Minutes of the Booster Commissioning Working Group held on 12th of June 2009

Present: W. Weterings, J. Borburgh, G. Bellodi, S. Maury, M. Struik, B. Goddard, D. Nisbet, B. Puccio, M. Vretenar, R. Chamizo, O. Aberle, C. Carli, T. Hermanns, K. Hanke, B. Mikulec.
Excused: T. Zickler

Agenda:

  1. Communications
  2. Follow-up of open actions
  3. Overview of the Beam Interlock System (B. Puccio)
  4. Linac4 and transfer line interlocks (K. Hanke)
  5. Interlocks related to the PSB injection region (B. Mikulec)
  6. AOB

1. Communications

The minutes of the last meeting have been approved.

K. Hanke and C. Carli will try to alternate the commissioning meetings of their Linac4 work packages. The usual time slot will be Thursdays at 9:30. It has been considered more sensible to write only one common document on commissioning strategies for both work packages.

3. Overview of the Beam Interlock System

B. Puccio presented an overview of the beam interlock system (BIS) already implemented in the LHC and SPS (BIC-Overview_L4PSB-12June09.pdf).
The BIS consists basically of an 'AND' of all relevant system conditions leading to a beam permit only in case all conditions are TRUE. There exist different possible architectures (single controller, ring or tree architecture) and their combinations. The BIC comprises beam interlock controller boards with 14 inputs each in a VME chassis. A FESA class has been developed for monitoring and remote testing. Dedicated User Interfaces installed in the user system's rack connect the user system through a copper cable. The inputs are current loops. Always 2 independent inputs are required for redundancy; there are as well redundant power supplies provided per user interface. One more requirement for the user system is to be able to change the user permit to test the interlock chain.
Opto-couplers check if current is present at the input; if the current exceeds at least 10 mA, the user permit state is transmitted in RS485 format.

Of the 14 BIC inputs 7 can be masked by the operators (e.g. in case of error debugging), but the masking is automatically removed when the 'Safe Beam Flag' becomes FALSE (condition of a 'safe' beam has obviously to be defined before, but could be for example when the beam current exceeds a certain threshold). A history buffer is available with us accuracy.

B. Puccio has asked that it should be defined which PSB equipment should send user permit signals and which reaction would be adequate. Once available, the hardware requirements can be calculated translating into a cost estimate. Currently the implementation of a BIS is included into the work package of TE/MPE, but only for Linac4 without the PSB injection region. A cost of ~60 kCHF for a single BIC with 10 connections has been quoted.

4. Linac4 and transfer line interlocks

K. Hanke listed all present Linac2 interlocks for the different linac parts and gave a comparative list of Linac4 interlock conditions in his presentation (l4_interlocks.pdf).

It was proposed that the DTL interlock conditions should be integrated into the RF interlock. There should be a layer between the power converter interlocks and the BIC maybe implemented as a software layer. This should be discussed with PO. Current limits for the transfer line magnets were judged to be only necessary for the 4 bending magnets (in addition to LTB.BHZ20, 30 and 40) as the quads might change frequently for tuning purposes. A vacuum interlock has to be implemented and might be connected to the RF interlock. The current Linac2 watchdog system cuts the beam when the readings of selected transformers along the line differ by a pre-defined value; some kind of watchdog system should also be kept for Linac4 operation. B.Goddard believes that there is a need for a general software interlock system combining several software applications.
BLM's have to be used in addition to the other interlocks.

Assigned to Start date Description State Result
K.Hanke, B.Mikulec 2009-06-22 Discuss with PO how to implement Linac4 power converter interlocks in the BIS framework. See EDMS document 1016233. edit

As the magnet LTB.BHZ25 is not used anymore (was used for proton injection into LEIR), it should be removed at a suitable occasion.

Assigned to Start date Description State Result
C.Carli 2009-06-22 Follow up removal of LTB.BHZ25 and fabrication of replacement pipe. edit

Additional interlocks: intercepting devices, LEBT and Linac2 beam stopper, LEBT, Linac4 and LBS line dump (water flow if applicable, temperature), fire and smoke alarms, RAMSES radiation monitors.

It seems necessary to use beam conditions maybe in the form of flags for the definition of interlocks. With the BIS it is possible to mask and unmask interlocks (one example would be for screens 'IN' during measurements). These masks can automatically be set/reset under certain conditions, e.g. a BCT threshold could define a 'safe' beam.
In case the PSB was down, it would make sense to cut the Linac4 source. Nevertheless exclusive Linac4 operation has to be possible (for commissioning or measurements or during PSB failure).

It is not yet completely clear how the beam can be stopped - this should be tested at the 3 MeV test stand. The 2 MHz rf generator may be the only way to stop the source rapidly; to put the HV of the source 'OFF' is not sufficient. Moreover the first bending magnet downstream of the PIMS should be set to zero to send the beam to the Linac4 dump.

Assigned to Start date Description State Result
D.Kuechler, R.Scrivens 2009-06-22 Identify the most efficient way to cut the Linac4 beam rapidly at the source level (3 MeV test stand). The BIS should send a signal to set the screen grid voltage on the source to 0 V (~50 us reaction time) and in parallel a logic pulse to the LL RF system (see minutes 7/12/2009). edit

5. Interlocks related to the PSB injection region

In the presentation by B.Mikulec (Interlocks_PSBinj.pdf) several interlock conditions related to the modified PSB injection region were proposed to be included into the beam interlock system:

  • BI.DIS magnet or triggering failure: beam would be lost in the head dump or might be sent entirely to one ring or to the tail dump.
  • BI.SMV magnet failure: beam would be lost in the septum - should there be pickup coils installed to measure the magnetic field in addition to the power supply checks?
  • BI.BS (chicane bump) failure: beam would be lost somewhere in PSB ring
  • KSW (painting bump) triggering failure: up to 100 turns would be injected on same spot at foil heating up the foil
Could all these kicker and septa magnets provide a sort of 'ready' signal to avoid single or combined error scenarios?
  • In addition it seems sensible to interlock as well BI.DVT40 to make sure that the beam is really deflected to the head dump if the distributor fails.
  • Dump conditions (temperature): monitoring and interlock. For the H0/H- dump the dump current should be measured in addition as a high current would be indicating a foil failure or degradation; set threshold for an interlock. Simulations should be made to check if BLMs placed next to the H0/H- dump could detect the increased radiation (beyond radiation background level at this location) after foil failure.
  • Intercepting devices: mask/unmask in BIS
  • BLMs: for setting up or debugging in case of problems it should be possible to disable single BLMs as well as to vary the BLM threshold. The beam should only be cut after a certain number of pulses above threshold for a selection of BLMs to be still defined. It is important to finalise the BLM specifications soon.
Assigned to Start date Description State Result
K.Hanke, B.Mikulec 2009-06-22 Obtain final input from the Linac4 colleagues to provide BLM specifications to BI. Done. The specifications have been sent to B. Dehning. edit

It should be studied if the already mentioned watchdog system could be extended with one fast transformer in the PSB ring to obtain a measure for the injection efficiency.

Assigned to Start date Description State Result
L.Soby 2009-06-22 Can the fast transformers in 8L1 be connected to the watchdog system? See Minutes 21/09/2009. edit

Various error conditions of PSB and ISOLDE equipment are combined in the 'External Conditions'. Depending on the played cycle a sub-set of these condition has to be fulfilled; otherwise the spare cycle will be played (if all external conditions are fulfilled for the spare cycle) or the Linac2 pulse gets cut. A similar design should be implemented under PSB operation with Linac4.
Some of the ISOLDE interlocks cut the PSB RF at c=400; this reaction should be reviewed to prevent excessive machine activation. The PSB RF is also cut in case one of the bendings in the PSB-to-PS transfer line is in undefined status, but this is unavoidable as the beam is already in the PSB ring. Nevertheless one should make sure that the following Linac4 pulse should be cut.

M.Vretenar questioned if it would be possible to implement a very fast interlock to dump part of the beam pulse for selected failure scenarios, for example via the pre-chopper. He estimated ~2 us as travel time of a signal from the PSB to Linac4 and a reaction time of the order of 10 us. The gain of such a fast interlock would be significant for a beam pulse length of 400 us. Such an option has to be studied.

It was decided to write an EDMS document exposing the Linac4 and PSB with Linac4 interlock specifications.

Assigned to Start date Description State Result
B.Mikulec 2009-06-22 Write an EDMS document defining the interlock specifications. EDMS document 1016233 has been published. edit

6. AOB

The next meeting will be devoted to the LBE/LBS line upgrade studies.

-- BettinaMikulec - 22 Jun 2009

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