The Time of Flight wall is a scintillating plastic detector used primarily for particle identification. The wall’s current configuration consists of two sections with each section consisting of 120 scintillators. Each scintillator is made out of BC404 scintillating plastic with dimensions of 20cm x 8mm x 8mm. A group of four scintillators is coupled to 2 Hamamatsu PMTs via acrylic light guides. This results in 60 tubes per section, a total of 120 tubes in all. These pieces described above are glue together and held in unison with an aluminum frame termed as a mounting fixture, as seen in gray in figure 1. The mounting fixture is attached to the TOF support frame.

The light guides are designed to make sure that the path lengths from each scintillator to the PMT cathode are similar. Also, they had to match the 1x4 geometry of the scintillator, since they line up in a row, to the 2x2 geometry of the PMT. Figure 2 shows a group of four light guides used in matching to a PMT, as since in figure 3.

One of the sections rests inside the magnetic support structure. The magnetic field at the wall inside the support structure is approximately 100G. A study had to be done as to whether magnetic shielding was necessary. Preliminary tests show that the level of cross talk inside the tube increases dramatically. On either end of the detector unit, the PMT is covered with a magnetic shield, which attenuates the field enough that it will not have an effect on our tubes.

To eliminate cross talk of light from scintillator to scintillator, each scintillator is wrapped individually. A thin layer off aluminum foil is used with a layer of plastic tape protects the wrapping from being peeled off.

After the unit is all glued together, the unit is prepared for its final light tight wrap. This will protect the scintillators and PMT from exterior light. Black silicon paste is used to fill in all the gaps that light could enter and destroy the tube. The length of the scintillators is covered with a single wrap of Al foil, which extends up into the region between the mounting fixture and the light guide. The foil is not protected with a layer of tape and can be easily ripped off.

The wall and final light tight wrap is protected with a blue plastic shield attached to the support frame and the mounting fixtures. This shield can only protect the wall from light bumps and taps. It does not have the rigidity to protect the wall from heavy blows.

The TOF electronics are very simple and will be discussed later on. The basic idea behind the electronics is that each signal from the PMT is split. One signal goes into a charge integrating ADC to measure energy deposited, and the other goes through a discriminator then into a TDC. More electronics are used either to allow the TOF to trigger on itself or to run certain subsystems of the TOF.

The TOF has four running modes, which consist to two subsystems being implemented. There is the normal physics running mode, where the trigger is generated using a hit in a trigger counter and its necessary electronics. The cosmic run mode is a self-triggering method that is used to collect cosmic events for diagnostic purposes. For further diagnostic test, a pulse is applied to the test input for the timing discriminators. These events are used to understand the timing hardware for the TOF. The fourth running mode is used to monitor drifts in gain on the photo-tubes.

An LED pulser system is used to monitor this gain drift. This system consists of four LED’s driven by a circuit and +120V. Each LED is used to distribute light into one half of a section, or a quarter of the constructed wall to-date. The LED’s are housed in a box mounted on the rear of the wall section to the support frame. The light from the LED is directed to the middle of the photo-tube face using a fiber optic cable.

II. Properties of the TOF

A. Scintillators.

The scintillators are made of BC404 plastic manufactured by Bicron cut to size and polished with a diamond drill bit to the size of 20cm x 8mm x 8mm. The characteristics of BC404 are such that its decay constant is 1.8ns and its moderate attenuation length is 1.6m. The wavelength of maximum emission is 408nm.

Aside from these manufacturer’s quotes on the properties of the scintillators, further studies of these scintillators resulted with more useful characteristics. The velocity of light inside the scintillator was determined to be 1.5x10^8 m/s. Each scintillator was tested to insure that the attenuation length of the cut scintillator slat was greater than 30cm.

The attenuation length is determined from using a well-collimated beta-source, Sr-90. A collimated beam of electrons was directed at a specific position on the scintillator. Using the energy ratio between the two signals from either PMT on each side, the slope of the ln of the energy ratios verses the position is the attenuation length. Each scintillator has an attenuation length greater than 30cm, as to assure that no more than 1/3 of the light isn’t lost in the wrapped.

The velocity of the light in the material is quoted as being 1.9x10^8 m/s. The measured value of 1.5x10^8 m/s is due to light that is generated in the scintillator having a random direction of propagation. Therefore, it will scatter through the scintillator, effectively increasing its path length, until it reaches a PMT. This path results in having a measured value less than the quoted but accurate enough for our purposes.

B. PMT

The PMTs used are Hamamatsu’s R5900-M4. The minimum effective area for the cathode of each tube is 18x18 mm^2. The tube is designed with 12 dynode stages between one cathode and a 2 x 2 segmented anode. The maximum supply voltage is +900V, and the tubes should never have a current greater than 400 microAmps. The tube is responsive to light with a wavelength of 300 to 650nm, and the wavelength of maximum response is 420nm. The tubes were ordered with a design specification that the current amplification (gain) for each anode was at least 2x10^6 or greater.

The gain was cross-checked at Rochester. This measurement only checked the average gain over the entire tube and not on each anode. By measuring the current over the cathode and similarly for the anodes in total, the gain can be easily calculated. The gain of each tube was measured to be greater than 2x10^6 with a supply voltage of +900V.

The gain of the tube is sensitive to the supply voltage. The ln of the gain is proportional to the ln of the supply voltage. The absolute gain of at a specific voltage is different from tube to tube. The rate of change in gain with respect to the rate of change in of the supply voltage is constant from tube to tube. The slope of a log-log plot of the gain verse the voltage is all we need to know to match the gain of the tubes by forcing them to all have the same gain at a specific voltage with respect to a reference tube. Any desired gain can be chosen over all the tubes with this information. A gain of 2.5x10^6 was chosen because this is the maximum gain of some tube due to the +900V supply voltage limit.

C. Detector

There are three properties of the detector unit as a whole that are important to know. This document will only list averages of these properties, yet the actual value can be looked up in any one of the TOF tables listing the specific characteristics from scintillator to scintillator. We are interested in the timing resolution, the position resolution, and cross-talk over the detector ending at the PMT.

The cross-talk was measured in each scintillator to ensure that no scintillator in a detector unit produced a cross-talk greater than 10%. This value refers to the amount of energy measured in neighboring channels when a signal was originated in a specific channel. The cross-talk was measured using a collimated electron source, Sr-90, directed at the center of a scintillator. The trigger was set such that all channels could generate a gate. Furthermore, cross-talk can occur in three places: between scintillators, between the light guides and the photo-cathode of the PMT, and between the cathode and the anode of the PMT. The later of these generates the most cross-talk. There should be minimal cross-talk from scintillator to scintillator because they are individually wrapped. The cross-talk between the light guide and the photo-cathode is small since the mounting fixture properly aligns the light guides to the face of the tube. Each scintillator used has at most 10% energy deposition measured in a neighboring channel as compared to the channel with real signal.

Using the timing information between both PMT’s on either end of a scintillator, the collision point of a particle with the scintillator can be determined to within a position resolution of 1cm. The position resolution was determined using a typical scintillator and finding the time difference measured between each PMT attached to the scintillator. The scintillator was illuminated using a well-collimated beam of electrons emitted by Sr-90 at a specific position along the scintillator. Once the linear relationship between the time difference and the position is understood, the velocity of light inside the cut scintillator can be found. The velocity was determined to be around 1.5x10^6m/s. With the timing resolution determined, our detectors can determine the vertical position of a hit in our sicntillators with a position resolution of 1cm.

The most important property of the TOF is the timing resolution. This characteristic was the most studied, and the final quality tests on the scintillators had to result in a timing resolution of 100ps or better. It is also known that the energy deposited is inversely proportional to the resolution. All preliminary quality assurance tests were done with Sr-90, a beta source. The amount of energy deposited from the electrons is at least half of that deposited from what is expected during the normal operation of RHIC. The resolution was found in a specified energy region through out the energy spectrum from the electron source. The relation between the resolution and the energy goes as one over the square root of the energy. As the energy increases, the resolution will decrease until an intrinsic resolution of the detector is reached. The average resolution of all the scintillators over a range of +/- 10% of the energy peak in the electron spectra is 80ps. This resolution was measured at Rochester, and this number will be effected by RHIC environment.

III. TOF Geometry

The geometry of Phobos is such. The y-axis points up away from the center of the Earth. The x-axis is pointing out from the center of the RHIC ring. This requires the z-axis to point in the clock-wise direction of the beam.

The rough design geometry of the TOF wall with only two wall segments covers only 1.42% of the solid angle. The wall was designed to have a 15% occupancy, which is way the scintillator slats cover a 20cm x 8mm area with respect to the interaction point with a 1mm gap between each scintillator. Therefore, the total length of a wall segment is 1080mm. The inner segment covers angles in theta, the angle with respect to the beam pipe, of 90^o to 55^o and has a distance of 1.7m at 90^o from the interaction point. The outer segment covers angles of 55^o to 32.5^o with a distance from the interaction point of 2.6m at 55^o. At these distances, the angle in phi, the angle with respect to the x-axis, for the inner wall is 7^o and for the outer is 4^o. Both of the two wall segments cover a pseudo-rapidity range of 0 to 1.25.

IV. Electronics

There are the four running modes (physics, cosmic, LED, and timing calibration) that require most of the same electronics but with variations. Each system other than the physics has a specific trigger and/or pulse generator that has to be routed into the event manager. The physics mode requires no trigger generated by the TOF wall. This trigger is generated by the trigger counters, and the TOF wall requires the least amount of electronics in this mode.

The base line electronics of the TOF for physics consists of a series of discriminators, ADC’s, TDC’s, and a high voltage supply. The gates for the ADC’s and TDC’s is generated using the trigger electronics and will not be discussed here. Any signal from the tube is split using a tee. From the tee, one end is sent through delay BNC cable directly into an ADC to measure energy deposited. The other end is sent into the discriminator that rests in a Camac crate below each wall. These discriminators are set at a common threshold and hold sixteen channels. The output of the discriminator is sent through a twisted pair ribbon cable into a TDC to measure the relative timing.

There is a sum output on the rear of these discriminators. This sum output will generate a –50mV NIM signal per channel fired. We can use this signal to trigger on the TOF itself for a cosmic run. Each discriminator used in normal physics mode, timing discriminators, has its sum output signal channeled into another discriminator, the trigger discriminator. We can set the threshold of this trigger discriminator such that we can accept so many PMT anodes firing per group of 8 scintillators. The sum output of the trigger discriminator is sent into another discriminator in the counting house. This discriminator has a threshold of about –30mV and will accept all signals from the trigger discriminator. The purpose of this discriminator is to make a good NIM signal for further logic. The signal from the final discriminator goes into a 4-fold logic unit, and from the logic unit, the signal is sent into the trigger electronics.

Another feature of the discriminator is that it has a test input, which fires all channels when there is a signal in the test input. We can use this feature for the TDC calibration and timing hardware tests. The signal is sent out to the discriminators through 2 fan out units, which put out 16 signals each. Each of these units is feed from a fan out unit that is in side the counting house with the signal originating from the stop of the timing calibration unit. The start is sent into the 4-fold logic unit mentioned above.

The timing calibration unit has two controls to it. You can choose a range of time over which you want to generate pulses. The period is the time between pulses. With this in mind, the range must be greater than the period. As an example, if the range is 10 microseconds and the period is 2 microseconds, then pulses will be generated at a relative zero, two microseconds after the zero, four microseconds after the zero, six, eight, and ten microseconds after the zero. The rate at which these pulses will fire is controlled using the rate knob at the bottom left of the module.

There is another pulse generating system in the same NIM bin as the timing calibrator. It is used for the LED gain monitoring system. The delay output of one gate generator is sent into the start of another, and the delay output of the later is sent into the start of the former. This loop generates standard NIM pulses, which can be varied in time by changing the width (delay) of the output signal. The loop is begun by pressing the trigger button on the gate generator. One of the gate generators puts out a NIM signal that is feed into a fan out. Four channels go into the tunnel to drive an LED circuit, while another goes into a gate generator to be properly delayed. These LED circuits require a pulsed signal and +120V DC. The voltage is supplied using two dual HV units, which are located in a NIM bin above the Lecroy HV mainframe. From the LED circuit, a signal is sent into an LED to strobe light into a bundle of optical fibers, which are routed to PMT’s. A pin diode is used to monitor variations of the LED light. Any signal from the pin diode is sent into a fast amp and then in to an ADC channel.

The PMT’s are supplied with at most +900V. This is controlled using the Lecroy 1458 High Voltage Mainframe. Each tube is connected to the supply voltage through a patch panel above each Camac crate.

V. Moving the TOF/ the TOF carts.

It isn’t advisable to move the TOF at any time unless it is necessary. Both of the walls can be moved on carts, which were designed by engineers in Poland. The cart can also be used as a stand during normal operation. There are many aspects to the cart that should be discussed first.

The cart has a pair of rails running along the top to where the TOF support structure rests. The support structure is locked into placed placing a mandrel into a raised hole that is between the two rails. The rails allow the support structure to be slide on and off the cart easily. There are horizontal and vertical adjustments on the cart. The horizontal adjustments allow movement parallel and perpendicular to the rails on the cart. Parallel adjustment screw is found at one end of the cart near the top. There are four perpendicular adjustment screws located along the topsides of the cart. You can loosen them to adjust the TOF position, and then tighten them again to secure the wall in place. The vertical position is adjusted by screwing three bolts located underneath the sliding plates. Furthermore, the carts are give wheels that can move up and down in order allow the wall to rest on three floor plates, which are drilled into the floor. The wall is secured in place with respect to the floor using large brass dowel pins that slide into aluminum lined holes through the floor plates and in the floor and using floor clamps.

The wall on the floor has to be moved aside to pull out the wall in the magnet. To move the wall on the floor side, a few cables need to be disconnected. After turning off the Camac crate and stopping the Camac controls VI, the GPIB cable can be disconnected. The sum output cable from the trigger discriminator has to be disconnected. The test-input cables don’t need to be disconnected, but they have to be loosened as to have enough slack for the move. Finally, The high voltage and signal cables for the LED boxes need to be removed. Any other cables that do not have enough slack have to be removed as well, and a check of the set up should be preformed before the wall is moved and cables are ripped out of their sockets.

Once all necessary cables are removed, the wall on the floor can be unclamped from the floor. There are three floor clamps holding the wall in place, which need to be unscrewed from the floor. After the floor clamps are removed, the dowel pins that sink into the floor need to be retracted. They are held in place with a large brass pull pin being inserted into the hole through the dowel pin. The cart’s wheels can now be raised such that the weight of the cart is solely on the four wheels. The wall can be moved to the side where there are three extra holes for the clamps to be inserted. Once the wall is in the proper place over the three clamp holes, screw the clamps in the holes to hold the wall in place and out of the way.

Since the outer wall is out of the way, the inner wall’s cart can be attached to the magnet support structure in order to remove the inner wall. The cart’s height should be properly aligned such that the brass dowel pins on the side of the cart easily slide into the brass holes in the angle bracket attached to the magnet. At a proper height, the cart can be rolled up against the angle bracket and attached to it by using the brass bolts, which need to be removed before the cart is rolled into place.

With the cart in place, all the cabling in the back of the patch panel below the wall has to be removed and tied up to the TOF support structure. The cables going into the LED boxes have to be removed as well. After a final check that all the necessary cabling is removed, the wall is ready to be slide on the cart.

The only place to grab the wall to slide it either in or out is by the blue handles on either end of the wall and at the base of the support structure. There is a locking pin that runs through the base of the wall and needs to be lifted before the wall is slide out of the magnet. Also, the alignment between the rails on the cart with the rails on the magnet needs to be correct. One person needs to push on the negative z side of the magnet, while the other person can pull from the other side while lifting the locking pin. After the wall is on the cart, it can be worked on or moved around easily.

To put the wall back in, the cart has to be attached to the angle bracket on the magnet. All the necessary alignments should be checked, and the wall should slide in and lock into place with the locking pin. A survey of the wall shouldn’t be necessary unless an adjustment of greater than 1mm is made.

VI. Operations

A. High Voltage

During any running mode, the high voltage should be on and monitored. The person on shift is initially responsible for making sure there is no flaky behavior of the high voltage on any of the TOF PMT’s. The high voltage is controlled and monitored using the HV Slow Controls VI in Labview on the Plastic HV & Camac Slow Controls computer located on the console. The details on using this VI are located in the manual. A template has been generated which is located on this computer, and it holds all the requested voltages of each PMT in the TOF and in the trigger counters.

B. Discriminators

The discriminators in the tunnel have to be set to remote mode during any running mode. This is achieved by running the Camac Controls VI in Labview on the Plastic HV & Camac Controls computer in the console. The details on using the VI are located in the manual. All channels need to have to be unmasked and have a threshold of at least 25mV to cut out noise. The width should be set at 100ns. When the discriminators are in local mode, the thresholds are set to 500mV and the widths are approximately 110ns.

C. Physics Mode

Once the high voltage and discriminators are set properly, there is nothing else to do. The discriminators most likely should be set to 500mV with a width of 100ns, and all the channels should be unmasked. These values are subject to change but are the most common mode of operation. The high voltage values should be in the range from +700 to +900V. Any disabled or tripped channels will be noted in the database, but an effort should be made to insure all channels are working properly.

D. Cosmic trigger mode

There are a few changes to be made for a cosmic run as compared to a physics run. Neither the discriminators nor the high voltage need to be changed. The threshold for the trigger discriminator, which is located in slot 20 as seen on the front panel of the Camac controls VI, should be set at a proper level. A level of 75mV is the most common, since this specifies that at least two channels in either wall segment has to fire. At this level, the count rate should be approximately around 100 counts per second. A higher level can be used to look at cosmic shower events, since it requires more scintillators to be hit at once. On the other hand, if the threshold of the trigger discriminator is set to 25mV, the number of events with only one PMT anode firing can be found. This number in the past was found to be zero, but if it increases, they have to be considered in the analysis.

The 4-fold logic unit used in the TOF self-triggering system, which is located above the Fastbus crate, has to be set to a one coincidence level with channels A and B unmasked. Channels C and D need to be masked. The output has to be routed into the trigger electronics.

TOF cosmic events are to be taken as a separate run and documented as such. When performing a run, document the threshold levels of all the discriminators in the run logbook. A cosmic run should last for about 20minutes or 100,000 events, which ever comes first, and preformed at most once a week but no less than twice a month.

E. Test/ Timing Calibration mode

This running mode is designed to calibrate the TDC’s and to perform a diagnostic test on the timing hardware of the TOF. A timing calibrator, the function of the unit is explained above in section IV. Electronics, generates a pulse which is sent to each of the test inputs of the discriminators. This is the stop pulse from the calibrator, where as the start is sent into the 4-fold logic unit.

Channels A, B, and C have to be masked to the logical unit with channel D unmasked. The output is routed to the trigger electronics the same way as in the cosmic run.

The timing discriminators only need to be on, yet it doesn’t matter if the PMT’s are off or on. For a cleaner test, it is better to turn off the PMT’s.

A calibration run should be taken at least once a month. Since there is a signal in each channel for all events, it is only necessary to take up to 30,000 events for statistical purposes.

F. LED gain monitoring

The LED gain monitor system is used to identify any drifts in the gain of each tube separately. A pulse is generated using two gate generators in a loop, which is sent out to the tunnel to the LED circuits. The circuits send a pulse to one of four LED’s in a box mounted on the back of each TOF wall section. A pin diode inside the box measures and drift in light intensity of the LED, whose signal is sent into a fastamp and then into an ADC channel. A bundle of fibers grouped together inside the box as well direct light to the face of each tube.

The LED circuit requires +120V DC to operate. The voltage is supplied from within the in the counting house. There are 2 dual high voltage units in a NIM bin above the Lecroy high voltage mainframe. These units should only be on during an LED run only. 120V should not be exceeded because the voltage can damage the LED and/or the pin diode not to mention the tubes.

The trigger for the LED system is first sent through a gate generator to delay the signal properly and then into the 4-fold logic unit. Channel C needs to be unmasked, as the other channels are masked. Like with the other running modes, the output gets routed into the trigger electronics the same way.

The light measured in each photo-anode in each PMT is different, and some of the signals are too low to be useful. This isn’t a concern since at least two anodes need to fire to track the history of the tube’s gain because any lose in the gain should be seen over the tube uniformly. Furthermore, not all of the channels produce at least a 500mV signal, and therefore, the discriminators need to be set at a lower level. Setting the timing discriminators to 50mV is sufficient in obtaining signal in the TDC’s.

Out of all the diagnostic tests, this test is the most important. There has to be at least one LED test per week regardless. These tests will be documented as TOFLED tests, and the discriminator thresholds should be documented in the run logbook. The run should have at least 30,000 events.

VII. In the Event of an Alarm

The systems that have an alarm are the Fastbus crate, the Lecroy high voltage mainframe, the Camac crate controls VI, and the high voltage controls VI. Each one of these systems has an auditory alarm, and the Labview VI’s also have visual alarms. In the event of one these alarms going off, the person responsible for the system should be notified.

The only known case for the Fastbus crate to sound an alarm is when the power to the back panel of the crate was disconnect by the displacement of the safety bar, which run along the bottom of the modules. If the Fastbus does give an alarm, take note of the voltages and currents on the front panel by dialing through the digital display. Turn off the DC power by hitting the DC off button. The safety bar should be checked to see if it is resting properly, not allowing the modules to be pulled out. Turn the DC power back on and listen for an alarm. If none sounds, the Fastbus should be fine. If the alarm persists, repeat the steps above again. Andrei, Erik, and Edmundo should be called, and all action should be noted in the logbook.

The Lecroy high voltage mainframe may sound an alarm. If an alarm sounds, switch the key on the front panel of the mainframe to local. Press the HV Off button. If the alarm still sounds, toggle the power. If the alarm persists, there is a serious problem. Keep the power off. Review the manual, for any solutions to the problem. Cabling should be checked. The HV controls VI’s channel history needs to be inspected for any anomalies. Erik and Edmundo should be reached, and all information should be recorded. If the mainframe has a problem, all modules are to be moved into the same mainframe and the HV should be run from that unit.

The HV mainframe is controlled using a VI in Labview. This VI will give an auditory and visual alarm. This alarm is generated under three trip conditions, and each of them will disable the channel the trip occurred. The three conditions are a voltage hardware limit trip, a current limit trip, and an out of range limit trip. The hardware voltage limit is set on the rear of the high voltage module using a small common head screwdriver on a potentiometer. The measured threshold voltage is 1/100 of the limit voltage. The TOF modules are set to +900V. This trip occurs when the measured voltage is greater than the limit value, which usually occurs when the requested voltage is set too high. The current limit is a software limit, which is set during the initialization stages of the high voltage controls VI. This limit cannot be changed during the running of the VI, and the TOF tubes are set to 400 microAmps. This trip usually occurs when the tubes are being saturated with light. The out of range trip occurs when the measured voltage is +/- 5V out of range of the requested voltage. This is the most serious of the three since something is wrong either with the read out of the mainframe or something internal of the mainframe. The most common reason why this occurs is that a channel’s requested voltage is zero but is enabled. In this setting, some channels measure at most 10V, which will trip the channel. If the requested voltage is at zero, the channel should be disabled.

When the high voltage alarm trips, a large button will appear on the screen with a buzzing noise. The operator should press the button to acknowledge that the trip has occurred and should inspect the status display on the front panel of the high voltage controls. The color of the block, which represents a channel in the mainframe, will tell the operator why the channel was tripped. The channel’s history show be inspected using the information in the database, seen through the counting house portal on the web, and using the history plot on the front panel. The history plot on the front panel only displays the channel’s history over 24 hours, but with a greater resolution than what is written to the database. If the history of the channel looks normal until the trip, the cables to the mainframe should be checked. If there is access to the tunnel, the cables inside the tunnel should be inspected as well. If the PMT appears to be unharmed, that is to say that no odd changes in current of voltage were found, then the channel can be enabled again. The only way to enable the channel is by turning the HV off and then on. If the channel trips again without reason, then leave the channel off and further investigate the problem.

The final alarm is the Camac controls communication error warning that will appear on the same computer as the high voltage trip alarm. This warning occurs there is a problem in being able to communicate to the plastic Camac crates. The major reason for this occurring is that the crate is off. If the tunnel is open, check the status of the Camac crates, making sure that they are on and their status is OK. A good initial check to see if the alarm was only an anomaly is to press the "Read Out All Crates" button. If this operation performs correctly, then there is nothing to worry about.. To know that the operation performed properly, the X and Q values have to be valid , and the settings need to be other than a baseline value. For the TOF, these values have all channels unmasked, all the thresholds equal to 9mV, and the width is 0ns. The Camac crates should have continuous power to them since they are hooked up to a UPS each, whose information is displayed on the counting house portal on the web. Any problem with the UPS’s will be monitored through the silicon slow controls VI. If everything checks out OK, expect that the VI still producing an alarm. Restart the VI. If this does fix the problem, switching over to the optical to GPIB system can be done while the problem with the Ethernet to GPIB system is investigated for problems.

In the event of a fire or other event that might cost life, limb, or property damage, hit the Panic Off button on the high voltage mainframe. This will switch off the high voltage to all the channels instantaneously. Other systems might have to be turned as deemed necessary.

VIII. Trouble Shooter

This section is designed for constant additions as problems develop and are solved. If any original problem occurs, it should be noted in this section for future reference.

A. High count rate in cosmic trigger mode

The reasons a high count rate in the cosmic trigger mode can be due from the time calibrator is on, the high voltage to the LED’s are on, the thresholds to the discriminators are set too low, or there is a light leak in the detector.

B. Camac controls VI constantly gives an error alarm and all settings are at baseline

The power to the crates can be off, or the VI is in a funny state. If reading out the crates operation doesn’t work, restart the VI.