## **POWER SUPPLY SYSTEMS (WBS 1.1.3)**

### Introduction

The extraction/primary beam power supply system consists of the power
supplies for the beamline elements, their local controls and regulation
equipment, the cables and connections from the power supplies to the 480
VAC power panels and the cables and connections from the power supplies
to the devices that they drive.

**Table 4.3‑1** summarizes the number and types of power supplies needed
for the NuMI beamline. For beam tuning and focusing, each trim and
quadrupole magnet has its own power supply. On the other hand the bend
circuits use several 500 kW supplies in series (or for the V108 circuit
a Main Ring Power Supply) in order to obtain the desired voltage levels.
All power supplies are standard refurbished FNAL power supplies, with
the exception of the kicker power supply and horn power supply. Some of
the MI correction element power supplies will need to be built, but from
a standard, existing FNAL design. The kicker and horn power supplies are
designed and built specifically for the NuMI application. The horn power
supply uses a transmission line to supply current to the two horns. The
kicker power supply uses standard RG220 cable. The following sections
describe the power supply system, starting with the conventional, mostly
refurbished power supplies, then the kicker power supply and finally the
horn power supply and its transmission line. Cables are covered briefly
at the end.

  ---------------------------------------------------------- ------------
  Type                                                       Number

  Kicker Power Supply (requires a 60 kV charging power       1
  supply)                                                    

  Horn Power Supply (requires 2 charging power supplies and  1
  a transmission line)                                       

  PEI 240 kW (horn power supply charging power supplies)     2

  Main Ring Style                                            1

  PEI 500 kW                                                 10

  PEI 20 kW                                                  23

  MI Correction element power supplies                       19
  ---------------------------------------------------------- ------------

**Table 4.3‑1** Summary of Number of Power Supplies and Types

### System Description: Conventional Power Supplies

**Table 4.3-2** through **Table 4.3-4** list the power supply circuits
(except for the kicker), corresponding magnet types, numbers of magnets,
their resistance, inductance, cabling information, current and voltage
information, power supplies required and their corresponding voltages,
currents and power. The two 240 kW power supplies used for charging the
horn power supply capacitor bank are discussed in the section on the
horn power supply. The others are discussed here.

Table 4.3‑2 : Power Supplies in MI60

(See document TDH_V2_4.3_Tables_2-4.xls for tables 4.3-2 through 4.3-4)

Table 4.3‑3: Power Supplies in MI62

Table 4.3‑4: Power Supplies in Target Service Building

All the magnet supplies will be ramped. There will be seven high-current
bend circuits: the kicker magnet (I:KPS6N), the first Lambertson magnet
(I:LAM60), the second and third Lambertson magnets (I:LAM61), the
C-magnet (E:V100) and three bend circuits (E:HV101, E:V108, E:V118). The
power supplies are located in three areas, MI-60, MI-62 and MI-65. The
extraction system power supplies (I:KPS6N, I:LAM60, I:LAM601, E:V100,
E:HV101), the first 12 corrector element power supplies, and the first 6
quad power supplies are located in MI60. The second bend power supplies
(E:V108), one 20 kW power supply (E:H104), and 6 quad power supplies are
located in MI62. The final bend power supply (E:V118), one 20 kW power
supply (E:H117), 9 quad power supplies and 9 corrector power supplies
are located in MI-65.

The kicker power supply is covered in Section 4.3.3. The first
Lambertson magnet, due to aperture restrictions in quad Q608 downstream
of it, is run at a lower current than the last two Lambertson magnets.
Thus there are two separate 500 KW power supplies for the three
Lambertson magnets (I:LAM60, I:LAM61). The C-magnet is powered by a 500
kW supply (E:V100). The first bend string (E:HV101) consists of six EPB
magnets powered by three 500 kW supplies in series. The second bend
(E:V108) consists of six B2 magnets powered by a Main Ring type power
supply. The circuit E:V118, the four B2 magnets, is powered by a four
500 kW supplies, run as 2 sets of 2 500kW supplies in series. There will
also be 21 quadrupole circuits, each with a 20kW power supply and two
dipole circuits, each with a 20kW power supply. There are nineteen
low-current circuits for Main Injector corrector magnets. Several
quadrupole circuits may be combined in the future to run from one power
supply if it is shown to be an effective way to operate. The critical
devices will be the E:HV101 and I:LAM61 circuits. Standard FNAL hardware
is used for the critical device circuits.

#### 4.3.2.1 Upgrades and Improvements to Conventional Power Supplies {#upgrades-and-improvements-to-conventional-power-supplies .unnumbered}

All of the large NuMI power supplies (240kW, 500kW, Main Ring) and most
of the smaller NuMI power supplies (20 kW and MI corrector power
supplies) are re-used power supplies from decommissioned beamlines. The
20 kW and MI corrector power supplies did not need to be upgraded or
refurbished. The others were re-furbished and upgraded to meet the
anticipated 10-year lifetime of the NuMI beamline. The refurbishing
included new voltage regulators, new gate firing circuits, water lines,
and ramp calculators were installed. The power supplies were also
modified for two-quadrant operation (invert) by removing diodes and
adding silicon controlled rectifier switches (SCRs). Each circuit is set
to use the maximum power supply voltage tap possible.

#### 4.3.2.2 Power Supply Regulation {#power-supply-regulation .unnumbered}

To meet the beamline specifications given in Section 4.1 particular
concern needs to be given to the six bend supplies; the criteria are
somewhat less stringent for quadrupoles and dipole correctors. There are
three sources of current variation for magnet strings. One is the 720 Hz
line ripple. The other two sources of current variation are line voltage
changes and load changes. Simulations of a particular power supply (or
series of power supplies) can be used to see the effects of these
changes on the resulting flattop current. The present cost estimates for
the NuMI beamline power supply regulation include costs for standard
regulation plus the costs of a filter choke for three of the six magnet
strings. An analysis of the power supply stability requirements for the
new beam optics has been completed and is shown in **Table 4.3‑5**
through **Table 4.3‑8**. Details are given in Section 4.1. A change
request will be made to incorporate these requirements into the present
cost and schedule. These beam stability criteria listed in Section 4.1,
lead to the stability limits listed in **Table 4.3‑5**, where
instability in ppm is the plus or minus variation allowed in that loop
relative to its operating current at flattop.

  -------- ------------ ----------- ------------------- -------------------
  String   Maximum      Peak        Corresponding       Allowed Instability
           Current of   Current     target RMS in       in ppm
           PS           (amps)      microns             

                                                        

                                                        

  Lam60    2500         916         160                 900

  Lam61    2500         1985        300                 730

                                                        

                                                        

                                                        

                                                        

  V100     5000         2692        200                 670

  HV101    2500         1670        20                  100

  V108     4250         4442        200                 60

  V118     5000         4173        200                 70
  -------- ------------ ----------- ------------------- -------------------

Table 4.3‑5: Power Supply Regulation Requirements due to Beam Stability

The power supplies also need to regulate well to minimize beam loss. The
fractional losses at 4x10^13^ppp in the primary beam line should be kept
below 10^-4^ in most locations and 10^-6^ in the central region of the
carrier tunnel. MARS simulations of losses along the beamline are nearly
complete. The results will be summarized in **Table 4.3‑6**. One can
clearly see that the requirements for power supply regulation to limit
beam loss for groundwater activation are much less than those needed for
beam stability and physics. (This is known from the data we have from
the present study of beam loss using MARS and STRUCT.)

  -------- ---------- --------- --------------- --------------- ---------------
  String   Maximum    Peak      Corresponding   Allowed         Allowed
           Current of Current   Fractional Beam Instability in  Instability
           PS         (amps)    Loss            ppm             Percentage
                                                                Change

                                                                

                                                                

  Lam60    2500       916                                       

  Lam61    2500       1985                                      

                                                                

                                                                

                                                                

                                                                

  V100     5000       2692                                      

  HV101    2500       1670                                      

  V108     4250       4442                                      

  V118     5000       4173                                      
  -------- ---------- --------- --------------- --------------- ---------------

Table 4.3‑6: Power Supply Regulation Requirements due to Beam Loss

#### 4.3.2.3 Line Ripple {#line-ripple .unnumbered}

Filter chokes are used to filter out the 720Hz ripple on the line. When
a PS current is changed, even if it is line-synched, it shifts slightly
on the 720Hz ripple, which is quite sharply peaked. As a result, there
is a fair amount of current variation despite line synching. Even
extraction can vary by up to 30 microseconds. **Table 4.3‑7** shows the
current variation that would occur assuming no filter chokes, for each
string. We will use filters on all the circuits listed **Table 4.3‑7**.
This requires 7 filters since the V119 string is two sets of 500 kW
PEI's in series and thus requires two filters. One might argue that the
Lam61 string does not need a filter, but the difference between
allowable instability and the level without a filter is only a factor of
2. The requirement numbers were obtained by looking at single string
variation, not multiple, thus we should err on the side of better
regulation per string than the allowed instability ppm numbers show.

  -------- ----------- ----------- ------------- ------------ --------------
  String   Maximum     Peak        Allowed       Variation    Variation due
           Current of  Current     Instability   due to 720   to 720 Hz in
           PS          (amps)      in ppm        Hz in ppm    ppm with
                                                 with no      Filters
                                                 Filters      

                                                              

  Lam60    2500        916         900           1606         209

                                                              

  Lam61    2500        1985        730           349          17

                                                              

  V100     5000        2692        670           528          14

                                                              

  HV101    2500        1670        100           225          12

                                                              

  V108     4250        4442        60            202          4

                                                              

  V118     5000        4173        70            324          7
  -------- ----------- ----------- ------------- ------------ --------------

Table 4.3‑7: Current Variation due to Line Ripple

**4.3.2.4 Current Variation due to Line Voltage and Load Changes**

Line voltage changes were simulated for the NuMI V108 string. Assuming a
constant reference voltage, a 5% change in line voltage was easily
corrected for at the level of 100 ma (at a flattop current of 4250 amps)
by the standard voltage regulation loop of the power supply. This
corresponds to \~24 ppm change. This level of line voltage change is the
most one would expect and results in a current variation well below that
required by NuMI. Thus standard regulation is sufficient for line
voltage changes.

Load changes were similarly simulated for the NuMI V118 string. A 5%
change in load resistance (corresponding to about a 10^O^ C change in
the copper of the magnet, or the LCW changing 15^0^ C) resulted in a 1
amp change out of 4250 amps. This corresponds to a 240 ppm change. Other
magnet strings have not been simulated, but would probably come to a
similar result. **Table 4.3‑8** shows the current variations due to load
changes when using special FNAL electronics. Due to beam requirements
and concerns about ease of bringing up the beam,, special FNAL
electronics will be installed on circuits all 6 strings.

  -------- --------- --------- ------------- ----------- ----------------- -------------------
  String   Maximum   Peak      Allowed       Variation   Variation due to  Extra Factor Needed
           Current   Current   Instability   due to Load Load Changes with (regulation/spec)
           of PS     (amps)    in ppm        Changes     FNAL Electronics  
                                             (ppm)       (ppm)             

                                                                           

  Lam60    2500      916       900           653         326               0.36

                                                                           

  Lam61    2500      1985      730           277         138               0.19

                                                                           

  V100     5000      2692      670           287         144               0.21

                                                                           

  HV101    2500      1670      100           304         152               1.52

                                                                           

  V108     4250      4443      60            191         96                1.59

                                                                           

  V118     5000      4173      70            240         120               1.72
  -------- --------- --------- ------------- ----------- ----------------- -------------------

Table 4.3‑8: Current Variation due to Load Changes

#####  Regulation Requirements

The conclusion is that filter chokes and FNAL electronics will be used
for all 6 strings and either a BμLB or JITtER system will be installed
for the three major bend strings (HV101, V108, V118). A BμLB system is
more expensive and regulates throughout the ramp where as the JITtER
system, under development in Beams Division, will sample and correct at
the start of flat top. The JITtER system should be easier to support and
less expensive and sufficient for NuMI, if the development shows it to
be a reliable system.

Autotune will greatly help, but has its drawbacks as one must have beam
and working beam position monitors to use Autotune. When beam first
starts up, Autotune will not be able to correct things immediately. Thus
we will use both Autotune and an additional level of power supply
regulation. In addition, each string will be tuned for the maximum
bandwidth. This is the standard way of starting up a power supply
system.

The remaining types of power supplies in the primary beam line are 20 KW
PEI's for the quadrupole magnets, 200 turn switchyard dipoles, and Main
Injector (MI) trim power supplies. The 20kw PEIs have standard
regulation of +/-0.05% of the maximum current of the power supply (100
or 200 amps). The MI trim magnets standard power supply regulation is
+/-0.1% of the maximum current of the power supply (12 amps). We believe
that this level of regulation is sufficient for the NuMI beamline.

#### 4.3.2.6 Controls {#controls .unnumbered}

The NuMI power supplies will have the same controls as the P1, P2, P3
and A1 lines. Operations will have only to adjust one point per load.
The groups of supplies will be regulated by one current regulator, and
thus will act as one. Each supply will have an SCR Unit with a closed
voltage loop, the same as the single supplies. The supplies will all
receive the same voltage reference. Each magnet load will have one
current reference. We use C468 ramp generators, which are current
referenced. We are installing a local DAC, which has better temperature
drift numbers, in the current regulation system to improve the noise.

### Extraction Kicker Power Supply

The requirements on the extraction kicker are similar to those of the
long-batch kicker, which is operational at MI52. The normal operating
mode will be one in which six Booster batches, each consisting of 82 x
18.9 nsec bunches, fill the Main Injector. The first Booster batch is
sent to the antiproton source and the remaining five are extracted to
NuMI. However, for periods when antiproton is not in a stacking mode it
will be desirable to be able to extract six Booster batches to NuMI.
Three kicker magnets are to be used in NuMI. The magnets are to be
located in the region downstream of quadrupole Q602, with the power
supply upstairs in the MI60 South Power Supply Room.

The kicker power supply will power two of the three magnets in series
and then those in parallel with a third kicker magnet. The pulse-forming
network (PFN) consists of two 32 section 10 ohm PFN's in parallel with
one thyratron switch driving the magnets. A 60 kV power supply will be
used to charge the PFN.

#### 4.3.3.1 Specifications {#specifications .unnumbered}

The specifications for the kicker system are given in **Table 4.3-9**.

#### 4.3.3.2 Thyraton {#thyraton .unnumbered}

**Figure 4.3‑1** shows the NuMI thyratron enclosure. The CX1592C from
Marconi Applied Technologies (née EEV) was selected for the thyratron,
with thought of minimizing pre-fire rates. This is the same thyratron
used for proton extraction for pbar production. A new triggering method,
recommended by Marconi, will be used to give a longer thyratron life
because of the longer length of the current pulse.

  -------------------------- --------------------------------------------
  Kick Angle @ 120 GeV       900 µrad (3.6 kG-m), to radial inside of MI,
  protons                    nominal

  Current Per Magnet         2460 A Nominal/ 2730 A Maximum

  Nominal integrated field   3.6 kG -- m (1.2 kG-m per magnet)

  Maximum integrated field   4.0 kG-m
  (110%)                     

  Field Rise Time (1%-99%):  1.30 µs

  Field Fall Time:           N/A

  Field Flattop Time:        9.78 µs minimum (6 batches)

  Flattop During Pulse:      +/- 1%, best effort to +/- 0.5%

  Flattop pulse to pulse:    +/- 0.5%

  Maximum PFN Charge Voltage 60 kV

  Maximum PFN Output Current 6000 A

  Repetition Rate:           1.9 seconds

  Maximum Charging Time:     1.5 seconds

  Pulse Forming Network      11.5 µs minimum (=9.78 µs + 2 x 0.60 µs +
  Length                     0.50 µs )

  MI reset to transfer/next  1.25 seconds/1.83 seconds
  MI reset                   
  -------------------------- --------------------------------------------

Table 4.3‑9: Specifications for the NuMI Kicker Power Supply

![](media/image1.png){width="6.490277777777778in"
height="5.0152777777777775in"}

Figure 4.3‑1: Thyratron Enclosure

#### 4.3.3.3 Pulse Forming Network (PFN) {#pulse-forming-network-pfn .unnumbered}

The design of the PFN must have a ripple period close to magnet transit
time for best performance. The design of the PFN has to meet not only
electrical constraints, but also physical size and cable routing
constraints. The NuMI kicker power supply has two PFN's in parallel.
Each PFN has 32 sections, 20 nF/section, 2.0 μH/section and a 49 kV
nominal kick. The NuMI PFN also has increase coupling (12% vs. 2%) and
longer lifetime capacitors versus the MI-52 design. **Figure 4.3‑2**
shows a schematic of the PFN design. **Figure 4.3‑3** will show a
simulation of the total integrated field. The simulation used as much
detail as possible concerning the magnet and PFN. The purple line is for
two magnets in series, the red line is for a single magnet. Once can see
the rise time requirement of 130 nsec may be hard to meet with 6 Booster
batches.

![](media/image2.png){width="6.4944444444444445in"
height="8.404861111111112in"}

Figure 4.3‑2: NuMI Kicker Design Schematic

Updated figure has not been made yet.

Figure 4.3‑3: Simulated Kicker Integrated Field

#### 4.3.3.4 Charging Power Supply {#charging-power-supply .unnumbered}

The charging power supply specification has been written. (ES-370-035),
and needs to be reviewed.

#### 4.3.3.5 Controls {#controls-1 .unnumbered}

The kicker will use a NIM bin based controls system. The modules are
copies of the existing kicker controls for MI. Two special cables have
been installed between MI-52 and MI-60 for fast inhibit & permit
signals. **Table 4.3‑10** shows the kicker fault signals that will be
monitored.

+--------------------------------+-------------------------------------+
| #### Reset and if cle          | **Investigate before resetting**    |
| ars no problem {#reset-and-if- |                                     |
| clears-no-problem .unnumbered} |                                     |
+--------------------------------+-------------------------------------+
| Personnel Safety               | HV Power Supply in Range (Absolute) |
+--------------------------------+-------------------------------------+
| Trigger Supply Out of Limits   | Magnet Current in Range (Absolute)  |
+--------------------------------+-------------------------------------+
| Filament Supply Out of Limits  | Thyratron Prefire                   |
+--------------------------------+-------------------------------------+
| Thyratron Oil Level Low        | Thyratron No Fire                   |
+--------------------------------+-------------------------------------+
| Thyratron Temperature High     | Open Fault in Cable or Magnet or    |
|                                | Loads                               |
+--------------------------------+-------------------------------------+
| Magnet Fluorinert Level Low    | (Magnet I)/(Charge V) Out of Limits |
+--------------------------------+-------------------------------------+
| Magnet Load Temperature High   | Shorting Fault in Cable or PFN or   |
|                                | Loads                               |
+--------------------------------+-------------------------------------+
| Magnet Load Fluorinert Flow    |                                     |
| Low                            |                                     |
+--------------------------------+-------------------------------------+
| Magnet Load Fluorinert Level   |                                     |
| Low                            |                                     |
+--------------------------------+-------------------------------------+

Table 4.3‑10: Kicker Fault Signals

### Horn Power Supply

#### 4.3.4.1 Horn Power Supply Specifications {#horn-power-supply-specifications .unnumbered}

The horn power supply must deliver 200 kA (average, ± 2.5%) pulses every
1.9 s. with a pulse-to-pulse repeatability of 1% and current monitoring
to 0.4%. As a safety margin the power supply system will be designed to
operate at up to 240kA. This results in a system load current of 7250
Arms operationally (8700 Arms design). The specifications are given in
**Table 4.3‑11**. The horn power supply system is located in the power
supply room, underground, next to the Target Hall. The main components
are the charging power supply, the capacitor bank, the silicon
controlled rectifier (SCR) switches, the current transducers, and the
safety system. The *NuMI Horn Power Supply Manual*, revised 4/02 is the
most complete description of the horn power supply system.

  --------------------------------- -------------------------------------
  Pulse width                       2.6/5.2 ms

  Bank Voltage                      860/515 V

  Pulse                             1/2 sine

  RMS current                       5125/7250 A

  Peak current                      205 kA peak

  Average flattop current           200 kA (average, ± 2.5%)

  Pulse to pulse repeatability      1%

  Current monitoring                0.4%

  Repetition rate                   1.87 seconds

  Duty                              continuous

  di/dt, horn                       268/146 A/us
  --------------------------------- -------------------------------------

Table 4.3‑11: Power Supply System Output, operational level

In the horn power supply system, energy is stored in a capacitor bank
and switched via a parallel array of SCR switches into the horn load. A
parallel strip transmission line is used to connect the power supply to
the horns. The circuit is a damped LC discharge circuit that will reach
peak current when the SCR switch releases stored energy from the
capacitor bank to the horns via the transmission line. The horn power
supply can provide either a 2.6 msec or a 5.2 msec "flattop" pulse,
depending on how the capacitors are connected. **Table 4.3‑12** shows
the design parameters for the horn power supply operating in these two
modes. Also shown, for completeness, are the parameters for the
prototype horn power supply used for testing horns at MI8.

+-----------------+-----------------+-----------------+-----------------+
|                 | Prototype Horn  | Operational     | Operational     |
|                 | Power Supply    | Horn Power      | Horn Power      |
|                 |                 | Supply          | Supply          |
|                 |                 |                 |                 |
|                 |                 | (5.2 msec)      | (2.6 msec)      |
+-----------------+-----------------+-----------------+-----------------+
| Operational     | 200             | 205             | 205             |
| Current (kA)    |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| Peak Possible   | 200             | 240             | 240             |
|                 |                 |                 |                 |
| Current (kA)    |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| Peak Voltage    | 800             | 550             | 1100            |
| (V)             |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| 1/2 sine wave   | 800-850 μsec    | 5.2 msec        | 2.6 msec        |
| pulse base      |                 |                 |                 |
| length          |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| Repetition rate | 0.5 Hz (up to   | 0.5 Hz          | 0.5 Hz          |
|                 | 1.5 Hz)         |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| Peak Current    | Varies          | 2 kA            | 4 kA            |
| per capacitor   |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| RMS current per | Varies          | 72.5 A          | 145 A           |
| capacitor       |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| Total           |                 | 0.9 F           | 0.225 F         |
| Capacitance     |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| Comments        | Current depends | 12 sets of 10   | Change 120      |
|                 | on the          | capacitors      | parallel caps   |
|                 | resistance of   |                 | divided into 12 |
|                 | the circuit and |                 | cells to 60     |
|                 | the voltage     |                 | series pairs;   |
|                 | limit of the    |                 | need two 240kw  |
|                 | PEI PS)         |                 | PEI's in series |
|                 |                 |                 | to get voltage  |
|                 |                 |                 | (1100V)         |
+-----------------+-----------------+-----------------+-----------------+

Table 4.3‑12 Design Parameters of Horn Power Supplies

#### 4.3.4.2 Horn Power Supply Overall Design  {#horn-power-supply-overall-design .unnumbered}

The circuit used to provide current to the horns is a damped R-L-C
discharge circuit as shown in **Figure 4.3‑4.** It achieves peak current
when the SCR (Silicon Controlled Rectifier) switch releases stored
energy from the capacitor bank to the horns via the stripline. The load
elements, listed in **Table 4.3‑13**, are for the full-length stripline
installation in the Target Hall and factor in skin effects and
temperature rise. Power dissipation is given for the two possible pulse
widths that can be generated.

![](media/image3.wmf){width="6.090972222222222in"
height="3.6770833333333335in"}

Figure 4.3‑4 Horn Power Supply system schematic diagram.

  ----------------------------- -------------- ----------- --------------
  **Element**                   **L, μH**      **R, mΩ**   **P~2.6~ /
                                                           P~5.2~, kW**

  Horn #1                       0.689          0.270       7.1/ 4.2

  Horn #2                       0.510          0.071       1.9/3.7

  Transmission line:                                       

  Transmission line: P. S. to   0.152          0.095       2.5/5.0
  beamline, 9.5 m.\*                                       

  Transmission line: Between    0.856          0.535       14.1/28.1
  horns, 53.5 m.\*                                         

  Cap. Bank, connections        0.1            0.050       1.3/2.6

  Stripline connections\*       0.1            0.010       0.26/0.52

  Total                         2.407          1.031       27.1/54.2
  ----------------------------- -------------- ----------- --------------

(\*Estimate; from drawings, 7-Dec-01)

**Table 4.3‑13** Horn Power Supply Beamline Load Elements

Energy to provide the high current pulse for the NuMI horns is supplied
by DC power sources (240 kW PEIs) that are used to charge the capacitor
bank during the quiescent period between horn pulses. When the capacitor
bank is configured to provide 2.6 ms pulse widths, the stored energy in
the bank is 85 kJ. When configured for 5.2 ms pulse widths, the
operating level of stored energy is 120 kJ.

With any array of capacitors connected in parallel, a capacitor
experiencing a fault will have to absorb in addition to its own stored
energy, the energy of all the capacitors connected in parallel with it
and do so without case rupture. For this reason the capacitor bank is
divided into twelve isolated sections, or cells, making the maximum
amount of stored energy in any cell 12 kJ or less. All of the cells are
isolated by diodes from each other and the charging source, and by SCRs
from each other and the load. Consequently, the cells cannot communicate
with each other under fault conditions. Having the capacitor cells
isolated from each other forces current sharing among each of the twelve
SCRs switching load (horn) current.

The style of case construction specified for these capacitors utilizes
14-gauge steel, instead of the normal 16 gauge, and have a fault energy
containment rating of 25 kJ to provide a safety factor greater than two
in each of the cells. The capacitor bank is assembled in four groups of
three cells. Each group of three cells is referred to as a 'quadrant.'
The quadrants are labeled "A" through "D."

The bank normally operates with 120 capacitors in service, 30 in each
quadrant. Provision was made to accommodate a maximum of 144 capacitors.
All safety margins are determined for the maximum capability (240 kA
design level) of the capacitor bank when used for NuMI beamline service.
A basic schematic diagram of the high power elements is shown in
**Figure 4.3‑4**. FNAL drawing #9820-MD-370111 includes additional
detail.

To minimize the voltage from the outer conductor of horn 1 to the
target, located within the throat of horn 1 for the low energy beam,
horn 1 is installed in the return side of the transmission line, nearest
(electrically) to the capacitor bank. To achieve current flow in the
proper direction, i.e. current in the center conductor of the horn in
the same direction as the beam, it is necessary to make the positive
side of the capacitor bank 'ground.' The capacitors in the bank are
non-polarized and the PEIs can operate equally well with either terminal
declared 'ground' since the PEI output floats.

The low-side bus from each capacitor cell (row) within each quadrant is
connected to all of the others, and then connection to the enclosure
frame is at a single point. All connections to an earth ground and the
horn modules in the beamline installation are made to this point via the
LEM^®^ current monitor. The LEM provides for detection of fault currents
in the grounding cables. The LEM signal output is tied into the controls
interlock chain to terminate system operation in the event significant
ground currents are detected.

Any electrical fault from the stripline or horns to the mounting
structures or shielding steel in the beamline installation will allow
the capacitor bank output current to return to the capacitors by a an
alternate path, and ultimately through the cables connecting to the
single point frame ground of the enclosure. The LEM current transducer
will detect current in these cables.

#### 4.3.4.3 Capacitor Bank Electrical Components {#capacitor-bank-electrical-components .unnumbered}

The capacitor bank specifications are given in **Table 4.3‑14**. Based
upon the inductance and resistance values provided for the two horns and
the transmission line, the capacitance required for the bank is 0.90
Farads. The capacitor bank will be recharged by two of the standard
Fermilab 240 kW power supplies. During operation of the horns the
calculated power consumption is 83 kW. The required voltage for
operation is 515 volts. To avoid creating transients on the power line a
1 mH inductance will be inserted between the power supply and the
capacitor bank. The design uses 120 parallel capacitor units (7.5mF,
670V) divided into 12 cells, 10 units per cell and two empty slots per
cell in case more capacitance is needed to make up for less than
expected inductance for the target hall circuit. This design provides
the 5.2 msec pulse. To obtain the 2.6 msec (half pulse), the 120 pairs
in parallel are switched to 60 series pairs (with each pair being
3.75uF, 1340 V) in parallel. This yields a total capacitance of 0.225F
or 1/4 the full pulse design amount. The 2.6 msec operational setup
requires two 240 kW PEIs to run in series to obtain the 1100 volts
needed for operation. This has been done before at Fermilab. The pulse
waveform is given in **Figure 4.3‑5**.

  --------------------------------- -------------------------------------
  Peak current, maximum             240 kA (Design Rating; 120%)

  Peak current, operating           205 kA

  RMS current                       8700 A (Design Rating; 120%)

  Capacitance/unit                  7,500 +/- 5% uF

  Number of cells                   12

  Installed capacitors/cell         10

  Total No. Caps installed          120

  Max. No. capacitors/cell          12

  Maximum No. capacitors            144

  Capacitance/cell                  18.75 mF / 75 mF

  Installed Capacitance             0.9 Farad

  Max. capacitance                  1.08 Farad

  Capacitor voltage rating          670 V~Working~ /1340 V~Hi-pot~

  Switching element                 SCR array, 12 parallel devices

  SCR Mfg, Part Number              Eupec, Inc., T2710N20TOF
  --------------------------------- -------------------------------------

Table 4.3‑14: Capacitor Bank Specifications

![](media/image4.wmf){width="4.183333333333334in" height="1.5875in"}

Figure 4.3‑5: Capacitor Bank Pulse Train Waveform

We have chosen the metalized polypropylene construction for the
capacitors specifically because they fail gracefully, or experience soft
failures. They are fitted with pressure switches to detect any pressure
build-up co-incident with soft failures and these switches will be tied
into the interlock system of the controls. We have specified a capacitor
case containment rating of 25 kilo-Joules when the maximum operating
energy in any one cell is 15.7kJ. The nominal operating energy in each
cell is 10.6 kJ. The absolute max energy available, assuming the PEI
goes to full it\'s full output of 800 volts, is 22.4 kJ per cell. All of
the cells are isolated from each other by semi-conductors, SCRs or
diodes.

*Capacitor Row Buses*

The capacitor row bus extension tabs are constructed of 0.063" copper
sheet stock with tab extensions to the respective positive and negative
bushings of every second capacitor in the row. This every-other-one
arrangement allows the free terminals of the capacitor pairs to be
connected in a series, or parallel arrangement depending on the pulse
width desired. For 2.6 msec operation the parallel arrangement is used.

*Silicon Controlled Rectifier (SCR) Modules*

The SCRs used in the capacitor bank to switch stored energy from the
capacitors are assembled into modular sub-assemblies. Twelve assemblies,
one for each capacitor row, are used in the capacitor bank. The assembly
includes two water-cooled heat sinks, an SCR, bus bar terminals, and a
compression clamp to hold the SCR under 10,000 lb. pressure. The modular
approach is instituted to allow quick change-out in the event of an SCR
failure. A snubber network is installed across each output SCR to
protect it from voltage transients. The combination of a 1 uF capacitor
in series with two parallel-connected non-inductive resistors is used.
The respective snubber circuits are mounted adjacent to each SCR.
**Table 4.3‑15** shows the SCR ratings.

  --------------------------------- -------------------------------------
  V ~DSM,~ V ~RSM~                  2,200, 2,300 V

  I ~av~                            3,700 A

  I ~rms~                           5,800 A

  I ~tsm~                           54,000 A
  --------------------------------- -------------------------------------

Table 4.3‑15: SCR Ratings

*Firing Circuits*

Firing circuits provide the signal to the respective SCR gate terminals
that initiate conduction of the devices. The firing circuits used to
trigger the output SCRs are adapted from the Fermilab Low Beta Power
Supply system. Circuit modifications are incorporated to increase the
trigger pulse current amplitude to 6 Amps during the initial
microsecond, decaying in several additional microseconds to 1 Amp for
the remainder of the pulse. These modifications are documented by FNAL
drawing \# 9820-EC-370116. Each of the 12 output SCRs in the capacitor
bank has a dedicated firing circuit. Three identical circuits are
included on a single printed circuit board. Four printed circuit boards
are installed, one for each quadrant of the capacitor bank. The over-all
pulse width of the gate signal for the SCRs is controlled by the
electronics in the Trigger Fan-out Box and must be adjusted such that
the pulse width does not exceed the on time of the SCRs.

The output SCRs of the capacitor bank float at the operating voltage of
the system. The firing circuit board components provide 1,500 Vdc
isolation between the low-level input pulse and the 120 Vac power, and
the output pulse to the SCRs. Consequently, the majority of the
components on the circuit board and the co-axial cables carrying the
trigger pulse to each SCR float at high voltage as well. The co-axial
cable outer jacket is not rated, with respect to ground, for the
potentials the system may be operating at. Subsequently, the gate pulse
co-axial cables are dressed away from structures at ground potential, or
double insulated in areas where structures are unavoidable. Red colored
RG-58 co-ax cable was installed to signify the application is operating
at high voltage.

*Trigger Fan-out Box*

The trigger fan-out box is mounted to the ceiling of the enclosure,
above the 'C' quadrant capacitor structure. It receives the 'SCR
Trigger' pulse from the controls via fiber optic cable. A second fiber
optic cable carries a 'status' signal back to the controls to verify
that the trigger fan-out circuit has all of the appropriate voltages
present. The status information is included in the interlock chain and
must be present for system operation

Four parallel outputs from this circuitry are connected to the
respective SCR firing-circuit pc-board of each quadrant. Two additional
'sync pulse' outputs are generated within and are available externally
at the connector feed-thru panel, located above quadrant 'C.' The two
sync signals are 1-μs in width, TTL level, buffered and synchronous with
the trigger for the capacitor bank output SCRs.

*Voltage Dividers*

A voltage divider is installed in each of the capacitor cells (rows) to
monitor the performance of the respective cells. The control electronics
monitors these signals on a continuous basis throughout the operating
cycle, looking for any imbalance. The frequency compensated voltage
divider circuitry includes a voltage to current converter with a low
impedance output. This approach was implemented for improved noise
immunity and the ability to drive long signal lines to the control
electronics.

*Output Current Transformers*

A passive current transformer (CT) is installed in the low-side bus of
each capacitor row. Its output is 1 volt/kA and appears as a voltage
source with 50 ohms in series. The twelve individual signals, one from
each CT, pass through the connector panel located above quadrant C of
the enclosure. The 50 ohm input impedance of each channel of the control
electronics provides termination for the current transformers.

*Reverse Energy Discharge Resistor and Diode*

Energy reflected from the load inductance will be stored in the
capacitor bank, but have the opposite polarity. Because of the
relatively large amount of resistance in the stripline and horns the
amount of energy reflected is approximately 1.5 kJ (15%), to low to have
made the additional components necessary for energy recovery circuitry
economically worthwhile. Consequently, the reverse energy is dissipated
in a resistor switched into the circuit by a freewheeling diode. The
resistor-diode combination is connected in anti-parallel across each
capacitor cell. The diode for each cell is mounted as a water-cooled
assembly to the capacitor low-side bus, adjacent to the current
transformers.

*Humidity Sensor*

A humidity sensor is installed within the capacitor bank enclosure on
the ceiling of "C" quadrant. It was included in the equipment to monitor
enclosure humidity. It has a measuring range of 0-100% and an accuracy
at 20˚C of; +/- 2% from 0 -- 90% RH, +/-3% from 90 -- 100% RH.
Temperature dependence: +/- 0.02 ˚C /˚C. It operates on +5 Vdc and has
an output of 0 --1 V with respect to common for 0 -- 100 % RH
indication. Connection to it is via a dedicated connector on the
enclosure feed-thru panel.

#### 4.3.4.4 Charging Power Supply Design Issues {#charging-power-supply-design-issues .unnumbered}

Two 240 kW PEI power supplies are used for charging the capacitor bank.
Their specifications are given in **Table 4.3‑16**. These PEI power
supplies used for the capacitor bank were originally designed for
powering magnets under constant current or programmed functions. When
used for charging capacitors, the charging current will go to zero once
the capacitors have achieved the desired voltage, confusing the power
supply regulator. As an aid to voltage regulation, a resistor is
installed across the PEI output to pull a small amount of current at all
times. The resistor is constructed of four series connected,
water-cooled elements as used in domestic electric water heaters. Their
combined series resistance of the four elements is 138 Ohms. These
resistors are mounted within the capacitor bank.

  ----------------------------------- -----------------------------------
  PEI (Power Energy Industries)       240 kW

  Maximum output voltage, Volts       200/400/800

  Maximum output current, Amps        1200/600/300

  Voltage regulation                  0.1 %

  Current regulation                  0.05 %
  ----------------------------------- -----------------------------------

Table 4.3‑16: Charging Power Supply Specifications

A 10 mH inductor is connected between the PEI charging source (supply)
and the capacitor bank. Its purpose is to limit undershoot current that
occurs as a result of reverse recovered charge on the capacitor bank at
the end of each discharge pulse. Design specifications of the choke are
provided in FNAL Specification \# 9820-ES-370036.

A by-pass diode is located within the capacitor bank enclosure, adjacent
to the choke. This single diode appears electrically across the multiple
series by-pass diodes of the PEIs and is meant to carry all of the
remaining undershoot current, diverting it around the PEIs. Its anode is
connected to the input end of the choke (PEI negative connection) and
its cathode to ground (PEI positive connection).

Diodes are installed between the capacitor bank side (electrical) of the
charging choke and each capacitor cell of the bank. Their purpose is
two-fold. First, they provide isolation of the PEIs to prevent the
delivery of stored energy from the capacitor bank into any fault that
may occur in the charging supplies. Their second purpose is to provide
isolation from cell to cell, preventing stored energy delivery into a
faulted cell from the remainder of the capacitor bank. The diodes are of
modular construction and are installed in sets of three on water-cooled
heat sinks. The assemblies are located between the capacitor support
structure and the G-10 SCR panel, in each quadrant, near the floor of
the enclosure.

#### 4.3.4.5 Electrical Safety {#electrical-safety .unnumbered}

*Bleeder Resistor P.C. Board*

When the capacitor bank is configured with series pairs (2.6 or
5.2?msec) of capacitors, bleeder resistor boards must be installed as a
safety measure. The low side terminal of all series pairs is grounded
via the high current bus in each capacitor row. The high side terminal
of the pair will be grounded when the LOTO procedure is carried out to
completion. The mid-point between the capacitors, however, is not
grounded and could retain a charge relative to ground. The installation
of the bleeder resistors (100 kOhm) will provide a leakage path to
effect discharge of any remaining stored energy after the system is shut
down. Additionally, bleeder resistors will prevent any accumulation of
stored charge from incidental energy sources. The resistance value is
high to keep power loss in the aggregate of the bleeder networks to an
acceptable level. Redundancy for safety is established on each PC board
by the use of four resistor elements connected in a bridge
configuration, two in series by two in parallel with the mid point of
the series resistors connect together. Hence, two resistors must fail
before the bleeder network becomes inoperative.

The time required to achieve full discharge is equal to five R-C time
constants (63 minutes). The bleeder resistors are not to be relied upon
to discharge the capacitor bank for maintenance purposes. LOTO
procedures must be followed before any maintenance is to be performed
within the capacitor bank enclosure or the PEI power supplies.

*Energy Dump Resistors and Shorting Relays*

A separate dump resistor is installed for each capacitor cell and is
connected to a common shorting (grounding) relay, maintaining the
cell-to-cell isolation necessary for safety. A second identical set of
resistors and shorting relay is also installed to provide redundancy.
These resistors are air-cooled and rated to absorb 27 kJ each,
sufficient for the maximum stored energy of system operation with
greater than a factor of two safety margin. When system shutdown occurs
during a charge cycle, or an interlock interrupts normal cycling, energy
stored in the capacitors will be switched by the shorting relay into the
dump resistors where it will be safely dissipated.

*Ground-sticks*

A pair of ground-sticks is provided on each side of the capacitor bank
enclosure, secured to the inside of one of the center bay doors. One of
the pair includes a resistor assembly that will limit potential
discharge current to a safe level. The 'hard-ground' stick does not use
resistors. The two ground-sticks are inserted into the retaining mounts
on the center bay door of one side of the enclosure. The storage points
on the doors are equipped with interlock switches to assure the system
is not energized while a ground-stick may be applied to the capacitor
bank circuitry. When the ground-sticks are stowed it is essential they
be fully seated in the holders in order to make-up the interlocks.

#### 4.3.4.6 Controls {#controls-2 .unnumbered}

*General Description*

The control system was established as a joint development effort between
the NuMI and MiniBoone projects since the two systems are similar in
most requirements. Some functions required by the MiniBoone system are
not used for NuMI. Hence, some LEDs are not illuminated during normal
operation when in use for the NUMI horn system. The controls system
consists of five plug-in modules in a rack-mounted frame. Two modules of
the same model are used to monitor current and voltage balance in the
capacitor bank, however they are not interchangeable due to different
calibrations for the respective functions. A separate chassis mounted
just below the controls chassis provides DC power for the control
modules.

Monitored system parameters:

1.  Output current of each cell to 0.4 % or better

2.  Current in each transmission line pair

3.  Current imbalance between stripline pairs

4.  Total output current

5.  Capacitor voltage in each cell

6.  Capacitor bank over voltage and over current

7.  PEI over current

8.  Ground faults

9.  Over temperature conditions of horns

10. Coolant flow loss to horns, PEIs, capacitor bank

11. Capacitor over-pressure

12. Equipment entry

The local resident power supply controller, beside permitting local
operation of the equipment separate from control-room operators, is to
monitor all of the operating parameters watching for of limit conditions
and safely shutting the system down when such condition are detected.
All safety related interlocks would be by hardware. We do not depend on
software of personnel safety. There is no other solid-state device that
even comes close to the switching capability and ruggedness of SCRs. It
has be recognized that the very nature of SCRs is that once triggered
there is no way to turn them off other than there being an occurrence of
a subsequent \'current zero. We will, however, detect any and every
fault in the equipment and turn it off to prevent a second pulse.

**4.3.4.7** **Cooling System**

**Figure 4.3‑6** shows the capacitor bank water system schematic. With
two exceptions, all the heat generating components, resistors, charging
choke, diodes and SCRs associated with the capacitor bank in the
enclosure, are cooled directly by water. The first exception is the
capacitor energy dump resistors, which operate only momentarily when the
system is turned off or the interlock system interrupts normal
operation. Consequently, a negligible amount of additional heat is
dissipated within the enclosure from these resistors. The second
exception is the stripline. It is convection cooled and releases its
heat to the air within the enclosure. A cooling water supply temperature
of 95˚F, contributing some heat to the enclosure, plus the heat given
off by the stripline serve to keep the enclosure internal temperature
well above the ambient dew point during operation. This heat is
conducted through the capacitor bank enclosure walls and radiated to the
exterior environment.

Water Flow, typical:

Capacitor bank 9 gpm @ 80 psi differential

PEI, each 6 gpm @ 80 psi differential

∆p Switch setting 60 psi, PEIs and Cap.Bank, each

Water is carried either by copper pipe or Nylo-Seal^®^ nylon tubing.
Nylo-Seal has a working pressure rating of 400 psi., and a burst
pressure rating of 1200 psi. Swagelok and Parker fittings are used
throughout for the plastic tubing. Flow balancing valves are installed
internal to the enclosure to establish the flow rate to the various
parallel water paths. A self-regulating flow control valve controls the
total water flow rate for the capacitor bank. The 10-gpm device is
installed in the supply side water line.

![](media/image5.wmf){width="6.029861111111111in"
height="4.795833333333333in"}

Figure 4.3‑6: Capacitor bank water system schematic. (See Drawing
#9820-MC-370054 for complete information and symbol key.)

#### 4.3.4.8 Mechanical Design {#mechanical-design .unnumbered}

*Enclosure*

The enclosure is constructed to Fermilab specifications per FNAL drawing
number 2782.000-ME-314551. It measures 75" high x 210" long x 69" wide.
We have specified a cabinet constructed of 14 Ga. steel to offer an
added layer of personnel protection. It is constructed of mild steel and
built in three sections; a center section housing the SCR switch
assembly, and the two identical capacitor bank sections, one on either
side of the center unit. All are constructed as a floor pan and a roof
pan, separated vertically by mullions that form the corners and supports
for the enclosure doors*.* The sections have mating flanges secured by
multiple bolts to make up the complete enclosure. In the area adjacent
to each flange bolt the steel has been left un-painted and silver-plated
by the enclosure vendor. The plated areas were coated with moisture
excluding grease prior to assembly to preserve optimum electrical
contact between the enclosure sections. All sides of the enclosure are
equipped with doors to allow full access to internal components. The
door mullions in front of the capacitors in each quadrant are removable
to facilitate capacitor replacement. **Table 4.3‑17** lists the
enclosure mechanical parameters.

  ------------------------- ---------------------------------------------
  Length                    209 inches, (5.31 m), without doors installed

  Width                     70 inches, (1.78 m), without doors installed

  Height                    79 inches, (2 m), \[81" including C-channel\]

  Weight                    22,000 lbs., (10,000 kg)
  ------------------------- ---------------------------------------------

Table 4.3‑17: Enclosure Mechanical Parameters

All doors are readily removable, with the exception of the two doors on
the end of the enclosure adjacent to the output stripline. By necessity
those two doors have been modified to slide on tracks, rather than
swing, and are not easily removed.

*Oil containment*

The most likely capacitor failure mode, in terms of oil leakage, is the
loss of seal under one or more bushings. Placing capacitors with their
bushings "up" would be the preferred orientation, negating any leakage
concerns. However, to facilitate removal and replacement and to permit a
compact design that could be lowered as an assembled and tested unit
into the underground cavern, the capacitors are mounted horizontally
with their bushings toward the outside of the enclosure. The two-inch
lip-height of the floor pans in the capacitor sections of the enclosure
provides 14 gallons of potential oil containment in the event of
capacitor leakage*.* The capacitors used in the capacitor bank are
impregnated with rapeseed (Canola) oil, a biodegradable vegetable oil.
Each capacitor contains approximately 2.5 gallons of oil. Therefore, as
many as 5 units in either enclosure end-section could spill their entire
contents without exceeding the oil containment capacity for that
section.

All penetrations in the enclosure floor pans have been sealed or curbed
to prevent leakage to the outside. With any capacitor losing oil, it is
likely that electrical failure of the capacitor will follow at some
point. Any capacitor electrical failure will contribute to a current
imbalance of the capacitor bank output and eventually be detected by the
local controls, resulting in shutdown of the power supply system.

*Capacitor Support Structure*

The capacitors constitute 50% of the total weight of the enclosure
assembly. During transport the structures supporting the capacitors in
each quadrant are lifted directly via the four hoist rings on top of the
enclosure. Each hoist ring is rated for 10,000 lbs vertical lift
capacity. Internal and external structural members cross brace the
capacitor supports to allow transport of the capacitor bank as a single
unit. The balance of the weight of the components within the enclosure
is carried through the enclosure structure to the capacitor supports.
The 1" thick G-10 panels that mount the switching SCRs in each quadrant
also serve as torsional webs to give the enclosure torsional stiffness.

*Ground-cable Penetration*

Ground cables connecting the capacitor bank low-side terminal to the
horn modules, via the LEM, for ground fault detection exit the enclosure
through a curbed hole in the base of the enclosure on the output
stripline end. The purpose of this curb is to maintain the oil
containment capability of the enclosure floor pan. The cable opening is
sufficiently large to allow for the installation of two 900-mcm-ground
cables with some room to spare. The excess opening should be sealed off
after the installation in the underground power supply room to prevent
the entrance of vermin.

### Transmission Line

#### 4.3.5.1 Overall Design and Specifications  {#overall-design-and-specifications .unnumbered}

A parallel strip transmission line is used to connect the power supply
to the horns. The circuit is a damped LC discharge circuit that reaches
peak current when the SCR switch releases stored energy from the
capacitor bank to the horns via the transmission line. A transmission
line consisting of a four-layer assembly of two parallel plates is
necessary to connect the output of the power supply system to the horns.
**Figure 4.3‑7** and **Figure 4.3‑8** show the layout and dimensions of
the transmission line. In **Figure 4.3‑8** the upper portion of figure
shows the stripline cross section at a typical joint, held at 28,000 lbs
by the spring style bar clamp. The lower portion of figure illustrates
the mid-line style of aluminum bar clamp. An insulator separates each
pair of aluminum alloy bus conductors. Aluminum spacers separate
adjacent pairs. Inside the Target Hall beamline shield the insulation is
a 1cm air gap with TS ceramic spacers. Outside the shield, Kapton
polyimide insulation of 0.5 mm total thickness is used. The completed
assembly is held in compression by ceramic sleeved through bolts at the
spacer locations and compression clamps in the region where Kapton is
used (if it is used). This configuration yields an equivalent
transmission line width of 1.2 meters in a compact cross section.
**Table 4.3‑18** lists estimated transmission line dimensions and
parameters.

![](media/image6.wmf){width="6.0in" height="3.832638888888889in"}Figure
4.3‑7: Stripline Pictorial Representation

![](media/image7.wmf)![](media/image8.wmf)

Figure 4.3‑8: Stripline Drawing and Pictorial Cross Section.

The transmission line must deliver 200 kA (average, ± 2.5%) pulses every
1.9 seconds to the horn. As a safety margin the power supply system,
including the transmission line, is designed to operate at up to 240kA.
This results in a system load current of 7250 A~rms~ operationally (8700
A~rms~ design). The estimated circuit parameters were listed in **Table
4.3‑13**. These calculated load values include effects of DC resistance,
skin effect, temperature, transmission line conductor cross section and
spacing.

  ------------------------------------ ----------------------------------
  Conductor material                   6101-T61 Aluminum alloy

  Conductor width                      12 inches, (30.5 cm)

  Conductor width at horn joints       8 inches, (20.3 cm)

  Conductor thickness                  0.375 inches, (0.953 cm)

  Conductor spacing                    0.375 inches, (0.953 cm)

  No. parallel pairs                   4

  Inductance @ 100Hz                   4.9 nH/ft., 16 nH/m of length

  Resistance @ 100Hz                   3.05 uΩ/ft., 10 uΩ/m of length

  Power loss, 2.6 mS                   80 W/ft., 260 W/m of length

  Power loss, 5.2 mS                   160W/ft., 530 W/m of length
  ------------------------------------ ----------------------------------

Table 4.3‑18: Transmission Line Parameters

The transmission line is a 12,000 lb. structure and thus its support is
non-trivial. The transmission line is in approximately 20' long
sections. Transmission line joints are to be welded except where
connection/disconnection is needed. One piece of the transmission line
runs across from the Target Hall to the horn power supply room (see
**Figure 4.3‑9**). The second long piece of the transmission line runs
along the Target Enclosure to the horns. Disconnects/connects are will
be located in the horn power supply room, in the Target Hall where the
transmission line emerges from the penetration, above the shielding at
each horn and inside the shielding at each horn.

![](media/image9.wmf){width="4.388194444444444in"
height="7.079166666666667in"}

Figure 4.3‑9: Target Hall and Power Supply Room Cross Section Conceptual
Drawing

*Transmission Line Cooling*:

The target chase is cooled by 28,000 cfm flowing in the beam direction
in the horn region. The beam heating in this region is less than 183
KW/m^3^. The electrical heating is estimated at \~27 KW/m^3^. For the
stripline between the remote disconnect clamp block and the horn, the
air flow through the target pile for the target pile cooling provides
satisfactory cooling of the stripling to remove the energy deposited
from beam heating and from i^2^r losses. The thermal analysis results
are shown in **Figure 4.3‑10**. The highest temperatures seen are 88^o^C
at 4E13 ppp.

![](media/image10.png){width="4.45in" height="6.708333333333333in"}

Figure 4.3‑10: Transmission Line Beam Heating with AirFlow, Horn 1
Region

#### 4.3.5.2 Transmission Line Joints {#transmission-line-joints .unnumbered}

The transmission line joint, where the transmission line connects to the
horns, is a complicated region. **Figure 4.3‑11** and **Figure 4.3‑12**
show the plan and elevation view for the design in the area. The eight
strips of the transmission line must connect to the bell shape of the
horn. For horn 1, some amount of movement (+/- 3 mm horizontally and/or
vertically) is desired also. This area will become highly radioactive
and thus the desire is to have the joints last as least as long as the
horns do. Add to this that they will be pulsed every 1.9 seconds with
200 kA, which causes some amount of vibration and one can see the
difficult issues with this area of the design.

![](media/image11.wmf){width="5.3909722222222225in"
height="4.977083333333334in"}

**Figure 4.3‑11**: Horn, Remote Clamp and Transmission Line Elevation
View

![](media/image12.wmf){width="5.169444444444444in"
height="4.7652777777777775in"}

Figure 4.3‑12: Horn, Remote Clamp and Transmission Line Cross Section

*Fatigue Lifetime:*

The part of transmission line connected to horn, the joint, will be
replaced each time a horn is replaced. The horns are designed to last at
least 10 million pulses. Thus the joints are designed to last 10 million
pulses also. The horn fatigue lifetime safety factor for 10 million
pulses is about 3.5. The maximum force desired on the horn upon
displacing horn 1, is \~ 400 lbs. A fatigue lifetime safety factor
similar to that of horn 1 is desired with this design. ANSYS analyses
have been completed on the horn 1 joint design, using the appropriate
thermal loads (88^o^C), magnetic loads, and the maximal (3mm) offsets.
They indicate a fatigue lifetime safety factor at least as large as that
for the horns.

The horn 2 joint is based on the same design as the horn 1 joint, but
scaled up to horn 2 dimensions. ANSYS results show that it is flexible
enough to accommodate the expansion of horn 2. Horn 2 expands 0.033 cm
and the ANSYS results show a maximum force of \~ 50 lbs on the horn.

![](media/image13.png){width="6.490277777777778in"
height="3.748611111111111in"}Figure 4.3‑13**: Horn 1 Joint Cross Section
and Elevation**

![](media/image14.png){width="6.490277777777778in"
height="4.377777777777778in"}Figure 4.3‑14: **Horn 2 Joint Cross
Section**

#### 4.3.5.3 Transmission Line Routing through the Shield Block and Beyond {#transmission-line-routing-through-the-shield-block-and-beyond .unnumbered}

The transmission line joint fingers connect with the transmission line
section through the shield block at the remote clamp, as shown in
**Figure 4.3‑12**. The routing through the block is such to minimize
weight and residual activation levels at the top of the block. Clamps
and snubbers are used to minimize vibration. There are "quick"
disconnecting joints at the remote clamp at the bottom of the module, at
the top of the module, and beyond the edge of the T-blocks. In this
manner, one can remove the section of stripline from top of module to
beyond the module sides. Then one can remove the T-blocks, and the
stripline-stuffing block. Next one removes the horn with transmission
line joint and remaining stripline part in the module to work cell for
replacement. At the work cell, one disconnects the section routed
through the module from the joint and horn by disengaging the remote
clamp.

The part of the stripline within stripline block (including the clamp)
does not have to be replaced every time a horn is replaced. It is
designed to last the lifetime of NuMI (10 years). The concern is that
the fingers of the transmission line will "weld" together or somehow the
remote clamp will not be able to disengage the transmission line and
horn from the remainder of the assembly. Thus the stripline block is
bolted together such that the transmission line internal to the
transmission line block can be removed and replaced.

Airflow through stripline stuffing block from top of module to horn
cannot be obstructed (this airflow cools stripline). However, an air dam
is needed at the H-block cover between the module and the stripline
along the target hall wall (this is a lower radiation area, so a wider
choice of materials is available). The air dam is intended to contain
air-borne radiation.

The transmission line along the target hall wall will be covered with a
sloping "roof" to keep people from leaning on it or putting items on it.
This will also help minimize the accumulation of dust and dirt on it.

#### 4.3.5.4 Transmission Line Internal to the Horn Power Supply {#transmission-line-internal-to-the-horn-power-supply .unnumbered}

The internal stripline of the capacitor bank is constructed of 1/4" x
12" copper extruded bus. Provision is also made to allow the output
current direction to be reversed by the exchange of "jumper" placement.
The output stripline is that section leading from the center bay of the
capacitor bank to the outside of the enclosure. It is constructed of
3/8" x 12" 6101-T6 aluminum electrical bus conductor alloy.

The assembly of eight conductors, four conductor pairs, is held together
by bar type compression clamps and utilizing G-10 insulating spacers
between layers. The clamps are spaced at 12-inch intervals. The assembly
is supported from an aluminum I-beam running the length of the
enclosure. The I-beam serves two purposes. It serves as a spreader bar
when the enclosure is being lifted by a crane for transport, but more
importantly it facilitates the removal of the output stripline should it
become necessary for repair or replacement. In the cavern installation,
the output (stripline) end of the capacitor bank is closely positioned
with respect to the cavern wall, preventing removal of the output
stripline on that end of the enclosure. The stripline suspension
incorporates a jacking mechanism and is equipped with rollers that
trolley on the I-beam, allowing the suspension and stripline to pass
through the enclosure and out the opposite end. Pre-drilled holes in the
I-beam flanges at each end allow extensions to be coupled and secured to
the beam, as needed, to extend trolley travel.

#### 4.3.5.5 Compression Clamps and Stripline Contacts {#compression-clamps-and-stripline-contacts .unnumbered}

At locations where it is necessary to couple/decouple the eight-layer
stripline, a special compression clamp is utilized. The clamp
incorporates twelve spring-loaded pistons in each bar to establish equal
pressure across the width of the stripline conductors. The spring on
each piston is comprised of a series stack of 2,700 lb. rated conical
(Belleville) compression washers. The clamp assembly is capable of
30,000 lbs. total clamping force.

### Power Supply Cables

**Table 4.3‑2** through **Table 4.3‑4** give the number, type, and
approximate length of the cables needed for the power supplies, with the
exception of the RG220 cable that is used for the kicker power supply.
Klixon cables are not shown in this table, but are installed in the same
manner as elsewhere at FNAL. All cables in new construction will be fire
retardant.

### Performance Monitoring Plan

For the kicker and horn power supplies, the predicted line locked ripple
will not noticeably affect the beam dynamics, and Autotune will correct
slow drifts. Other power supplies will have regulation as described in
Section 0. All power supplies will also be continually monitored by the
ACNET alarm system (with tolerances set appropriately). These alarms
plus logged data will point out required power supply repairs. All
supplies will have current error detectors, which will inhibit beam if
the supply is not tracking the ramp.

### References

The following references need to be made into NuMI notes.

Zhijing's Notes

Horn PS Manual (too large?)

Safety Docs for MI8

> T