1. Introduction to the beam

Responsible for beam documentation: C.BIDAUT

Last modified: April 14 2016 12:05:02.

1.1 Aim of the beam

STAGISO beam is a "staggered" beam delivered from the Booster to Isolde. The specificity is the time desired between the bunches : about 10 Ás (or 16 Ás).
For constraints of one of the recombination kickers , only rings 2, 3 and 4 can be used (the 3 Ás high front of BEX.KFA20 is too short for this ejection pattern).

Differently than the "normalized" Isolde beams, STAGISO fix target is a liquid target.

 

ISOLDE (On-Line Isotope Mass Separator) is a source of low-energy & radioactive isotopes beams used to study unstable nuclei. The radiocative ions are produced by the impact of protons from the Booster (green arrow on the right drawing) on various targets (composition helium to radium). Ions produced by this impact are separated by mass and accelerated to be studied. Applications cover nuclear, atomic, molecular and solid-state physics; biophysics and astrophysics...

ISOLDE consists of 2 mass separators:

- the GPS = General Purpose Separator
- the HRS = High Resolution Separator

Depending on the desired separation precision, Isolde team installs the target on the GPS or HRS Front-End.
So, at the end-line of the BTY line, the beam coming from the Booster is deviated to the corresponding Front-End by the horizontal bending magnet BTY.BHZ301.(-> see BTY transfer line).

Isolde beams usually consist of high intensity, which requires special interlocks (-> see interlock systems)
!!! Special note : Isolde watchdog is dependant of BCT settings which need to be changed for STAGISO !!!

 

1.2 General description

Final destination PSB Ring used
Isolde complex 2,3 & 4

Cavities used at acceleration Radial loop used? Harmonic at ejection
C02,C04,C16 YES H1
Description Notes

2. Specifications

Intensity/Intensity range measured with ring transformers before extraction 340[E10 p/ring]
Horizontal normalised emittance Measured with FWS before extraction 5[mm mrad](1σ)
Measured with SEMgrid in BTM 5[mm mrad](1σ)
Vertical normalised emittance Measured with FWS before extraction 4[mm mrad](1σ)
Measured with SEMgrid in BTM 4[mm mrad](1σ)
Longitudinal emittance Matched area measured with tomoscope at C=802 1,6[eVs]
Full bunch length at extraction Extracted from tomoscope measurement 230[ns]
Momentum spread Δp/p Extracted from tomoscope measurement 1,35[E-3](1σ)
Bunch spacing of extracted beam Measured with OASIS 10000 or 16000[ns]
Kinetic energy at extraction From samplers 1,4[GeV]
Extraction momentum From samplers 2,1[GeV/c]
Specs notes

3. Documentation

3.1 Injection

Kinetic energy at injection From samplers 50[MeV]
Injection momentum From samplers 320[MeV/c]
Approx. injected intensity Samplers and OP Display 380[E10 p/ring]
Approx. intensity after capture (c=295) 280[E10 p/ring]
Horizontal tune at injection Measured with BBQ 4,27
Vertical tune at injection Measured with BBQ 4,60

HOW TO ADJUST INJECTION:

1. optimise the injection efficiency (70-75% in the field "injection" in the OP display). This can be done by :
- check and correct if necessary the steering in the transfer line (LT-LTB-BI)
- tune the injection angle and position
- adjust the kicker slow timing

2. find the best working point : adjust Q strips (for 13 turns with BRx.QCHZ-VT position and angle)

3. adjust capture with: RF : BAx.GSC04PHC02 at injection. (C04 predominant or C02)

 

Injection trajectories
injection trajectories

Q strips
Qstrips WS Qstrips

 

3.2 Intensity regulation

Horizontal shaving Y/N Vertical shaving Y/N Longitudinal shaving Y/N Vary number of injected turns Y/N Number of Turns (if fixed)
No No No VaryT NofTurns

Intensity regulation is performed by changing the number of turns.
IMPORTANT: the total current measured on the target(s) during a complete supercycle must not exceed 2 uA (limit imposed by RP).

op-display intensity sampler

 

3.3 Ring

TFB Control, Energy and momentum
transverse feedback
energy and momentum

 

Radial position
MRP measured with all BR pickups, ring selection through workingset OP-SPEC>PSB:RING_SELECTED
MRP - ring 2 MRP - ring 3 MRP - ring 4
RPOS measured with only 4 pickups : #4-6-12-14

 

Tune Evolution (kicker excitation)
Ring 2 : Q calculated - Q measured (H&V)
Qcalc - R2 QHmeas-R2 QVmeas-R2
Ring 3 : Q calculated - Q measured (H&V)
Qcalc-R3 QHmeas-R3 QVmeas-R3
Ring 4 : Q calculated - Q measured (H&V)
Qcalc-R4 QHmeas-R4 QVmeas-R4

 

Bunch Mountain Ranges and Tomograms
R2-tomo
R3-tomo R4-tomo

 

FWS Horizontal plane
R2-EH R3-EH R4-EH

FWS Vertical plane
R2-EV R2-EV R4-EV

 

SEM grid
...

 

Bunch shape measurement
BSM

3.4 RF

The RF control is mainly based on GFAs and knobs. The cavities follow a programmable voltage function (based on magnetic field variation).

Both the C02 and C04 cavities are used at maximum voltage (8kV) shortly after injection to maximise the longitudinal acceptance. After ~C=740, the C04 voltage is slowly ramped down to approximately 1.2kV at extraction (a certain voltage is necessary due to beam loading).

The C16 cavity is used between C=305 ms and C=680 approximately for :
- the longitudinal blow up (the variation of the voltage function amplitude and/or duration results in a bunch length change)
- an homogeneous proton repartition in the bucket.

 

RF control
RF control RF frequences
RF-R2 RF-R3 RF-R4

 

3.5 Ejection

STAGISO uses the "fast extraction" mode, where the rings are extracted one after one, but with a specific time between bunches (10 µs or 16 µs). For constraints of one of the recombination kickers, only rings 2, 3 and 4 can be used. So the standard pattern ejection Ring 3, Ring 4, and Ring 2 is respected, without ring 1.

Such a time structure (about 10 µs between bunches) can be achieved ejecting one ring after the other with a much longer delay between each ejection. That is, ejecting ring 3, then wait for about 10 µs before ejecting ring 4, and finally wait for some more 10 µs before ejecting ring 2. The exact time between bunches is still a multiple of PSBTrev (a multiple of 572.8 ns), close to 10 µs.

Obsiously, we have to set adapted timings to BEx.KFA14L1, BT4.KFA10, BT.KFA20.

ejection figure

 

Ejection trajectories
ejection trajectories

 

Longitudinal view ejection moment (ring 3) & bunch spacing (16 us and 10 us)
BSM-2
ejection PU Bunch spacing 10 us 10 us spacing

 

3.6 Synchronization

STAGISO 1,4 Gev synchronisation is same than the others beams, during the "flat top", phase and frequency are synchronising each others.

During acceleration, DFP counts B train pulses number.

Sum of these pulses represents dipoles ring 3 actual bending field . After that and from this field value, frequency corresponding to a centered beam extracted and sent to the 3 rings.

4. Additional remarks

BTY TRANSFERT LINE

The STAGISO beam can be sent onto GPS or HRS target.
The direction is determined by the setting of the horizontal bending magnet BTY.BHZ301, which has zero current for the GPS destination and around 453 A for the HRS destination.

Isolde end-line steering :
Isolde end line
NB : All equipments for GPS (= target 2) are named "two hundred something"
All equipments for HRS (= target 3) are named "three hundred something"

ISOLDE BEAM SAFETY : INTERLOCK SYSTEMS

stopAs Isolde beams are usually with high intensities, some monitors are in place to ensure the safety of lines and targets and to optimise the target particules production.
If one of these tools is engaged, it stops the beam immediatly (inhibits RF). All these switches are viewable on the Isolde vistar :

vistar

- beam intensity interlocks
> To protect the target, a threshold for final beam intensity is defined. These limits are chosen in function of the target, and the radiation level admitted in targets area.
pps = protons per second
ppp = protons per pulse
The measurement is taken by:
- BTY.TRA325 for HRS
- BTY.TRA213 for GPS.

- Position checking
> verify the value of vertival/horizontal correctors employed at the end of BTY line. The value for these equipments is set by Isolde team for each target change to optimize the performance (maximum of particules produced). This operation is called "proton scan". Done on :
- BTY.DHZ/DVT323 and BTY.DHZ/DVT324 for HRS
- BTY.DHZ/DVT211 and BTY.DHZ/DVT212 for GPS

- Focus checking
> check the value of quadrupoles employed in the BTY line :
- BTY.QDE321 and BTY.QFO322 for HRS
- BTY.QDE209 and BTY.QFO210 for GPS
If the value of one of them is not in tollerances, the focalisation/defocalisation is deficient.
NB : The value of these equipments is defined in function of the exctraction energy (usually 1.4GeV).

- Isolde Watchdog
> compares the intensities ejected by the booster and received by the target. If the difference is too high (>300E10), it means there are too much losses into ejection/transfert line and it can damage lines or equipments. The measurements are done between BT.BCT10 and :
- BTY.TRA325 for HRS
- BTY.TRA213 for GPS
The watchdog have to be RESET to have beam back.

- Proton current limitation
> restricts the total integrated proton current at 2uA, in accordance with RP, to limit air radiations into targets area.

 

!!! Isolde watchdog is dependant of BCT settings. As the bunches are more distant between them in "staggered" beam than in "normalized" Isolde beams, the BCT's gate length have to be longer to measure the 3 bunches!!!
This setting is usually saved and drived during mapping, but if you experience some problems with the watchdog, have a look on it :
1/ for the BT.BCT10
2/ for the BTY.BCT325 on HRS destination or BTY.BCT213 on GPS destination.

BCTFPSProcedure :
1/ open the BCTFPS expert application (CCM PSBOP > Measur > BI Expert)
2/ open the desired device (Devices > cfv-361-bctft > BCT desired) - NB : be carefull, it opens a new tab at the bottom!
3/ select the appropriate user on the top (STAGISO in our case)
4/ suscribe to BCT datas ("Status" tab > tick the channel 1 > "Suscribe")
5/ aquire actual settings to visualise the measurements ( "User settings" tab > "Get")
6/ Check if all the bunches are well included in the measurement gate (= first white area)
7 >>> If not, adapt the "meas GateLength(ns)" field and send it ("Set" button). It is usually ~2500ns for normalized beams and ~34500ns for staggered beams.