Stability of the electron energy Stability of the electron energy

Recycler department meetingApril 5th, 2006

A. Shemyakin, M. Sutherland

2

MotivationMotivation

In calibrations of the electron energy by cooling of pbars with RF off, we saw the energy shifting by more than 1 keV at the same settings

Sometimes adjusting the Pelletron voltage seemed to improve the cooling rate

Part of the problem is combination of a drift of the charging current and a finite amplification of the HV regulation loop

3

Regulation circuitryRegulation circuitry

-30

-20

-10

0

10

20

30

40

50

90 110 130 150Chain current, microA

Nee

dle

cu

rren

t, m

icro

A

Gri

d v

olt

age,

V

4.316

4.318

4.32

4.322

4.324

4.326

4.328

4.33

4.332

Ter

min

al v

olt

age,

MV

R:GRIDV

R:TPSPRB

R:GVMVLT

Terminal

Chain current Needle

current

Resistor chainPelletron HV regulation circuitry

0

5

10

15

20

25

30

35

40

45

50

-25 -20 -15 -10 -5 0

Grid voltage, V

Nee

dle

cu

rren

t (R

:TP

SP

RB

),m

icro

A The terminal voltage (GVMVLT), grid voltage (GRIDV, and the needle current (TPSPRB) as functions of the chain current. 4-Apr-2006. The voltage changes as 0.15 kV/A.

Needle current as a function of the grid voltage

Generation voltmeter (GVM)

4

Dispersion – based energy deviation Dispersion – based energy deviation measurementmeasurement

U-bend

BYD08

BYA07

BYA05

CollectorGun

1050 mm

The idea is to use the high dispersion in U-bend to trace the energy changes, while Autotunes keep the beam positions constant in BPMS A05 and A07

5

BPM driftsBPM drifts

RMS of the BPM noise corresponds to ~20 eV

BXD08S

BYD08S

36 hours

0.02 mm

BPM readings of a calibration signal. 32.05 kHz modulation, 1 Hz recording. Standard deviations in 2 hours are 1.8 m for X and 3.4 m for Y.

6

CalibrationCalibration

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

4.310 4.315 4.320 4.325 4.330 4.335

GVM, MV

BY

D08

S,

mm

-1.980

-1.970

-1.960

-1.950

-1.940

-1.930

BX

D08

S,

mm

R:BYD08S

R:BXD08S

BPM D08 reading as a function of the Pelletron voltage. 14-Mar-06, Mary

The Y derivative is 0.219 mm/kV and is consistent with the bending radius.

The X derivative is -0.001 mm/kV.

7

Data from 3-hour runData from 3-hour run

GVM readings and BYD08S, BXD08S (multiplied by the calibration coefficient). 1 Hz data. 29-Mar-2006, Mary.

Deviation of energy with time. All points

9 9.5 10 10.5 11 11.5 124

3

2

1

0

Time, hour

dE, k

eV

GVM

dEx

dEy

8

Data with 10 sec averagingData with 10 sec averaging

9 9.5 10 10.5 11 11.5 124

3

2

1

0

Time, hour

dE, k

eV

The drift of the GVM value is 0.9 kV and is consistent with the drop of the chain current by 6 A.

The drift measured by BYD08S is 2.7 keV.

9

Comparison of energy deviations estimated in 3 Comparison of energy deviations estimated in 3 BPMsBPMs

Deviation of energy estimated by 3 BPMs

9 9.5 10 10.5 11 11.5 124

3

2

1

0

1

Time, hour

dE, k

eVi3 0 1 50 An energy change without

any response in GVM

10.2 10.22 10.24 10.26 10.283

2.5

2

1.5

Time, hour

dE, k

eV

6 min

1.5kV

BYD08

BYD07

BXD07

Changes of the beam positions in three BPMs multiplied by corresponding dispersion coefficients and adjusted to begin from zero.

10

Possible reasons for the discrepancy Possible reasons for the discrepancy

Drift of the GVM electronics Kermit is preparing a test of its stability

Drift of the GVM rotation frequency Kermit may try to measure the frequency

Changes in the distance between GVM and the terminal GVM measures the electric field, not the potential If the distance change, the measured voltage

deviates as 5.2 kV/mm Axially symmetrical thermal effect is 710-6/K The distance stays the same within 0.05 mm from

opening to opening of the Pelletron tank Non-axially symmetric motion is still not excluded

11

ConclusionConclusion

The long-term stability of the Pelletron voltage is poor, at least after turning the Pelletron on. Kermit plans to determine stability of electronics.

The procedure of measuring the energy deviation by the beam position in a high- dispersion region works to some extend. A beam motion upstream the bend seems to be an issue.

One can consider implementing similar procedure in the full line First, make an absolute energy calibration with pbars Save e-beam settings as “energy calibration” file In normal operation, compare readings in BYR01S with

the calibration

12

180 deg bend as spectrometer180 deg bend as spectrometer

Fix the beam positions in BPMs C90, Q01 with an Autotune

Measure shifts in BYR01S