Stability of the electron energy

1
Stability of the electron energy

• Recycler department meeting
• April 5th, 2006
• A. Shemyakin, M. Sutherland

2
Motivation

• 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 circuitry
Generation voltmeter (GVM)
Pelletron HV regulation circuitry
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
4
Dispersion based energy deviation measurement

• 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

U-bend
5
BPM drifts
BXD08S
0.02 mm

• RMS of the BPM noise corresponds to 20 eV

BYD08S
36 hours
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
Calibration
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 run

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

8
Data with 10 sec averaging
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
BPMs
1.5 kV
BXD07
BYD07
6 min
BYD08
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

• 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 7?10-6/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
Conclusion

• 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 spectrometer
Fix the beam positions in BPMs C90, Q01 with an
Autotune
Measure shifts in BYR01S