Before the run

Should the SEETRAM be calibrated?

• If absolute cross sections will be measured, the SEETRAM detector should be calibrated. This is either done using the new ionization chamber setup [please contact Fanny Farget or Arnd Junghans for detailed instructions!] or by comparisons with the target scintillator. In both cases the data acquisition must be prepared beforehand, including scaler and/or ionization chamber delta-E readouts.

Back to index

Entering FRS parameters into GOOSY

• Enter the Z value of primary beam to the data element FRS.Primary_Z. Set values of the dispersion and magnification of the second stage to the data elements FRS.Dispersion(2) and FRS.Magnification(2), respectively.
• Determine distances of S2 detectors (MW21, MW22, SC21, TPC1, TPC2, and TPC3) and nominal focus position from the quadrupole magnet TS3QT33. Set corresponding data elements (FRS.Dist_MW21, FRS.Dist_MW22, FRS.Dist_SC21, TPC.Dist_TPC1, TPC.Dist_TPC2, TPC.Dist_TPC3 and FRS.Dist_FocS2). Decide which two TPCs should be used for tracking (either 1 & 2 or 2 & 3) and set the bit TPC.B_tpc12 accordingly (= 1 if 1 & 2 are used). NOTE: Remember to update the focal distance if the beam optics are changed!
• Determine distances of S4 detectors (MW41, MW42, SC41, MUSIC1&2, TPC4, and TPC5) and nominal focus position from the quadrupole magnet HFSQT13. Set corresponding data elements (FRS.Dist_MW41, FRS.Dist_MW42, FRS.Dist_SC41, FRS.Dist_MUSIC1, FRS.Dist_Music2, FRS.Dist_MUSICA1:4, TPC.Dist_TPC4, TPC.Dist_TPC5, and FRS.Dist_FocS4).
  NOTE: Remember to update the focal distance if the beam optics are changed!

Back to index

TAC calibrations

• IMPORTANT: Verify the cabling of the scintillator detectors: the start for the TOF TACs should always be the detector furthest downstream -- otherwise the TOF calibration will be "backwards"!
• To ensure that the TOF (and scintillator position measurement) TAC ranges are appropriate, it is important to estimate beforehand the possible range of flight time differences. Calculate (with MOCADI) the S2-S4 (and when applicable, S2-S6 or S2-S8) TOF of the primary beam with no matter in the beam line and corresponding values for fragments of interest assuming the thickest target and thickest degrader + all scintillators are all inserted. Multiply the largest time difference by 1.5-2 and set the TOF TAC ranges to this value. (It should be possible to record the TOF for all desired separator settings using the same TAC range without sacrificing resoulution.) The L-R and O-U Delta-t TACs used for position measurements should in general have short (25 ns) ranges.
• Use a Time Calibrator to calibrate the time of flight (TOF) between SC21 and SC41. Look at spectra SCI_TofLL(2) (left-left) and SCI_TofRR(2) (right-right). Determine the slopes of calibration lines by least squares fitting (in ps/channel) and store them in data elements SCI.Tof_BLL(2) and SCI.Tof_BRR(2), respectively, in the SET_MEM_SCI.GCOM file.
  NOTE: Any additional TOF spectra, such as for S2-S6 or S2-S8, have index 3 or 4!
• The TOF shown in the spectrum SCI_Tof(2) is calculated as the average of left-left and right-right time of flights multiplied by the coefficients determined above and then shifted by the value of data element SCI.Tof_A(2). This value can be adjusted in order to put the TOF events within the spectrum limits. Another (better) solution is to later adjust the spectrum display limits -- in this case the SCI.Tof_A(2) element is set to zero.

Back to index

Preparing the particle identification code

• Make sure that the appropriate preamplifiers are connected to the MUSIC chamber(s). (Ask Christoph Scheidenberger!)
• Without biasing the MUSIC detectors, look at the energy loss spectra and, for each anode, record the low-energy cut-off of the noise peak (should represent the ADC offsets/pedestals). Enter the values as the data elements MUSIC.E1_Off(1...4) in the file SET_MEM_MUSIC.GCOM.
• To ensure that the range of the MUSIC DE spectra (MUSIC1_DE(1...4)) are appropriate, it is important to estimate beforehand the possible range of energy losses in these detectors. Calculate (with MOCADI) the DE in MUSIC1 (ca 60 mg/cm² Ar) of the primary beam with no matter in the beam line and the corresponding value assuming the thickest target and thickest degrader + all scintillators are all inserted. It should be possible to record the energy loss signals from both situations using the same gain setting without sacrificing resolution at lower Zs.
• Check the file CREATE_SPEC_ID.GCOM and verify that the ranges of the spectra ID_Z(2), ID_AOQ(2) and ID_Z_AOQ(2) are appropriately defined for the experiment.

Back to index

Primary beam, no target or detectors

Adjusting the primary beam

• Check that slits at S1 are closed and that the beam plug is in.
• Adjust primary beam with high intensity on target by means of the TS1MU1 and TS1MU2 dipoles. Observe the beam position (and angle) with the current grids CG01 and CG02.
• Have the HKR adjust the primary beam intensity to about 1000 ions per spill. Check it by inserting the target scintillator SC01: turn it on and observe the countrate. Warning: Only when you are sure that beam intensity is low, open the S1 slits and remove the beam plug! Serious damage to detectors can occur if they are hit by high intensity beam!

Back to index

Effective dipole radii

• Center the beam through the FRS with help of MWPCs, one dispersive/focal plane at a time (always remove upstream detectors!). Adjust the voltage on the MWPCs one at a time and check the sum conditions (MW_XSUM(1...6) and MW_YSUM(1...6)) with the command @MWnSUM, n=1,2,3,4 before looking at the position spectra. Optionally: run to tape after adjusting each setting. Plot the beam position pictures (MW1, MW_FOCS2, MW3, MW_FOCS4). If the TPC detectors are in use, also plot the pictures TPC_FOCS2 and TPC_FOCS4. Save the FRS settings to file with the SRMAG program. Note down the dipole field settings.
• Update the condition window limits in the file CREATE_SPEC_MW.GCOM!
• Starting with the SIS extraction energy (ask HKR), use ATIMA to calculate the primary beam energy on target, accounting for the SEETRAM and the SIS vacuum window. ATIMA also calculates the corresponding Brho value. Deduce the effective radii of the 4 FRS dipoles by dividing this value with the corresponding B fields (from the Hall probe program) needed to center the beam in each FRS segment. Enter the average of the D3 and D4 dipoles effective radii to the data element FRS.Rho0(2). (First stage not needed.) Update the file SET_MEM_FRS.GCOM.

Back to index

Primary beam, SC21 in

SC21 effective thickness measurement

• Insert SC21 in and bring it into operation. Center the beam from S2 to S4 using the MWPCs. Plot relevant pictures (MW3, MW_FOCS4, TPC_FOCS4). Save the setting to file with SRMAG. Note the B fields. Using ATIMA, deduce the effective thickness of SC21 and calculate the equivalent Al thickness, see below. (The latter is good to know when calculating S2 degrader settings below...)

Back to index

Startup of S4 detectors

• Now is the perfect time to verify the operation of detectors at S4. Bring the SC41 and MUSIC detectors into operation. Signals from MUSIC anodes (picture MUSICn_E, n=1,2) should give peaks around channel 1000 (of 2000). In the TOF spectra (SCI_TOF(2), SCI_TOFLL(2), SCI_TOFRR(2)) the peak should be positioned at the high end on the spectrum (see above).

Back to index

Absolute TOF calibration and MUSIC velocity correction--step 1

• When the detector voltages and electronics (delays etc) have been adjusted properly (especially for the MUSIC and scintillator detectors -- they can not be touched after this point! -- take data to tape and record the 1st calibration data point. Note the B3 and B4 field values. Plot the relevant spectra (with integrals on peaks): SCI_TOFLL(2), SCI_TOFRR(2), SCI_TOF(2), MUSIC1_DE and MUSIC1_DECOR.

Back to index

Primary beam, target and SC21

Target effective thickness measurement

• Insert the primary production target. Using the MWPCs, center the beam at S1 and S2. Record the B fields and plot the relevant spectra (MW1, MW_FOCS2, TPC_FOCS2) with integrals. Save settings to file with SRMAG. Using ATIMA, deduce the effective target thickness (see below).

Back to index

Absolute TOF calibration and MUSIC velocity correction--step 2

• Run on tape and record the 2nd calibration data point. Note the B3 and B4 field values. Plot the relevant spectra (with integrals on peaks): SCI_TOFLL(2), SCI_TOFRR(2), SCI_TOF(2), MUSIC1_DE and MUSIC1_DECOR.

Back to index

S2 position calibrations with defocussed beam

• Put MW21 and MW22 in. Defocus the beam at S2 by setting the field of the first of the S2 X-focusing quadrupoles (TS3QT31) to zero. Run on tape. If necessary, sweep the beam with the D2 dipole to cover the X-range from -10 to 10 cm. Look at the spectrum SCI_TXMWX(2). At the end of the sweeping procedure, plot this spectrum and export it to disk (command: EXPORT GD specname OUTPUT= filename). Also plot the spectra MW_TPC_X(1:3) and MW_TPC_Y(1:3) and save them to disk. Take out MW21 and MW22.
• Evaluate SC21 position calibration: Use the SATANGD program to fit a line to the dependence of the SC21 position on the X-position (obtained from the MWs). Set corresponding data elements in the data base (offset: [data]SCI.x_A(0,2), slope: [data]SCI.x_A(1,2)).
• The calibrated position is shown in the spectrum SCI_X(2). Select the range of acceptable positions by setting the condition window SCI_X(2) on this spectrum.

Back to index

Primary beam, target, SC21 and nominal S2 degrader

Degrader effective thickness measurement

• Load the setting saved in the previous step (beam centered with target and SC21 in). Insert the S2 degrader with the nominal thickness. Center the beam from S2 to S4 by using the MWPCs. Record the B fields and plot the relevant spectra (MW3, MW_FOCS4, TPC_FOCS4) with integrals. Save settings to file with SRMAG. Using ATIMA, deduce the effective degrader thickness (see below).

Back to index

Absolute TOF calibration and MUSIC velocity correction--step 3

• Run on tape and record the 3rd calibration data point. Note the B3 and B4 field values. Plot the relevant spectra (with integrals on peaks): SCI_TOFLL(2), SCI_TOFRR(2), SCI_TOF(2), MUSIC1_DE and MUSIC1_DECOR.

Back to index

Primary beam, target, SC21 and thick S2 degrader

Degrader effective thickness measurement

• Increase the total degrader thickness to the maximal value desired. Center the beam from S2 to S4 by using the MWPCs. Record the B fields and plot the relevant spectra (MW3, MW_FOCS4, TPC_FOCS4) with integrals. Save settings to file with SRMAG. Using ATIMA, deduce the effective degrader thickness (see below).

Back to index

Absolute TOF calibration and MUSIC velocity correction--step 4

• Run on tape and record the 4th calibration data point. Note the B3 and B4 field values. Plot the relevant spectra (with integrals on peaks): SCI_TOFLL(2), SCI_TOFRR(2), SCI_TOF(2), MUSIC1_DE and MUSIC1_DECOR.

Back to index

S4 position calibrations with defocussed beam

• Defocus the beam at S4 by switching off the first X-focusing quadrupole at S4 (HFSQT11). Run on tape. If necessary, sweep the beam with D4 dipole to cover the entire X-range from -10 to 10 cm. Look at the spectrum SCI_TXMWX(5) (MW41 and MW42 must be turned on and functioning!) and export it to disk in SATANGD format. Also plot the spectra MW_TPC_X(4:5) and MW_TPC_Y(4:5) and save them to disk.
• Evaluate SC41 position calibration: Use SATANGD program to fit a line to the dependence of the SC41 position on the S4 X-position (from the MWs, projected at the SC41 position). Set the corresponding data elements (offset: SCI.X_A(0,5), slope: SCI.X_A(1,5)), and update the SET_MEM_SCI.GCOM file.
• The calibrated position is shown in the spectrum SCI_X(5). Select the range of acceptable positions by setting the condition window SCI_X(5) on this spectrum.

Back to index

Optional position calibration of MUSIC1.

• Look at the spectra MUSIC1_TMWXn (n=1...4) showing the X-position (as calculated from the S4 Mws) at the anodes 1-4 of MUSIC1 vs. the respective anode drift times. [MW41 and MW42 must work!] Export the spectra in SATANGD format. Select the range of the drift time where the calibration is linear by setting the condition windows MUSIC1_T(1...4) on the spectra MUSIC1_T(1...4).
• Evaluate the position calibration of anode 1 with the help of SATANGD. (Fit a line to the data as in the cases of SC21 and SC41.) Set the corresponding data elements (offset: MUSIC.X_A(0,1), slope: MUSIC.X_A(1,1)). The calibrated position is shown in the spectrum MUSIC1_X1.
• Repeat the procedure for anodes 2, 3 and 4.
• Look at the spectrum MUSIC1_R showing the rms distance of four position points (at the four anodes) from the line fitted to these points. Select a range of good events by setting the data element MUSIC.R1 representing the upper limit of acceptable rms distance. The average X-position of the 4 anodes, calculated at the Z-position of MW42, is shown in the spectrum MUSIC1_X. The angle, X', is plotted in the spectrum MUSIC1_A.

Back to index

Position correction of the MUSIC1 DE signal

• Decide if the correction will be based on position determined by MUSIC1 itself (data element MUSIC.B_SelfCorr = '1'B) or on position given by MW41 and MW42 (MUSIC.B_SelfCorr = '0'B) . In GOOSY, set the data element (set mem ...) and update the SET_MEM_MUSIC.GCOM file.
• Look at the spectrum MUSIC1_DEX showing the average energy loss from 4 anodes vs. the X-position in the middle of the MUSIC1 chamber. Export the spectra in SATANGD format. Use SATANGD to fit the position dependence: in order to properly describe edge effects, an odd-order polynomial (max. 5th order) should be used! Store the coefficients in the corresponding data elements: MUSIC.Pos_A(0...6,1) and update the file SET_MEM_MUSIC.GCOM.
• The corrected spectrum is plotted in the spectrum MUSIC1_dECor. Attention! On an event-by-event basis, if a DE event is not (could not be) corrected, then the spectrum MUSIC1_dECor is incremented according to the uncorrected DE value.

Back to index

Before proceeding...

Prepare for high beam intensity

• This concludes the list of steps requiring a low primary beam intensity. Before you proceed, verify that all points above have been covered and that the corresponding spectra and settings have been saved and recorded.
• Important: Close the S4 slits and insert the S1 beam plug (TS3SV3). You are now ready for high beam intensities!

Back to index

Optional SEETRAM calibration

• If you need to perform a SEETRAM calibration, now is a good time! Ask the HKR to increase the beam intensity stepwise (ca 20 points between 102 to 104 ions/s should be registered). Write data to tape (verify scaler and/or ionization chamber operation first!).

Back to index

Evaluation procedures

Determination of effective thicknesses

• By calculating energy loss in a layer of matter (with ATIMA) and comparing to the measured difference in energy (or, equivalently, magnetic rigidity) between the incoming and outgoing beam, the effective thickness of the matter can be estimated. Calculate the magnetic rigidities Brho (the product between the effective dipole radii (see above) and the corresponding B fields needed to center the beam) before and after the matter. These values are then entered into ATIMA and the corresponding matter thickness is determined from the energy loss. (It is sometimes useful to calculate an equivalent thickness of Al or C.) NOTE: The possibility to enter energies in terms of rigidities (simply type in the Brho values followed by ", br") is an undocumented feature of ATIMA!

Back to index

TOF calibration

• Determine the value of Brho2 in the second FRS stage and, using e.g. the Alpha program FRSFAQ, calculate the particle velocity beta for the 3-4 different calibration points obtained with the primary beam. (At least 2 points are needed for the TOF calibration.) Evaluate the TOF calibration by fitting (with e.g. SATANGD or a calculator) the linear function y = k + mx, where y = TOF×beta and x=beta (beta=v/c), TOF being determined from the peak position in the SCI_TOF spectrum. Set the data elements ID.Path(2) = -k and ID.TofOff(2) = m. Update the file SET_MEM_ID.GCOM!
  NOTE: The two coefficients have some physical meaning: -k×c is equal to the average S2-S4 flight path, while m (although being the slope of the fit) represents the TOF offset of the GOOSY calibration function!

Back to index

MUSIC velocity correction and Z calculation

• In each step of the TOF calibration, the DE value of MUSIC1 should be recorded from the spectrum MUSIC1_dECor. Using the velocity values from above, fit a 3rd order polynomial to the dependence of corrected DE on the velocity beta (=v/c). Set the corresponding data elements: MUSIC.Vel_A(0:3,1) and update the file SET_MEM_MUSIC.GCOM. These corrected DE values are used to calculate the Z values shown in the spectrum ID_Z(2).

Back to index

Setting up the A/Q identification

• Decide if the position in X at S2 will be taken from SC21, from MW21 and MW22, or from TPCs by setting the data element ID.X2_SELECT to 0,1 or 2, respectively. Do the same for the S4 position by setting the data element ID.X4_SELECT. Update the file SET_MEM_ID.GCOM.
• Set the present values of the magnetic fields (in Tesla) of the dipoles D3 and D4 to data elements FRS.BField(3) and FRS.BField(4), espectively. Attention! Don't forget to change these data elements every time the FRS setting is changed!
• Set the data element ID.TofCorr(2) to zero. (Update the file SET_MEM_ID.GCOM!) The calculated mass over charge ratio, A/Q, is shown in the spectrum ID_AoQ(2). The very useful 2D-spectrum ID_Z_AoQ(2) shows the Z of each particle vs its A/Q. (Compare the "raw parameter" spectrum ID_DETOF(2).)
• Set the polygon conditions ID_Z_AoQ1(2)...ID_Z_AoQ5(2) on the spectrum ID_Z_AoQ(2). A number of spectra are gated by these conditions: ID_X2C(2,1..5) show X position at S2 and ID_X4C(2,1...5) show gated X-positions at S4.

Back to index

Miscellaneous

Fitting with SATANGD

It is convenient to use the program SATANGD to perform fits of both one- and two-dimensional spectra and other functions. In the following we describe a procedure for fitting 2D calibration spectra (originating from GOOSY and exported into SATANGD format via the command : EXPORT GD specname OUTPUT= filename). 1D fits can conveniently be made by adapting some example input file, such as FRS$ROOT:[PROFI.GENERAL]satan1Dex.dat.

Manipulating the input file

The input file is an ASCII file containing a zero-suppressed matrix of channel contents. Because of a limit in SATANGD, no number may be larger than 32767. For this reason, first edit the input file and look for such large numbers (especially towards the end!). For instance, the last entry might be (73456)0 [indicating 73456 consecutive channels with zero content]. The program can be cheated by changing this into (30000)0 (30000)0 (13456)0 -- as long as the total number of entries is correct there will be no problem!

Running SATANGD

• Make sure the correct display address is defined:
  $> set display/create/trans=tcpip/node=... (node where you work)
• Start SATANGD: $> RUN FRS4$ROOT:[KHSCHMIDT.GRAF]GRAF
• At the "Enter command:" prompt, type gr/fit2d. This starts the 2D fit mode. (Omit the fit2d qualifier to fit a one-dimensional spectrum!)
• Enter the file name (with extension!) at the "data set" prompt.
• Display the spectra with gd. It is preferrable to simultaneously enter some formatting parameters for the display, e.g. scal(0.7) [overall plot scaling factor], symb(2) [crosses?], poly(1) [fitting polynom order, 2 is default]. The x- and y-ranges are defined with xmin(), xmax(), ymin() and ymax(), respectively. (An example: gd/scal(0.7) xmin(20) xmax(200) )
• The program will ask if you want to define a fitting window in x. Answer y and a cursor will appear. After you define an x-interval, SATANGD will attempt to fit the spectrum with a polynomial of the order defined above. The results are displayed on the screen.
• The data set including the data, format options and fit results can now be saved with gsave.
• The fit results can be stored in PostScript format with the gp command: gp/dev(post) produces a postscript disk file whereas gp/dev(p60) sends the plot directly to a printer (p60).
• Repeat the display and fit procedure. If desired, text can be placed on the plot with the command gwrite (asks for a text string which can then be placed with the help of the cursor.)
• Since the gp command actually opens a postscript file, this has to be closed with the command gend before it can be printed/written to disk. (If you choose the file option, you will have to edit the file before printing!)
• To exit from SATANGD, simply type exit.

Back to index

Concluding remarks

This concludes the "On-line calibrations" part of the FRS data acquisition manual. If you want more detailed information, please refer to the suggested reference litterature or contact the "experts"! If you have suggestions for improvements and/or updates, please contact Klaus Sümmerer or the author.