last update 06march2004@20:03 by pfm
last update 12march2005@17:00 by kei
Data collection will take place in Data-U2. The experimental account is 02001, with the nominal betanmr password (please see paul or kei with questions). The details are below. All acquisition files are located in the directory
/user/02001
|
Files
for: |
Location |
|
DAQ |
/user/02001/readout |
|
Scalers |
/user/02001/scaler |
|
SpecTcl |
|
|
PI & H0-rf on/off |
/user/02001/spectcl |
|
4AP |
/user/02001/spectcl/4AP |
|
T1 |
/user/02001/spectcl/T1 |
|
RF
Control |
/user/02001/rf |
|
Gauss
Meter |
/user/02001/magnet |
The abbreviations are: “PI” = Particle Identification, “H0-rf on/off” = external magnetic field or rf in NMR technique is on and off every 60s, “4AP” = pulsed rf technique, in which the initial direction of polarization is inverted and the obtained ratio is 4AP where A is the asymmetry parameter and “T1” = pulsed rf technique, in which the polarization is measured as a function of time (spin-lattice relaxation time) after beam is chopped. Any of the three main programs, along with the applications for the gaussmeter and rf control, can be started from the 02001 home directory in Bash shell. You can chose Bash shell from KDE controller at the bottom left in the monitor. Only the Readout program (goreadout) is executed in spdaq26. You need to login to spdaq26 from Linux machines in data-U2 by typing “ssh spdaq26” then run goreadout. All other programs should be run in the Linux machines in Data U-2 (u2pc1, u2pc2 and u2pc3).
The appropriate programs are:
|
DAQ |
goreadout |
|
Scalers |
goscaler |
|
SpecTcl |
|
|
PI & H0-rf on/off |
gospectcl |
|
4AP |
go4ap |
|
T1 |
got1 |
|
RF
Control |
gorf
& gorfam |
|
Gaussmeter |
gometer |
The definition file for SpecTcl is ~/spectcl/def.tcl. In gospectcl, an analysis of life time is available, for which the primary beam has to be pulsed. The default time bin is 50 ms. Also, the online analysis for the pulsed AFP method (go4ap) and for the relaxation time of polarization (got1) are available.
To start the NMR magnet G156DH, you will need to open up a panelmate application, which can be done in the DATA-U area or the S1 vault. Open the file
\\mordor\nscdata\Panelmate\S1expA.mt2
and go to page 0. Select the G156DH button and click on the start button to
turn on the power. If the G156DH button states <
When the magnet power supply is turned on, the LCW water lines should be opened to provide cooling to the magnet coils. Both the supply and return lines must be opened. The valves to operate the LCW for the NMR magnet are located on the north wall, behind the NMR magnet, in the S1 vault.
The current for the magnet can be controlled through the labwide epics system. We normally access the magnet using the Anet MDI application, which is available on lab pc's in the DATA-U and vault areas. Usually the application is found in the NSC folder located on the Desktop. Start the application and select File>New. A Select Size window will appear, and you can click "OK" to accept the 2 x 2 window. A window with four control boxes will appear. Left-click on the top left input area and enter G156DH. Read and Set values should appear in the appropriate windows. Left-click on the set area and enter the desired power supply current in amps. Both negative and positive values can be entered, and sign does matter. The maximum current is 200 Amps. The field calibration for the NMR magnet was measured and available at:
http://www.cem.msu.edu/~mantica/field_calib_20040303.html
and recent measurement at:
It takes about 5 min to stabilize the temperature of the magnet. You would see ~0.5% change of the magnetic field at maximum although it is samll compared with the modulation width of rf in β NMR.
A gaussmeter is available to get a rough idea of the magnetic field. The Gaussmeter is a FWBell Model 5080, and the user manual is available in the bnmr cabinet in room N109. Daniel Groh wrote a tcl application to control and read-back the gaussmeter remotely. The control is via RS232 through a single-port ethernet connection. The program is available in the experimental account 02001. Simply type "gometer" at the bash (unix) prompt.
The readout of the gauss meter is written in a file ~/magnet/field every 10s throughout the experiment. To start auto saving, push Status à Write Output to File button.
The radiofrequency source for the rf measurements is located in the S1 vault, on top of the RPMS wien filter. The system is an HP Model 33120A Function Generator. The user's manual is located in Paul's office (W205 Cyclotron). Control of the Function Generator is via remote access using an RS232 through a single-port ethernet adapter. Daniel Groh wrote a tcl application to control and read-back the rf generator remotely. The program is available in the experimental account 02001. Simply type "gorf" at the bash (unix) prompt. The rf generator should be run with a sine wave output. Frequency modulation is available, and should be operated using a ramp function.
The output of the function generator is amplified using a Model 150CR 47dB 50W rf power amplifier placed right back of the NMR magnet. The input/output impedance are 50 ohms and the maximum input is 1 Vpp. In order to turn the amplifier on, a 24 Vdc has to be supplied between pin 1 and 2 of the amp-connector at the back panel and it is supplied by a DC power supply placed below the amplicier. The maximum power for the circuit is ~35 Watts and typical input to the amplifier for the power is 250 ~ 300 mVpp. With more than ~35 Watts, the gain will be saturated and the wave form will be distorted. The output impedence of the amplifier (50 ohms) is matched with the rf coils using an R (50 ohms 50 Watts) in an RCL resonance circuit placed at the back of the NMR magnet. The capacitor is Jennings CVC500, a variable (~100 - 500pF) vacuum capacitor. It can be tuned manually to optimize power drop in the rf coils. A ~100 – 1000pF vacuum capacitor (CVCD1000) is also available. More details on the rf coils are available on the beta website:
http://groups.nscl.msu.edu/beta/
The RCL circuit is monitored using an rf probe. The probe converts the AC signal to a DC voltage, which can be read on a voltmeter.
For an rf application in pulsed AFP method, a transformer without 50 ohms resistor is used to step the input impedance down to several ohms of the rf coils. This is to get higher resonance Q, thus a narrower FM band, and higher power for the NMR. The ratio of the wound line around a ferrite core (transformer) is typically
Input : Output = 5 : 2,
hence about 4/25 step down from 50 ohm. The voltage across the coil is monitored through a "voltage dividing capacitors bridge" by a probe of oscilloscope. There are 5 capacitors in series (3.3 pF each, total 0.7 pF) in the bridge and the voltage of the last one is monitored. The ratio of the voltage of the monitor point and the actual one is about 25.
There are 3 rf coils.
|
Turns |
L(uH) |
R(ohm) |
a(Oe/A) |
Freqency
range (kHz) |
|
30+30
|
64.5 |
1.03 |
6.7 |
700
– 1450 |
|
15+15
|
20.8 |
0.61 |
4.3 |
1500
- 2400 |
|
15+15
#2 |
23.3 |
0.64 |
4.5 |
1500
- 2400 |
|
7+7 |
5.2 |
0.20 |
1.85 |
3000
– 5500 |
The inductance (L) and resistance (R) are measured by a LCR meter, which is available at the electronics shop, with cables used to make LCR resonance circuit. The a (Oe/A) is a magnetic field generated by the coil with a current of 1A. The magnetic field for the NMR is calculated from the monitored voltage as:
H = V(DVM)/50 * a / sqrt[2] : for RCL circuit monitoring the voltage drop
across R
H = Vpp(monitor) * Ratio * a / (2 * pi * freq * L) / 2 / 2 : for CR circuit
monitoring the voltage drop across L, e.g. C bridge
The maximum field by the present system is about 3.5 Oe. The frequency range is a range of resonance frequency that can be tuned in the present resonance system with the rf coil and the variable capacitor.
An Amplitude Modulation may be needed for the pulsed AFP method to get higher efficiency for the inversion of polarization. The output from the HP Model 33120A: FG1 (center frequency +- FM) is mixed with an appropriate sine wave generated by another HP Model 33120A: FG2 borrowed from Dave Morrissey. A hand made Double Balanced Mixer is used for the synthesis, which is placed at the top of the second function generator. The composed rf signal is then gated at the Tennelec Linear Gate and sent to the amplifier. Typical settings for these two function generators to generate FM + AM signal are
--- FG1: center +- FM ---
Frequency = center frequency
Amplitude = power you need
Sweep mode
Sweep Trigger = External Trigger
Sweep Time = 20 ms (typ.)
Start Frequency = center freq - FM
End Frequency = center freq + FM
--- FG2: AM signal ---
Burst Modulation mode
Burst Cycle = 1
External Trigger mode
Amplitude = 1.2 Vpp
Frequency = 25.1 Hz
DC offset = ~ 15 mV
Both function generators operate in trigger mode, for which a TTL signal (rf on) is given to the BNC connector at the back panel of the FGs. The function generator for the AM can be also controlled through the ethernet. Simply type "gorfam" at the bash (unix) prompt.
The settings of function generators can be written in a file ~/rf/settings manually by pushing Status à Write Output to File button. You should save the settings of function generators after every NMR run. The new settings are appended to the old saved settings.
For experiment 02001 the magnetic field, the rf field and the beam will be pulsed for normalization and AFP purposes. The electronics driving the pulsing circuit are located in a NIM rack in S1 placed on top of the RPMS wien filter. The pulsing time is set using a Tennelec Pulser, a Dual Scale Down, a Lecroy 222 Gate Generator and logic modules. A typical cycle time (Ton/off) is 60 s on/ 60 s off for magnet/RF pulsing, e.g. 1s pulsing at the pulser and 60 times scale down at the scale down module. A counter is placed in the NIM crate, and can be used to monitor the count-up time for the off status.
For a pulsed AFP method, a timing program of
Beam1 - rf - count1 - rf - Beam2 - norf - count2 - norf - Next cycle
will be used. To pulse the beam, a TTL signal is sent to the cyclotron control room. A high level is beam off. Typical times in the timing program are beam Tb = 250ms, rf Trf = 20 ms each and count Tc = 400ms for 57Cu (T1/2 = 200 ms). The timing program consists of 2 beam-count cycles, one with rf and the other without rf. In the rf-on cycle, the counting time is sandwiched by rfs so that the inverted polarization does not affect the next counting time, in which the polarization points an opposite direction. These times are set using LeCroy 222 modules. It has to be noted that the total time should be shorter than the cycle time, namely
Ton/off > Tb + 2*Trf + Tc.
For example, for 60s/60s H0 pulsing, set Tennelec Pulser 1 Hz and Scale Down factor 60. For 60s/60s rf pulsing send “mag/rf on” signal as a gate input to Tennelec Linear Gate. For pulsed AFP method, set Tennelec Pulser 100 Hz and Scale Down factor 56 and set each LeCroy 222s for appropriate values (beam 200 ms, rf 20 ms and count 300 ms). For pulsed AFP method, “rf gate” signal is sent as a gate input to Tennelec Linear Gate.
The cycle status is sent to the data acquisition system, where they are read into the INP registers on the V262 CAEN IO module as
INP0 master gate
INP1 H0-rf on/off
INP2 beam gate
INP3 count gate
A new fixture to mount the catcher and rf-coil at the right place has been installed in the NMR magnet. Just screw the flange, which mounts catcher and rf coil holder, on the fixture. In order to put the catcher at the center of the NMR magnet, 2 different spacers are used. A thinner one is for NaCl (3 mm) and a thicker one for Si (0.3 mm/piece).
If μ(57Cu) = 1.6 ~ 2.5μN, the resonance frequency at H0 = 1 kOe is 813.0 ~ 1270.3 kHz.
The particle delta E detector PIN1 is located in a pot in S1 just upstream from the NMR magnet. The detector can be inserted into and retracted from the beam path remotely. The control is through a panelmate application
\\mordor\nscdata\Panelmate\S1expA.mt2
The preamplifier is a Tennelec 4-channel preamp mounted to the pot close to the PIN 1 detector. The bias supply is located in the DATA-U2 area. The voltage is +50V. The typical leakage current is 510 nA.
A veto detector is placed at the end of the implant mounting device. This detector PIN2 is a T-mount detector, and uses the same 4-channel preamp module as PIN1. The 27-259B (TB-020-300-150) can be used. The typical leakage current at +50V is 520 nA. The 27-259A (TB-020-340-150) has been also tested but has worse resolution and larger leakage current (4.7 uA at +50V). At lower voltage (+30V, 3.0 uA), however, it may be usable but still worse resolution compared with that of 27-259B. Typical spectra can be found
Two thin (3 mm) and two thick (20 mm) plastic scintillators are used for beta detection. The detectors are designated B1 - B4. B1 (thick) and B2 (thin) are the up detectors, where B3 (thin) and B4 (thick) are the down detectors. The thick detectors are good up to 4 MeV electrons as a energy detector. The power supplies (power desing model 1570) for the beta detectors are located in a NIM rack mounted on top of the RPMS wien filter. The nominal voltages for B1 and B4 are -1700V and for B2 and B3 –1900V.
The S1 radiation safety system has been changed. There is a mid-room barrier chain that must be in position to secure the room. The following steps are necessary to secure the room:
The safety system timeout is 2 minutes after the second red button is depressed.
The daq code is fairly simple, involving the readout of only three modules, Input Register, ADC, and TDC, all in VME. The VME crate and spdaq26 computer are located in the S1 vault. The Data structure has the following format:
The master gate is an or between any of the 4 beta detectors, the PIN 1 detector (for particle id), and the PIN 2 detector (for veto).
Default spectra parameters for SpecTcl are placed in the file
/user/02001/spectcl/def.tcl
The clock signal is supplied by CAEN V3820 Scaler at ch 1. The frequency is 50 MHz and it operates in "free run" mode. It starts to count from 1 to 2^32 then back to 1 again and cycles forever. A 25 MHz mode is also available.
The up/down detector ratios are calculated automatically in SpecTcl. The spectrum summing limits (both high and low threshold limits) are set in the SpectTclInit.tcl file, located in /user/02001/spectcl. These values are loaded automatically when SpecTcl is started.
The online analysis for the pulsed AFP method are also available in /user/02001/spectcl/4AP and /user/02001/spectcl/T1. In 4AP mode, the ratios are calculated only when count gate at INP3 is presented. In T1 mode, the ratios are calculated as a function of time (50 ms bin * 10 by default) after the beam is chopped.
Two scalers (CAEN Scaler C3820) will be used. One is read by Scaler Display software and the other by Readout. For the scaler display, a scaler is declared in /user/02001/readout/BNMRSkeleton.cpp and initialized in /user/02001/readout/CMyScaler.cpp. A configuration file is /user/02001/scaler/scaler.tab. The module for scaler display will be cleared, for example, every 10s, which is a preset value in the Readout GUI, by scaler display software. On the other hand, a scaler for Readout is declared and initialized in /user/02001/readout/BNMRSegment.cpp. In the present experiment, a 50 MHz clock signal at ch1 is read and put in the data stream and thus the module is not cleared ("free run" mode).
A NaCl and/or a Si single crystals are used as implantation media for 57Cu.
Cu in NaCl single crystal is highly supposed to occupy a substitutional site of Na because of the similar ion radii between Na and Cu. The implantation depth is about 1.5 mm with the primary beam of 140 MeV/nucleon 58Ni. Our NaCl crystal is 3 mm in thickness. Because of its heavy mass, 57Cu easily gets electrons after passing through thin PIN detectors (300 um) even at the energy of 70 MeV/nucleon (more than 10% of 57Cu will be singly charged) and the hyperfine interaction between the electron and nucleus would destroy the polarization. So, after the wedge at the intermediate image 2, no material should be placed on the beam line.
Cu in Si single crystal occupies a little off substitutional site of Si towards <111> direction, which means an electric field gradient in that direction. If we choose <100> direction to apply the external magnetic field for NMR, the eqQ splitting would vanish because of a so called "magic angle". The Si single crystal we have is 70 mm in diameter and 0.3 mm in thickness. Since the range in Si is about 1.5 mm, a stack of Si plate will be used as a catcher. Several pieces of 20*20 mm plates are cut along <100> direction out from the bulk crystal. In order to stop 57Cu in the stack of Si crystals, plastic absorbers would be required, which should be placed right in front of the Si catchers. It has to be noted that even choosing the magic angle, there would be a higher order shift of the resonance frequencies (a single NMR line splits into 2), depending on the size of electric coupling constant. In that case, we may need a wider FM to cover the slightly split resonance lines.
A KBr and Pt single crystals may be used.