S. Zahariou

11, April 2001

RHIC Beam Diagnostics 

 

 

 

 

*        Beam diagnostics is essential to understanding what is happening to the beam as it is injected and stored in the RHIC. 

 

*       These systems detect different aspects of the beam, allowing us to perceive dynamic properties of the beam including and not limited to bunch intensity, beam position, bunch shape, tune, beam losses, etc ... 

 

*       I intend to discuss the RHIC Loss Monitor system.

 

 

Introduction:   

 

The goal of this long term order (LTO) is to serve as a first introduction to the RHIC loss monitor system and how to use the application programs that accompany it.  This paper is to be used as a tool for first time operators so that they may get acquainted with the system. Moreover I have included a troubleshooting guide, which may help an operator decide whom they should contact when the RHIC loss monitor display is not operating properly. 

 

v    The Purpose of the RHIC Loss Monitor system

 

The purpose of the RHIC loss monitor system is to provide quantitative loss data for tuning and archiving, to provide loss history data in the event of a beam abort, to protect sensitive equipment and prevent the quenching of RHIC magnets due to excess beam loss.  

 

All RHIC instrumentation is equipped to handle the potential radiation losses anticipated and prevention is the key.  Using materials that have proved to be radiation hard is obviously one way of delaying the onset of radiation damage to the equipment.  Monitoring losses with the RHIC beam loss monitors and tuning the beam accordingly so as to reduce the radiation levels is another way that equipment is protected.  Yet another

more aggressive approach has been to link certain loss monitors to three relevant links: the permit link, the blue quench link, and the yellow quench link, so that when losses exceed acceptable levels, the relevant link is pulled thus triggering an abort event (either ev-beamabort for the permit, ev-bquench or ev-yquench for a blue and yellow quench event respectively). 

 

 

v A Brief Description of the RHIC Loss Monitor System

 

To monitor beam losses in the RHIC ring 367 argon ionization detectors, a.k.a. beam loss monitors (BLM’s), are distributed around the ring and approximately 30 moveable BLM’s are available and can be connected to the system when required for studies.  Incidentally there are also 100 BLM’s located in the ATR (AGS to RHIC) line.  198 of the RHIC ring BLM’s are mounted on the quadrupole cryostats between the rings using stainless steel “belly bands,” as seen below [ref].

 

 

 

 

 

In the arc regions,

 

 

the BLM’s are shared by both the blue and yellow rings.  In the insertion regions, the beam optics is more complex and as a result more BLM’s are installed [ ref ].  Loss monitor data may be viewed and settings changed via three main application programs: 

 

v    RHIC Loss Monitor Display

v    RHIC Loss Monitor Threshold

v    Post Mortem (PM) Viewer

 

 

 

 

 

 

 

 

Personnel in the Main Control Room (MCR) can view losses via the RHIC Loss Monitor Display program,

 

RHIC Loss Monitor Display Program

 

which should always be running when RHIC is in operation.  The RHIC Loss Monitor Threshold program can assist personnel in the event that modifications to the thresholds of individual BLM’s are required.  The Post Mortem Viewer program provides loss history in the event of a beam abort.  All three applications can be found in the StartUp application program that is easily accessed at any MCR computer terminal. 

 

To access the Loss Monitor Display application program go to:

 

Start Up à Start à RHIC applications à Loss Monitor Display

 

To access the Loss Monitor Threshold program go to:

 

Start Up à Start à RHIC applications à Loss Monitor Threshold

 

 

To access the Post Mortem program go to:

 

Start Up à Start à General Programs à PM Viewer

 

 

¨     A Tour of the RHIC Loss Monitor Applications

                                      

v    Loss Monitor Display application

 

The Loss Monitor Display program allows operations personnel to view periodically updated loss monitor data.  The nominal update rate is around 1Hz, with the option to update from 0.1 Hz to 10 Hz.  Data is displayed in a typical graph with the x-axis indicating the S-coordinate position in meters and the y-axis indicating losses in units of mRad.  The data is also displayed in a waterfall style so that you can easily view your progress by seeing in one quick glance how losses change over time.  When the program is running it shows every BLM and magnet located in the particular section(s) of the ring chosen by operations personnel to be displayed, thus allowing for simultaneous display of beamline with locations of BLMs.  This program also allows operations personnel to zoom in on particular sections of displayed data by a simple click and drag procedure.  Moreover, the axes can be adjusted, thus allowing for the normalization of BLM data to the beam current.  

 

The Loss Monitor Display program accesses BLM data through either the blmGroup ADO’s (Accelerator Device Objects) or by circumventing the BLM manager and going directly to the madcChannel ADO’s to get individual BLM data, as illustrated in the figure below.

 

 

 

The MADC (Multichannel analog to digital converters) system collects data at 720 Hz and the MADCGroup ADO takes and averages this data at 10 Hz and depending on the ADO parameter requested (fast or slow), a report rate of 1 Hz or 10 Hz is acquired.  The BLM manager retrieves data from the madcGroup ADO’s and is used as a server of BLM data to applications.  The BLM manager essentially repackages and enhances this data for applications [ref].

 

v    RHIC Loss Monitor Threshold application

 

There are 1,740 superconducting magnets in the RHIC ring.  Excessive radiation losses can cause any of these magnets to quench.  In the Interaction Regions (IR’s) the triplets are very sensitive magnets near each insertion point and require protection.  During the RHIC FY2000 run, we had several real “quench” events at beam energy g=70 due to large beam losses.  All the real quench events were associated with the Q2 magnets in the triplets.  The fact that only non-arc quadrupoles in the triplets were quenched indicates that that the triplet quadrupoles are effectively more fragile than the arc quadrupoles [ref].   Therefore monitoring losses at these points and limiting radiation levels delivered to these magnets is vital.   However, due to time constraint, the threshold system has not yet been commissioned with beam.

 

Nevertheless, in response to the aforementioned permit and quench link requirements, thresholds for both fast and slow losses have been established.  Slow losses can be characterized as chronic with relatively low loss levels observed over a 20 ms period, while fast losses are characterized as acute with large levels of radiation at a particular location in the ring arriving over a 100 ms period.  To give you some perspective of these timescales it helps to know that the revolution period for stored beam in RHIC is 13 ms. 

 

The following loss thresholds have been established:

 

§        Slow loss thresholds (trip levels) are based on the limited experimental data acquired during the FY00 RHIC run and have been set to 2000 rad/hr.

 

§        Fast loss thresholds have been set to 200 rad/hr.

 

Please note that for the fast and slow thresholds, crude scaling with beam energy was provided by Alan Stevens during last year’s RHIC FY00 run.  For the upcoming RHIC FY01 run, however, these thresholds will not be scaled with beam energy and will be

true for all energies.

 

 

v    Post Mortem (PM) Viewer application

 

Post Mortem Data Collection is triggered by the occurrence of a Beam Abort Event on the RHIC Event Link.  A total of 12 seconds of data is stored in the BLM manager buffer.  The PM Viewer moves all BLM data buffered in MADC’s up to the console after a beam abort for analysis.  Upload can take up to 5 minutes. Analysis includes finding peaks, displaying evolution ring-wide and for a single channel.  The PM Viewer program logs 11 seconds of data before the beam abort event and 2 seconds after the beam abort event, making it a valuable tool for diagnostic purposes. Post Mortem actually detected a few real quenches in the Fy00 Run [ref].

 

 

v    A Tour of the Data Pathway – a simple introduction to how the signal is processed and gets from the individual loss monitors to the MCR computer terminal for observation

 

The raw signal from the loss monitors is processed before viewing at the operation terminals as it travels through versa module europa (VME) modules, front end computers (FEC’s) and MADC’s, etc…  All the beam loss monitors (BLM’s) are controlled by eleven FEC’s through the VME interface as shown on the following page.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


                                                             Loss detect to    

                                                                                       Beam Permit Link

Flowchart: Process: VME BUS  

 

 

 

 

 

 

 

 

 


VME

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Up to eight BLM’s are connected to an 8-channel V119 loss monitor module (card).  Eight V119 modules are plugged into the VME crate.  All eight V119 modules are managed by a V118 module that is also plugged into the VME crate.  Among its many functions, the V118 module is responsible for sending detected losses to the beam permit link.  The analog outputs from all eight V119 modules are then input into an off board 64-channel 360 Hz anti aliasing filter that is used to filter the analog output before digitations by the 64-channel MADC.  The V118 module can operate independently of the VME FEC so that the beam loss monitor system will function in the event of a VME FEC crash, a situation that operations personnel are familiar with.  The MADC communicates with the FEC through the VME bus.  The RHIC general purpose MADC system consists of a custom VME based controller module (V113) and a 14-bit 64 channel multiplexed A/D converter module (V114).  VME modules are quite noisy and the MADC’s are understandably sensitive to noise, therefore standard VME crates were modified for the special low noise needs of the VME bus. 

 

 

 

Troubleshooting:               

 

v    No beam in the ring

 

When acquiring data you expect to see no losses, but instead you see that one or more Loss Monitors, when reasonably zoomed in, have an offset, which you might mistake for noise, (but in fact the data is averaged and noise is too fast to see).  This means that your baseline has an offset and needs to be corrected:

 

v    Most likely it is an indication of a bad channel caused by either the electrical interference by surrounding cables or even a faulty cable, both of which are classified as a hardware failures.

v    Although it is best to have such a failure fixed by the appropriate technician, a temporary solution may be to compensate for the noise by changing the offset and subtracting it out.

v    If levels of a Loss Monitor exceed 100-1000 units, however, then an expert must be contacted.

 

 

v    Beam in the ring

 

§        If no data sets appear, then check the Manager status from the RHIC Loss Monitor Display program for any abnormal behavior.

 

§        If you know that you are generating relatively large losses, yet you see a big dip in the loss levels when viewing the displayed data, perhaps the High Voltage power supplies that power the loss monitors are not operating within the specified parameters.  You can first check the RHIC alarm display for an alarm indicating that the voltage is beyond +/- 20 mV of the threshold value.  You can then open up a pet page (FEC à Instrumentation àBLM à HV) to check the status of the power supplies.

 

1.     If the High Voltage is OFF, then Mei Bai can give us a script to turn them on.

2.     If the High Voltage is ON, then this could be a hardware failure and operations should contact the RHIC Beam Instrumentation Group.

 

v    FEC’s deliver data to the Manager and in turn the Manager listens to all FEC’s.  If operations personnel encounter a problem with either of these systems then they should be aware that these systems are overseen by the Controls Group and in the event that there is a problem with either of these systems, Controls should be contacted.  In particular, Bob Olsen (x2516) and Ted D’Ottavio (x7992) from the Controls Group may be contacted.

 

 

v    Gain Issues and Baseline Correction:

 

§        Baseline correction for the RHIC Loss Monitors is automatic in the Ring Manager (RingMan) only when Sequencer is used for ramping the magnets for acceleration in the RHIC ring.

§        This means that for ATR, first turn, and manual ramping, that we do not have automatic baseline corrections for the Loss Monitors.  It is therefore important to remember that when Sequencer is not running and consequently ramping is done manually, i.e. park2inject, that operations personnel must summon the Manager pet page to manually take a baseline.   For Fy00 Bob Olsen was responsible for this feature and would be able to demonstrate how to perform such a correction.

 

v    Missing Data:

 

If chunks of data are not displayed then go to the Diagnostics pull down menu in the Loss Monitor Display, there you will find Manager Status Info.  Click on that and a pop up window indicating either to stop and start a manager or that an FEC is down.   Follow up on the advice and either start and stop a manager or restart an FEC.

 

v    Power Dip:

 

During a power dip, MADC’s are rebooted and may not be in the proper state.  If this happens, then an MADC may not be working properly and you should restore the most recent MADC settings.  First place to look is in the Diagnostics pull down menu of the Loss Monitor Display program, where you will find MADC ADO’s.  If you click on that, a pet page will pop up with information concerning MADC’s status.  All parameters / settings of MADC’s can be found on that pet page. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

RHIC Beam Loss Monitor System – a summary note written by Mei Bai.

 

v     What is the system used for?

 

The goal of the RHIC beam loss monitor system is to:

 

v     To monitor beam losses around the ring during the injection, acceleration and storage – RHIC Loss Monitor Display application.

 

v     To protect the superconducting magnets from quenching due to a large beam losses- RHIC Loss Monitor Threshold application.

 

v     What does the system consist of?

 

The RHIC beam loss system consists of two major parts:

 

v     Hardware: beam loss monitors, HV power supplies, Electronics, Front End Computers and control modules.

                                 

v     Software: the main applications are the RHIC loss monitor display and RHIC loss monitor threshold setting pet pages for controlling the loss monitor system settings and the PM Viewer.

  

v     Whom you need contact when you need help on the beam loss monitor system?

 

Loss monitor manager: Bob Olsen (x2516)

Loss monitor display application: Bob Olsen (x2516), Ted D’Ottavio (x7992)

Loss monitor threshold application: Seth Nemesure (x5595)

Loss monitor threshold ADOs: Rob Michinoff (x5885)

Loss monitor hardware: Tony Curcio, Dan Lehn (x4542/x4095), Thomas Russo    (x7330), Paul Ziminski (x2343)

System commissioner: Mei Bai (x3397), Pat Thompson (retired)

 

v     Where do the Loss Monitor applications reside?

 

Three RHIC BLM applications reside in StartUp. All except PM Viewer can be found under RHIC Applications.  PM Viewer can be found under General Programs.

 

v     Loss monitor Display

v     Loss monitor Threshold

v     PM Viewer

 

v     What is the Beam Loss Monitor manager?

 

The BLM manager is designed to retrieve the data from the madcGroup ADOs and pass the data to the applications. There are two different managers for BLM, one is the ATR BLM manager and the other is the RHIC BLM manager. Make sure the BLM manager is running properly.  The manager can be started and stopped from StartUp.

 

v    RHIC BLM display application – discusses the different options offered by the Loss Monitor Display and the Loss Monitor Threshold applications.

 

As previously mentioned, the RHIC beam loss monitor display application is designed to read and display the readings from the beam loss monitors distributed along the ring and also in the ATR line.

 

v     The Loss Monitor Display application user interface:

 

v     Menu bar at the top of the interface. The options are:

 

Setup: allows one to choose different set of loss monitors. The option “hardware setup” loads the settings of the MADC and control’s hardware from file “run…”.

Data: allows one to either save the BLM data to a file or to automatically log the BLM data.

Display: allows one to set the X-Y plot to be in Log scale.

Diagnostics: the “Manager status info” option is very useful tools for diagnosing if BLM manager and FECs run properly. In case the MADC are turned off, one then can use  “Start all MADC” option to restart all the MADC. 

 

v     Dataset table – Can be found just below the menu bar. This table contains all the datasets currently stored in the memory. A maximum of 120 datasets can be stored. There are five columns in the table.  They are, from left to right, dataset name, source, graph, data, lock.  The default value of graph, data and lock is “No”.

                       

Info=”yes”: enables an info area between the Dataset table and the Waterfall display. This area contains the time stamp of the selected dataset. A comment field also allows one to put other related information about this dataset.

Graph=”yes”: shows the dataset on the X-Y plot.

Data=”yes”: tabulates the dataset in the Data table at the bottom of the use interface.

Lock=”yes”: show both the locked dataset and the  most current dataset on the X-Y plot.  

 

v     Waterfall display - Shows all datasets. All the datasets are displayed on top of each other depending on the order of their arrival. The latest dataset always appears at the top of the waterfall display. Different beam loss values correspond to different colors.  

 

v     X-Y plot of the BLM readings as a function of their s-coordinate position around the ring (in meters).  This plot is below the dataset table. The displayed BLM reading is in units of mRad.  Both axes can be customized. By clicking the right mouse button on any part of the plot, a window with axis setting pops up. In general, the BLM readings are all positive values in the presence of any beam loss. The higher the beam loss, the bigger the BLM reading.

 

v     Beam line display below the X-Y plot shows the corresponding lattice where the BLMs displayed on the X-Y plot are associated.

 

v     Data table for the selected dataset. This table is located at the bottom of the interface. It shows the beam loss at each individual loss monitor. The loss monitors are shown as their site wide names. It will not show up unless the dataset is switch to “yes” on the Dataset table. If no dataset is selected, this table is hided.

 

 

v     Acquiring Data buttons. There are two buttons places at the top right corner of the interface.  The BLM data can be read and displayed either once by pressing the “Acquire Once” button, or can also be obtained periodically if the “Acquire Continuous” button is chosen.

 

v     Beam intensity. The readings from the beam current transformer are also available below the two acquisition buttons.

 

 

Important features of the Loss Monitor Display application:

 

v     Selection of the set of BLMs.  There are two sets of loss monitors associated with this program, the ATR line and the RHIC ring, both of which are available in this application.  There are a total 367 BLMs placed around the ring and 100 along the ATR line. One can choose either one of the two sets of BLMs from “Setup” on the menu bar.

 

v     “Ring mode” and “First turn mode”. These are two different modes for the BLMs distributed in the ring. In “Ring mode”, the BLM MADC is scanned at event 720 Hz. In “First turn mode”, the BLM MADC is triggered at either the blue febBunch event or the yellow febBunch event. This is also true for the ATR loss monitors.

 

 

v     Diagnostics on the menu bar.  The “Diagnostic” on the menu bar is designed for diagnosis and troubleshooting. There are 4 different options under “Diagnostic”. The option “status” is a very useful tool for checking the FEC status and can tell which FEC does not running correctly.

 

 

v     The RHIC Loss Monitor Threshold application

http://www.rhichome.bnl.gov/Controls/doc/RhicLossThreshold/RhicLossThreshold.html

 

The RHIC BLM system is also designed to protect the superconducting magnets from being damaged due to excessive beam loss. This could be either an instant beam loss or a cumulative loss over many turns. A set of thresholds is assigned to all the loss monitors around the ring. If the detected beam loss exceeds the value of the threshold, the beam abort event is then triggered. Unlike the BLM Display application, the threshold application only applies to the ring loss monitors.

 

Due to the change of beam energy, the threshold setting is expected to be different for injection, ramp and storage. The nominal value of the RHIC BLM threshold for an instant beam loss is 78.3rad at injection and 49.3rad at 100Gev/c. The nominal value of the RHIC BLM threshold for an slow beam loss is 0.25rad at injection and 4.07rad at 100Gev/c. By the same token, it is also expected to have different threshold settings at different time of the ramp.

 

v     The Application User Interface:

 

v     Menu bar at the top of the menu bar.

v     Event List Area below the menu bar. It shows the associated events in the threshold setting. By selecting one event from the list, the corresponding threshold setting for each individual loss monitor is displayed  in the Threshold Setting Table. One can choose multiple events for setting different threshold values at different time of the acceleration. When the selected event comes,  the corresponding  threshold setting is loaded into the hardware. The available events are: green FebBunch for the injection, RHIC flat-top event for the storage and 6 blm events for the ramp.

v     Information Area below the menu bar on the right of Event List Area. This shows the event which is chosen to be displayed in the table and the unit used for displaying and editting.

v     Threshold setting table below the information table. It shows the threshold setting for all the loss monitors in the ring. The following parameters are shown in the table.

   

v     Loss monitor side wide name Fast mask: to disable/enable the corresponding  loss monitor from tripling the beam permit link due to an instant large beam loss.

v     Slow mask: to disable/enable the corresponding loss monitor from tripling the beam permit link due to a cumulative large beam loss.

v     Fast threshold: set the threshold value for the corresponding loss monitor. If an instant beam loss is detected to exceed this value, the beam abort is triggered assuming the loss monitor is not masked. Two units are available both for display and editing, engineering unit (mrad) and counts.

 

v     Slow threshold: set the threshold value for the corresponding loss monitor. If the cumulative beam loss over many turns is detected to exceed this value, the beam abort is triggered assuming the loss monitor is not masked. Two units are available both for display and editing, engineering unit(mrad/hr) and counts.

                              

v     Gain: defines the resolution of the threshold system. This is not available when the engineering unit is chosen for editing.

           

v     Current setting button: to get the current threshold setting in the RHIC loss monitor system.

 

v     Add event button: to add an event on the threshold event list.

 

v     Delete event button: to remove an event from the threshold event list.

 

v     Save button: to save the threshold setting to a file.

 

v     Make Live button: send the threshold setting to the hardware.

 

 

v     RHIC Loss Monitor pet pages

 

For every FEC of the RHIC loss monitor, there are several pet pages available for the MADC settings and BLM controls. They are under pet-Tree->FEC->Instrumentation->BLM->FEC. The useful information is:

 

    MADC trigger event:

 

v     GreenFebBunch for ATR BLM’s or RHIC ring BLM’s in first turn mode. Event 720 Hz for BLM’s in ring mode.

v     BLM delay event: GreenFebBunch

v     HV ps setting: 1400volts

v     HV ps leak current: < 10

v     Gain: X1(low gain), X10(high gain)

 

 

v    RHIC Recipes

 

 

FY00 RHIC BLM Threshold System Commissioning plan – this recipe is a bit out of date because the application has been modified.

 

·     Dry Run

 

1.   Check the HV ps status, check the Madc status, check the FEC status. The nominal HV setting is 1400 ± 10 volts.

2.   Reduce the HV setting to about 500 volts and record the readings of all the assocociated loss monitors.  The beam loss on the Loss Monitor Display application is in unit of mrad.

3.   Repeat (2) for all the loss monitors around the ring. This invloves all the  eleven ring BLM HV power supplies.

4.   Start the Loss Monitor Threshold application from StartUp. Click the button current setting to get the current threshold values in the hardware. The event list should be empty.

5.   Due to the geometrical position, each individual loss monitor has different sensitivity to the beam loss. We start from the loss monitors more sensitive to the beam loss. For a particular loss monitor, on the Loss monitor threshold application, set the Fast threshold value to be below the signal level due to the HV change. Unmask the loss monitor if it is masked. The Slow threshold setting remains to be above the signal level.

6.   Increase the HV to full voltage. This change of HV is expected to produce a significant signal which is above the threshold set in (4).

7.   The RTDL event beam abort should be triggered if the detected beam loss exceeds the threshold value. Record if the event doesn’t occur.

8.   Check whether the threshold system is masked. If not, record.

9.   Reset the threshold system for the next testing. Reset the BLM status from “Loss” to “Normal”. Trigger  the reset permit link event (evt.237)  to re-establish the permit link.

10.  Repeat (5-8), but keep the fast threshold setting to be above the signal level and the slow threshold to be below.

11.  Repeat (5-9) for all the ring loss monitors.

 

 

·        With Beam, assume it is possible to generate the beam abort event without pulling down the beam permit link and causing magnet quench.

 

            The commissioning of the Loss Monitor Threshold system will be integrated with the Commissioning of RHIC beam abort system and  RHIC beam permit link system.

           

 

 

 

-    At injection energy

 

1.   Check the HV ps status, Madc status and FEC status. The nominal HV setting is 1400 ± 10 volts.

2.   Start the RHIC Loss Monitor Threshold application. Load the threshold setting for the injection energy into the table and use event blm1 to load the setting into the register.

3.   Start from the loss monitor at the end of the beam dump. Use the upstream dipole kicker to generate a local beam loss. Increase the kicker strength until the beam loss exceeds the fast threshold set by the RHIC Loss Monitor Threshold application. The beam abort system is expected to be activated upon the beam abort event.

4.   Unmask the loss monitor and re-establish the beam permit link.

5.   Repeat (3-4) to test the slow threshold system. In this case, the kicker is used to generate a moderate local beam loss. The accumulative amount of the loss over 10 ms should be above the slow threshold value set through the application. 

 

-    At storage

 

Repeat the procedures at the injection energy.