Minutes of the BEAST meeting
Friday March 26th, 1999 JST

A meeting was held immediately after the conclusion of the BGM to discuss issues raised about the current beam abort system as a result of lessons learned during ongoing BEAST operation and a recent KEKB review.

  • BEAM ABORT system:

    Attendees: Moffitt, Peak, Tsuboyama, Varner

    Peak presented a number of figures and diagrams of the current system and abort diode testing in Australia. This information was disseminated to Tsuboyama and Varner. A few major issues about the diodes were raised, and the responses are paired as follows:

    1) DIODE I_LEAK AFTER IRRADIATION - testing shows a significantly smaller increase in leakage current with irradiation for the S3590-08 + readout than for the BEAST diodes. An offset adjust is provided to allow maximum dynamic range to be used.

    2) GAIN FOR UNBIASED OPERATION - concern was raised about knowing the actual dose measurement during unbiased operation. Data was provided from tests with a couple of different radiation sources. Matching with EGS gives different estimates of the nominal "depletion depth". Proper knowledge of the sensitivity of unbiased operation shows an energy spectrum dependence and is thus to be considered as "under study". Peak has pledged to write up a summary of previous calculations/studies in a tidy form and distribute for discussion.

    3) TEMPERATURE STABILITY - A plot of the temperature stability of the diode + preamp was shown. Below 30C the thermal-induced shifts are tolerable. Operation at higher temperatures was deemed unlikely, given the proximity of the abort diodes to the cooling pipes. At any rate the diodes are installed and there is little to be done at the present time. Solutions will be sought only if problems exist.

    After this, a general discussion was held on modifications necessary to the current NIM abort module to be compliant with the recommendations of the KEKB review, as well as issues of dynamic monitoring. It was decided that the current module be modified to provide:

    = independent analog/digital outputs for monitoring
    = a 0.5-2s shaping output ("slow output" to compliment the current fast one)
    = possibility to issue a reset from computer control (with a physical "lock-out" switch to override and require manual reset).
    = packaged as either 2 separate single-width or 1 double-width NIM module
    = external NIM logic shall be employed to provide separate "beam abort" and "injection throttle" signals as necessary, from the outputs of the module

    Please see the attached set of items from Tsuboyama-san about testing and cabling issues in the current system. It was decided to leave the NIM module that has already been provided to KEK and tested by Tsuboyama-san as a prototype to run with until a "final version" is ready. This reduces some of the time pressure in developing such a final module. Communication of the upgrade criterion will be made by Peak, upon receipt of final specifications.

    Summary of action items:

    - Moffitt will summarize (in conjunction with Browder) the requirements on the outputs from the beam abort module. This should happen ASAP.

    - Peak will communicate these modifications to the engineer in Sydney and provide a delivery estimate after discussions there.

    - Tsuboyama will "cable in" and prepare the prototype module for operation after roll-in until an upgraded module becomes available.

    - Moffitt (with help from Browder/Tsuboyama) will test the beam abort diodes that have been installed on BEAST but not read out until now. Currently there is no DAQ space allocated for this, but space shall be made, as this is a rather critical issue.

    - Varner will repeat baseline shift versus dose rate/annealing measurements with the HARDCORE system within the next couple weeks.

    - Peak will provide a write-up of the testing/simulation results for knowing unbiased abort diode gain. Peak and Varner will compare testing results and agree on a general procedure for quoting the dose rate measurement [mRad/s = C * V_out]

    Progress on these issues should be presented during the next few SVD video meetings.



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    Here is the status of "beam dump" from T. Tsuboyama:

    (1) Cabling between Accelerator and BELLE electronics hut is done last week. The module inside the E-hut accepts NIM "level" signal. Reasonable filtering (response > a few msec?) is done in the receiver(accelerator) to eliminate noise.

    (2) Sydney PINs are installled both into BEAST and BELLE SVD. Cables are ready in the cage(BEAST) and E-hut(BELLE).

    (3) The PIN driver circuit was built by Sydney group as a NIM module. It was tested by Sydney group before shipping to Japan. Tsuboyama confirmed the function again in early March.
    It accepts 8 PIN-diode signal(*1). Each channel has a comparator and threshold can be adjustable. Multiplicity logic and latch are integrated to generate dump request.
    It outputs 8 analog signal for data logging(*2) (by IOTECH?) and a TTL level "dump" request(*3).
    --> The module is not computer controlled.
    You must go to the E0-hut in order to reset the "dump" request. This is a kind of fail safe(**).

    (4) We need to assemble (*1) a 26 pin connector to receive signal.
    The module has 8 potentiometer which is not described in the TDR. I do not have an idea how to solder the cables.
    (*2) a 9 pin connector to data logger
    Trivial but neither BEAST nor SVD has unused 8 channels in IOTECH.
    (*3) a standard lemo cable.


    (5) We might add some logic interface circuits -> to know which channels were caused a beam dump.
    -> to reset the "dump" signal through computer (contrary to the idea of (**))


    (6) How to test: System test and threshold determination could be done by BEAST without dumping the beam.

    (7) These days people pursue me that not only "beam dump" but also an "injection pending" signal should be prepared.