Stability of the electron energy Recycler department meeting April 5 th, 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 Terminal Chain current Needle current Resistor chain Pelletron HV regulation circuitry The terminal voltage (GVMVLT), grid voltage (GRIDV, and the needle current (TPSPRB) as functions of the chain current. 4-Apr 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 measurement U-bend BYD08 BYA07 BYA05 Collector Gun 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 drifts  RMS of the BPM noise corresponds to ~20 eV BXD08S BYD08S 36 hours 0.02 mm BPM readings of a calibration signal 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 mm/kV and is consistent with the bending radius. The X derivative is 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. GVM dE x

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 6 min 1.5 kV 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  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  /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

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