# Presentation: 660110

##  SNS Beam Loss Monitor ElectronicsFinal Design Review

**D. Gassner, R. Witkover**
**Brookhaven National Laboratory**
** **

- SNS BLM Electronics, BNL

- July 23, 2002

## SNS BLM Electronics Outline

-  **Requirements**
** ****Dose Rate Estimates **
** ****Gain and Threshold Control**
** ****Dynamic Range**
** ****System Block Diagram**
** ****Cable interface**
** ****Analog Circuit Schematic**
** ****Front end Stage**
** ****Fast Loss Integrator (MPS Trip) Stage**
** ****Viewing Stage**
** ****1 W/m stage**
** ****Thermal Drift**
** ****VME & Digitizers**
** ****Data Acquisition**
** ****HV Bias**
** ****Summary**

- SNS BLM Electronics, BNL

- July 23, 2002

## Provide measurements of loss for tuning

Protect the machine from high activation due to slow, low-level losses
		(1W/m criteria)

Protect the machine from radiation damage due to fast high-level losses 
		 MPS Input (Beam Permit/Inhibit Link)

Not for personnel protection.

**Protect the machine from high activation due to slow, low-level losses**
**	****	****(1W/m criteria)**
**Protect the machine from radiation damage due to fast high-level losses **
**	****	**** ****MPS Input**** ****(Beam Permit/Inhibit Link)**
**Not for personnel protection.**

***BLM System Electronics Requirements***

- SNS BLM Electronics, BNL

- July 23, 2002

## Dose Rate Estimates

**Slow Loss: 1 W/m criteria**
- Corresponds to ~10- 4  loss distributed around 248 m Ring.
- Beam-off activation approximately 100 mrad/hr at 1 ft.
- “Rule of thumb”: Multiply by 1000 to get beam-on dose rate (100R/hr).
- Same as 0.5 R/sec during the 1 ms SNS pulse.
- Need to resolve 2 decades below, or 1% of 1 W/m.
**What is maximum high-end loss?**
- 1% local loss (of 2 MW) = 20 kW requested.
- Pre-integration to extend dynamic range.
**Total range is equivalent to 21-bits + sign**
- Low-end resolution limited by noise and BW, upper end by detector and/or electronics saturation.

- SNS BLM Electronics, BNL

- July 23, 2002

## Required Gain and Threshold Control

- Programmable Gain (local & remote)
- Beam intensities
- Linac and HEBT range: 15-38 mA
- Ring increases 103 during macro-pulse
- RTBT can vary 103 between single turn, full intensity
- Detector shielding by beam line components
- Beam energy dependence
- Programmable loss limit thresholds
- Individual channels
- Separate thresholds for Fast and 1 W/m losses
- Trip outputs can be masked through MPS for studies

**  **

- SNS BLM Electronics, BNL

- July 23, 2002

## Electronics Dynamic Range 

_**Fast Response for Beam Abort **_
**For 10us rise time, BW would be 35 kHz. (550 pA noise scaled from RHIC)**
**This limits resolution to 30 Rad/hr.**
**Intention is to observe large fast losses ~ 10****6**** Rad/hr**
_**Signal Upper Limit**_
-  **1% of 2MW, in Linac and HEBT, uniformly over pulse = 644uA**
**Lost fast in one place (RTBT) = 644 nC (very large)**
_**Lower Limit**_
**1% of 1W/m = 324 pA**
**Total dynamic range of 126dB (324pA – 644uA)**
**Need separate signal paths for Fast and Slow losses.**
** **

- SNS BLM Electronics, BNL

- July 23, 2002

## System Block Diagram

- SNS BLM Electronics, BNL

- July 23, 2002

## BLM-Cable Interface

**In order to balance rise time due to signal cable length variations, a BLM-Cable interface panel will be included which will hold capacitors at the transition from the coax to mass termination connectors.   Example:**
**Belden 9054 is 16 pf/foot, runs will vary from 75 to 300 feet, yielding 1200 – 4800 pF.  **
**470 Ohm AFE input R, rise times will vary from 1.2 to 5us (assume 2.2 X RC = rise time)**
**We can extend the dynamic range for RTBT fast loss signals by pre-integrating the signal by choosing input caps for a 50-100 usec time constant. This would allow us to get to several times 0.1% single point loss without saturating the 1 W/m & Viewing stage electronics.**
**NOTE: Belden 9054 is a *****low Tribo-electric***** cable which significantly reduces noise due to friction. It is essential when measuring signals in the nA or lower region.**

- SNS BLM Electronics, BNL

- July 23, 2002

## Analog Front End

*Analog Front End*

**80kHz**

**80kHz**

**1.5kHz**

**1.5kHz**

- SNS BLM Electronics, BNL

- July 23, 2002

## Front End Amplifier Stage

**Trans-impedance amplifier**:
- Burr-Brown OPA627BP
- low offset voltage, Vos = 100 μV max (un-trimmed)
- Drift 0.8uV/0C, max
- Bias current, Ib = 1 pA
- GBW = 16 MHz. Open loop gain 120dB.
**Selectable gain settings:****	****	****	**** **
- Normal Linac		62k Ohm	**	**** **
- Normal Ring		6.2k Ohm	**	**** **
- High Controlled loss 	1k Ohm	**	**** **
**Noise**** voltage: **gain is set by the resistors Rf and Ri, 6200/470 = 13.2, but the signal is only set by Rf, (IC ideal current source).  RHIC noise = 10 pA for 10 Hz BW.  Using a 100 kSa/S ADC, BW will be limited to 50 kHz. Scaling between these cases gives an equivalent noise current of 0.71 nA and an _output noise voltage of 4.36 μV. Johnson & Amp noise = 4.1 μV._
**Thermal Drift: c**alculated worst case is 100 μV, actual data (better) shown later.
**Trim Pot**
**Protection Diodes**

- SNS BLM Electronics, BNL

- July 23, 2002

## Analog Front End

*Analog Front End*

- SNS BLM Electronics, BNL

- July 23, 2002

## Fast Loss Integrator (for MPS)

***Fast Loss Integrator (for MPS)***

- 		Experience at LANSCE has shown that a beam inhibit signal should be based on integrated dose rather than dose rate. Hardware damage is normally due to amount of energy rather than rate of energy deposited.
- 		An integrator will be used to provide a signal to a comparator to generate a signal for the MPS when the programmable reference is exceeded.
- 	_Response time 10 us _(input RC, FE, this stage response.)

_**Leaky Integrator**_**  vs.**
-  Simple
-  Adequate ?
-  Non-linear
-  Residual offset

_**Gated Integrator**_
-  More complex
- Gating & Reset
- Charge injection
-  Precise

**16.6 ms**

**Circuit components values related to**
**MPS Comparator range (unknown).**

- SNS BLM Electronics, BNL

- July 23, 2002

## Analog Front End

*Analog Front End*

**80kHz**

**80kHz**

- SNS BLM Electronics, BNL

- July 23, 2002

## Viewing Stage

_**Features: **_
**Isolation to drive 100kS/s digitizer**
**Remote gain setting X1, X10 and gain readback.**
**Change viewing gain without changing MPS trip threshold.**
_**Noise:**_** ****Calculated 110 ****μV (< than LSB) with no trim pot this stage. With trim pot, better 20 μV.**
_**Drift:**_** See upcoming plot**
_**Saturation problem in RTBT, solved by:**_
**Added capacitors in Cable Interface,  50-100us time constant**
**Jumper selectable AFE signal routing**
**Linac & Ring: routed directly from first stage.**
**RTBT: routed through integrator.**
**Should yield several times the 0.1% single point loss without saturating the electronics.**
** **

- SNS BLM Electronics, BNL

- July 23, 2002

## Viewing Stage Data Acquisition

**Data Acquired:**
**Baseline (1 msec) + BLM signal (1 msec + ion collection time) **
**Digitizer – 16 bits (incl sign), 100 kSa/s**** **
**2 bytes/sample, 500 bytes/SNS cycle**
**+/-****5 V, LSB = 152.6 μV**
**Only selected BLM’s send full data (10 max for entire system).**
**Sum of losses per BLM, per macro-pulse, sent once per second.**
**Input to waterfall type display.**
**1000 point FIFO history at the console level for use in the event of an abort.**

- SNS BLM Electronics, BNL

- July 23, 2002

## Analog Front End

*Analog Front End*

**80kHz**

**80kHz**

**1.5kHz**

**1.5kHz**

- SNS BLM Electronics, BNL

- July 23, 2002

## 1 W/m Stage

**Philosophy: **
**Reduce noise by reducing BW.**
**1kHz allows enough settling time so digitizer can acquire baseline.**
**Reduce amplitude of fast loss spikes so we don’t saturate.**
**Gain added ( X 10) so we can use 16-bit ADC rather than 24 bit**** ( see slide ) **
**1 W/m loss during the cycle (32.4nA X 6.2k X 10) will yield 2mV.**
**1% of 1W/m = 20uV**
**Trim Pot**
**Data: Baseline (1 msec) + Beam On (1 msec) + Residual signal (1 msec)**
**Digitizer:**
**Slow loss viewing – 16 bits (incl sign), 100 kSa/s **
**2 bytes/sample, 600 bytes/SNS cycle**
**+/-****5 V, LSB = 152.6 μV**
**Data accumulated over 10 second or longer interval **
**Processed to compare against a 1 W/m reference (alarm) in IOC.**
**Pre-averaged low-level data will be available as a waterfall, or a strip chart display.**** **

- SNS BLM Electronics, BNL

- July 23, 2002

## Thermal Drift

***Thermal Drift***

- 1 LSB

- SNS BLM Electronics, BNL

- July 23, 2002

## SNS BLM Digitizers

***SNS BLM Digitizers***

**Simulated slow loss signal measured by a 16 and a 24 bit digitizers (Yongbin Leng)**

**1 W/m loss generates 32.4nA, **
**through 6.2k = 200uV, **
**for 1 ms pulse. **
**Times 10 gain. **
**1% of 1W/m yields **
**2 x 10****-8**** V****.****S. **
** **

- 1% 1W/m

- 600 pulses
- 10 seconds

- SNS BLM Electronics, BNL

- July 23, 2002

## VME Implementation

**Non-VME,**
**Linear power**
**supplies**

- SNS BLM Electronics, BNL

- July 23, 2002

## Data Acquisition and Control

**Controls Interface**
**Readback front end gain jumper setting **
**Set & Readback Viewing Stage Gain (X1, X10) **
**Timing for Integrator (MPS) gating**
**Set loss threshold, fast loss (trip), slow loss (alarm)**
**Digitized loss data (fast and slow)**
**Gain and calibration data folded into resolved data.**
**Set and readback of High Voltage, On/Off bits**
**System test**

- SNS BLM Electronics, BNL

- July 23, 2002

## HV Bias

- ISEG HV Bias Supply
**VME High Voltage Power Supplies in 2 slot width **
**1 channel and 2 channel versions in same dimensions **
**LCD display for voltage or current **
**variable rate of change of output voltage **
**switched polarity **
**integrated protection and control circuits **
**output overload and short circuit protected **
**SHV connector on front side **
**Full control via VMEbus**
**EPIC’s drivers **
**$1.2k/channel**
**Model VHQ 204L, 0-4kV, 1mA**

- SNS BLM Electronics, BNL

- July 23, 2002

## SNS BLM System - Summary

_**BLM Electronics **_
-  **Provide loss measurements for tuning.  **Three local gain ranges.
-  **Low level signals (1W/m)**
-  Expected low-end signals within the range proposed system.
-  Bandwidth limit 1kHz.
-  Process data over 10 second interval.
-  Goal 1% of 1W/m.
-  **Higher ****level signals (larger fast losses)**
** **Wideband (50kHz) viewing.
-  Additional remote gain control.
-   Fast RTBT loss signals pre-integrated to extend dynamic range.
** ****Machine Protection (Integrated loss)**
-  10 μsec response, programmable thresholds and masks.

- SNS BLM Electronics, BNL

- July 23, 2002

## Back-Up Slides

-  Rack Layout
-  Analog Front end (Leaky integrator)

- SNS BLM Electronics, BNL

- July 23, 2002

## Rack Layout

- _Location__	__	__	__# Ch__	__#FBLM__	__#Crates__	__Note_
- DTL_Diag:Cab401		  5		1
- CCL_Diag:Cab301		12		1
- CCL_Diag:Cab302		12		1
- SCL_Diag:HB13Cab01		29		1
- SCL_Diag:HB1Cab02		30		1
- HEBT_Diag:Cab07		40	    3	2	     1
- Ring_Diag:Cab05		55	   12	2            	     2
- Ring_Diag:Cab06		44	    0	2	     3
- RTBT_Diag:Cab04		28	    3	1	     4
- Note 1: 12 HEBT ch located in Ring racks
- Note 2: Includes HEBT ch beyond ground break
- Note 3:Includes 12 ch from RTBT before ground beak
- Note 4: 12 RTBT ch located in Ring racks

- SNS BLM Electronics, BNL

- July 23, 2002

## Analog Front End (LI)

*Analog Front End (LI)*

**80kHz**

**80kHz**

**1.5kHz**

**1.5kHz**

**36Hz**

- SNS BLM Electronics, BNL

- July 23, 2002