# Presentation: 274061

## RFQ simulation results

- Gennady Romanov
- September 7, 2006

## We committed to perform 3D simulations of RFQ 

- Original solid model

- Solid model from MWS

- Input/output radial matcher are introduced

_**We committed to perform 3D simulations of RFQ **_
_**with radial matchers**_.

- Gennady Romanov

- 09/07/2006

## Original vane ends shape without matchers

- Original vane end shape. 319 MHz

- Original vane end shape
- with fingers. 318 MHz

_**Original vane ends shape without matchers**_

- This low frequency is OK with and without tuners, because plunger tuners will
- increase frequency.

- Gennady Romanov

- 09/07/2006

## Input matcher

- The frequency of the end area is higher then nominal, because the matcher reduces
- capacitive loading.
- The fingers don’t help much – they lower frequency only by 1 MHz (327.8 -> 326.8)
-  for given model length of 150 mm.

_**Input matcher**_

- Gennady Romanov

- 09/07/2006

## Mesh density enhancement

_**Mesh density enhancement**_

- In MWS mesh density may be defined separately
- for separate bodies. Introducing fake metal tips
- (rods) one gets an opportunity to dense mesh in
- critical area without limitations of automeshing .
- This trick makes the simulations of full or 1⁄2  length
- models more reliable.
-  J.Staples et al presented at Linac06 the detail simulation  of SNS RFQ, and
- they think that MWS is already accurate enough to simulate RFQs.

- Gennady Romanov

- 09/07/2006

## Model of 1⁄2 of full length with input matcher 

- Field distribution and frequency  of Q-mode vs finger length. Field is evaluated along line with x=y=2.4 mm

- 1⁄2 of full length, magnetic
- boundary at the open end

- At nominal length
- of tuners = 24.5 mm:
- Fq = 324.1 MHz
- Tilt = 5.5 %

_**Model of 1⁄2 of full length with input matcher**_

- ≈ 0.25 MHz
- for ≈ 30 mm stroke

- Nominal

- Nominal

- Gennady Romanov

- 09/07/2006

## Model of 1⁄2 of full length with output matcher 

- 1⁄2 of full length, magnetic
- boundary at the open end

- Field is evaluated along line with x=y=2.4 mm

- 18%

_**Model of 1⁄2 of full length with output matcher**_

- At nominal length
- of tuners = 24.5 mm:
- Fq = 324.6 MHz
- Tilt = 18%

- Gennady Romanov

- 09/07/2006

## Model of 1⁄2 of full length with output matcher 

- Field distribution and frequency of Q-mode vs finger length

- 1⁄2 of full length, magnetic
- boundary at the open end

- Field is evaluated along line with x=y=2.4 mm

_**Model of 1⁄2 of full length with output matcher**_

- ≈ 0.18 MHz
- for ≈ 30 mm stroke

- Output matcher has higher
- frequency and it is less sensitive
- to end-wall tuners.

- Gennady Romanov

- 09/07/2006

## Field distribution  and frequency of 2nd dipole mode

_**Field distribution  and frequency of 2**__**nd**__** dipole mode**_
_**  **__**vs finger length**_

| Mode | MHz |
| --- | --- |
| 1 | 316 |
| 2 | 322.3 |
| 3 | 334 |
| 4 | 352.2 |

- Dipole mode spectrum. Finger length
- is one inch.

- ≈ 1MHz
- for ≈ 30 mm stroke

- Fq = 325.4 MHz
- Fq-Fd2  3 MHz

- Gennady Romanov

- 09/07/2006

## Conclusion.

_**What could be done with the matchers**_

- Cut-backs can be increased slightly to bring frequency  down. The cut-backs can be done of rectangular
- shape, or deeper, or both.

- The bigger rounding off decreases  frequency too and makes surface current distribution more uniform

- These additional tuners are not very effective. But can help.
- Diameter 20 mm, h = 5.26 mm

- Gennady Romanov

- 09/07/2006