I have prepared new (fresh) dye solutions of Fluorescein 27: 2 charges. They are in the Safety Cabinet (Sicherheitsschrank) in the ESR Laser lab

• 3 Loops
  
• 501 Steps
  
• 15 Shots / Step
  
• From 550.4 nm to 547.9 nm. In total 2.5 nm @ 0.005 nm
  

We roughly adjusted the timing based on attachment 1, for ions to be in center of electron cooler (east arc), corrected for PMTs being 2.5m closer to the north on the west arc
then did a new 30 injection accumulation (10.8k counts on particle detector) and readjusted the timing to fine tune this
(attachment 2, first settings right peaks, adjusted towards left)

Then we did a 60 injection accumulation (only 7.6k counts?) to check the settings and shift the timing by half a revolution (324 ns = 98 bins)
(attachment 3, data saved in /data.local2/2025_229Th/2025_229ThDAQ1_0099.lmd with DAQ1).

Checked these settings and particle counts with another injection (2.8k counts)
(attachment 4, data saved in /data.local2/2025_229Th/2025_229ThDAQ1_0100.lmd with DAQ1)


Estimated bunch width: 20bins = 67ns;corresponds to 20/200 of 1 evolution, so about 12m
                                     assuming v+0.5c0: 11m

We exchanged the old BBO of the Cobra's FCU with a new one. The output power of the Cobra was around 120mJ. In the end, we achieved a UV power of about 21mJ. In addition, we optimized the fiber-coupling to the wavemeter. 

Cobra's FCU was recalibrated. Table saved as FCU_547-554_RS_2024-06-25.fcu.

Test scan to see whether laser spot is moving while scanning

Aborted accumulation because SIS stopped. 12.9k counts
saved as /data.local2/2025_229Th/2025_229ThDAQ1_0103.lmd using DAC1 only

We filmed it and will try to attach it later
1. After resetting to high wavelength, the MRC stabilization takes a bit longer to adjust, beam not centered for the first 1-2s
2. During the scan the beam does not seem to jump around more than usual, but there might be a minimal wavelength dependent drift (maybe 1/3 of laser beam diameter towards bottom right over entire scan range)

1. UNILAC running again, so we resumed the beam tuning wherre we stopped yesterday at 14:00

2. Goals: Reduce intensity and lifetime of "antibunch" contamination while maximising intensity for main bunch/on PD
   Adjusted bucketsize, el. cooler current, cooling times,.. 
   Managed to get bunch width to 6-8 bins and get 10k counts in 15 mins with only 20 injections
   but el. cooling still takes long and sometimes bunch phase jumps by 90° in "measurement manipulation"

4. Checked scan range again and found small discrepancy

3. Decided to switch el. cooler voltage (1st cooling) by +100V, 
   ion beam position in el. cooler should not be afected by this too much, at the scrapers at which the dispersion is maximal it shifted the beam by 5mm

new revolution frequency: 1.54315 GHz
new electron cooler voltage: 104506 V(+95 V; slightly adjusted to match revolution frequency   
"antibunch" vanishes within first 10s
bunch on PD wider, but might be missmatch of HF and cooler voltage

• right side: the thorium beam.
  
• left side: a satellite peak (isobar).
  

We noted that the dark countrate of PMT north is about 20x higher than that of PMT middle. 

We went into the ESR cave to look for stray light. 
We decided to put a black cloth over all the PMTs. 
Also we made the tubes of the N2 airflow to the PMTs black (tape around). 
This did not make a significant change. 

We exchanged PMT north (same type 9423B) to see if that made a difference. 
It did not really change either. 

PMT north = 2650 V 
PMT middle = 2700 V 

The first picture below shows the dark rates for these two voltages. 

At about 17:00 we changed the voltage of PMT north to 2700 V. 
This did not change anything. 


Carsten swapped the cables of PMT north and PMt middle (inside ESR, before the amps) at 17:14.
The second picture below shows the result of that. 
Now black and red are exchanged. 


Carsten swapped the cables back again (17:20). 
Carsten and Kristian will look at the PMT signals in the ESR cave. 

Carsten and Kristian changed (18:00) the thresholds of PMT north and PMT middle in the ESR cave. 
See picture below. The effect is negligible. 


Carsten will now (18:05) change the channel of the pre-amp of PMT north. 

We have made two foam rings (outer diameter ca. 70 mm with a thickness of 10 mm each and placed them successively underneath PMT north. 

ring 1: ID = 55 mm 
ring 2: ID = 47 mm 

Without rings we had measured ca. 20 counts per channel in a time of about 7 minutes. (1st picture below) 

With ring 1 we have measured ca. 18 counts per channel in 7 mins. 

with ring 1 and ring 2 we have measured ca. 15 counts per channel in 7 mins. (2nd picture below)

It is clear that the rate of PMT north decreases with increasing distance from the beampipe. 

At this point it is not yet clear to us if the experiment will benefit from the 2 rings. 

If the rings should be implemented, we propose to have one proper ring (20 mm high) made by the mechanical workshop.