# Presentation: 297151

## SNS Laser Wire Final Design Review

***Diagnostic Groups: BNL, LANL,LBNL***
***And  ORNL***
***Collaborators: SLAC, FNAL***
***Presented by Saeed Assadi***

**July 23-25, 2002**

- Progress Report.
- 2) Summary of the collaboration Since May-20-2002 Presentation.
- 3) Measurement results from MEBT and BNL 200 MeV line.
- 4) Electron detection, magnet design, transport layout and more
- 5)  What’s Next

**Outline:**

**Multi-National Laboratory Diagnostic Collaborators**

**ORNL**

**Tom Shea, Sasha Aleksandrov, Saeed Assadi, Willem Blokland, Craig Deibele, Warren Grice, Ted Hunter, Danny Mangra, Dave Purcell, Dan Stout****David Purcell**

**BNL**

**Peter Cameron, Roger Connolly, Craig Dawson, Chris Degen, Sheng Peng, Marty Kesselman, Bob Sikora, **

- LANL

**Mike Plum, John Power, Bob Shafer, Jim Stovall**

- LBL

**Larry Doolittle, Darryl Oshatz, Alex Ratti**

**Joe Frisch**** , ****Keith Jobe,****  Marc Ross, Jim Crisp (FNAL), Bob Webber (FNAL)**

-  SLAC

- Present Baseline Diagnostics

- Dave Purcell

** **

- Proposed Laser Wire Installations

**Injector**

**2.5 MeV**

**RFQ**

**1000 MeV**

**DTL**

**86.8 MeV**

- To
- Ring
- and TGT

**CCL**

- 402.5 MHz

- 805 MHz

**SRF, ß=0.61, 0.81**

**186 MeV**

- HEBT

- _MEBT_
**5 WS (elec. only)**
- 6 BPM (elec. only)
- 2 Sl&Col (act. only)

-   _DTL_
-  ** ****5 WS **
- 10 BPM
-   6 CM (p/u only)
-   5 ED/FC

-  _CCL_
**  ****8 WS**
- 12 BPM
-   2 CM (p/u only)
-   1 ED/FC

- _SCL_
**32 WS (16 elec.)**
- 32 BPM

-  _HEBT_
-  ** ****3 WS (dumps)**
- 22 BPM (elec. only)

- _RTBT_
- 1 Harp

- _D-plate (7.5 MeV)_
**1 WS**
- 3 BPM
- 1 CM (p/u only)
- 1 ED/FC
- 2 Sl&Coll emit
- 1 Phosphor screen
- 1 8 seg. halo scraper
- 1 Beam stop / F-Cup

**MEBT**

- _Key_
- WS = wire scanner
- BPM = beam position monitor
- Sl&Col = slit and collector emittance station
- CM = current monitor
- ED/FC = energy degrader & Faraday Cup

*Laser Wires*

- 380 MeV

** **

-          Laser Wire
- Minimal impact on normal operation
- Virtually no impact on SRF cavities or vacuum
- Low signal to noise ratio but using electron collector works
- No parts inside the vacuum
- Radiation hard @ <1500nm

-    Conventional Wire
- Requires off-operation with 100 s macro-pulses at low rep rate
- Ablation from the wire may contaminate the SRF cavity
- Signal to noise not a problem
- Maintenance requires vacuum access
- Very radiation hard

- Why Choose Laser-wire over Conventional Wire?

**Recent Progress:**

- Better data set from 200 MeV beam at BNL.
-  Conventional wire data v.s. laser-wire from BNL 200 MeV is obtained.
- More refined data is obtained from MEBT.
- More advanced data analysis.
- Electron detector is designed
- Dipole magnet is designed and under construction
- Vacuum beam box is designed and is being detailed for manufacturing.
- Tunnel optics boxes design are being detailed.
-  Penetration access to tunnel is constructed
- We have started setting up a laser room at RATS. We have received two free laser tables.
- We are in a process of buying parts for Oct-02 studies.

- 1) Electron collector design is complete.
- 2) Magnet design simulation is complete. Detailing of the magnet is complete. The magnet is sent for prototyping.
- 3) Vacuum beam box design is 80% complete.
- 4) Data acquisition: EPICS is installed on the oscilloscope, Runtime LabVIEW is running on the scope. Shared memory is running on the scope and serving data.
- 5)  What’s Next

** **

**Progress Report Since May-20-2002:**

- What does the Laser do? Photo-neutralization

- Requirements
*High peak power*
*Small spot size*
*Transverse scan*
*Temporal stability*
*Detection*

*h***

*H**-*

*H**0** + e*

- Cross-section is well known therefore stripping efficiency calculation is a matter of
- algebraic manipulation (tech. notes)

- Calculated stripping efficiency r [%]

|  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- |
|  |  | 1.5 x 2.5      mm | 2 x 2      mm | 2.5 x 1.5      mm | 2 x 3.5      mm | 2.8 x 2.8      mm | 3.5 x 2      mm |
| 200 mJ | 300MeV | 19% | 23% | 30% | 14% | 17% | 23% |
|  | 1GeV | 13% | 16% | 21% | 9% | 12% | 16% |
| ∞
 | - | 20% | 25% | 33% | 15% | 18% | 25% |

- Nominal emittance

- 2 x Nominal emittance

- It is safe to assume stripping efficiency of 15%

**12ns**

- Ibeam

-  % of Ibeam

*H**-*

*time*

**Calculated efficiencies at 400 MeV**

- To speed up the laser wire data acquisition, and analysis, we are integrating EPICS
- and LabView in the scope and serve the results to users.

**More Refined Data Acquisition, Better Data Analysis**

- Raw data is
- Sent through
- A LabView
- program for
- further  analysis

- MEBT laser
- Profile and fit

**BNL 200 MeV line data**

- Carbon Wire [RED]
- Laser Wire [Blue]

- wire=5.7mm and LPM=6.69mm

*Reasons for the difference in measured width?*
- The width of the laser beam should add 0.3mm,
- 2.     The laser energy is drifting slowly.

- We will not use the original SCL beam box due to cost

- SCL

- Raft design will not change with the new laser box.

- Signal strength (number of electrons x 108) for 20mA beam

|  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- |
|  |  | 1.5 x 2.5      mm | 2 x 2      mm | 2.5 x 1.5      mm | 2 x 3.5      mm | 2.8 x 2.8      mm | 3.5 x 2      mm |
| 200 mJ | 300MeV | 2.8 | 3.5 | 4.5 | 2.1 | 2.5 | 3.5 |
|  | 1GeV | 1.9 | 2.4 | 3 | 1.4 | 1.7 | 2.3 |

- Nominal emittance

- 2 x Nominal emittance

- It is safe to assume number of released electrons of 2·108

- U = 2e8*1.6e-19/12e-9*50 = 133mV  on 50 Ohm load (laser at beam center)

- Laser beam

- Electron collector

- Bending magnet

- Detection of released electrons

- Advantages:
- large number of electrons
- charge integrating amplifier similar to BLM
- Energy of electrons is well defined
- Electron beam is well collimated
-  Drawbacks
- External magnets are required
- In vacuum collectors are required
- Might suffer  from beam loss background

- } easy to collect

- } good S/N

- 3-D model of the electron detector is complete and 60 dB or noise (rf)
-  rejection is obtained

##  We expect to measure 120 mV from electron collector at 38 mA, expected noise is about 1 mV (-60dB– Green Curve). 

- 3-D view of the SCL BPM and the electron detector electrode

- 3-D view of the SCL BPM and the electron detector assembly

- Choosing:

**Required Magnetic Field to Collect Electrons in SCL:**

- Required magnetic field spans from 70Gs at lowest energy to 190Gs at the linac exit. As beam energy can deviate from design values during commissioning/operation it is desirable to have magnets with variable field.

- Note that electron detector been discussed is not an imaging device therefore high quality of the field is not required.
-   Deflection of the ion beam is negligibly small an can be corrected by baseline steering correctors therefore no compensating magnet is required.

- Magnet assembly

**Schedule and Goals**

**Schedule and Goals**

- SCL Warm section: Laser ports, magnet and the electron detector
- is shown

- To calibrate and evaluate the electron detector, we will use two BCMs

- Laser Transport from HEBT Service Area to the Tunnel

##  Cross Section of Optics Line in the Tunnel

- Optics
- Pipe

- Location of the Laser Room in the HEBT Area

- Advantages of a single laser
*Laser expense shared between stations*
*Laser not exposed to radiation*

- Laser
- Room

- Transport Line

- HEBT

- Warm Section

**Transport Line**

*Modular Design*

*Boxes secured to building walls, ceilings, etc.*
*Designed to accept a variety of optical components*
*Cable feedthroughs*
*Pipes mounted between boxes*

- HBET Service Building

- LINAC tunnel

**Beam Pick-offs**

*The beam will be diverted from the main line by a pneumatically driven stage.*

*OFF*

*ON*

**Optics Box under consideration**

*Laser Wire*

**Optical Layout is underway:**

- 90 mm

- 120 mm

- 60-74 mm

- 66-80 mm

*Layout*

**Maximizing the scanning range**

- 35 mm

- Variable ratio of H-minus to laser beam size

- Lens translates
-  14 mm

- Spot size ranges
- from 10 μm to 2 mm

*Adjustable Spot Size*

- Spot sizes and peak energy densities for 200 mJ pulse

- _Mirror_
- d = 25.4 mm
- U = 0.11 J/cm2

- _Entrance window_
- d = 15.0 mm
- U = 0.22 J/cm2

- _Exit window_
- d = 12.7 mm
- U = 0.28 J/cm2

- _Lens_
- d = 25.4 mm
- U = 0.16 J/cm2

_*Damage threshold ~ 5 J/cm*__*2*_

**Position of mirror, lens and windows**

- Reflected beam comes to a focus upstream of pick-off mirror.

- Reflected beam diverges harmlessly.

*Reflected Beams*

**Schedule**

*FNAL*
*Study*

- FY 02

- FY 03

- FY 04

***Design and Build Prototype (16 ManMonths)***

***Software Development (6 ManMonths)***

***Design Transport Components (2 ManMonths)***

***Fabricate Beam Boxes (5 ManMonths)***

***Fabricate Transport Components (2 ManMonths)***

***Laser Room Construction (2 ManMonths)***

***Transport Line Installation (3 ManMonths)***

***Equip Laser Room (1 ManMonths)***

***Safety System Installation (2 ManMonths)***

***Transport Beam Alignment (2 ManMonths)***

***Final Installation and Verification***
***(18 ManMonths)***

***Total Effort: 4.9 ManYears***

**Schedule and Goals**

- Magnet design will be completed by July-22-2002, request
-       for cost estimate will go out by the end of July.
- Complete the electron detector drawing and sent to the shop
-        (August-10-2002)
- Complete the beam box by August-10-2002. Send for prototype
- 	on August-20-2002.
- Refine the data acquisition and analysis programs (Aug-30-2002).
- Verification of the new laser beam detection at BNL’s 200 MeV line
-        (October-2002).
- 6)    Collaborative effort on testing laser wire at FNAL (October-2002).

**Schedule and Goals**

- 7) Electronics design just started. We are relying on off the shelf
-     components such as LeCroy charge collector module.
- 8) In tunnel laser-optics box is started. Various mounting schemes
-     are under considerations.

- Backup Materials are posted on the web
- _[http://www.sns.gov/diagnostics/documents/Lasermain.htm](http://www.sns.gov/diagnostics/documents/Lasermain.htm)_

**Proposed Laser**

**Laser Wire Dipole Field Lines**