How to set up the Fragment Separator
Sicherheitsabnahme safety check done by safety department of GSI. Before the participants need to have a special FRS safety instruction and confirm this by signing the safety book. The experiment has to be set up, dangerous parts removed, HV clearly labeled and more.
The FRS will be controlled and monitored from the console in the FRS Messhütte. Test detectors offline and check computers and programs on the console. Test magnets by applying once some current to them.
Before first Beam
Calculation of settings
Prepare a data set in ATIMA
or LISE with layers of matter (targets, detectors, windows and degraders) and optics mode.
For the primary beam ATIMA
alone is enough (on LINUX /u/weick/JavaAtima). For the calculation with fragments and optics LISE or MOCADI
can be used. LISE++ runs on KP2PC119
in the FRS console. picture: screenshot of LISE++.
start online analysis program GO4
- login on LINUX on profi account (for password as FRS expert)
>cd Go4/r115 (or other directory for your run)
- click "Launch analysis client", Name=MyAnalysis, [start]
- configure analysis: "Event Source"=Remote Event Server, Name = computer where remote event server is running, e.g. lxg1018, [submit]
- start acquisition (green arrow button)
Generate a pulse with the pulse generator and distribute it to all MWPCs anodes. With a scope you can check the cathode signals. In the analysis raw spectra you will see sharp peaks.
The MWPCs in vacuum can also be tested with an electron source mounted near the out position of these detectors. You will obtain a broad spectrum centered in the upper left corner of the detector. Inserting the detector in the beam line will move them away from the source. Details on MWPCs here.
Close the doors of the caves, call HKR (tel. 2222) and ask to switch to controlled access mode.
Radiation safety person will come and check the areas called NE4 and NE7.
Do this before 22:00h otherwise they have to come from at home as "Rufbereitschaft" !
Wait until you hear the horn and the red light at the gate is on.
Primary beam on production target
Switch on magnets
Switch on power supplies in the hall by turning the two keys. Otherwise, hands off from the power supplies (dangerous high current !).
Prepare beam request
Change the 6 switches in the electronics rack FRSMHE1 (SIS timing interface) to the desired virtual accelerator machine (usually #8 or #9). The upper switches should not be changed.
Then the display of the "Pulszentrale" in the FRS console should show also the number off the machine, still with a red LED as there is no beam yet. Once you really request beam the green LED shines.
To activate the switch beam on/off the lemo connector at the back of the display inside the FRS console has to be plugged at the right position corresponding to the virtual machine shown in front.
Start control programs
On screen of terminal TCL056 select the beam beamline:
- SIS TS - HFS and press definieren, (for FRS to S4)
- SIS TS - ESR and press definieren, (for FRS to ESR)
- SIS TS - HTA (HTB, HTC) and press definieren, (for FRS to Cave A (B, C)
Start the programs SD, SRMAG, MGSKAL, HALL82, green means they are running, click again to stop them.
MGSKAL, SRMAG and HALL82 will appear on the small monochrome screens.
- SRMAG is used for saving / loading of magnet settings.
- MGSKAL scales parts of the FRS magnet values by a factor.
- HALL82 shows the B field determined by the Hall probes in the dipoles.
SD on the big one of AXP641, in program SD on screen of AXP641 activate Piktogrammzeile.
The number of the selected virtual accelerator machine and the beam particle/energy should be written on top.
Some magnet power supplies have to be changed according to the beam line selected. Do this with the SD program
- "Sonderoptionen" -> "HFS-Magnete für Strahlführung zum ESR einschalten" for beam to ESR
- "Sonderoptionen" -> "HFS-Magnete für Strahlführung Fragmentseparator einschalten" for beam to FRS (S4)
- "Sonderoptionen" -> "HFS-Magnete für Strahlführung zur Tagethalle einschalten" for beam to Caves A, B, C
Finally, in SD program call Sonderoptionen -> Aktivieren der Magnete für aktuellen Beschleuniger
Open vacuum valves
The valves are controlled from the SD program in the line "Gateventil". There are two modes [F] for "Fahren" (drive) and [M] for measuring. You can switch between the two by clicking on the buttons at the beginning of the line, red means active.
Make sure you are in mode [M], left mouse click on a certain valve.
The pressure measured in the section upstream of this valve will be displayed in the blue box in the top of the screen, e.g..
(P1) 8.98*10-7 mb 8.98*10-5 Pa
(P2) 1.10*10-6 mb 1.10*10-4 Pa
There are always two measurements (P1, P2) for safety.
Some pressures are measured directly inside the pump. Those values are usually to good and don't really represent the pressure in the beam pipe. This is indicated by the extra line Druck abgeleitet aus Pumpenstrom P1, P2 .
Typical values are 10-9 to 10-8 mbar in front of target vacuum window and 10-7 to 10-6 mbar behind in the FRS. In case the pressure rises above 5*10-6 mb in one section the valves around this section will close automatically. An independent pressure measurement and display is at the back of the electronics racks.
go to mode [F], left mouse click on valve, the red cross indicating a closed valve should change to a green circle, then for safety back to mode [M].
Close slits for safety
With SD program close the slits behind the target (TS2DS3
V,H), in front of S1 (TS3DS2H
) and insert the beam plug (TS3SV2
The slits are driven by step motors and can be found in the line Schlitze. Leftclick on point, a dialog box will open, click on I on all sides until the green bars cover the whole area.
Prepare Beam Diagnostics
Insert current grids at the target called CG01, CG02 or TS1DG5
, respectively. With SD step motor control move them to position 0.0 (not I ), see picture. They are very slow.
Apply voltage to them with the help of terminals in electronics room. Usual are 80V.
Start current grid display program. In the SD program the box on top of the corresponding slit motors. A program called Profilgitter will appear on the neighboring screen.
Start program DI from terminal TCL056, will appear on the screen TCL05?. Choose correct virtual accelerator by clicking [+] many times then click on [A]. Choose the detector from the menu (e.g. SEETRAM is named TS1DI4S
), press [Start input] and [automatic]. If there is beam you will see a histogram of counts per time.
The SEETRAM has to be set to the correct virtual accelerator first. Choose the program NODAL on terminal TCL056. At the prompt on one of the small monochrome screens type
, then select
"Ausgewählter Detektortyp: " (type of detector),
"Ausgewählter Detektor: " for TS1DI14S
"Virtueller Beschleuniger: " e.g. for machine no. 8.
Set Synchrotron (SIS)
Ask operators to set SIS machine to demanded energy.
phone 2222, a virtual accelerator machine should have been prepared before and name the energy.
load optics setting for part from SIS to target.
Set magnets for ion optics
Load optics setting for part from SIS to target. (More details about the FRS ion optics).
a) from theory
in SD program choose Sonderoptionen -> Theoriewerte setzen -> select filename of optics setting (SISTSHFS$_SISTA2006B_TA1_LO.SET, SISTAHFS$_SISTA2006B_TA1_HI.SET or SISTSHFS$_SISTA2006B_TA2.SET), view file with Anzeigen and apply it with Setzen. Make a printout of the magnet status to spot errors compared with Anzeigen. More details on these settings on the MOCADI
b) from old setting
look in log book but remember the target geometry was changed in Oct2006. Older settings are not good anymore.
Switch keyboard to terminal where SRMAG is running. In SRMAG select Datensätze -> Suchkriterien and enter the Schlüsselwort written in the log book (e.g. R122_03), then press [DO] on keyboard. Next Datensätze -> Datensatz laden -> Save setzen, the program will ask for the first and last magnet in the beam line to set. Enter TE1KY1 + [Return] and TS1MU2 + [Return]. On the question "Magnetwerte bla bla ...", answer keine and press [DO] again. If you like you can print the error status but one error is normal.
Check Magnet Values
Make print out of magnets status, click MagStat
in SD program and wait until the status appears on the printer.
Do the magnets have roughly correct values? I.e. are the dipoles and quadrupoles scaled by a factor corresponding to the new Brho divided by the old Brho (for R122_03, 12C6+, E = 200 MeV
/u, Brho = 4.2852 Tm). If not try again to set the values!
Request beam by pushing the green button for beam to HFS (S4), for the caves put 50 Ohm to some cable, for ESR simply start machine #14.
The scope on top in the console should then show a SEETRAM signal of the spill as well as the DI program.
Adjust beam position
Look at beam position on the two current grids CG01, CG02 (TS1DG5
). To adjust scale use mode "halbauto". Be patient the program updates only slowly.
The beam should be as narrow and centered as in the example shown above. Sorry, the picture is only black and white. You can use the program MIRKO to center the beam. On screen TCL056 select MIRKO. MIRKO should appear on TCL05?. With MIRKO you can change all magnet settings of the FRS and even more beamlines, so be careful! Better use only the one option described here.
From a field of many numbers select your virtual machine number, then you should see an ion optics plot of the FRS showing beam envelopes. On the left of this window there is the option [gerade legen]. This opens another window where you can enter the actual beam position "ist" on TS1DG5
. "Soll" should be zero. This can be done for x and y direction. To cause changes click [Korrektur berechnen + setzen], then watch the current grids whether further corrections are necessary.
Adjust the intensity
The Seetram is used to to measure the intensity for intensive beams. There is a default calibration factor by the DI program. But you can also use predict one with the Brohm program called (SEETRAM). You might have to adjust the Seetram sensitivity, this is done in the DI program by choosing a value from 1 to 7, which corresponds to values of 10-4 to 10-10. On a screen at the back of the FRS electronics you can monitor the SEETRAM setting using a camera in the target area. Different lights indicate the SEETRAM sensitivity.
Scheme of lower left module, SEETRAM set to sensitivity 10-9.
Watch the number of particles per spill shown by the DI program measured with the SEETRAM. This should be roughly correct (10% error). For better values you need to calibrate the SEETRAM.
Compare the number of particles on SEETRAM with those in SIS (ask operators for beam transformator value), for longer runs it has to be at least 70% !
If necessary attenuate / increase the beam intensity (ask operators).
To work with primary beam on particle detectors the beam has to be strongly attenuated, until no or almost no counts on SEETRAM. Then insert the scintillator SC01 (TS2DI1
_S at position 0.0mm + TS2DI1
_P in) and switch on HV, check signal height and CFD threshold, then intensity on scaler, ask for fine adjustment of intensity.
Primary beam through FRS
Load optics setting for FRS
a) from theory
in SD program choose Sonderoptionen -> Theoriewerte setzen -> select filename of optics setting (e.g. SISTSHFS$_RUN81-TA2B.SET), view file with Anzeigen and apply it with Setzen. Make a printout of the magnet status to spot errors compared with Anzeigen. More details on these settings on the MOCADI
b) from old saved setting
Use SRMAG to load an old setting documented in an old log book.
The safe way is:
choose file: Datensätze -> Suchkriterien -> enter Schlüsselwort+[Enter]. No error message? This means the file exists
Load file: Datensätze -> Laden -> Setzparameter and change the parameters of the beam to those as they are on the old printout, Then Save setzen. Enter first and last magnet then press [DO]. Magnets see plan of FRS over your head. Magnetwerte in Sättigung fahren say n.
Check values: Now you should have exactly the same values as in the old experiment, compare the printed magnet status.
Scale FRS to correct Brho
The loaded setting still is for a different Brho of the beam and the FRS magnets have to be adjusted. Even if the factor is 1.0 do the scaling because of hysteresis.
Calculate the energy and Brho of the beam after the target and the factor missing to the loaded setting.
In MGSKAL select part of FRS to scale. Gruppe auswählen e.g. TA-S4.
Scale selected part by factor Magnetwerte skalieren -> Skalieren mit Faktor -> Enter calculated factor -> confirm with y.
"Rampenprozedur fahren, (k)eine, (d)ipole, (a)lle ?", choose "d"
Wait about 2 min until the ramping procedure is finished.
Beam to S1
Open slits and remove beam plug (TS2SV3
Apply HV to MWPC detectors. Use small terminals in electronics room that control the power supply crate 2 and 3 in the rack FRSMHE6 ???.
Look at MW11 at S1 in GO4 online analysis program and adjust the sum conditions.
Measure beam position (x), x can be off because off a mismatch in Brho.
To center beam at S1 scale FRS parts (TA-S4). The factor F is calculated using the dispersion coefficient (x,D)TA-S1.
F = 1 - x / (x,D)TA-S1 (the minus comes from different coordinate systems used on detectors and in optics calculation).
The fact that the beam is centered along with the measured B-field defines the effective radius of the first dipole.
Beam to S2, S3, S4
Do the same at S2, now scale only S1-S4 (or S6,S8), use dispersion coefficient (x,D)S1-S2.
Again the same for S3, S4, if there is not removable matter at S4 try to calculate the Brho afterwards as precise as possible.
Save magnet setting
This is already something and should be saved in SRMAG.
Choose file: Abspeichern
-> add a comment (beam, energy, target, Brho)
-> enter Schichtmannschaft (your name) and Schlüsselwort (keyword) to find the file again.
Print a magnet status, clue it into the log book and write the keyword next to it along with the Brhos and energies of the beam for this setting.
Calibrate target and degraders
Insert a target, click on target pictogram an choose from list (TS1ET5
and center again at S1, this defines the effective target thickness.
You can calculate backwards in ATIMA
to see what the real or effective target thickness is.
Insert degrader at S1 or S2 and again center the beam in the following of final focal plane. This defines the effective degrader thickness. With variable degraders it is better and easier to adjust the thickness until the beam is centered.
Save the magnet setting with SRMAG.
Fragment beam through FRS
Calculate fragment Brhos
Use LISE or MOCADI
to determine the best Brho of the FRS for the fragment setting (highest transmission, least contaminants). After matter at S1, S2 or S3 the Brho will change. Knowing the Brho of the previous setting one can calculate the necessary scaling factor F.
Again in SRMAG Magnetwerte skalieren -> Skalieren mit Faktor -> Enter calculated factor F -> confirm with y -> "Rampenprozedur ?" enter "d"
Wait about 2 min until the ramping procedure is finished.
You will have to increase the intensity now, ask operators, watch SEETRAM.
Look for fragments on detectors
Watch MWPCs and scintillators (S2, S4) to see some kind of beam. You can look at the raw signals with an oscilloscope or with the online analysis program Go4.
The basic equation for identification is:
Brho = m / q * c0 *beta * gamma
We want to measure Brho, charge = Z and the velocity (beta = v/c, gamma = Lorentz factor) via time-of-flight. Then we can calculate the mass.
First the Time-of-flight (TOF) needs to be calibrated. For this you take primary beams of 3 well known energies. Either change the SIS energy or use well calibrated targets or degraders and calculate the exit energy with ATIMA
. Get the beam centered and measure the TOF from the scintillator at S2 (Sc21, TS3ESA
) to the scintillator at S4 (Sc41), (Some experiments measure from S3 to S4 or S2 to S8). The scintillators have photo tubes on both sides. First measure the time differences (dTll = Sc21_left - Sc41_left) and (dTrr = Sc21_right - Sc41_right). The total TOF is the average of dTll and dTrr. Plot TOF as a function of the velocity (beta=v/c). Of course it should be linear but there can be quite some offset due to the dT in the cables. Fit a line and use the coefficients in your analysis program. The slope can be also obtained from a calibration of the TAC with a time calibrator.
In Go4 plot the histograms SCI(2)_TofLL and SCI(2)_TofRR for each energy. The TOF (dTll or dTrr) will be shown as raw data in TAC channels. The real TOF you get from the distance between the scintillators and the known velocity. Fit a straight line into a plot TOF (dTll, dTrr) versus TAC cannels (ch). Don't be surprised about the negative slope, for the TAC shorter TOF means more channels.
dTll = tof_all - tof_bll * ch , dTrr = tof_arr - tof_brr * ch .
Enter the path length (id_path) and change the calibration coefficients tof_bll, tof_brr (edit setup.C and run ".x setup.C").
Note, the offset (id_tofoff) exists only once, it is the average of the offsets for left and right (tof_all, tof_arr). Path length is in units of pico seconds, which means path length in meters *104 / 2.99792458.
The formulas used in Go4 are:
sci_tof2 [ps] = (tof_bll * dTll + tof_brr * dTrr) /2
beta = id_path [ps] / (id_tofoff [ps] - sci_tof2 [ps])
gamma = 1 / sqrt(1-beta^2)
The calibrated sci_tof2 is in the histogram SCI(2)_Tof2. But this is still not the real TOF because it still has the wrong sign and an offset.
figure: Velocity distribution for a setting on many fragments after calibration from Run120, F0016. 22Ne primary beam at 292 MeV
/u to produce 18Ne and other fragments. For identification see below.
One has to know the Brho which corresponds to a centered beam. Either you started with a well known Brho of a centered primary beam and remember by which scaling factor you have changed this setting, or you noted the B-field value of the Hall probes with a centered primary beam. Then you can read the actual B-field and calculate Brho from the ratio.
This is only valid for a centered beam. The Brho for an off center ion you deduce from the measured particle position together with the dispersion coefficient (D) and magnification (M) for the optics setting used. The coefficients and the centered Brho should be entered in your analysis program.
The formula used is:
Brho = Brho_cent. * [1 + (xS4 - MS2-S4 xS2) / DS2-S4],
x at S4 (XS4) can be measured with the MWPCs, at S2 the rate is usually too high for the MWPCs. In this case one can take the position information from Sc21, however, with less accuracy. But the MWPCs can be used for calibration of the Sc21 position. The optics coefficients usually come from the theory values calculated with GICOSY. These coefficients are independent of the absolute Brho, as they are sensitive only to relative deviations.
In Go4 DS2-S4 is named dispersion in the file setup.C, MS2-S4 is magnification. The centered Brho is calculated from the B-fields as shown by the Hall probes and the effective radius of the dipoles (rho0). The latter can be calibrated with a well centered primary beam of known Brho.
Brho = B * rho_eff.
Go4 uses only one value, namely the average of the radii of both dipoles in the second half of the FRS. rho0 in meters and the B-field values in Tesla have to be entered again in setup.C.
The flags x2_select and x4_select (hidden in the code) switch between positions measured by the MWPCs in the focal plane (=1) or by the scintillators (=0). MWPCs are calibrated with the coefficients mw->x_factor[i] and mw->x_offset[i] which can also be found in setup.C. To derive the values in the focal plane also the distances inside the FRS are used (dist_MW21, dist_MW22, dist_MW41, dist_MW42). Scintillators use a 6th order polynomial to get mm values from the channels (x_a[0-6][i] in setup.C). Calibration can be done comparing the MWPC spectra with SCI21_X or SCI41_X and looking at the two dimensional histograms SCI21_TxMWx or SCI41_TxMWx.
figure: Uncalibrated position from Sci21 vs. the position measured by the MWPCs. Setting on fragments to fill the whole momentum acceptance and to obtain a broad distribution at S2, from RUN120 F0016.
Calibrate the MUSIC
The charge is determined from the energy deposition (dE) in an ionization chamber (MUSIC).
First you measure a setting with a target but the FRS set on primary beam. At this moment you still have no calibration and you look simply at the energy deposition as an output of a QDC. The biggest peak in the MUSIC spectrum corresponds to the primary beam. Smaller ones will appear on the left, may be also one peak on the right for proton pick up. You can count downwards and assign the channels an atomic number. dE depends roughly on Z2.
Next dE depends on the velocity of the ions. Though this dependence is well known from theory (ATIMA
) one can also calibrate it as one needs the 3 different energies for TOF anyways. Plot dE as a function of beta, fit it with a polynomial and use the coefficients in your analysis program.
As dE in the MUSIC is a function of the position (x) where you enter the MUSIC you can still improve the resolution. Make a broad beam by switching off the preceding quadrupoles or scan the beam with the dipole over the whole MUSIC aperture. The position can be measured with the MWPCs. In a plot dE as a function of x you will notice the reduced energy deposition at the sides of the MUSIC. You can fit this curve and again use the values in the analysis program.
In Go4 the coefficients for the 6th order polynomial for position correction (pos_a1[0-6]) are used as follows:
dEc = dE * pos_a1 / ( pos_a1 + pos_a1*x + pos_a1*x2 + .. + pos_a1*x6 )
The position information (x) is taken from the MWPCs at S4. The two histograms MUSIC1_dEx, MUSIC1_dExc show the energy deposition as a function of x-position in the MUSIC without and with correction, respectively.
The velocity correction is derived as a fourth order polynomial from beta. From this the atomic number is calculated as
v_cor = vela + vela*beta + vela*beta2 + vela*beta3 + vela*beta4
v_cor also includes the nomalization of the square root (dividing by the dEc for the primary beam).
Z = primary_z * sqrt( dEc / v_cor ) + offset_z .
This means pure Z2 dependence is assumed, an assumption which is not so good for high Z. Only close to the Z of the primary beam (primary_z) used in the calibration it is safe. offset_z can be used to match the integer number Z better. All coefficients are set in setup.C.
figure: Go4 example from Run120 file F0016, setting on 18Ne.
The best separation you get in a two-dimensional plot of TOF vs. energy deposition in the MUSIC. Calibrated it becomes A/Q vs. Z. Here different fragments show up as separated blobs like in the examples below.
In Go4 such a plot you can see as the histogram ID_Z_AoQ. Many conditions, ID_Z_AoQ(0-4), can be put onto it to gate other histograms.
figure: identification plot for a setting on 18Ne from Run120, file F0016. Still needs a small shift in A/Q to the right.
- A drive (step motor) does not want to move by control from the SD program: possible help:
- Try moving the same step motor from the bottom line in the SD program "Piktogrammzeile" instead from the pop up window appearing when clicking on top.
- Go to mode reset in SD program and click on the icon or restart the SD program completely.
- Go to the back of the electronics rack and put the drive in manual operation. Switch remote to manual, select channel number for wanted detector (see list on sticker), move drive with the red and yellow buttons. Afterwards switch back to remote control.
- A magnet fails, i.e. it turns red in the "Piktogrammzeile" and the icon starts blinking.
- Go to mode status in SD program and click on magnet, read information in pop up window. Red lines correspond to errors.
Does the error cause an interlock and block the SIS (SiSt
- One typical error is cooling water, Try to switch on the magnet again. Set SD-program to mode EIN and click on magnet. If it persists call people on call to repair it.
- Another famous one is SiSt-Interlock due to high radiation on radiation safety detectors or a cave not ready to take beam.
Check whether the cave is closed properly and call HKR to tell you what caused the alarm. Radiation safety might have to come to clear the situation.
- Suddenly no beam any more:
- Check whether you used the correct scaling factor for the magnets (typos are very common).
- Call HKR there might be a failure of the accelerator (also very common),
- Check whether the accelerator machine still is getting a reset after each spill, otherwise your machine might have been switched off. You can look whether the scalers (see picture) still go back to zero after a spill.
- A magnet failed and caused an interlock, see point 2.
- music80_manual.pdf: Testfile