

2

3

4

5

dG

VM

, kV

R:BYR01S R:GVMVLT

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

6 8 10 12 14

Time, hr

dE

(b

y R

01),

keV

-5

-4

-3

-2

-1

0

1

2

3

4

5

dG

VM

, kV

R:BYR01S R:GVMVLT

5

Long run details: response to a corona currentLong run details: response to a corona current

There were 3 nearly identical events when both GVM and BPM-restored energy moved at the same time Most likely, those are response to an increased corona currents

• Happen time to time, more frequently after opening the tank

• Usually are mitigated by software regulation loop

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

0 1 2 3 4 5 6 7

Time, hr

dE

(b

y R

01),

keV

-5

-4

-3

-2

-1

0

1

2

3

4

5

dG

VM

, kV

R:BYR01S R:GVMVLT

-4

-3

-2

-1

0

2.2 2.25 2.3 2.35 2.4

Time, hr

dE

(b

y R

01),

keV

-2

-1

0

1

2

dG

VM

, kV

R:BYR01S R:GVMVLT

3 min

6

Long run details: energy fluctuations in a quiet periodLong run details: energy fluctuations in a quiet period

In a “quiet” state, BPM signals are highly

correlatedno correlation with GVM

• GVM scatter probably represents primarily ADC noise

• It is not clear what goes into the HV regulation circuitry

HV noise is ~100V rms (0.001 - 1 Hz)

Main component of energy scatter is a slow (hours) drift

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-8

-7

-6

-5

-4

-3

-2

-1

0

1

0 1 2 3 4 5 6 7

Time, hr

dE

(b

y R

01),

keV

-5

-4

-3

-2

-1

0

1

2

3

4

5

dG

VM

, kV

R:BYR01S R:GVMVLT

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0 0.005 0.01 0.015 0.02

Time, hr

dE

, k

eV

-3

-2

-1

0

dG

VM

, k

V

R:BYR01S R:BYR03S R:BYR04S

R:BYR05S R:GVMVLT

Standard deviation, keVInterval R:BYR01S R:BYR03S R:BYR04S R:BYR05S R:GVMVLTAll points 0.243 0.266 0.241 0.253 0.2221-2 hrs 0.097 0.103 0.095 0.098 0.1970.68-0.97 0.087 0.090 0.086 0.100 0.199

Correlation between parameters and BYR01SR:BYR03S R:BYR04S R:BYR05S R:GVMVLT

0.898 0.997 0.961 0.047

Quiet periodStDev of (R:BYR01S-R:BYR04S)

0.017 keV

7

Long run details: energy jumpsLong run details: energy jumps

There was one 8-keV jump and many (~10 per hour) ~1-keV jumpsNo corresponded response on GVM

• Therefore, GVM is to blame for generating them

2-3 sec length• Different from what was caused by

broken GVM bearings (several minutes-long fluctuations)

Should not affect operation noticeably

R:BYR01S

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-8

-6

-4

-2

0

2

0.5 0.7 0.9 1.1

Time, hr

dE

, ke

V

-10

-8

-6

-4

-2

0

2

0.51 0.512 0.514 0.516 0.518 0.52

Time, hr

dE

, ke

V

R:BYR01S R:BYR03S R:BYR04S

R:BYR05S R:GVMVLT

-1

-0.5

0

0.5

0.67 0.672 0.674 0.676 0.678

Time, hr

dE

, ke

V

-1.5

-1

-0.5

0

R:BYR01S R:BYR03S R:BYR04S R:BYR05S R:GVMVLT

8

Energy deviation parameterEnergy deviation parameter

To track the energy deviation with BPMs in a high-dispersion region, a new ACNET parameter R:DENRGY was created

Calibrated in keV of electron energy Takes into account the e-beam position in the cooling section

The parameter shows the energy deviation from a nominal if Trajectory upstream the 180-deg bend is stable The magnetic field in the 180-deg bend is stable

• This is questionable, because NMRs do not work in the magnet• coil currents are stable, but the magnetic field still may drift (temperature,

stray fields, radiation…)• Kermit hopes to have new amplifiers and sensors in a couple of weeks

The parameter seems to work in hours - scale It is difficult to use other Y-BPMs in the return line for energy

tracking The problem is sensitivity of beam position to MI ramps Attempts to sum them with “good”coefficients to subtract effect of MI

ramp were unsuccessful• Time dependence of various BPMs seem to be different

]7.00084.001[32.0][ SBYCABYRkeVDENRGY

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Energy dependence on the Pelletron temperatureEnergy dependence on the Pelletron temperature

The energy changes by several keV after turning the Pelletron on ~0.5 keV/C, but not linear with any of temperatures (at start, DENRGY

changes faster)• Thermal expansion should ive ~30 V/C• Mechanical motion of the column?

1 keV

2 C

3hr

GVM

SF6 temperature

Tank temperature

MI-31 temperature

Energy deviation

10

Energy dependence on air temperatureEnergy dependence on air temperature

When temperatures are close to an equilibrium, energy oscillates with the frequency of MI-31 air temperature (~0.3 keV/C) but out of phase Can it be electronics?

• Greg: GVM amplifier, TPS box, reference signal…

GVMSF6 temperature

Tank temperature

MI-31 temperature

Energy deviation

5hr1 keV

11

Indications of 180-deg bend driftIndications of 180-deg bend drift

On 22-Apr-08, R:DENRGY was close to zero, trajectory upstream the 180-deg magnet was as before, but the momentum distribution became flat Increase of the Pelletron voltage by 1.5 kV made it peaky again The only explanation that I have is a drift of the bend field

7MeV

12

Energy ripple at frequencies above 1 HzEnergy ripple at frequencies above 1 Hz

Snapshots of several BPMs were recorded outside of MI ramps (with MI in energy conservation mode), and data were e-mailed 720 Hz, 2046 points, “Fast” signals, 29-Apr-08 (BYR01F, BYR04F, BYR05F), (BXR01F, BXR04F, BXR05F),

(BYC00F, BYC10F, BYC20F), (BXC00F, BXC10F, BXC20F) +I:IB FFT of the BYR01F, BYR04F, and BYR05 signals normalized by dispersion

0 10 20 30 40 50 60 70 800

1

2

3

4

Frequency, Hz

FF

T c

ompo

nent

s

In low-dispersion BPMs, main components are 30, 60, 180 Hz, set of peaks at < 10 Hz, and, what’s new in comparison with 2005 data, peaks around 40 Hz

In high –dispersion channels, there is a strong enhancement of signals below 10 Hz and 40 Hz lines Chain ripple ~1.8 Hz

13

SummarySummary

Presently, HV stability is most likely at its best level With infrequent adjustments of the HV set point, the stability is

satisfactory for operation at present level

HV readback by R:GVMVLT has the noise level of 200 V rms. Resolution of the energy measurement with R:BYR01S is ~20 eV rms. The absolute value of energy offset calculated with R:DENRGY drifts

up to 1 keV, most likely because of drifting 180-deg bend field. There are seconds-long energy jumps caused by HV-regulation circuitry Temperature dependence of the electron energy is caused by both

mechanical changes and electronics drifts. It would be useful to look in details at energy fluctuations at frequencies

above 1 Hz Paul Joireman can record all BPMs at 300 Hz (with MI not ramping) Alexey can trace signals from the cooling section to the return line to

exclude everything but energy It looks like there is a 40 Hz perturbation that was not in 2005 spectra

14

Summary tableSummary table

Frequen-cy, Hz

Energy change keV

Primary suspect

Possible remedy

Comments

< 0.0001

(many hours)

Up to 2 Bend field+ adjustments by a human

NMR repair

Good value of R:DENRGY can be adjusted according to sharpness of the momentum distribution

~ 0.0001

(hours)

~3

(~0.5 kV/C)

Mechanical distortion of the column,

Adjust by DENRGY

Drift when Pelletron heats up after being off

~0.001

(tens of min)

~1

(~0.3 keV/C)

HV regulation electronics

Thermal stabili-zation ?

MI-31 temperature is usually stable +- 1C

0.01 -1 0.1 Corona, GVM, …

?

1 -10, 40

(30, 60 ?)

0.2 Chain current fluctuations

? Plan to measure